UK Cherub Website Techical Articles

Designing your own Cherub

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Disclaimer

This document is compiled by an amateur, not a professional. It has been compiled in good faith, but almost certainly contains errors and inaccuracies. Its also very much based on how this amateur goes about drawing boats. A trained professional will doubtless approach things differently. If you feel unable to take responsibility for your own actions and errors without resorting to the legal profession then you are advised not to read it, let alone build anything based on information here.
I should also point out that I've never built a Cherub to any of my paper designs*, although I have built a one-off singlehander.

One of the aims of the Cherub Class has always been to provide a platform for people to design their own boats. Quite a few careers have started with designing Cherubs and related boats. John Spencer was the first, the original Cherub being the start of his career, but Russ Bowler, Iain Murray, various Bethwaites and the UK's Andy Paterson all had Cherubs at or near the start of careers that have included significant designs in other classes.
There are quite a few ways of going about designing boats, and those of you with appropriate training will be able to make your own choices. Apart from the obvious choices of naval architecture and mechanical engineering quite a few successful designers had trained as civil architects.

Some thoughts on design extremes.

People's first boats tend to be extreme. Obviously you want to go with your ideas, and there's no point in doing what Uffa Fox did, which was not to put his radical ideas in practice until his third 14 footer, the legendary groundbreaker 'Avenger'. On the other hand you don't really want to end up with a boat that is way out on a limb and only effective in some conditions (as I rather fear I did with my one off single hander). Off hand though I can only think of one first boat in recent years which was an unqualified success - the Italian Bistro. So its probably worth considering designing both your radical new idea and a moderate version of it, and take a long hard look at both before deciding which one to build.

Balance is Everything

Julian Bethwaite will tell you that the most important thing he does is to travel with his eyes open and his mouth shut. You'll also find that you start drawing you don't really know what a boat looks like. It sounds ridiculous until you try and draw a familiar boat like a Laser from memory...
Look at the whole picture. Think about where you will be sailing the boat, how heavy you are, whether you are brilliant boat handlers who can manage a tricky boat or whether you'd be faster in a stabler platform. Think about the rig you are going to put on. The rig needs to match the hull needs to match the crew needs to match the foils needs to match the rig...

Start with an Idea

The most important thing is to be familiar with Cherubs, to have sailed in the class and observed how different boats behave, and how you see the benefits of different shapes. Its also helpful to have a starting point - "What I'd like is a boat a bit like an Italian Bistro, but finer at the bow, narrower and with the beam further aft". Maybe you get a sketch like this.

Make Sketches

From there I suggest you arm yourself with a drawing of your starting point and a sketch pad and start sketching ideas. It's important to consider the boat as a whole, not just as sections, profile etc. In order to do this I find it useful to draw waterline and to a lesser extent buttock sections through the boat. You also should have a good idea about how you want the waterlines and buttock lines to look, because this is how the water is flowing past your boat, which in the end is what is most important. I usually start by drawing sections, and then work out the waterlines from them, and then modify the waterlines to nearer what I think I want and alter the sections to suit. Through a few dozen pages of sketchesyou are getting a fairly good idea about what your boat will look like. You'll find as you go through the sketches that your ideas will change, especially as you start converting sections into waterlines and vice versa and get a real feel for how the different factors inter-relate to make a complete boat. Once you get past the initial sketches graph paper starts making a lot of sense for this business of matching sections to waterlines and back again. It sounds like a lot of work - and it is. You need to be thorough though - you are going to be building this boat for six months or more and maybe sailing it for five years. It's a long time to be saying to yourself that you wish you'd thought more about the transom. You want to be able to visualise the underwater shape of the complete boat before you get past this stage.

Detailed Scale Drawings

At this stage most of us will want to turn to the computer and a drawing package. To a large extent it probably doesn't matter what you use, but the Australian PackageHullform, from Blue Peter Software, has been used for at least one Nationals winning Cherub. What you are using the package for is basically as a tool to do some of the donkeywork of mathematical calculations and of fairing lines and sections. Simon Roberts and Dave Roe both use their own custom computer drawing systems for boats, which they've steadily evolved to suit their particular requirements. The Italian Bistro was actually designed on a high-end programmable calculator. Alternatively - and especially if you have the required technical capability - you may prefer to carry on with pencil and paper, but perhaps move to larger scale drawings and a proper drawing board. Julian Bethwaite is certainly one top designer who's a firm advocate of staying clear of the computer.
Perhaps at this stage - or better still while you were sketching - you first come across a nasty surprise when you discover that some of your most prized ideas won't work together. When I drew my first Cherub I wanted a flat midsection with lots of turn up near the chines, a V section bow, and straight waterlines in the bow with no lumps and hollows. I discovered you can't get that. With straight waterlines a flat mid section gives you a flat-bottomed bow. So you have to start making compromises. Perhaps three quarters of the art of sailboat design is the art of selecting the best compromises!
I don't propose to produce a manual to using Hullform, but note that Cherubs are quite tricky boats to put into a hull design package. You will need to get into the program thoroughly and use some of the subtler features to get the best out of it. This especially applies when drawing the deck line and snout area, where most Cherubs have angles and straight lines that the default settings of the program don't handle well. I also advise you to get into a regular regime of saving new copies of your drawing so that you have old versions to look at and maybe go back to if a particular idea doesn't work out. Its also good to get a version of your master design - and maybe one or two others - into the package so that you have a starting point for looking at the figures that it produces for you.
The major advantage of using a computer is that the process of fairing the sections can be automated, and also that you can do any number of "what if" variations on a theme and evaluate them. However a significant disadvantage is that it is all too easy to make a change in one place that affects another part of the hull through the fairing process, which you may miss. Another factor is that changes that look quite small on a computer screen can turn out to be some inches on the finished boat.

Models

I have ony ever heard of one Cherub design being tank tested, and you're not going to have the facilities yourself (unless you're studying Ship Science at Southampton, in which case I imagine reading this article is unnecessary). However I still find it useful to build a balsa wood and cardboard model of my design, just so that I can look at it from different directions and get a real feel for what the finished boat will look like. I'd especially (bitter experience here folks) make sure you build a model of your final design. I didn't for the single hander, and I suspect that if I had I might have started getting worried about just how flat it looked. As it was I didn't really get concerned until I saw the building jig - at which point it was a bit late! The intermediate design that I did build the model of had a lot more rocker...

Go For It

You don't really know how satisfying it is to have a boat that you have designed yourself until you get in it and sail it. Even though my singlehander is less than a complete success I don't regret doing it at all. And maybe next time I'll get it right!

Starting Points

I hope to have a few designs available electronically to give a starting point.
Paterson 6a 1994 design with flares and snout added to 97 rules.
Unbuilt Design This is a 97 rules boat which I've sketched out, loosely based on a Bistro as outlined above. Its not remotely "ready to build" and almost certainly not quick, so be warned!

Coming later should be Dave Roe's Pasta Frenzy design - when I can make an electronic version.

Jim Champ, 2000

*Though I wish I'd got round to building my 1978 Cherub design- when I look at the drawings it bears a distinct resemblance to the highly successful mid 80s Kiwi design Tasman Express!

Building Your Own Foam Sandwich Cherub.

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Why Foam Sandwich. Planning the project. Building the Jig. Materials. Building The Boat. Cost & Time.

Disclaimer

Why Foam Sandwich.

The first thing to realise about foam sandwich construction is that it is easier for the amateur to build a strong light foam sandwich Cherub than it is to build a plywood one. The second thing to realise is that the materials involved are inherently more hostile to humans than those used in building wooden boats, and rather more handling precautions need to be taken. This is especially true for those of us who are used to being up to our wrists in Aerolite 306, with no greater precautions than a bucket of water to wash off acid spills (not that such practices are a good idea).
There are two stages in building a foam boat. The first stage is to build the mould or jig that the hull is to be made about, and the second is the construction of the boat itself. The alternatives are to build the boat from a female mould, a male mould or a jig. Building a female mould is a very lengthy business, as it involves making a complete model of the finished boat, absolutely fair, or taking a mould off an existing boat. Renoving the boat from the mould when finished can bring its problems too. However the finished boat needs minimal fairing and finishing, which is why this is the preferred option for batch or series production of multiple boats. A male mould is used if the boat is to be vacuum bagged. If you have vacuum bagging facilities available - and there are ways and means of doing it on the cheap using old freezer pump motors etc - then you won't need me to tell you about the advantages. A male jig - which consists of battens over frames without a solid surface- is used when the layup will be hand consolidated. This is the most popular and probably the simplest option.
Planning the project.
This is vitally important with a foam boat. Whereas with a wood boat you can move fittings about easily, on a foam boat it's a good idea to have plywood or high density foam pads built in at an early stage. It is possible to do this later, but it's hassle. Before you start work out your internal layout as best you can, including any likely changes in the future (!) and draw up a diagram showing exactly where you are likely to want fittings. You can neither screw nor bolt fittings into foam sandwich, no matter how big a backing plate you put on.

Building the Jig.

It is often possible to borrow a jig from someone else who has made a boat. In the UK most jigs seem to be used quite a number of times. However if you are building to your own design you have no choice. Spend a considerable amount of time on this. if the mould is not true, fair and symmetrical then the final boat won't be - one or two of the early Bistros are a little crooked about the transom at deck level for this very reason. The mould is normally constructed of 12mm plywood formers at 12" intervals with battens at reasonably close intervals. Mark out the plywood formers using templates drawn on drafting film, not forgetting to allow for the thickness of your battens. Also build a ply keel former (longitudinal). This is used to help align all the transverse formers. The formers should be screwed down to a pair of rails, 4" by 2" is adequate, to keep the whole thing solid. Once you are confident that they are all in exactly the correct place you can start putting on the battens. 1/2" square is perfectly adequate for these. Start with the chines gunwales and centre line, double and triple checking that everything is fair. They are best screwed down so you can alter them. Once the main battens are in you should put in sufficient others to support any large areas of foam, especially in areas like the underside where space is critical. Once they are all on it is a case of sanding and adjusting until you have exactly the shape you want. After some 4 months graft you will be in the same position as the someone who is borrowing a jig!
If you have vacuum bagging facilities then there are considerable advantages in constructing a male mould, basically just by putting a layer of plywood over the battens. This is filled and faired, covered with parcel tape and then inner skin, foam and outer skin successively bagged down on top of this.
Picture - Part Built Boat
[Photo - Paterson 7 under construction (c) Bloodaxe Boats]
The jig needs to be at a reasonable working height. On the one hand you need to be easily able to work on the middle of the hull, but on the other hand you don't want to have to bend down all the time.

Materials.

One advantage of being an amateur is that time is less of a constraint. If a pro goes a couple of days over building a boat than he doesn't eat for a few days, whereas an amateur just doesn't get to sail so quickly. Therefore there is less need to compromise on materials in favour of speedy construction. The other factor is that you are saving so much money on the cost of a new boat that it is easier to spend a bit more money on the constituents.

Foam.

8mm or 10 mm Airex, Termanto or Divinycell is normally used. If you have both then use the thicker gauge for high load areas such as the space frame and the bottom of the hull. The hull floor and the false floor should be 75/80kg/m3 for dent resistance, but 55kg/m3 is adequate for topsides and other verticals. Many people use the same density throughout. Use the heavy foam for sidedecks and anything else likely to be exposed to the dreaded trapeze hook! Pads for fittings can be made from 200kg/m3 foam. The size of the bubbles in the foam and thus the hollows in the outer surface will affect how much resin and filler you use, and thus the weight and cost of the boat. Airex is generally considered best for this.

Fibres

Rudyard Kipling wrote
"There are nine and sixty ways of constructing tribal lays
And every single one of them is right!"
Exactly the same applies to Cherub fibre lay-ups these days. If you talk to people about fibre lay-ups you will get about as many opinions as people you ask, some of them contradictory! There are several choices of fibre lay-up that will work well. Most boats now are either glass with local carbon or all carbon, but part Kevlar lay-ups have their fans too and certainly seem to lead to bullet-proof boats. The different fibre combinations have different characteristics, and different people seem to have different experiences. Kevlar is always a pain to wet out, and cannot be sanded, but has superb impact resistance. Carbon can give wetting out problems, isn't too great on impact resistance, sands well and provides the stiffest boat. E Glass is cheap and easy to work with, with reasonable impact resistance.
Glass is probably the best choice for a first boat with a hand consolidated wet lay-up. All-carbon boats are much better vacuum bagged. All else being equal a glass boat will come out about 5kg heavier than a carbon one, but you should still easily be able to get under the minimum weight limit.

Glass.

There are two lay-ups in common use, one being two layers of 200g/m2 E-glass on the outer shell inside and out, and the other 1 layer of 300g/m2 with a second layer on the outside skin only over the bottom of the hull. The main fibres should be arranged at 45 degrees to the centreline, but where there are two layers the second layer should be 0/90.
The best weaves to use are either 45/45 bi-directional or crows foot. Bi-directional is strongest and easy to use. Crows foot weave is very easy to shape and might be a bit cheaper. Standard weave is difficult to get to run over corners and chines, and also weakest.
It's a good idea to add some local carbon reinforcement to an all glass shell. Unidirectional carbon tape is the favourite, as it is very easy to use. It should go in the areas subject to heavy loads from the rigging, front bulkheads, space frames etc. You should put it under the outer layer of glass in order to avoid sanding it all off again when you fair the boat.

Carbon.

A good lay-up is 200g/m² carbon plain weave, inner skin at ±45°, outer skin at ±45° with an extra layer at 0°/90° over bottom, 500mm from stem to 1m from the transom. Then add a thin layer of 100g/m² glass which adds thickness and protects the carbon from being removed during the fairing/sanding process...- if it goes black, stop sanding!

Kevlar/Carbon

If you want to go for a Kevlar skin on the undersurface - and this could be a good idea if you launch on lots of stones and the boat gets bashed a lot, then use the above lay-up, substituting a skin of 165g/m2 Kevlar for the 0°/90° carbon layer above, and run it from stem to stern. You need to be especially careful in the fairing stage to make sure that you don't cut through the glass into the Kevlar, because the ends of Kevlar will not sand off, but stick out through the fibre as a light fuzz. Not Smooth.

Resin.

The major choice is between polyester and epoxy. Polyester is cheaper and easier to use, Epoxy is more expensive, but makes for a much longer lived boat. Polyester also smells absolutely disgusting, and as far as I am concerned is right out if you are building the boat in the living room or a garage attached to the house. On the other hand epoxy is mildly carcinogenic and can cause allergic reactions, but in both cases it is important not to get the stuff on your hands. Barrier cream and plastic gloves are firmly recommended.
Epoxy is recommended unless money is really tight or for some reason (perhaps a wild idea you want to try) you're not that bothered about longevity. In any case only use polyeseter with a primarily glass boat. Scott Bader (Strand Plastics) are a good supplier for polyester resin and SP Systems are most commonly used for Epoxy.
There are many epoxy resin formulations and the one you should use does depend on your facilities. SP Ampreg 20 is the most commonly used. However if your are vacuum bagging Ampreg 22 has advantages in health and safety terms provided that you have a heated workshop - it can get very viscous at low temperatures, and especially provided that you can keep it stored at an even temperature. It reacts very badly to getting cold, although all epoxy formulations will suffer if stored outside their recommended range.
Epoxy resins like to be post cured, which basically means heating the structure up quite a bit for an extended period of time. There is much more in the suppliers' handouts and technical documents - here are some references.
SP Systems Guide to Composites (PDF File)
West Systems Epoxy User Manual
Marine Composites (US) - a considerable publication in PDF format.

Building The Boat.

Attaching the foam to the jig.

First cover the jig with plastic sheet to stop the foam getting glued to the jig - most embarrassing. Obviously don't get any wrinkles on the battens because it will stop you fastening it down properly. Next attach the foam. Tie it on with wire, the handiest to use is probably 1.5mm PVC coated (inner core of telephone cables! ). Use large pieces of foam where possible, but where there is much curvature - bow etc. - you will need to use smaller pieces to prevent it cracking as it is bent. Take a lot of trouble over this, get it absolutely flush to the battens, and keep gaps between sections to an absolute minimum. At this stage you should put ply or high density foam pads in where any fittings will go - bow fitting, shroud plates, etc.
Next you should fill all the gaps and fair off the foam. Use lots of very light filler as all this is adding unhelpful weight. Be careful fairing off the foam, it is very easy to sand away lots of foam and leave the filler standing proud ! All raised portions must be lost, but small shallow dents don't really matter too much. Once all the foam is in place, all gaps filled, and all is fair - check 3 times! - coat the foam with a mixture of resin and microballoons or litecell. The aim is to fill all the open cells on the surface with light filler, otherwise it will get filled with heavy resin when you put the glass on. The best tools to apply this are a one-foot plastic ruler or a piece of Formica with a straight edge.

The Outer Skin.

Apply the laminates next. Use a brush and a consolidating roller to ensure full impregnation - which can be a problem with Kevlar - and good resin to glass ratios. Remember you need enough resin to fully impregnate the fibre, but any more is just parasitic weight. Peel ply can be used and is very effective. Supposedly you can get a peel ply like nylon fabric from dressmakers which works nearly as well. I think I might be a bit wary of something like that in a vacuum bag lay-up though! A resin to glass ratio of 1.1-1.3:1 is achievable with polyester, and 1.8:1 with epoxy.

The Inner skin.

Once you have done this cut all the wire ties and turn the hull over. It will be very floppy (don't panic!) so support it in a good cradle. This can be used as the basis for a trailer when you've finished the boat. Put some extra reinforcement around where the centreboard case will come.

Space frames and bulkheads.

These can be made outside the boat and cut to shape and fitted later. Even if you don't have vacuum bagging you can (because they're flat) still compress them while they are curing. Do this with a couple of sheets of flat wood (chipboard is fine), covered with melinex - polythene may wrinkle. Put one piece on a flat floor, add your lay-up, and put the other sheet on top and weigh down with anything to hand - I used the last 5 years of Yachts and Yachting and Boards magazines. If you can't get melinex readily use Parcel tape - yes, the brown stuff! Epoxy won't stick to it so its great for these sorts of jobs. It can even be used instead of a release agent on moulds. You do - of course - have to be very careful not to get wrinkles and creases in the tape when you stick it down. Bulkheads can have one layer of 200g glass (or carbon) each side, but the space frame and high load points should have uni-directional carbon reinforcement under the glass. The bulkheads can be glued straight in with epoxy fillets, but the space frame should be glassed in to distribute the loads. It should hit your ply pads too!
The exact layout of bulkheads depends on your fibre lay-up. A carbon boat needs less in the way of internal bulkheads. Below the floor a Glass boat will at least have a full length central spine, a bulkhead under the mast, one at the back of the daggerboard case at the mainsheet takeoff and one in the middle of the helmsman's stamping area. There's not normally a need for an extra bulkhead in front of the mast, but it is good to add some extra reinforcement as this area takes a pounding upwind in a chop.

Daggerboard case.

Use 55kg/m3 foam if you have it. Glass one side of the foam and allow to cure. Then bend each half of the case around the daggerboard and clamp in place. Don't forget the parcel tape/plastic sheet to stop it sticking. Glass around the outside, then remove the board and cut the case down leading and trailing edges. Coat the inside surface with a gel-coat type layer, preferably with graphite in, so that the fibres cannot get worn down. The two sides are then spaced apart a bit with foam or wood, and the whole lot glassed together again.

Foam sandwich Cherub shell
[Photo - Bistro shell by Wiz Deas ready for home completion. (c) Alison Wilde]

Decks and Interior.

Made in much the same as the bulkheads. You can use a jig - especially if you are making neat rolled side-decks, or use the bulkheads as a jig. Don't forget pads where fittings will go - jib sheets, cleats etc. etc. Get the parcel tape out again to hold the decks down!
There are currently three interior layouts in use. Most common is still the traditional flat side-deck and side tanks with a slightly concave false floor. However there are also two variations on the "scooped deck from side to side theme. Andy Paterson builds his boats without side decks at all. The false floor comes up to the point where topside meets flare, and the crew sit on the inside of the outer skin. An alternative is to have a steeply raked in side deck which meets the false floor in the same way, but still having a side deck.
If you are opting for the side deck less route you will have to have a substantial gunwhale structure to stiffen up the boat as you won't get the box section effect from the tanks. However in all cases there is a considerable advantage in having a gunwhale arrangement that leaves a lip under the topside. When you have capsized and inverted the boat you need to climb on top. This is lots easier if there's a nice lip at the edge to rest your feet on.

The False Floor and Finishing Touches

Use 75kg/m3 foam. This area is prone to dents (!). Glass on the bottom layer before you put it in the boat, using one layer of 200g/m3 glass. Put a fair bit of light resin/filler paste on top of the bulkheads and weigh it down (Y&Y again ?) until it is cured. Once it is firmly attached you can put the top layer of glass on. Use two layers of 200g/m3. Leaving the top layer off while you attach it leaves the floor more flexible while you fasten it down.
Lastly run an extra layer of glass over the gunwale where hull and decks join, partly to keep the whole thing together, and also to give some abrasion resistance for rigging on concrete and to help protect against unplanned impacts from solid objects!
Odd brackets for fittings etc can be jigged up on little moulds/jigs made from wood covered in parcel tape, but its easy to spend hours making little jigs to not much benefit. There's a lot of mileage in making up a largish bit of foam coated in glass each side and cutting things out of that. If you are compressing down small bits with jigs then, even if you don't use it for the big jobs, peel ply is recommended. It can make a big difference to how neat the bits come out and how much finishing work is needed, which is a big plus if its an awkward shaped bracket.

Fairing and smoothing

Absolutely crucial of course, not for strength but for boat speed. Use the lightest filler you can afford, mix it in resin, and spread it on as evenly as you can. A plastic ruler is very good for this. Once it is cured you can start sanding it all off again, the aim being to get down to a fraction of a millimetre above the top layer of cloth. In practice you are bound to end up sanding some cloth off, but make sure it is the very bare minimum. If you have a layer of Kevlar you must not expose it. Kevlar doesn't sand off - it leaves little fibres sticking out !
Different jobs on the boat need different fillers. Fillets and things need some colloidal silica for strength - a mix that is solely bubbles is very soft. For really high load applications, and especially in tension, microfibres are great, but they soak up a lot of resin and so get heavy.
You can load up the resin with a great deal of filler - if you are simply filling with no need for strength then it can be almost "dry". Be aware that these mixes are very soft though, so if the area needs dent resistance you will need to have some silica and a higher percentage of resin in the mix and accept the weight penalty.
The lightest fillers are plastic bubbles - Fairlight or something similar, but are very soft. Microballoons - - the brown phenolic resin bubbles - are significantly stronger.
For really serious filling you can make a brushable filler. Make up a reasonably thick filler mix - still a bit "sinking," maybe 80% of maximum amount of filler you can mix in, and then add a little epoxy solvent - proportions perhaps 50cc resin, 250cc filler and 20cc of solvent and you have a brushable filler that will sand off readily. An adequate substitute for epoxy solvent - at least for cleaning and so on, is a general purpose industrial solvent of 90% methanol, 5% xylene 5% toluene.

Cost & Time.

It will take you in excess of 200 hours to build a hull once your jig has finished. Most people seem to take about 4 months to fit it all in including fitting out etc. Foam sandwich is a more expensive option than wood, but the final total will depend tremendously on materials. As of 2001 the materials cost is probably about UK£1200 for a glass/polyester boat, going up to UK£1750 for an epoxy/carbon hull. In the US it works out at around US$2600 for a predominantly carbon boat.

If you don't want to do the whole job yourself, whether through lack of time, skill, or inclination, an obvious alternative is to start with a part built shell. Quite a nice option is to buy a shell complete with false floor, which means that the trickier jobs are done.

Jim Champ.

This article was compiled in 1991 with the help of Dave Roe, Alistair Cope, Bill Deeley, Simon Baker and Simon Roberts, and updated slightly in 1998 and 2000 with help from numerous others, including Robin Russell, Matt Searle, Andy Paterson and David Lee. Especial thanks to Andy Paterson for teaching me about Parcel Tape!

If you wish to have fuller construction details for building a foam sandwich boat then it would be worth considering purchasing a set of plans from Bloodaxe Boats, which contain much more detail than is practical to include here.

Building your own Ply/Glass Cherub.

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You have arrived at an old part of our website, to find the latest information please visit our new page about building your own Ply/Glass Cherub. The new portal for the site can be found at www.uk-cherub.org please visit this for up to date news about the UK-Cherub class.

Introduction. Design. Preparation. Recommended materials. Construction. Cost & Time.

Disclaimer

Introduction.

These days foam sandwich is the popular option for the home builder of Cherubs. It is probably the easier material to work in and gives a low maintenance boat. On the other hand wood is still a nice material to work with and does produce a really pretty boat if you get it right! A wooden boat built in the hi-tech manner described here, which is some way removed from traditional boatbuilding, will also be a little more proof against knocks and dents than a foam boat. This is intended as a selection of hints about Cherub building in particular, not a complete "how to". There are many books available in shops and from libraries that will give you most of what you need. Other good sources of information are the suppliers of boat building materials. Traditionally Cherubs were built out of Aerolite 306 or Aerodux. These still work fine for all wood boats, but the techniques are very different to those described here, and weight is a major problem with this sort of construction. The best wood boats before fibre/reinforced plywood became used were probably the cold moulded ones, either fully or just the area below the chines.
Cold moulded Cherub.
Home building is usually a rewarding process. A mixture of blind determination and some skill in handling tools is important, although enough determination and patience can make up for a shortage of skill! Probably the most discouraging factor is the air of mystery that surrounds boatbuilding. Just remember that skilled traditional boat building is an arcane and complex art that has almost nothing in common with building a modern Cherub!
I suppose it has to be conceded that the Cherub, being a very light boat with considerable performance and very high stresses, demands careful consideration in the building process. It means among other things careful assessment of materials, quality of jointing, use of suitable adhesives, and above all finding out what other people have done successfully - and unsuccessfully in the past. There is no substitute for talking to other people who have built new boats or owned second-hand boats. The class association will always be happy to put you into contact with people who have had considerable experience of wooden construction. Fortunately Cherub sailors tend to be a friendly and open bunch, and are always ready to help with genuine enquiries.

Design.

There are a great many designs of Cherub. Most recent designs were designed for foam sandwich, so you may be a bit on your own working out details of bulkheads etc. However the designer will always be happy to make suggestions, and most have enough experience of wooden boats to be able to give you some extra information in exchange for their design royalty. In selecting a design it is best to talk to others in the class. At any given time there is usually a dominant design that is a safe bet, and they can give you advice on what suits your crew weight or sailing area.

Preparation.

Having selected your design and bought your drawings you will have, at best, a large selection of drawings, a table of offsets, a selection of detail sketches, and a list of suggested materials. At worst you'll just get a series of scale drawings and sections. If you don't have a table of offsets you will have to cross check regularly as temperature and humidity changes can distort drawings.
The aim is to get as fair a hull shape as possible and one as near to the designer's intentions as possible. You will need to end up with a set of formers no more than 18" apart (12" near the bow), set on a rigid foundation if you are to produce a fair and symmetrical hull. There are two ways of doing this.
Firstly you can trust to luck, make the formers to the shapes given and, once it is all set up, fill in the dips and pare down the bumps that will almost inevitably appear when sighting from various directions. This sometimes works well, especially when you are on your 5th or 6th boat and have had some practice! It can also be a bit risky if some of your measurements - notably rise of floor - are near the limits before you start paring!
The second method is to 'loft' the lines, which is basically drawing them out full size (emulsion painted sheets of hardboard are good), having drawn an accurate grid of station and water lines on which to plot the offsets. If you don't have a table of offsets you can scale them from the drawings, although this is tedious and it is easy to make mistakes. The great advantage of lofting is that by referring back and forth between elevations and plan you iron out bumps and hollows and can easily check that measurements are within the limits allowed. Another benefit is that many of the construction details can be plotted and the details taken off by paper patterns. For information about lofting refer to 'Complete Amateur Boat building' by Michael Verney (pub. John Murray) and 'Boat Building' by Howard Chapelle (pub. Allen & Unwin). Don't refer to them too much for constructional details though!

Recommended materials.

Hull floor
4mm ply. 60g kevlar or 105g glass coating on the inside, 105g glass on the outside skin.
Topsides, decks, bulkheads, daggercase sides etc.
3mm ply
all the ply should have a layer of 105 g glass or 60g kevlar on the inside.
Use lightweight Gaboon ply (hardwood veneered looks very nice but can be a bit heavy). Nowadays by far the best source is Israeli made WBP gaboon, which is light, strong and very cheap.
Stringers, stem, other strip wood.
Western Red Cedar is favourite. It splits very easily, and needs to be coated from ply surface to ply surface with glass.
'Decorative' stripwood - Gunwhales etc.
Spruce or mahogany. Spruce is lighter, mahogany is more durable, but can be very heavy. At the most a thin capping is all you should use. Really good clear pine may be almost as light as spruce and is easier to get hold of. Getting suitable wood can be a problem, and be very careful about adding weight. If you are not worried about getting a Grand Piano appearance then use cedar and glass coat it.
Some people have even used balsa wood coated in glass for glass coated stripwood, but of course in this case the wood is doing no useful work, and serious quantities of balsa wood get very expensive.
Building jig.
Formers are best made from something like 3/8" building grade plywood. Slightly damaged sheets can often be got cheaper. Strip wood can be anything that's reasonably solid and cheap. If you're using second-hand wood make sure you get every nail out!
Glues.
Use Epoxies. SP320 is the best for the sort of fibre re-inforced ply construction we are talking about here, SP106 or West 105 are cheaper.
Tools.
You can never have too many G cramps A staple gun is essential for fastening plywood down. It is cheaper and lighter to tack down with staples and remove them afterwards than to use expensive marine-grade fasteners and leave them in. Otherwise normal carpentry tools are fine, but you can never have enough G cramps. If you have less than about 15 get borrowing!

Construction.

Advice is always helpful, but make sure you understand it completely! Be a bit careful of people who have built 5 Enterprises. They will probably tell you that such and such a bit has to be that thick or glued on that way. It may well end up too heavy and not strong enough! If advice does not seem to add up pay attention to your own inner murmurings. One excellent piece of advice is to have a comfortable 'thinking chair' in which you can put your feet up with a cup of tea - or something else relaxing - and look and think hard about the current problem. Thinking time is rarely wasted - especially if it means you don't have to do something twice!

Cherub Specifics.

I will assume that you are building a self draining boat, to be quite honest if you don't you will curse yourself when you start sailing it!

Ply joints.

Any place where two bits of ply join at an angle needs a generous lightweight fillet, preferably with glass reinforcement running 1" or more from either side of the join. Beware weight. Use the lightest possible filler. The glass over the join should be cut on the bias at 45 degrees - it will go round corners more easily and is twice as strong.

Bulkheads.

Wooden boats are like banana skins. The longitudinal seams will split open unless they are sufficiently braced across the join. This is mainly achieved by transverse bulkheads. Locate these about halfway between the mast and the bow, under the mast, at the rear of the daggerboard case, under the mainsheet position, and between the mainsheet and the transom. The transom itself forms the final bulkhead. This one needs to be 6mm wherever rudder fittings will attach, and really solidly glassed in. Cherubs are notorious for rudder fitting problems. It is better to have a smallish drain vent in the transom rather than a completely open one, both for strength and for sailing. A longitudinal bulkhead will run from bow to stern. Don't forget to arrange for the minimum 3 buoyancy tanks.

Outer Skin.

Absolutely vital is a really good join at the centerline and chines on the outer skin. Some people cold-mould the bottom out of thin ply strips, and this gives a really strong boat if you have the time and skill. In the days before false floors two layers of 3mm ply for the bottom skin were recommended, and in this case the joints were staggered.
A single of 4mm ply is recommended. A lot of modern designs are very flat floored, and it might be possible to get away with a single sheet, but this will very much depend on the amount of rocker. Normally you will need a joint in the middle. For the reinforcement you could put stringers on the inside, (and in any case one light stringer will probably be needed to keep the profile correct), but a much better way of stiffening up and supporting the outer skin is run the inside fibre coating over epoxy fillets onto the hog and chines. This provides a really good support with a minimum of hard spots. The hull skin should also be glass coated on the outside, and this should be done last of all, running from the underside of one gunwale to the other.
You will need to scarph joint two pieces of wood for the bottom panels as twelve foot 6" lengths of marine ply are rarely available, and this is best done on a flat surface before putting the panels on the boat. You may well find that vertical strips need to be cut in the skin on the centre line near the bow because of double curvature. If you have a really complex shape you can make it up from all sorts of odds and bits. In any case, once the boat has been turned up, you will need to add a lot of stiffness in this area, which takes a real pounding going upwind in a chop. Probably the most suitable method is to use two layers of uni-directional carbon criss-crossed diagonally from chine to hog, and then a layer of glass over that. Try to fillet and shape the hog to let the glass go in one piece from chine to chine. This area used to be a common point of failure in the old days, and is one where the use of modern materials really pays off. Extend this extra reinforcement to about six inches behind the daggerboard case.
The glass coating needs to be made with a very low resin to glass ratio. Beware of adding weight! The way to achieve this is to use a heat gun to warm up the resin and a roller to really spread it out. Don't be tempted to warm up your pot full of epoxy though, it will go off in no time at all, leaving you with a beautifully moulded epoxy casting! It is wise to keep your resin in a tray once it is mixed as it will not go off as quickly.

Mast support & Space Frame.

This is an important issue. With the sort of rig tension used these days the peak loads going down the mast probably approach tons! Exactly how you step the mast is up to you, but the favourite location is on the false floor. It is conventional to support the mast with a space frame. This is not the sort of alloy contraption you find on some boats, but a ply/carbon/strip wood construction integrated with the main bulkheads in this area. Longitudinally it runs from the keel under the mast up to the top of the bow, from there up to the prodder anchor point, back down to the mast foot, and from the mast foot back down to the hog. Maybe also back to the post. Laterally it goes from the mast foot and the hog out to the shroud anchorage points, the front bulkhead being angled back on both sides. Arrange it so that the mast sits on the crossing point of the longitudinal and transverse bulkheads. You will need a really strong point for the prodder. It is advisable to have a foredeck on a wooden boat as it does a lot to stiffen up the front of the boat and support the rig loads. The basis for the prodder support can be the beam down the middle of the foredeck, which meets the upward extension of the space frame. Put a transverse bulkhead across too, but make it very light as it will take very little load (except when the crew crawls across the foredeck to disentangle the kite. The bulkhead supporting the foredeck will also be angled, but should run from the shrouds to just in front of the mast.
With the typical Cherub rig of lower shrouds and prodder you will not need to support the mast at deck level, but you might want to put a bit of strength there in case fashions change.

Daggerboard case.

Fortunately the false floor does a lot of the support for the daggerboard case. If you have a stringer each side of the daggerboard case to support the false floor they can support the sides of the daggerboard case. You may well want to bring the daggerboard case up a bit higher as the foundation of a tunnel. This keeps control lines out of the way, and gets the bowsprit out of the way when retracted, and can be used to stow the kite. The tunnel is probably best made from two layers of 3mm ply to give stiffness.

False floor.

You will have a variety of bulkheads to mount the false floor on as detailed before. Naturally all those which are not required to be watertight will be reduced to webs. These should have slim battens mounted on the top. You should also have stringers running down in the main stamping area. Work out exactly where the battens etc. are going to run, and put an extra layer of glass on the underside extending 25mm each side of where the bulkhead will touch. This will reduce the hard spot considerably. The floor should be 3mm ply with a layer of 100g kevlar on the underside. On the topside put a layer of 105g glass, and run it up over the fillet where the sidetank joins. This will stiffen it up, add wear resistance, give you a non-slip surface, and make holes much more unlikely. While on the subject of false floors, you will no doubt need hatches in them, but never put them where they can be stepped on. The hatch causes a hard spot which will crack. Right in front of the transom is a good place, and it also gives good access to bolt on rudder fittings.

Side tanks

If you have a reasonably deep false floor you can probably do without side tanks. However I would still advise side decks as they stiffen up the gunwales so much. The join between tank side and floor is a common point of failure, give it a good fillet and glass reinforcement. You may as well have some kind of side tank , because the box section gives so much extra stiffness, but you may well want to run sheets and things through forward.
Starting on the Interior.

Time.

Probably 200 hours or so with experience, and maybe approaching 300 for the first time builder. Cost of materials depends vastly on what you use and where you can get it. As of 1991 you would probably spend between UK£300 and UK£600 pounds on the hull, which is appreciably cheaper than foam sandwich.
Finally - don't forget: If in doubt - think. If still in doubt, ask a few people and think again. "Think twice and cut once is a very appropriate maxim. Have fun!

Jim Champ, adapted from Dick Jarrett. Andy Paterson of Bloodaxe Boats, who is by far the most experienced builder of glass/ply Cherubs gave me a great deal of help in preparing this piece, in particular in the choice of materials and other details of fibre-ply sandwich construction.
Photos (c) Bloodaxe Boats, Jim Champ, Bloodaxe Boats.

If you wish to have fuller construction details for building a ply sandwich boat then it would be worth considering purchasing a set of plans from Bloodaxe Boats, which contain much more detail than is practical to include here.
If you would like details on the methods traditionally used to construct ply Cherubs then the best source I am aware of are the drawings & construction plans for Farr Design #48 from Farr Yacht Design Ltd.

Building Carbon Masts

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I never managed to get anyone to write this for me, so, as I was acting as an amateur journalist, I thought a journalists trick would do. I sat Simon Roberts and Dave Roe down with a pint each, turned a tape recorder on, and asked stupid questions. Some might also consider it characteristic that Simon ended up buying the pints because I didn't have enough cash on me.

Introduction. Design. Materials. Layup. Finishing Off.

Disclaimer

Introduction

Mast building is probably the most challenging laminating job the amateur boat builder is likely to take on. It means handling a lot of material in a particularly tricky lay-up, and the consequences of getting it wrong are serious. If you build part of your boat with an unnecessarily strong lay-up then you've wasted a little bit of material and added a few grams of unnecessary weight, and if you make it too light then there'll be a small loss in stiffness and possibly the need to reinforce it. The kind of lay-ups described in other sections of these articles are very much on a "that will be plenty strong enough and adequately light" basis. Masts are more difficult. OK the possibility of making it badly and it ending up breaking is there, but that.s not the major issue. What's more serious is that the actual stiffness on the mast has - of course - a huge effect on the performance, and the actual difference between what we'd regard as a stiff mast and a bendy one is not really very much. This means that's its reasonably easy to end up with a telegraph pole or a fishing rod...
Don't take on a mast until you've done a good lot of laminating and can consider yourself reasonable skilled. You're also well advised to do a boom or a bowsprit first because the much smaller size makes the project easier, there's less of a worry about it ending up too stiff, and in any case its not such a big lump of cash in the bin if you get it very badly wrong.
This article is also rather less of a "how-to" than the others in the series, and rather more of a "how we did it". The folk who are building masts within the UK fleet are doing it with the benefit of some years experience and several boats behind them. There's no substitute for "getting your hands sticky". Its also well worth pointing out that there's no consensus as to the best way of building masts yet, and there are other methods that work just as well - maybe better.

Page Index

Designing the Section.

Its possible to start with a theoretical list of stiffness values and so on, and then go from there. This is what the companies who build big one off yacht masts and so on must do. All any of us have done is to start from a know alloy mast with published data as a basepoint, and then say - well, a bit stiffer sideways, much the same fore and aft, bendier at the top and so on.
Working out the values for mast taper is mostly informed guesswork as the figures are not published, and although we have tried to measure one, we didn't really get any results that we had too much confidence in.
Designing the section isn't about the cross sectional shape itself, so much as identifying the dimensions and fibre lay-up that will give you the stiffness you want. The maths is roughly Mechanical Engineering graduate student level, which may not daunt you, but rather does me. If you have access to reliable information that other people have worked out then all well and good. Basically a carbon mast tends to consist of a substantial layer of unidirectional fibres sandwiched between two layers of woven carbon which are primarily there to keep the unidirectional carbon in column and prevent buckling and peeling.
There are two ways of going about working out what this this lay-up should be.
One is to start with an existing mandrel or mould and then work out what lay-up is going to give you the stiffness you want.
The other alternative is to work out what lay-up you want to use, and then build a mandrel or mould to give you a section that will do the job you want. For instance Dave Roe's 1997 mast was based on 4 layers of unidirectional fibre. The actual mathematics required to design the lay-up is beyond the scope of an article like this - suffice to say if you haven't got either the mathematical skills or access to someone who has, or access to the technical information on the materials you propose to use, then probably you shouldn't be getting into mast building at the present state of the art
As an example one starts with the stiffness value of the particular carbon that you intend to use for the main structure of the mast, take off an allowance for the amount of resin that is likely to be in the lay-up, add allowances for internal and external skins (usually an order of magnitude smaller than the main unidirectional fibres), add an allowance for the mast track and then see what sort of figure you arrive at. This result may be unsatisfactory for one reason or another, in which case you have to repeat the exercise until you get something appropriate. A particular consideration here - especially with dinghy masts - is that they get bashed about a fair bit, what with beaches and trailers and roof racks and so on. Its probably fair to say that anything with a wall thickness of less than 1.5mm will be too prone too damage when not in use, no matter how appropriate the structure is for sailing with.
A couple of rules of thumb that can be of use are:-
Carbon rigs tend to be at least 20% stiffer than the equivalent section in alloy. This means that you can usually go one section size down when basing a carbon rig on an existing alloy one.
A 200g carbon cloth makes for about 0.2mm of section thickness in a lay-up.

Page Index

Material

You must be using a low viscosity resin with a very long cure time. It will take you hours to laminate up the tube. Resins from the Ampreg range are the conventional choice - Ampreg 26 is good. There are several reasons for using the Ampregs, which are, on the face of it, very expensive, but basically it boils down to "you get what you pay for" and in the case of the Ampregs you get an easy to handle lower toxicity resin with lots of desirable properties like low heat sensitivity, especially when cured. Don't economise on resin. Especially, whatever you do, don't consider using polyester resin!
There are all sorts of nasty small scale phenomena that can occur in carbon masts which just aren't an issue in a relatively low stressed hull construction that can cause all sorts of problems. One of the worst is "microcracking" which occurs if the resin takes up load before the carbon and cracks. Suddenly the carbon is unsupported and... I'm sure you can guess what happens next.
In the UK we tend to use fairly ordinary grades of carbon, which seem quite adequate. For the woven cloth inside and out we use a single layer of 200gsm carbon, which is the most economical currently available. Two layers of 100gsm carbon, aligned in different directions would be superior, but four or five times the cost. Higher grades or carbon could certainly reduce the size and weight - Dave Roe has calculated that he could make a 1.5 inch diameter mast that would be around 70% of the weight of the current ones, but that the material cost would be something like three times greater...

Laying it Up

Release Agent

In the past we've used a lot of paraffin wax as a mould release agent that can be melted out. If you have appropriate facilities and are using an aluminium mandrel then laminating and curing at a relatively high temperature can help considerably as the thermal expansion of aluminium exceeds that of carbon lay-ups. Experience seems to indicate that ordinary mould release agents just won't guarantee you to be able to get the mast off the mandrel. This is an area that the commercial mast makers are looking at a lot, and will need to be solved before true mass production mast making can happen.

Consolidation

Lay-up consolidation is absolutely essential. The best bet seems to be vacuum bagging. There are people who use tape successfully, but there are a number of dangers in this, most especially that of dragging the lay-up round the mast in a spiral which will probably result in less stiffness than was planned. I don't propose to go into a full treatment of vacuum bagging for the amateur here, but there's space for a few pointers. Supposedly there are some good books on the subject, but we've all learnt from talking to people. There's a lot of people who use the techniques in one industry or another these days, at least in our part of the world.
Peel ply is essential. Perforated release film is good, but hopefully the peel ply will soak up the resin unless you've got far too much in the lay-up anyway. Breather cloth is quite cheap, and you may as well use the real thing, even though some people use Chopped strand mat instead (about all its good for!). Even old blankets from a car boot sale will do the job at a pinch though, and are much better than nothing. You can use virtually any airtight sheet plastic for bag film but proper bag film is very thin which leads to smaller wrinkles, a better finish and less extra work. You will need to smooth the bag down as the vacuum goes in to minimise the wrinkles. Where the vacuum goes in is important - in practice bags always leak, and so if you have a leak near the inlet you may not get much vacuum at the other end. A tube with holes in to distribute the vacuum is thus a very good idea to equalise things out. SP recommend no more than 0.5 bar for the vacuum but by the time you've spent 4 hours laminating it up so the first layer is half set, you're working maybe in 16 degrees instead of the specified 21 then you may need to go higher simply because the viscosity is higher and the mix has half gone off as well. In practice if all the bleed cloth is saturated in epoxy you won't get much more resin out of the mix, and if you've put 4 layers of unidirectional on that's about right. The danger with more tractable lay-ups is that you can actually suck so much resin out of the cloth that the strength is badly compromised
Having said that the lower the resin ratio the better (well almost) and carbon masts need to be as dry as you dare go. At a maximum you should be looking at a lay-up that is one gram of resin for every two grams of fibre. If you're not confident about achieving that then maybe you want to tackle another boat before you do a mast. Unidirectional cloth that has glass binder is useful for helping you see how well wetted out the lay-up is. Its also worth noting that the consolidation effect of the vacuum increases exponentially with the decrease in pressure, and at the far end small improvements can lead to big changes.

Inner Layer

The technique we've used is to lay the mast up around a mandrel - effectively a male mould - and vacuum bag the mast onto that. Others have apparently made spars by making a female mould and using a bag on the inside to consolidate the lay-up. I guess that this would be more work on the mould, and more trouble to lay up, but be considerably easier to remove mast from mould.
The first (inmost) layer of lay-up is local reinforcement where fittings and so on will go. This is usually plain glass, and then a layer of light kevlar. This has two roles. The first is to add local strength where fittings and so on penetrate the mast, and the second is that the glass insulates the electrochemically active carbon from the fittings. Kevlar is chosen because its excellent for resisting crack propagation and so on, but has a tendency to go "furry at the edges", which glass doesn't suffer from.
The next layer should be Carbon cloth, 45/45 degree aligned for torsional strength. This is adequate for a dinghy mast, but something bigger will need to be designed more carefully. Its worth noting that, in contrast to a metal mast, fibre masts are not made out of a homogenous material, and can and will have significantly different properties according to the alignment of the fibres. It is not especially easy getting the fibres properly aligned and can be wasteful of cloth. None of this job is easy!

The Main Fibres

Once these layers have been cured and tidied up the main lay-up of uni-directional fibre can be commenced. This needs to be done as a single job, which will take several hours. Obviously it needs to be done carefully, making sure that all the fibre is properly wetted out (not always easy to tell with carbon,) and that there are no voids and that the fibres are correctly distributed round the spar.
Fair up this layer before you put the outer skin on. Here you've got to be careful with the (virtually inevitable) wrinkles. If you have longitudinal wrinkles of carbon sticking out then you can sand them down without too much worry. After all what they principally represent is fibres that have been squeezed out as the laminate compresses down, so you can take them out without compromising strength or lay-up thickness. Horizontal wrinkles are trouble because if you sand them off you are breaking into the carbon at a single point, making a spectacular weak point. This is mainly a matter for very careful vacuum bagging.

Mast Track

The track - provided you aren't making a trackless mast for a sleeve luff rig - should be made from half inch diameter pultruded tube from whatever your handiest source is. Glass is cheaper, heavier, and has less impact on the final bend characteristics. Carbon is more expensive, lighter, and contributes more to stiffness, especially fore and aft. Glue the track on with a reasonably strong filled epoxy mix, and then fair up the gap between tube and mast to your preferred shape with something a bit lighter.
In New Zealand they take a different approach. They make their tracks from a rubber type caravan awning track which bends very easily but does not seem to lose the bolt rope out of it. This is glued onto the mast using a particularly flexible adhesive called Sikaflex.
Take a good look at the end of the mast track where the sail feeds in. Its very easy to let the luff rope get trapped across the groove. This puts a very big load on the track and has bee known to actually crack the track, after which the luff rope gets in the slot more and more often, rigging is a pain, and the luff rope can pull out of the groove whilst sailing.. Rainforce the last inch of the track so that this doesn't happen. Similarly be very careful about the end of the slot. If its too sharp a corner you may risk tearing the sail, but a very even taper means the luff rope getting caught for sure.

Outer skin

Lastly on goes an outside layer of 200gsm carbon, this time aligned 0/90 degrees to the mast, plus appropriate local reinforcement where needed. It goes round the mast track of course. Should you ever wish to modify the stiffness of the mast by adding (not always successful without great care) or removing fibre, you should sand off this entire layer and then replace it when you've made the changes. One has to be very careful about adding extra fibres later, because its very difficult to get really first class bonding between the original and added structure, which means that there's always the possibility that the load won't be distributed between the fibres that well. There is no especial constructional reason for having the 45/45 layer on the inside and the 0/90 layer on the outside other than it is easier to make a neat job of the 0/90 lay-up. As mentioned above the optimum would be a thinner layer of both each side of the uni-directionals.

Page Index

Getting it off and Putting the Fittings on.

A lot of people commercially are working on reliable release and easy lamination. It can be big trouble. Quite often its easier to simply cut the mast down one side and take it off like that. After you do that you'll need an outer layer of carbon again, but its not as disastrous as you might think because your cut is aligned with the majority of the fibres anyway. If you have an alloy mandrel you can make it as cool as possible to shrink it out from the lay-up, if you used wax then very hot water down the centre of an alloy mandrel gets it out a treat, or alternatively you can melt it out with a heat gun (don't get the lay-up too hot!).
Cut out the slot in the mast track. I suppose in theory the slot reduces the effect of the outer layer of fibres, but the track itself contributes plenty of strength in that area, and it doesn't seem to be a problem.
Fit out the mast out pretty much as normal - but be *very sure* that the fittings have been placed where the reinforcement for them was. Corrosion is a significant consideration - carbon is electrolytically active and there's a considerable potential between it and aluminium. Make sure there's no contact between aluminium and carbon - stainless rivets are definitely preferred. This applies to other fittings as well. Again glass can be used as an insulator, but resin coat the alloy fittings too and generally do your best to keep them isolated. In this context its worth noting that I've heard reports that RS600 mast bottom sections - which have an aluminium sleeve to shorten the mast to reduce sail area - have, in some circumstances, actually failed because of the expansion caused by corrosion of the aluminium. Be very careful with rivets and avoid them if you can. In particular make sure that the holes you drill for rivets are as tight as possible in order to avoid the rivet expanding in the hole and causing a local distortion in the structure. For similar reasons backing washers on rivets are nothing but a good thing if you can possibly get them on.
Finally paint it. The main reason for painting the tube is to provide UV protection. This most especially applies to a mast, which unlike the boat tends to be out in all weathers uncovered - at least if your boat lives at the Club all year round. For this reason I painted my carbon mast white, as this should reduce the amount the layup gets cooked on hot days. Having said that all the mass production companies seem to think a clear lacquer to stop the UV is more than enough, and if, like many Cherubs, your boat lives in the garage, not the sailing club then its not nearly such an issue, so paint it all the rainbow colours you like!
Jim Champ, 1998, with grateful thanks to Dave Roe, Simon Roberts & Tim Dean.

Fitting Out A Cherub.

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Disclaimer

Rigging

Keep It Simple.

There is absolutely no need for complex controls on a Cherub. The modest sail area means that the rig is kept powered up most of the time, and spectacular rig controls only distract from the serious business of sailing the boat as fast as possible.

Rig Tension

Most modern Cherubs use loads of rig tension - enough for many SMOD boats to just fold up! 300lbs plus on the shrouds is not unusual and often a lot more. The primary reason for using lots of rig tension is because the crew is on the trapeze. If you have 100lbs of rig tension on the windward shroud, the leeward shroud just slack, and the spreader holding the mast straight - as might be the case on a sit out boat - then when your 140lb crew gets out on the trapeze the windward shroud will go slack and there will be 40lbs tension on the leeward shroud, with its spreader pushing the mast mid section up to windward, depowering the whole rig. This is slow! Consequently most boats start with 200lbs plus of rig tension. On the other hand you have to be sensible with older boats. If I put the 400lbs odd tension I use on the foam sandwich and carbon reinforced Bistro on my 3mm plywood topsides 1972 Farr then the poor old lady would just bend up and probably break. A good clue is to watch the foredeck as you put the rig tension on. If the boat is distorting the gunwales will spread between the mast and the forestay, and the foredeck will distort and go into humps and hollows. You have no foredeck? Another reason why its a bad idea to lose it! Obviously extra rig tension also tightens the jib luff etc, but I suspect that by the time you've got enough tension to make the spreaders work right with the crew bouncing on the wire the behavior of the jib luff has ceased to be an issue. Its good to have the shroud anchorages as far outboard and aft as possible to reduce the peak loads when nosediving etc, although obviously you also have to be able to let the boom out.

Standing Rigging.

Cherub rigs need to be strongly supported at gooseneck height. The short boom and big roach means there will be a lot of kicking strap load which will try very hard to bend the mast sideways and dump all the power. All fittings must be stronger than you think. Everything should be bolted on, and attached to something secure. If you have the slightest nagging doubt about something it will break. Cherubs seem to put phenomenal loads on fittings, and most especially anything to do with lower shrouds.

Gooseneck Level Control.

The anchorage point for the lowers needs to be incredibly strong T terminals are the only choice in an alloy spar. Any kind of rivet will either snap or pull through the mast. A plateround the mast front like an RS800 is about the only alternative. On a carbon mast T terminals are also OK, and another good alternative is s/s rings bonded in with a lot of carbon. The other end should be absolutely rock solid, bolted, and ideally putting its anchorage in compression - e.g. running round the gunwale. A well monted anchorage loaded in sheer will also be fine, but any trace of tension and it will just peel off.. On a foam sandwich boat a stainless steel ring firmly located with a lot of unidirectional carbon is a good solution. On single spreader rigs you normally need what we in the UK call a prodder - a strut to gooseneck height from the foredeck.They do, of course, preclude self tacking jibs. On twin spreader rigs the extra control of the mast further up seem to make these less essential, and it seems to be possible to get away without them, especially as a prebent rig resists mast inversion - one of the most common causes of failiure (other than fittinsg breaking!). An alternative you will see is to have the mast supported by "rigid" lowers - struts to the gooseneck to replace lowers, which at the cost of a bit more windage lock the mast very rigidly. Gavin Sims currently has a post to gooseneck height supported by rigid struts, with the mast stepped on top. The twelve foot skiffs use a similar arrangement without the struts - just a post of truly massive construction integrated into the hull. This weight goes into the hull weight total and is towards the middle of the boat so its quite acceptable on a new boat. The loads at gooseneck level are magnified by this arrangement as the rest of the rig doesn't assist, so don't underestimate the loads involved. Your editor did back in the late 1980s and put a mast through the foredeck twice in 3 days.

Single Spreader Rigs

This was the most common setup prior to the extra sail area introduced in 1997 and will still be found on older boats.
Two shrouds, one set of spreaders, lower shrouds to gooseneck height, and prodder - used as much to induce pre-bend as anything else, so needs to be strong in tension as well as compression. The lowers don't need to be adjustable, but you need an easy way to tension them. A kevlar/spectra/other high tech rope lashing is as good as any, very cheap, and very effective. Kevlar 's tendency for unannounced failure is always a worry though. Although in theory raked back spreaders lead to better gust response in practice on a Cherub you are hunting for power much of the time, especially with a pre 94 rig, and so spreaders would be neutral or slightly angled forward to keep the lower mast straight in conjunction with the prodder, leaving the top mast to flex and provide what gust response their is. This is probably still the best solution for a boat with an alloy mast. Tall alloy masts with twin spreader rigs seem generally to have too much weight aloft and performance suffers upwind. I think Andy Paterson was the only person to manage a competitive two spreader alloy rig. The spinnaker halyard can be appreciably above the hounds. You can probably go to about two feet or 60% safely, although this depends some on the mast section. The most extreme was probably my rig seen on earlier picture of 2641 on this site, but I had a particularly solid mast section.

Twin Spreader Rigs

With the greater sail area since 1997 and the much lower weight of carbon spars these are pretty much universal on newer boats. A typical two spreader rigs with masthead upper shrouds will have quite a lot more wire. The most common setup is to have conventional spreaders to a conventional height, plus "D2" or checkstays running from the shroud plates to the root of the spreaders. This locks the bottom of the mast fairly rigid. The masthead shrouds are actually diamond stays, normally running through spreaders on the hounds then through the main spreaders, and then back to the mast around gooseneck height. These shrouds will reduce sideways bend considerably, and also support the tip of the mast for a masthead spinnaker. You can also use them to induce considerable pre-bend in the top mast, similar to a skiff/49er rigs.
There is a lot of variation in the staying arrangements. Most UK rigs use shorter upper spreaders, with the caps attached to the lower spreaders about halfway from the end to the root. The cap spreaders are heavily raked aft, introducing greater or lesser amounts of prebend, according to your sail cut. Most prebend is seen on the Andy Paterson designed Superspar/Caws rigs, and least on Batt based rigs like Dave Roe's and Robin Russell's. At the lower spreaders the caps are set with relatively little deflection so that they have little effect on mast bend. Some rigs - noticeably Andy Paterson's and Robin Russell's have the caps pulling the mast forward at the lower spreaders and the shrouds pulling the mast aft and acting against the pull from the caps. This has the effect of locking the mast to a certain extent at spreader height and can mean that you can do without the check stays and all their extra windage.
By contrast my New Zealand designed C-tech rig has a lot of aft rake on both sets of spreaders and full length spreaders at the hounds. Both sets of spreaders are well raked back, and the check stays are vital, taking at least as much tension as the shrouds in order to hold the mast straight. This holds the mast very firmly with a lot of control of the prebend, which is largely above the hounds.

Over Rotating Masts - Wing Masts

It hasn't been done in this country for many a year, but in Australia a couple of boats have recently been seen with over-rotating semi wing masts, based on NS14 sections. This is a classic example of the wheel turning round, as such rigs were used in the early 70s, although the masts were spruce and balsa then. Such spars ought to be effective if you get them right. Supporting the bigger UK kites, especially masthead ones, could be a challenge, but it can be done - Alex Vallings of C-tech Spars in New Zealand has recently won an R Class Championship with a mast which has the tip supported by rotating spreaders. He tells a story of spending some time with a model made from broomstick and string working out how everything needed to be set up to avoid wires clashing as the mast rotates. In 2002 we permitted a mast with a greater chord than previously provided the area is measured in, and there is probably a performance benefit to be gained for a project with a considerable development curve. Bethwaite is good on the subject in "High Performance Sailing".

Necessary Gear

Main sheet
Jib sheet
Spinnaker Sheet
Spinnaker halyard/retrieve
Pole or Bowsprit/retrieve
Kicking strap
Cunningham
Outhaul

Optional Gear

Jib slot (barber hauler etc.)
Prodder adjustment
Main halyard

Unnecessary Gear

Jib halyard
Adjustable standing rigging
other trendy trivia

Mainsheet.

There are two popular mainsheet systems. One is to have a central post (like a hoop, but lighter and cheaper), and the other is to have a fixed bridle at the transom which joins the mainsheet at boom height. In either case the mainsheet is led to the centre of the boat, has a ratchet block, and if there is a jammer it should be arranged so that the crew can use it from the trapeze. Very often the mainsheet is lead from a ratchet block on the boom direct to hand, and not to the floor. This is definitely the preferred setup if the crew will take the mainsheet on the beats. This may sound weird, but try it!

Jib sheets.

They can be led to anywhere convenient, with a jammer that can be freed and jammed from just about anywhere in the boat, since the crew will be trapezing right at the back of the boat on windy two-sail reaches. Inboard from the shrouds is a good place, out of the way but accessible. Continuous jib sheets are popular. Sheets should be long enough for the crew to be able to fully free the sail from on the trapeze at the back of the boat. If they are too short you will regret it!

Self Tacking Jibs

The sailing techniques are different, especially upwind, where you don't just leave it and forget it - see the heavy weather sailing article. They're best done with a track and roller bearing car - the smallest available say Frederiksen 020. The track is bent to slightly less than the radius from the tack of the sail to clew. The sheet is 2:1 under the deck, with the final lead exiting and going round a cheek block just behind the sail tack. The track is bent in one plane (forward but fitted angled up slightly , i.e. the ends are slightly higher than the middle). The ends are fixed in foam/carbon supports, and one screw in the middle into the mast step structure. It's a very good idea to have two bolts in the track at the ends, because if the track comes undone you will not only break the track, but also lose all the bearings out of the car. You also tend to hold on to the track launching, so it needs to be prettu substantial. The track is angled/bent/fitted so that heavy sheet tension will pull the car to the centre of the track in no wind.
The wind pressure in light winds and low sheet tension is enough to move the car to the ends of the track. In stronger winds it also works fine, but needs rubber stops at the end of the track.. In general people don't seem to have stops for sheeting angle, so it would be wise to have numbers or marks on the track. Sheet tension varies the leech tension as required. The pulley on the track is suprisingly tricky. It wants to be as light as possible for light airs, but it takes a lot of abuse when the jib flogs. A block with plastic cheeks will waer theough quickly, and it takes quite a bashing so should be strong.
Most people have a swivel jammer not unlike a mainsheert jammer for the jib, and a single sheet. This is probably neatest. An alternative would be to split the sheet to each side and run them to a conventional sort of location. In any case remember the crew will still need to play the jib sheet on two sail reaches and while tacking. And just because there's a two to one purchase don't use a thin rope. The crew needs to be able to use the jib sheet to pull themselves back to the boat if you teabag. Given a 4mm line and a cold day this just doesn't happen. Trust me in this!
The clew position on the sail is crucial. You'll probably end up getting the sailmaker to change this once the setup is all sorted out. Mutiple holes on the jib clew give you a choice of slot angle/twist in the jib against the sheeting angle.
It can be a good idea to add backing lines. These are a couple of light lines running from the car to the shrouds on each side, long enough not to restrict the normal movement of the jib. If you need to back the jib for some reason then pull on the line. To heave to between races hook it over something handy! But if you find they get snagged take them off, they're not that vital!

Spinnaker sheets

These are invariably continuous. Ratchet blocks are essential, and the same comments on jammer location apply. The turning point for the spinnaker sheets will never need to be aft of the mainsheet, and may be as far forward as the shrouds with some sails. Not everyone has jammers, but I find them handy for keeping the sheets in the boat upwind, and for quicker hoists in light airs (keeping the sheet jammed). Mind you if you hoist with the sheet jammed in 25 knots you'll swim. Most boats with snouts have a hollow in the gunwale line between the snout and the shroud. This makes spinnaker sheets especially prone to be washed into the water on the beats. Andy Paterson has small "hooks" made from very flexible polyethylene on his gunwale. Flick the sheet onto this and it stays on board, but they're too soft and flexible to snag anything or damage the spinnaker. Again sheets should be long enough for the crew to be able to fully free the sail from on the trapeze at the back of the boat.

Other Spinnaker Gear.

The adoption of asymmetrics has simplified spinnaker handling a lot. There is no spinnaker guy, and the sheet is really easy to handle and rarely cleated. The spinnaker halyard will double as the retrieve line. A double patch system is normal, with a chute or hatch about a foot behind the stem to reduce tangles with the jib foot. The halyard and the retrieve should be arranged so that helm or crew can handle it. Launching and retrieving is quicker if one takes the halyard and the other the pole and sheet, but if its blowing 30 knots the helmsman will be a little preoccupied with keeping the black plastic pole with the translucent sheet above his head rather than below the water.

There's more than one way of dealing with the bowsprit of course, and there are some ingenious "one string" systems about. Much less hassle when they work properly, although you do end up with more halyard to pull up. The following is probably the simplest system to rig and set-up. The Tack of the kite is attached to a "guy" coming through the pole and to an anchor point in the boat. Its set up so that the line is taut and the spinnaker tack pulled right down to the pole end when the pole is pulled right out. A second line runs up to the bow and back to the end of the pole to pull the pole out. Depending on the friction in the system and the strength of the crew you might wish to have a 2/1 purchase on this. There's no retrieve for the spinnaker pole as such, the act of pulling the spinnaker back into the chute is enough to bring it back in.

If at all possible have a spinnaker pole strong enough to be unstayed. But if your spinnaker pole isn't strong enough to operate without a bobstay then the best way of arranging one is to have the "guy" running through the end of the spinnaker pole and out again and then down to the bow. In this case the line is tidied up by having it pass through a ring or pulley inside the pole, which in turn is pulled back with shock cord. This works well enough, but you'll probably need a little more purchase on the outhaul to make sure the bobstay is tight enough. You might get the occasional snaggle inside the pole too.The anchorage at the bottom of the bow is also a problem. Apart from the water resistance if its not made strong enough you can pull the bottom of the stem off.

Sail Shape Controls

Kicker and Cunningham are usually led back to mid length so that the helm can adjust them while sailing. You will need at least 6/1 Cunningham with a Mylar mainsail, and probably more.

One important tip with the cunningham - attach it to the boom. What I mean is that the fixed end of the purchase needs to be pulling up on the boom. This means that the ciunningham load offsets the kicker load and thus reduces the strain on the gooseneck fitting. Don't laugh - they break!

Kicking strap purchase should probably be 16/1 or 24/1, but it all depends on where the take-off on the boom is, and how low the other anchorage is. The boom take off should be a nylon strap. Proctor make very good and extremely expensive ones for the 14s, but any sailmaker will be able to oblige. A cascade type purchase is most common, but is quite draggy. DAve Roe uses an old fashioned differential winch, but with rope rather than wire, and this certainly makes for a much cleaner boat, although no-onme else does this.

The outhaul is normally cleated on the underside of the boom. You may not use it much when actually sailing, but you will need it when you see exactly what the wind is doing when you get out to the start. 6/1 is probably about right as you won't get a good pull at it.

Optionals.

The jib slot normally has a lateral control on a short length of track. About 3" of movement is all you will ever need, but if you don't know where that 3" is going to come you will want it longer. A lot of people have a height control, but it can be as simple as a cleat on the track, because you usually adjust it on the opposite tack. Don't clutter up the crew's area with a lot of string designed to let you adjust the slot in any direction at any time. He'll only trip over it and fall out on the last tack when you were about to win your first Cherub race.
Some people have a control to adjust the prodder. I don't bother because I want a rigid prodder to induce pre-bend. A length of track on mast or foredeck with a locking pin on the prodder slider is normally all you need. If you are inducing prebend make sure the prodder is strong in tension!
If you sail in some places you may feel the need of a main halyard. Wire is probably still best if you don't have a halyard lock. Be very cautious about Kevlar in this application because its notorious for breaking without warning. Spectra on the other hand seems prone to slippage or stretch due to the polyester sheath. With a 10/1 cunningham you can stretch just about anything, and of course the halyard also increases compression loads on the mast. A reliable halyard lock is great - again Proctor make a really good and expensive one for 14s. Personally I consider the loop of rope and hook approach to be far safer since you - or the rescue boat - can get the main off so much faster when capsized. Don't use kevlar for the loop though - it breaks. Use pre-stretch terylene - the length isn't enough for stretch to be a problem.
Whilst on the subject of main halyards I'll mention my favourite technique for landing on lee shores. Bring the boat hove to a little short of dead upwind of your destination. Pull both foils right out of the water (daggerboard rudders are great for this). Now you can just drift in sideways until the water is shallow enough, then immediately let the boat capsize, pick it up and carry it up the beach. (Don't try this at home with a Laser 5000 people). Even at inland clubs I find this easier than using a jetty.

Unnecessary.

A jib halyard is basically a device to put a 2/1 compression load down the mast. As no one uses a forestay you can't take the jib down while sailing, and rigging a boat on its side is so much more civilised. Have a wire strop and a T terminal, and use a short lashing to get the tension.
Adjustable standing rigging has never been used in Cherubs. Its heavy, expensive, and complicated.
Other gadgets also have no place..
Most of all, remember that the boat is weighed dry. Take all those ropes, weigh them, soak them in water and weigh them again. The difference will amaze you!
Finally, don't spend too much time worrying about gear. Instead go sailing! Provided all the gear works and is reliable then it is probably good enough. Being able to change the sail shape in the middle of the race is unlikely to make much difference to your final position, but capsizing at every gybe mark certainly will. There is absolutely nothing that improves boat speed as much as crew speed!
Gear & Fittings Installing a Bowsprit Building a Rudder Gantry Building a Rudder Stock
In the old days making your own gear used to be a part of the game. Nowadays you can get most things ready made, but there is always scope for a bit of ingenuity to complete the job. This neat jib tack cover is from Dangerous Strawberry.
Pic - Tack cover
[Picture : Jim Champ]

Installing a Bowsprit.

The Pole.

Unstayed Carbon fibre poles are now more or less standard. Most are now home built, but a the lower section of a sailboard mast (7.4 or better stiffness) will also be good, as is the bottom section of a carbon dinghy mast. If you can get a broken one with the right bit left so much the better. The length of the pole is not restricted, but 1.8m from the stem is typical. Give the pole a nice rounded end, with a central hole for the string. A tapered pole is much to be preferred as it retracts much more easily.

Spinnaker Pole Mountings

New Boats.

Now that snouts are allowed getting the pole in becomes a lot easier. Because the pole is allowed to be 300mm from the end of the snout when retracted its possible to have the pole exactly on the centreline because it won't reach the front bulkhead when retracted. The snout will need to support the bowsprit in two places, and these will need to be very strong. The snout itself also needs to be very firmly attached - thoroughly integrated into the boat really! You'll probably be anchoring the job to the end of the snout too, so the loads will be pretty serious. The jib takeoff point will probably be right above the hole for the pole. This is not great engineering wise, because there will be a tendency to pull the hole oval - which, apart from the loss of rig tension, would also jam the pole! It would be as well to fabricate a carbon ring, about 2 inches long by about 5mm thick, and integrate the jib fitting into this. Its probably best to use a stainless steel D-ring or a shackle and bond it in place with generous quantities of uni-directional carbon The second point should be a small bulkhead about 300mm or so further - the stem position.. Have two rings with proper bearing surfaces. Probably the best is Tufset, from (Inter alia) RS Components as its a polyurethane that bonds well with epoxy. Nylon is also a very good bearing surface, but must be mechanically fastened as it won't glue in with epoxy. The whole assembly needs to be very thoroughly glassed in. The whole structure must be rigid, and you may have to reinforce the topsides, especially if its a wood boat. (You're not really building a new wood boat are you!).

Old Boats.

Life is a bit tougher for you. If you're doing major surgery and building a snout its just the same as above really. Otherwise the pole will be coming right back in the crew area, ideal for tripping up the crew every tack. Ideally the boat would have a tunnel besides the plate case for the pole - as we did on new boats in the days before snouts - but the chances of having a suitable tunnel on an unconverted boat are minimal. I don't know of any UK built boats which have one. Rather than coming through the bow on the centreline, a conversion will need the pole offset to one side, through the topsides just to starboard, so that it clears the mast. As far as the kite is concerned the existing stowage arrangements will do, but don't forget the longer luffed asymmetric will come further back in the boat. Arranging the pole is very much a matter of compromise. It wants to be as low as possible in the boat so the crew doesn't trip over it too much, but you will be limited by the height of the bow tank, not to mention the need to keep the end out of the water! If you have a full height bow tank then you will either have to rip the foredeck off and put a low tank in or else make a tube that extends right through the tank. If you do this the bowsprit will retract nearly back to the transom! The pole support arrangements will be much the same as on a new boat, but the bulkhead and anchorages will need to be looked at very carefully as loads are being put on that the structure was never designed for. Wood boats with 3mm topsides will have particular problems and will need extensive reinforcement.

Making the bits.

The tube that the pole slides through should be at least 4 layers of 200g glass (or better). Mould it round the pole. The technique used with mast building of coating the "mould" in wax and melting it out afterwards with hot water will be best, but failing that put on several separate layers of polythene sheet. It needs quite a few layers because the lay-up will shrink a little on curing. Unless you use wax you will have a lot of trouble getting the tube off the pole. Cooling the whole assembly down to shrink the tube helps.
I suppose foam sandwich is probably favourite for the bulkhead, even on wooden boats, because the width of the foam helps support and keeps everything stiffer. Glass it in well, and make sure its attached to something strong. If its just glassed onto topside and decking it will all warp.

Assembly.

This is definitely a job for measuring 3 times and gluing once. Start by fitting the bulkhead, but leave a bit of play where the tube comes through the topside. Check and double-check that everything is lined up correctly both with the pole in position and retracted. There is at least one boat where the kite tacks down 6 inches from the centreline - you don't want yours to be the second.
Gear & Fittings Installing a Bowsprit Building a Rudder Gantry Building a Rudder Stock

Building a Rudder Gantry

These are by no means essential. They help keep the back of the boat clear and aid steering on a two sail reach. On the other hand the loads are tremendous and a failure is a guaranteed race loser. A rudder gantry isn't that difficult an item to build, so here are a few pointers.

Materials

Successful gantries have been made out of:-
18mm diameter pultruded glass tube
Ordinary 1/2inch wood merchants dowel, reinforced with carbon or glass.
One inch balsa dowel core coated with carbon and glass
Aluminium tube
Titanium!
The trouble is that unsuccessful gantries have been made out of just about all these materials too.
The secret of a good gantry is the joining of all the components. The individual beams rarely fail, it's usually a join or the attachment to the boat. If you stick some bits of wood dowel together and bodge it with a bit of epoxy filler it's unlikely to stay together. Similarly if you attach a gantry - which creates considerable and variable tensile loads - straight to the outside skin of a foam sandwich transom the transom will delaminate and the outer skin will be pulled off.
Aluminium - let alone Titanium - fabrication is a rather specialised area, and best left to those with appropriate experience. Aluminium gantries assembled from pieces bolted together tend to fail, and an all welded construction is recommended. Without specialist facilities and experience you will be better off using composite construction.

The Bars

Sketch of gantry assembly. A typical gantry looks something like this. It consists of two V shaped assemblies top and bottom to take the loads, plus a further tube running diagonally upwards from the centre of the lower assembly to the transom to brace the structure further. Depending on exactly how your boat is engineered it may make more sense to have this brace running from the top downwards. Ready made pultruded tube has got to be the easiest material for the bars. Glass seems quite strong enough, but you can use carbon if you want to. If you feel like it and can reliably make good solid tubes then you could make some and use those for the structure, but purchasing the ready made stuff is not too expensive.

Assembly.

Gantry Build Stage 1
This is where the project will go right or wrong! I like to make up carbon brackets to join the components. I started by making up two V shaped assemblies for the top and bottom.
The join was made by making two triangular carbon/glass plates, about 3mm thick, and gluing them each side of the horizontal tubes with plenty of strong (with microfibres) filler. When this was cured I drilled and cut it for the next join. The vertical piece (that the pin slides through) was glued into the holes drilled in each bracket, and then the diagonal brace in the slot cut in its bracket. At this stage the joins look something like this.
Gantry Build Stage 2
Fill and smooth all the edges, fillet all the angles, and make all the corners nice and blunt. An angle grinder is quick and dangerous, a file slow and safe and essential in the trickier places. Now wrap every join with generous quantities of unidirectional carbon, and perhaps a layer of cloth over the top to keep all neat. Extend the carbon wrapping an appreciable way - maybe an inch - beyond the solid webs, and make sure that it tapers off neatly and smoothly to avoid "hard spots". The webbing of the joints with the plates, plus the tapered carbon wrapping, is what gives the construction its strength, so fiddle though it is, don't skimp this hassley job. The vertical tube can have nylon bushes top and bottom for the pin to save wear. If you have no other source buy RS400 ones!

Attaching to the boat.

Also vital. A solid stiff rudder and gantry assembly floating a few feet behind the boat has no effect on the steering! There is no substitute for having really stiff and solid mounting points built into the boat. Take the bars of the gantry right through the foam transom and glue them in with a nice strong filled mix. Cut them off flush with the inner edge, radiusing the corners. Cut some strips of unidirectional carbon about 4-6 inches long., "fray" one end, but leave the other end untouched. Wrap it into "sausages" and wet it out thoroughly with epoxy. You want to aim for enough strips that the sausages can only just be crammed into the end of the tube. Feed the good end into the bar for two or three inches, together with enough filler so that it is really thoroughly sticking to the inside of the tube. You'll need to use a small stick or something, but really get it in there. Now spread the "frayed" end, about another 3 inches, all over the adjacent inner skin, so that it fans out in every direction. In this way the loads from the gantry come right through the transom and are well spread out over the skin, avoiding the risk of delamination of the transom. On wood boats the bars should come right through the transom beams and be well epoxied and filleted in.

Fittings

A lot of problems with composite gantries and rudder stocks come when aluminium or stainless steel fittings are attached. It is virtually impossible to get a reliable bond between metal and composites. If you must use metal fittings then bolt them on solidly to ply pads - nothing else will do. Much better is to fabricate the fittings from epoxy/glass. A pintle will rotate just as happily in a glass tube as in a metal one, and you will find it a great deal easier to integrate the glass tube with the rest of the structure. No doubt it would be possible to create carbon pins for the male part of the fitting, but I prefer to have female fittings on both stock and gantry and run a single stainless steel pin right through the lot.
Gear & Fittings Installing a Bowsprit Building a Rudder Gantry Building a Rudder Stock

Photos (c) Jim Champ. They're of the gantry on my singlehander, not a Cherub, but its built like a Cherub!

Building a Rudder Stock

This is a Legacy Page

You have arrived at an old part of our website, to find the latest information please visit our new page about building a rudder stock. The new portal for the site can be found at www.uk-cherub.org please visit this for up to date news about the UK-Cherub class.

Most Cherubs seem to get a number of rudder stocks over the course of their lives, as its one of the most popular breakages. I'm probably not the best person to write this, because I'm no exception. However, I've had the request, so here goes.
Gear & Fittings Installing a Bowsprit Building a Rudder Gantry Building Foils

Disclaimer

This document is compiled by an amateur, not a professional. It has been compiled in good faith, but almost certainly contains errors and inaccuracies. "Best practice" also changes frequently with changes in technology and materials. None of the procedures listed are guaranteed to work, and some or all of them may be hazardous. If you feel unable to take responsibility for your own actions and errors without resorting to the legal profession then you are advised not to read it, let alone build anything based on information here. In any case you are advised not to build a composite structure without someone experienced in the materials to contact for advice.
I like daggerboard rudders, so that's what I'm going to describe. This is based partly on ideas from Andy Paterson, who has helped me out with some details from his Moth building guide.
Stock showing weak points.
The number one cause of trouble is an attempt to bond metal to glass or carbon. This is extraordinarily difficult to do, and is best avoided. The full length pin seems to be pretty standard, especially when the rudder is attached to a gantry. It does help keep things a little more rigid, and also means that you can make the stock entirely of epoxy/fibres, without any metal.

The Sleeve

Start by moulding the sleeve around the rudder blade. Its difficult to take too many precautions against getting epoxy on the blade - lots of work to remove. Cover the top half of the blade with parcel tape, with it overlapping the trailing edge of the blade, and apply release agent or candle wax. Suspend the board with the leading edge horizontal and uppermost. Laminate the case using an appropriate layup (100 g/m² glass + 2 x 200 g/m² carbon or 4*200g/m2 glass would be fine, allowing the fibre to overlap past the trailing edge. When its cured, trim the case to about 2mm oversize. Split the case from the foil, and add several layers of 18mm masking tape plus parcel tape to the trailing edge of the foil to make a thick edge to the foil. Replace the blade in the case, fill the open joint at the trailing edge, and laminate strips of glass around 20mm wide over the joint, with kevlar at the bottom (all held in place with masking tape). Its probably also worth putting a few layers of glass extra at the leading edge, as it tends to get a lot of bashes as you pull the blade in and out.
When cured remove the sleeve, remove all the packing from the blade and make sure it slides very easily through the sleeve. If you can't slide the sleeve off the blade at all, or if it seems stiff on the blade, then cut it neatly down the trailing edge and try again with more layers of masking tape! The sleeve will need to reach from the top surface of your stock to the lower edge of the bottom fitting. These means about 75mm greater than the distance between fittings, but make it bigger and trim later!

The Bottom Fitting.

This is a favourite breakage point, and needs to be stronger than you'd possibly believe! Dave Roe reckons that the peak sideways load on the rudder stock is in the close order of magnitude of 400lbs. If you want a mental picture of this imagine the boat sitting on its side with 80 (Eighty) bricks piled up on the top of the blade.
The best way seems to be to start by laminating up a solid carbon plate, about 4mm thick, about 75mm longer than the section length of the rudder blade, and 75mm wider than its thickness. This need a great many layers of carbon cloth, and make sure that the fibres are aligned both 45/45 and 0/90 degrees to the blade. This is a great time to use up all those odd bits that have been accumulating in the plastic bag of offcuts in the garage. Because I worry about point loads on the foil, I glue a piece of 8mm foam onto this, and then cover the other side of the foam in a couple more layers of carbon cloth, but Andy Paterson finds this unnecessary, and I'm sure he's right. Anyway, either way we now have a substantial black plate. Cut a hole in this so that it fits over the sleeve at 90 degrees to the foil with (of course) equal overlap. You may wish to have the plate angling up about 15 degrees fore and aft to clear the stern wave, but this depends a lot on your rudder gantry. Between the two you probably want the aft end of the plate about 100mm above static waterline. Make sure that the sleeve fits freely - its very easy to squash it so that the blade won't go through. When you are really happy with the fit (check three times!) then glue the bracket onto the sleeve. Use a nice strong filler mix - there will be load on this so use some microfibres and silica along with the light stuff. I suggest you wrap the foil in plastic again and put it through the sleeve to make sure it still slides freely while the glue is setting. Give a nice generous fillet with your favourite light filler between sleeve and plate, and put a layer of glass over the fillet - it all helps distribute the load evenly onto the blade.

The Tiller

There are a lot of ways of doing this. I suppose the best, especially if you happen to have a handy bit of carbon tube lying around, is to make the tiller from a piece of tapered carbon tube, cut a slot for the sleeve, and glue it in a similar way to the plate. You need to be quite careful about the tube you pick, especially about the resulting thickness at the leading edge of the blade where a lot of tube is cut away. I guess a lot depends on how much extra carbon you put on.
My normal method is to make a rectangular section core - on the last one I laminated up several layers of foam, ending up with a core about 50mm deep and 75mm wide at the pin, tapering to about 2mm by 75mm at the trailing edge, and 50mm by 25mm at the extension. This gives a shape something like this.
Complete Stock
Don't forget to put some high density foam or a wooden pad in the tip where you will be bolting on the tiller extension.
Andy does it slightly differently. H e uses exclusively HD foam and makes it 20mm thick tapering to 10mm and 60mm wide, tapering to 10mm, with an oval section rather than rectangular.
Opinion varies greatly how long the tiller should be. Basically the shorter it is the more room you (or your helmsman) will have round the knees when hanging desperately off the back corner on a nasty pitchpoling 2 sail reach, but the greater the loads will be. I think my stock on Halo Jones is about the shortest, 540mm from pivot to tiller extension, and most are probably nearer 700mm than 600.
Now its time to get the fibres on. My memory is very vague about what I used. I *Think* I used a layer of 200 g carbon cloth, aligned 45/45 on all four faces, plus two layers of unidirectional carbon on the sides, plus another couple of layers of carbon cloth top and bottom around the pin/leading edge area where the big loads are. Finally I gave the whole thing a couple of layers of 200g glass top and bottom, and overlapping the sides to keep all the carbon in place. As ever compress the layup - for this a Workmate and parcel tape is helpful.
Andy's recommended method is to laminate 1 layer + 1/2 layer uni-directional carbon (300g/m²) tape x 100mm , plus 210g/m² glass (spiral wrap of 50mm wide strip). This spiral wrap seems to work well and squeezes the excess resin out and holds the carbon down).
Anyway, once you have done that you can glue the tiller onto the sleeve. Basically the same technique, but this is your last chance to check that you have the distance between the two pieces correct, so measure lots of times. I tend to have a small fillet at the top, so the sleeve extends slightly above the tiller, the idea being to distribute the load from the top skin.
Finally its time to put the pivot in. Ideally you will have some pultruded glass tube exactly the right size for the pin. Believe it or not this is available! If not then make your own by wrapping cloth round a very well waxed pin, but you'll probably need to ream it out after the layup has shrunk on curing.
Either way drill through your tiller and bottom late with a drill big enough for the glass tube. If the bottom plate is solid, not partially cored, then you don't need the bottom tube, just make the hole big enough for the pin. There are spectacular loads coming through the pin, and it needs to be very strong. I dig out the foam core next to the skin top and bottom of the hole and create a void that can be filled with filler. If the core is high density foam then this is unnecessary. Glue in the tube., again with a very strong fibre and silica rich filler. It is essential to have the pin in while its setting to keep the top and bottom lined up, and equally essential to be very careful to make sure the pin is exactly in the middle and exactly parallel to the rudder blade. When the pivot tube has set put some more carbon round it to make sure that the loads are thoroughly transmitted to the skin, not the core. Get a good bit of reinforcement just at this point, because its a real trouble area.
The bottom plate can be trimmed to a more streamlined shape if you like, and certainly round off the corners. You will probably need to shape it rather more round the pin to make sure it doesn't hit anything. Have a good look at the "stop points" on maximum steering. You don't want the sleeve to get bashed if you jam the tiller hard over. Make sure that something substantial takes the thumps when you jerk the tiller hard towards you in a desperate attempt to bear away. If necessary build a couple of carbon stops. Finally fill, fair and paint as you deem necessary, then bolt or screw on the tiller extension. Now you can go sailing again!

Jim Champ July 1999 (with considerable input from Andy Paterson).

Building a Foil

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You have arrived at an old part of our website, to find the latest information please visit our new page about building foils. The new portal for the site can be found at www.uk-cherub.org please visit this for up to date news about the UK-Cherub class.

Gear & Fittings Installing a Bowsprit Building a Rudder Gantry Building a Rudder Stock

Disclaimer

The Core.

The best core material is probably high density PVC foam (200 kg/m³). If you're really keen it could be 130kg/m3 near the bottom. Failing that (and HD foam cores can be a hassle to work for the less experienced - you'll need very sharp tools), prepare an even thickness blank from timber strips (Western red cedar) approx. 50mm wide. Organise the strips so that alternate ones are turned end for end so that the grain runs in different directions in order to reduce the effect of any warping of the timber. This can even happen long after the foil is fully glass coated and complete, which is most unwelcome! Bond the timber strips with epoxy, and when its cured plane the blank to an even thickness. Cut the blade out to the required profile, but make it 5mm smaller than the intended finished size at trailing edge. (Apart from anything else this ensures that minor damage doesn't expose a wood core) Shape the foil, allowing about 1.5mm undersize for the laminate, fairing and painting. Make the trailing edge as sharp as you can, because the fibres will overlap here to create the true trailing edge.

The Layup.

Use skins of unidirectional carbon and woven carbon cloth, to give lowest weight and maximum stiffness. Start with layers of 200 g/m² unidirectional carbon, one layer over all of the foil, plus a second layer of 200 g/m² unidirectional carbon over the top half, and a third layer of unidirectional carbon, approx.150mm wide, over top part of the foil, extending approx.100mm past the bottom of hull when the foil is right down. Then add one layer of 200 g/m² woven carbon cloth, and finally a layer of 86 g/m² glass cloth, both covering all of the foil. If you wish you can use white pigment in the top layer to enable you to produce a white foil without painting it too.
Resin choice inevitably varies with temperature and speed of working, and probably what you've got left over from the last job too. SP320 slow is fine, as is Ampreg 20, although with the latter you'll want to use approx. 50/50 fast and normal hardener in summer, more fast hardener in winter, probably near all standard on a hot Australian summer day! Consult the data sheets for information about recoat times and so on.

Laminating it

Suspend the blank with the leading edge horizontal by means of screws in timber supports at the head and tip of the board. Cut the carbon oversize, approx. 50mm wider than the board. Using a roller, wet out the board with resin, apply the UD carbon, aligning the fibres along the leading edge. Wet out the fibres with epoxy, leave a few minutes to soak in and then wet again. Next comes the layer of carbon cloth. Again wet it out off the foil, wait a few minutes, and the roll on more resin. Finally add the layer of glass in the same way. Squeegee the excess resin away, remove air from the laminate, then squeeze along the trailing edge overlap to remove air. Check for bubbles under the glass, and squeegee out.
After approx. 1 hour its time to add filled epoxy which will be used to fair the foil. Make up a reasonably runny filled epoxy mix that will roll on nicely. If you're going for a pigmented foil then use glass bubbles and white pigment. If you're going to paint it anyway leave out the white pigment, and if you have ambitions for a clear finished foil (your laminating better have been really neat if you're attempting this) use silica in place of glass bubbles. Anyway roll on a coat of filled epoxy and repeat twice more ( 3 coats resin/glass bubbles). When the layup is part cured (still a little flexible, but no more than that) trim the excess glass from the head and tip with a sharp knife. Leave the foil to cure overnight
Remove the supports and screws, and trim the trailing edge to the finished size, using a jigsaw with a carbide tipped blade. Trim and sand the head and tip areas. Now its time to glass coat them. Apply 2 layers x 200g/m² glass to the head edge, and 3 x 200 g/m² cut on bias at ±45° around the tip of the foil. Cure overnight.
File / sand all the edges to shape. Apply 2 coats of resin/glass bubbles to the head and tip. Cure overnight, and then the next day post cure the foil at approx. 45°C for 3-4 hours (A wooden box & a fan heater does this nicely).

Finish

Now the hard work begins! Start by spraying on a guide coat ( car paint ) of some contrasting colour with the layup (bright red perhaps). Sand all the paint off! You should have enough filler to sand pretty aggressively (Andy Paterson uses a belt sander with 40 grit abrasive) without cutting (much) into the glass. On no account whatsoever cut through the glass, and cut into it as little as you possibly can. If it goes black stop immediately!
Now suspend the foil with the screws and blocks as before, leading edge up. Finish the foil with 2 coats of neat epoxy (with white pigment if appropriate. Leave the first layer to cure for approx. 1 hour, then a 2nd coat. The epoxy will fill and flow over the big scratches. When this has cured fill suspension holes, and apply 2 coats of epoxy on the head edge. Apply another guide coat of paint and sand, sand, sand, the finish coats. Wet sand it starting with 100 grit, working through 180/280/400 and then finish off with 600 wet sanded to give smooth matt finish. Most people think this is all the finish required, but feel free to carry on with 800 grit and 1200 grit and then an abrasive polish to get a real mirror finish. It will last at least a day on the beach!

Jim Champ August 1999 (With considerable assistance from Andy Paterson of Bloodaxe Foils)

Gear & Fittings Installing a Bowsprit Building a Rudder Gantry Building a Rudder Stock

1990s Designs

Earlier Designs 1980s Designs
The Paterson 6 was considerably influenced by current thinking in the International Moth Class. Andy Paterson's designs were influential in the Moths at that time.

Paterson 6
Drawings for this design with construction details for ply sandwich construction are commercially available from Bloodaxe Boats.

Chris Stimson, one of a new wave of U.K. yacht designers, teamed up with Cherub Sailors John Lobb & Martin Harrison to produce this design, named for a party at the Torquay Nationals where they started thinking about the design.
Flying Trifle

Drawings for this design are commercially available from Christian Stimson Yacht Design

Simon Roberts' Dog design was the first to use a double chine to further narrow the chine beam.

Dog 1

A development of the Bistro, the Pasta Frenzy utilised double chines for narrower beam at the waterline. A Pasta Frenzy took two seconds in the 1995/6 worlds, but then proceeded to break every spar on the boat.

A more moderate development of the Dog, the Platypus was compromised a little away from top speed and a little more towards controllability compared to its predecessor.

For those who are unaware, Death by Chocolate is a dessert of almost unsurpassed sweetness and stickiness! The design is notable for the low panel curvature at the transom which leads to finer waterlines aft.

Drawings for this design are commercially available from Christian Stimson Yacht Design

Designed by Iain Murray & Associates (now Murray, Burns and Dovell) to the UK rules and built by Dinghy Sports, The IMA Sports Cherub was the first Australian design built to the UK rules and fitted with an asymmetric spinnaker. With plenty of rise of floor at mid length and a fine straight entry it was quite different from contemporary designs in the UK. One of these designs won the 1995/6 World Championships

Quite unmistakable in appearance with flat sections aft.

Andy Paterson converted his mk6 with snout and wide flares and won the 1997 Nationals with it. As well as the obvious wings and snout, he actually extended the bow rather than the stern and so made the bow slightly finer.

The first true 1997 rules design, the Slug features a distinctively "wavy" flare line, and waterplane rather further aft than its rule-constrained predecessors.

Like the Slug, the Paterson 7 has the waterplane further aft than its predecessor. The shape of the bat is characteristic Axeman, with very vertical topisdes, and the flare is particularly flat.
Drawings and construction details in foam sandwich for this design are commercially available from Bloodaxe Boats.

Jonathan Garfitt's Velocipede was loosely based on a Pasta Frenzy, but extensively modifiied for the 1987 Rules.

Gavin Sims Buttplug featured low rocker, U shaped forwards sections, and slightly wider than minimum chine beam for weight carrying.

Notice

The drawings on this page are for information only and are not warranted accurate. Copyright and reproduction rights, including building rights reside with the designer.

UK Cherub Class Rules 2005

1 Introduction

The object of these rules is to provide a set of rules to which inexpensive high-performance dinghies may be designed and built.

2 Constitution

2.1 Administration

The Association shall hold an Annual General Meeting, normally at the National Championship. The date and venue of the A.G.M. shall be published at least one month before it is due to be held. The A.G.M. shall elect the following Association Officials:
President, Secretary, Treasurer, Registrar, Technical Officer.
It may also elect the following additional Officials:
Magazine Editor, Publicity Officer, Fixtures Secretary.
All these Officials shall be members of the Association Committee. The A.G.M. may elect additional committee members up to a total of ten.

2.2 Amendments To Class Rules

Changes to these Rules may only be made as a result of a 2/3 majority vote in favour in a postal ballot of all paid up members of the association. Proposals for changes to these rules may be submitted to the Association Committee at any time. Such proposals must be signed by five members and must detail the precise wording of the proposed change. The Committee shall consider each proposal and may suggest possible changes to the proposers. The final wording shall be agreed upon within four months of the original submission. The Committee shall, within a further three months, conduct a postal ballot of all members. The ballot shall include the full detailed wording of the proposals, any explanation submitted by the proposers and any comments from the Committee or Technical Officer. The ballot will close one month after the date of posting (this date to be stated in the ballot). The Committee shall decide the exact date on which any change shall come into effect. This shall be not less than three months or more than six months from the closing of the ballot.

3 General

3.1 Title

The class shall be known as the UNITED KINGDOM CHERUB 12ft. DEVELOPMENT CLASS.

3.2 Insignia

The insignia shall consist of a heart shaped silhouette of a size which would approximately be contained in a 300mm diameter circle. The insignia shall be placed on both sides of the mainsail, approximately one third from the top, and shall be of a colour contrasting with the mainsail.

3.3 Registration

On completion of measurement by an authorised measurer and subject to conforming with the class restrictions and payment of the prescribed fee, each boat shall be issued with a registration number by the Class Registrar. This number shall be displayed on both sides of mainsail directly under the insignia and on the spinnaker at approximately half height on both sides, in contrasting colours. The numbers shall be approximately 300mm high and have a trunk width of approximately 50mm.

3.4 Crew

The crew shall consist of two persons.

3.5 Interpretation

The CHERUB is a development class and these rules may not cover every eventuality. In cases where doubt exists, account should be taken of the intentions and spirit of the rules and the matter should be referred to the Technical Officer and Association Committee.

3.6 Advertising

UK CHERUB races shall be designated Category C in accordance with ISAF Appendix 1, Section 2- Advertising.

4 Class Restrictions

4.1 Hull

4.1.1 Length - Between Stem and Transom shall not exceed 3.70m. No part of the hull may extend more than 4.0m from the transom. (Note: For boats with inset or open transoms this measurement shall be taken from the after extremity of the hull skin at or below the waterline.)
4.1.2 Beam - The maximum beam shall be 1.80m. (Note: Footstops and footloops only may extend beyond this beam.)
4.1.3 Depth of Hull - Depth at mid-length, measured vertically from sheer to the lowest point of the hull, shall be at least 450mm.
4.1.4 Stem - The profile of the stem shall be approximately vertical for a minimum of 200mm from its bottom.
4.1.5 Chine(s) - Chines shall be fair and continuous curves. There will be at least one chine at least 2000mm long. Any chine at some point shall be at least 450mm from the centreline. No part of the outer skin above a chine shall be inside a vertical line passing through the chine.
4.1.6 Anti-multihull rule - In any cross-section of the hull, no horizontal line shall pass through the hull skin more than once either side of the centreline. (Note: It is not the intention of this rule to prohibit 'tubular wings'.)
4.1.7 Weight - The weight of the hull in dry condition shall not be less than 50kg. The weight shall include all permanently fixed fittings and bowsprit, but shall exclude sails, spars, standing rigging, centreboard, rudder and other loose gear.
4.1.8 Buoyancy - The hull shall be fitted with built-in buoyancy not less than 0.26m3 contained in at least three separate compartments of at least 0.02m3 each.
4.1.9 Centreboard and rudder - Centreboard and rudder shall not be ballasted (i.e. shall float). The centreboard shall be fitted on the centreline of the hull.

4.2 Spars

4.2.1 Spars - The area of spars shall be considered as sail area. The area shall be taken as:-
(chord-100mm)*length
Where chord= the diameter of the smallest circle through which the spar could be passed when stripped of all fittings. If chord < 100mm then the area shall be disregarded.

4.2.2 Spinnaker Pole - Either a Spinnaker Pole or a Bowsprit may be used for setting a spinnaker, but both may not be carried in any race.
4.2.3 Bowsprit - The bowsprit, if fitted, shall be retractable to within 4.3m of the transom. The outer end of the bowsprit shall be solid or capped. No sail other than a spinnaker may be set from the bowsprit.
4.2.4 Sail Height: The vertical distance from the lowest point of the hull to the mast step plus the distance from the bottom of the mast to the top of a measurement band, above which no sail shall be set, shall be no more than 7.1m.

4.3 Sails

4.3.1 Material - The sails may be constructed from woven fibre cloth, unwoven fibre cloth, flexible plastic film or composite materials consist of any combination of the three. All sails shall be stowable in sail bags of normal dimensions.(for the purpose of this rule, 'long' sail bags for the stowing of rolled up sails are regarded as normal).
4.3.2 Mainsail and Jib
4.3.2.1 Sail Area - The areas of the mainsail and jib will be measured in accordance with the IYRU measurement instructions(1979), part IV, measurement and calculation of sail area (printed in appendix 1). The following are excepted:
a) Section 2 (measurement of spars) shall not apply.
b) Section 6, spinnaker, shall not apply.
The combined area of the mainsail and jib shall not exceed 15.50m2
4.3.3 The mainsail must be removable without releasing the standing rigging.
4.3.4 Spinnaker - Spinnakers shall be measured in a dry condition. All measurements shall be taken with the sail pulled taut between the relevant points.
The following measurements shall be taken. Length of the Luff, Leech and Foot, and the cross width between the mid points of the luff and leech. The following parameters shall be calculated.
L = Mean of luff / leech length.
DL = Difference of luff and leech.
F = sq.rt.((Foot Length) ²-DL ²)
G = sq.rt.(Cross Width ²-(DL/2) ²)
Area = LF/6 + 2LG/3
The area of spinnaker may not exceed 21m2. Only one spinnaker may be carried on board in any race.
4.3.5 I.SA.F. rules 50.2 Spinnaker Poles, Whisker Poles and 50.4 Head Sails shall not apply.

4.4 Not Permitted

The following are not permitted:
a) Any contrivance other than a trapeze extending out board to support the crew or helm.
b) Spinnaker sheet catchers on the stem which may be dangerous to other crew or craft.

I.Y.R.U. (now ISAF) MEASUREMENT INSTRUCTIONS 1979

Part IV: Measurement and Calculation of Sail Area

As applicable to U.K. CHERUB Class Rule 4.3.2.1, Sail Area (mainsail and jib), as adopted by the CHERUB Class Owners' Association, U.K., effective from March 1997

1. General

1.1 The intention is to establish a reliable and simple method of measuring the whole driving area of the sail plan.

1.2 It is not possible to frame methods to deal with every eventuality and therefore in the case of unique or difficult shapes of rig the measurer may need to use his judgement in dividing he rig for measurement in order to calculate the area accurately. "Combination" rigs such as a soft trailing edge on a heavily shaped wing spar or a rig where the camber and shape is produced by tensioning when it is on the yacht, may be more conveniently and equitably measured in an "assembled for sailing" condition, rather than in component parts. In these cases the measurer shall record the method used.

1.3 Elements of the sail plan which are vertical, or nearly so, when the yacht is not heeled shall be measured. Elements of the sail plan which are horizontal or nearly so when the yacht is not heeled, such as fences and end plates, are not measured, provided that:
i) the surfaces of such elements are not able to make an angle, measured at right angles to the fore and aft axis of the yacht greater than 10 degrees to the horizontal when the yacht is not heeled, and
ii) the total area of their surfaces does not exceed ten per cent of the measured sail area excluding such surfaces.
For the purpose of calculating the area of horizontal, of nearly horizontal surfaces, only the area of one side of each fence and the surface of an end plate which is adjacent to the sail shall be included in the area.

1.4 A "soft sail" is any sail made up of cloth or other material which is flexible and can be rolled up or folded.

1.5 For the purposes of measurement of sail area the term "sail.." shall be deemed to be that part of a soft sail outside the spars and includes the headboard, tabling and battens which extend beyond the edge of the sail. It shall not include cringles which are wholly outside the sail or bolt or foot ropes which are inside the spars.

1.6 The area of any hole in the sail, the maximum dimension of which does not exceed 50mm, shall not be deducted from the measured area.

2. Spars & Wing Sails

(Not applicable. The area of the spars shall not be included in the measured sail area.)

3. Soft Sails set on Spars

3.1 When the sail is set on spars and between measurement bands the distance between the bands is used to obtain the primary dimensions of the main triangle.

3.2 Area using measurement bands

3.2.1 With battens set in their pockets the sail shall be pegged out on a flat surface with just sufficient tension to remove waves or wrinkles from the edoe rounds and to spread the sail, as far as possible, substantiallv flat. Once the sail has been pegged out in this wav all the required measurements shall be taken and no alterations to the tensions shall be made.

3.2.2 Needles shall be fixed at the head and clew, making allowance for that part of the sail inside the spars so that the distance between the needles is the length of the leech. A third needle shall be fixed at a point so that it is the distance between the measurement bands on the mast from the head needle and also the distance of the boom measurement band from the mast from the clew needle. If the boom is shorter than the foot of the sail or if there is no boom, the length of the foot shall be that found by measurement with the sail set on the mast. A thin line shall be stretched round these needles to define the main triangle. See fig (3).

3.2.3 The area of the main triangle shall be calculated from one of the following formulae or by a scale drawing.

(a) Area = SQRT(s.(s-a).(s-b).(s-c))

where s = (a+b+c)/2

and a = length of luff
b = length of leech
c = length of foot

(b) Area = ABx CP where CP is the minimum distance from C to 2 * the thread from A to B

3.2.4 The area of the luff round shall be calculated and added to or subtracted from the area of the main triangle. If the curve is fair and continuous its area shall be taken as two thirds of the product of the chord length and the maximum perpendicular offset to the chord. In fig (3) below the area of the luff round is 2g(AY)/3.The offset to the chord shall be taken as the maximum distance between the point on the sail corresponding with the aft edge of the mast, and the thread defining the main triangle.

3.2.5 The area of the leech round shall be found as follows:
either
(a) where the leech is a continuous fair curve from point A to point C in fig (3)
the area is taken as AC (1.16d + e + 1.16f)/4
where AC is the leech length indicated in fig (3); d, e and f are the perpendicular offsets between the points on the thread from A to C a quarter, a half and three quarters of the distance between the leech measurement points A and C and the edge of the sail. For the purposes of the measurement of the offsets, any hollows in the leech shall be bridged.
or
(b) where the leech is not a fair curve from point A to point C in fig (3) the area of the leech round shall be found by dividing the area into trapeziums, triangles and segments and measuring each. For the purpose of this instruction the area of a segment shall be taken as two thirds of the product of the chord of the round and the maximum perpendicular offset to the chord.

3.2.6 The area of the foot round, if the sail can be pegged out substantially flat, shall be measured in the same manner as the luff round.

3.2.7 Where the foot has a "shelf" or a substantial amount of shape so that when the foot is extended there is loose or bulging material above it, then the area of the "flow" of the bulging material shall be determined as follows (see fig. 4.. A measurement shall be taken from the straioht line joining the tack to the clew, in the wav of the greatest fullness, to an arbitrary point where the sail does lie flat. A second measurement is then taken from the arbitrary point to the point of greatest fullness following the folds or bulges of material. The difference between the two measurements represents the offset of the rounded foot. The area of the foot round is taken as two thirds of the length between the tack and clew multiplied by the offset.

3.2.8 The area of the shape BYTX in fig (3) is not deducted from the area of the main triangle.

3.3 Where there are no measurement bands on the spars

3.3.1 With battens set in their pockets the sail shall be pegged out on a flat surface with just sufficient tension to remove waves or wrinkles from the edges and to spread the sail, as far as possible, substantially flat.
3.3.2 Needles shall be fixed at the head, tack and clew. A thin line or thread shall be stretched tight between head, tack and clew to define the main triangle.
3.3.3 The area of the main triangle shall be calculated in the manner indicated in Section 3.2.3 above.

3.3.4 The area of the luff, leech and foot rounds shall be found in accordance with the instructions 3.2.4, 3.2.5, 3.2.6, 3.2.7 above.

4. Soft Sail not set on a Spar

4.1 A soft sail which is not set on a spar, such as a headsail, set on a stay or flying, shall be measured in accordance with instruction 3.3 above, except that if the leech has an offset not exceeding 5 per cent of the leech length and is a fair curve the area of the leech the area of the leech round shall be measured in accordance with 3.2.4.
4.2 If the luff of the sail is wired, sufficient tension shall be applied to remove bends or kinks in the wire.

5. Sail of Unusual Shape

The foregoing instructions assume that the sails are essentially triangular. If a quadrilateral or multilateral sail is to be measured the sail is to be divided into suitable triangles whose area can be measured and added. The areas of the luff, foot and leech rounds shall also be added, or subtracted as the case may be. The measurer shall record the method he has used to assess the area of the sail.

6. Spinnaker

(Not applicable. See CHERUB Rules and Restrictions, 1987, Rule 4.3.4 Spinnaker.)

A Guide to Cherub Designs

This is a list of U.K. Cherub designs compiled by various people over the years. It is believed to comprise all designs built in any numbers, and the vast majority of one-offs.

Note - the links to individual designs in this document load a page of graphics showing those designs. These should be helpful in gaining a feel for the shapes of the designs involved, but are definitely not warranted accurate. If you're interested in the principles of modern dinghydesign then the best book by far (even if it is rather uninformative in detail) is Frank Bethwaite's book "High Performance Sailing, ISBN 1 83510 757 3.

Late 80s and Early 90s

Fartpants(Cope)
Designed to be a weight carrier. slightly hollow V bow, low rise of floor, narrow beam, very flat floor with lots of turnup to chines, slight negative rocker aft. The first "narrow flat" Cherub. e.g. 2634

Handley
Radical round bilge design. No foredeck. lowish rocker, very flat floor aft, U bows. 2636

Deeley 6
More moderate development of mk 5

Italian Bistro (Roe Mk 1)
Very influential flat low rocker design. quite fine V bows, moderate beam, low rocker and rise of floor, mainly built in foam sandwich. First boat with flared topsides with a concave "chine". A few boats were professionally built from a female mould taken from Dave Roe's multiple Nationals winner Norwegian Blue, but attempts to organise serious production were unsuccessful. e.g.2637, 2641.

Yet more rule changing saw the introduction of bowsprits and larger spinnakers being permitted. This inevitably meant asymmetric spinnakers. A year or so was spent in intense development until the final rule was defined, which gives a sail of a nominal 140 sq. ft, (actually about 150-160 sq.ft.). This, coupled with the new flat narrow hull shapes and the 1984 rules has led to a boat with quite astonishing medium winds performance offwind.

Dog (Roberts mk 1)
Bistro development with double chines and slight hollow between chines. Very low rocker. The double chine helps to minimise waterline beam within the 1984 rules. e.g. 2645

Paterson 6
Moth influenced design with distinctive high foredeck. Very slab sided and flat floored. At least one later modified as 6a with snout, wider beam and flat foredeck. e.g. 2650, 1997 Uk Nationals winner.

Flying Trifle (Harrison/Lobb/Stimson)
Notable for extreme topside flare aft. Low rocker, flat aft. 2652

Pasta Frenzy (Roe mk 2)
Bistro Development with double chines and lower rocker. At least one later modified with snout and wider beam. e.g. 2660

Platypus (Roberts mk 2)
More moderate development of Dog. 2656.

Barr
Designed by Duncan Barr, I know very little about this boat. 2658

Death by Chocolate (Harrison/Stimson)
Fine bow with straight entry. Plenty of curvature at mid length with quite a lot of rise of floor. Curvature washes out to fairly narrow moderately V'd transom with no panel curvature. Moderate even rocker. 2663

IMA Sports Cherub(Iain Murray & Associates - now Murray, Burns & Dovell).
Single chine, low rocker, U'd sections throughout, maximum rise of floor at mid length and plenty of rise of floor at transom. Not unlike Deeley 5, but finer forward. 1996 Worlds winner. eg 2667

Hardon Clifton 1
Radical design by Simon Clifton with very low rise of floor and low rocker. 2669

1997 Rules

The 1997 Rule changes permitted snouts -bow extensions for jib and bowsprit, wider beam, and considerably reduced the rise of floor restrictions. These modifications were sufficiently compelling that many post 1990 boats were altered with the wider beam etc, including Bistros, Paterson 6a, Pasta Frenzies and at least one Roberts design.

Septic Slug (Roberts mk 3)
First 1987 rules design. Waterplane distribution rather further aft than earlier boats and "wavy" flare. e.g. 2673

Paterson 7
Development of Paterson 6a for the 1997 Rules. Very slab sided and flat floored with a great deal of topside flare carried right round to support the snout. e.g. 2676. One boat built with racks rather than flares. 2681.

Velocipede (Garfitt)
Moderate interpretation of 1987 rules, loosely based on a Pasta Frenzy. 2675

Butt Plug (Sims)
Low rocker, flat sections aft, U sections forward with chine not appearing until well back from the bow. 2682

2682

This list is inevitably going to require updating as new designs appear. I would also be very grateful for drawings of those designs - the majority - that have not been included as graphics here. Some of the older designs would be especially welcome in order to demonstrate development over the years. Information from New Zealand and Australia would be especially welcome.

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