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Gear & Fittings Installing
a Bowsprit Building a Rudder Gantry
Building a Rudder Stock
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 foil without someone experienced in the materials to contact
for advice.
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.
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.
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).
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
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