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cat daggerboard building
On 28 Apr 2004 08:51:40 -0700, (gjoyce) vaguely
proposed a theory
.......and in reply I say!:
remove ns from my header address to reply via email
FWIW
Dagger boards have very high point loadings, esp where they cross the
hull. I would check up the originals, to see how they were
constructed. They may have reinforced that area or even made it solid
for a bit both sides.
I have built boards and rudders from a ply core, and glassed over,
with epoxy/glass. I just liked the sheer uncrushability of ply as a
core in this instance.
IMO ply is more _work_ to fair as a core, but you are less likely to
gouge a piece out, and you can use the veneers as a great way to get
the trailing edge, in particular, nice and even.
There might a couple of kilos in weight between ply and foam. Maybe
use _ply_ at the hull/board interface and foam elsewhere.
Whatever, IMO some sort of cored construction will be the way to go
for stiffness to weight.
Also, when laying up, try to get wet glass on both sides, layer by
layer, to avoid warpage as the layup cures.
Making female moulds would not be so easy, with care, but of course
you get the original shape and the same both sides. If you make sure
that you provide good flanges that allow separation of the plaster
halves, and _while the whole thing is still attached to the board_,
bolt the two halves' flanges together. You then have a good mating
setup. Make the moulds VERY strong, with stiffeners, probably
diagonals of paper/rope/sackcloth plastered over with scakcloth
reinforced plaster. Or make the moulds from glass. Again reinforce to
stop warping. Even form a wood/steel "armature" for them.
Unbolt, make the two halves and remate for joining. It's probably best
to rejoin the two halves, suitably release-agented, while they are
still "green"(hard but not cured). Then allow to cure joined.
I would make a flange inwards for an inch or so on each side to allow
for plenty of gluing surface. If I was really paranoid I would even
screw/bolt through and then hide the heads.
I have not done a foam-filled one like this, but I believe the way is
to inject the right amount of foam mix at one end and let the excess
out the other. Only problem he
- density control
- avoiding voids.
- You could _probably inject the foam into the boards before you
finally join then, separate to check for voids, then finally join.
- making sure you have a hole large enough to let the foam out, and
that the foam gets there before any of it sets and blocks the passage
of the rest!
Now one day I will get around to replacing the useless, rotted-foam
deck on MY Hobie 18. :-
A theoretical question, so I don't want to bother anyone for explicit
details but....
I have a Hobie 18 ... the daggerboards are a mess ... for the life of
me I can't think how
you would go about building new ones.
I thought about using foam core. Would I shape that (like a surfboard)
and glass 'em?
If I used all glass how would I make a mold? Take it off the exisitng
one? Or is there another way? (I keep thinking a plaster mold or some
such because of how thin - relatively - they are. But then I'd have to
mate halves, and that's not a good idea, right)?
Is there some way to vacuum bag them? Never did that, but ... I still
can't envision how I get the shape and form ...
any thoughts, general direction, or KISS alternatives , et al, would
be IMMENSELY appreciated ...
Gary Joyce
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The Met Bureau is LOVE!
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