Glenn (s/v Seawing) wrote:

Good advise Lew, thanks. Have you worked with this foam before? Trying to
figure out how it is to work with and the general methodology of working
with it (& maybe some of the pitfalls).

Glenn.


I have.
It's a bit more challenging than plywood for one off coring.
But it would be the way I'd go if I were going to do this.
It's a weight issue.

For all the ins and outs may I refer you to the amateur built aircraft
industry - composite moldless construction as developed by Burt Rutan.

There is quite a bit of prior work to study there - and besides, you are
not worried about the wings folding so it's nowhere near as critical.


I recently made a pair of bunk shelves for my boat.
It's a Catalina Capri 18 - pretty small inside - although is seems big
enough outside.

The shelves are urethane foam cored with woven fabric skins. And West
resin - since that was what I had handy.

I used 5 ounce BID (BI Directional) glass (cuz that's what I had handy)
with 4 or 5 layers to get a good solid surface. Besides, the cores were
only about 3/16" thick, hence the heavy skins.

Wish I had taken pictures as I went along - but as usual I was too busy
wetting and squeeging.

They came out ok though. Haven't managed to paint them yet because I
took them out to the boat for installation fit - and they have been
there ever since...


For what you want to do I think I'd recommend something between 1/2 and
1 inch thick foam for the cores. I'd also make a plywood form to set
the desired curvature - and probably vacuum bag the skins.

Figure the bottom side could have lighter skins because (usually) nobody
will be walking on the bottom surface.

Look at what they call "units" in boat building rather than using woven
glass for something like this. (Cloth would be way expensive compared
to the boat unit approach). Units (as I understand it) are two (or
more?) layers of dissimilar materials - chopped strand matt and woven
roving or woven matt and woven cloth fabric.

I'd really like to buy Roger Long a cold beer and get all this straight
from the sea horse's mouth. All my experience is aircraft work - which
is quite a bit lighter stuff.


You may not absolutely need the vacuum bagging on a panel this size, but
if you've done it before you would know why you'd want to go to the
trouble and expense. (Better bonding to the core material - and a lot
easier surface finishing)

But it could be done as a straight forward hand lay up quite
successfully.

For a first time project this is really a bit big.

Building an airplane, one usually starts with a rudder and fin.
Small pieces to learn the techniques.

Then advance to the bigger and more critical structures.

I'd kind of like to do a project like you are discussing as the next
step before laying up an entire hull and deck.
'Specially if someone else is footing the bill


For what its worth, Glenn.


Richard Lamb



A few Marine Links:

http://boatdesign.net/articles/boatbuilding.shtml
http://boatdesign.net/articles/foam-core/index.htm
http://www.marinecomposites.com/ = excellent info!
http://microship.com/resources/micro-trimaran.html


Aircraft links:

http://www.maddyhome.com/canardpages/main (everybody)
http://www.maddyhome.com/canardpages...Dembs/Ch14.htm
http://www.ez.org/resource.htm