Foam Hulls

This is probably worth putting in a separate thread.

I suspect that the person who told Nate that a solid(ish) foam hull was too heavty was me. This is based on the design process for Easter Saturday.

Bob Boisvert wanted to use a foam hull much like Brent’s. Because I am not quite sure what the foam actually is, I asked Bob to make up some test pieces of foam coated with enough epoxide to give what he regarded as an acceptable surface finish. Applying the figures from the test pieces to the surface area of the Easter Saturday hull, we came out with weights of around 40 g for both a solid hull with an epoxide coating on the outside only and a hollowed out ‘thickish sandwich’ hull with epoxide inside and out. Compared with other methods of construction with which I am familiar (and with Brent’s boats) this is distinctly heavy. Using 2mm depron (fine-grained, smooth surfaced polystyrene foam) we would expect a hull weight of about 18 g.

Presumably the differece between our experiments and Brent’s numbers lies largely in the surface treatment. Anyone have any views?


You are probably correct in this assumption. BC1 (Blue hull/ bright deck) has a coat of thinned epoxy under its “Sharpie Marker” paint. It seems very ding resistant and durable. BC2 has two sanded coats of waterbased polyurethane under cheap white spray paint and more “Sharpie Marker” brightwork. BC “The Pink Boat” sails bare for now.

The waterbased poly is not ideal as the boat will still get some dings from racing and handling but nothing that makes it too fragile to race with. The major concern would be cosmetic only.

The foam I’ve used most is 2" thick Foamular 150 made by Owens Corning. According to their site it weighs around 1.5lbs/cubic foot. I now have some of the 3" thick blue Dow Styrofoam Bob was using for Easter Saturday. It weighs about 1.8lbs/cubic foot. Owens Corning Foamular 250 would be its equivalent. The heavier foam does have a higher compressive strength 25psi vs 15psi for the Foamular 150. You can tell the difference as it is easier to leave a fingernail mark in the lighter product. All are extruded polystyrene.
These figure should give some decent estimates for hull weights.

I’m guessing (no calculations) Easter Saturday bare would yield something under 30 grams. I helped Bob carve the foam ES and made a mistake using the deck template to cut the original plug so the finished hull had a narrower beam and lacked the tumblehome you intended. The hull design looked good but it needs the rig sorted for balance.

Take care,


Angus i will do an experiment with my foamed bottle boat and let you know