Question on foaming spaces.

What are the cons of using 2lb density floatation foam in these under deck spaces? Plan is to seal each chamber, using same materials in reconstruction, (glass and epoxy). Areas involved have never shown water ingress, exept from failed shower sump, which rotted out supports and framing.

 

Foam filling wooden spaces is problematic at best. Why not just seal them up tight and put in a deck plate so they can vent when the boats not in use.

 

I am no expert, but I know I have read some foams (especially Spray) can start water retention after a decade or so. If you are building a vessel you hope your grandchildren might sail someday this might be a bad thing.

Boat manufacturers under 20' must meet a positive flotation requirement, and that is a good reason to have foam. Even a capsized vessel will float until rescue. Safety first.

There are good block foam options if you do your research, but I'd avoid most spray foams if you like the idea of boat longevity.

 

4lb density is pretty well immune to water absorption, by many reports, but the weight could be an issue in some boats.

 

I only spec 5 pound foam for these types of applications and prefer they are encapsulated or bagged to prevent issues. A 5 pound foam then becomes a structural element if desired.

 

My method is to use block foam (not two part pour foam) and bag the foam in plastic sheeting.This prevents the foam from being exposed to water, and chemicals that can dissolve it, and you can then use simple cheap polystyrene foam which can be bought for a few dollars in large sheets. All the big box home improvement stores sell it as insulation foam. However do not use Styrofoam. It has a much larger cell size and is subject to breaking up from shock and vibration. So no water absorption and no foam deterioration.

You then cut it to size to fit the space.

see http://newboatbuilders.com/pages/SeaRay190.html

PS. The pink piece never gets wet and supports the sole. So I didn't page it, but who knows I may regret that. But it is easily replaced.

 

This picture was pre tabbing on the deck supports. It is all epoxy and glass to the deck line . The bottom of the deck is glassed with 1700 triax and epoxy, and will be glued down with milled fibre and epoxy. The idea was to help support decking and to add non floodable chambers, in case of holing. My area has lots of shoaling and debris, at the moment. Not that I paln on running onto anything.