Jon, I have to ask, why would they use a open cell foam rather than a closed cell foam in light of the recognized problem? And as far as the valve on the deck goes, I wouldn't want it anymore than I want the hatch.

Actually though you've touched on my solution so I may as well reveal it now. I'm thinking of displacing the air in this compartment with CLOSED cell urethane foam. If I fill this compartment with foam, there will be no air to expand and contract and this should provide plenty of flotation at the same time. Problem solved. The only thing I'm a little nervous about is the expanding foam might just decide to blow out the sides of the kayak rather than taking the path of least resistance and expand upward as it should (the forward deck is not on yet so it should expand upward). I'm more than a little nervous about this since once you pore the 2-part mixture in this cavity and it expands, it's a done deal.

I'm still listening if there are better ideas out there.

Jim...

> Many windsurfing boards share a similar problem. Some boards are made
> entirely filled with expanded polystyrene foam. This foam acts like an
> open cell foam since there is space between the foam beads that allows air
> to pass right on through. On a hot day these boards can expand and
> delaminate. To solve the problem manufacturers install a valve in the
> deck. When not in use, the valve is kept open to allow pressure to
> equalize. During the relatively short time that the board is used, the
> valve is closed so that water doesn't enter. Your problem may be solved by
> installing a valve in your deck. If you do this, the valve should be
> installed so that water that condenses inside the hull can be drained out
> through it.