Aye- but there's the rub. The foam itself is trapped air- thus "closed cell." The foam will expand and contract somewhat. And since it's not loose and flowing (like, say, strofoam peanuts) but stuck in place, you could still have problems, albeit locally. If you're committed to the idea perhaps you could add the foam prior to installing the deck and dam off the foamed area so that it will not be in coatact with opposing sides of the craft.
Haven't weighed the stripped Kaholo- we don't even own a bathroom scale so I don't have a practical way to do it. I'm guessing that any additional weight is due to glassing the interior so rigorously- something I'd do again in a heartbeat. I have no trouble cartopping the board by myself, and once I'm on the water I'm not concerned wiht an extra pound or two. I am by no means a fiberglassing expert and am not familiar with the style/weight of glass you're referring to, but I would imagine there is a point where going lighter offers no practical weight savings and yet does suffer loss of strength. The epoxy is a significant portion of the added weight. So for instance, you might end up using nearly as much epoxy to wet out your super thin stuff as you would if you'd have used 4oz, but the very thin material might offer substantially less strength than the hypothetical 4oz. Remember there's little reason to fill the weave on the inside of the craft. There are many on this message board far more qualified to speak to that notion than I.
Good luck!
Patrick
Right on, I agree about the thin stuff not adding much more strength, but it's all I have that's light. The 4 oz mat is just too much money for me to glass the inside of both boards I am building. I will be using the 4oz scrap pieces to sort of "tab" in the all the joints.
The stuff inside the closed cells is not air, it's gas that forms when the 2 parts are mixed. The millions of dead gas spaces make an excellent insulator, so a thin outer layer may heat up, but the vast majority of the gas will not. It's also an exothermic reaction, so the gas inside the cells shrinks when it cools down, but the cells are hardened by then.
Coupled with the fact that the foam has a very low coefficient of thermal expansion, there's pretty much no chance of a closed, completely foam-filled compartment bursting.
The dangerous situation is a large, uninsulated airspace with thin walls. Whatever other basis the decision is made on, fear of bursting is not an issue.
Have fun,
Laszlo
Interesting. Thanks for that good knowledge!
I agree with Lazlo that your Kaholo is unlikely to “burst,” Michael Bay-style, but I’d still be concerned about expansion/contraction damage over time.
Over the course of a few weeks the blowing gas used to create those foam bubbles does in fact come into equilibrium with plain old breathable “air.” Think of a helium balloon that remains inflated yet sinks over a matter of days as its helium is diluted. The foam loses a bit of its insulating power in the process. Regardless, the foam is filled with trapped gas that will expand and contract with changes in temp. Strap the board to your car on a nice day and the foam will heat up- insulation merely slows heat transfer, it doesn’t stop it. Now drop your preheated board into the relatively cool waters and the foam will cool down rather quickly. Unlike a solid foam board, the plywood shell and bulkheads will have different coefficients of expansion. These are certainly elements that can lead to joint failure. Whether it will happen before some other defect ultimately decommissions the craft- well, we’re all just guessing.
Me- I’m digging the ping pong balls.
Good luck!
Patrick