Replacing foam buoyancy CL16 dinghy

My point was not the thread, I didn't even read it, but that there is info online you just need to know how to find it.
Looks like you're getting some good advice now.
Good luck.

 

Thank you for that,
I read all about XPS, type V is about 3 pounds per cubic foot but most of the others are much less, down to 1.3 pounds.
I’m planning on putting the boat back together in a similar fashion to that you described, but I do have some 8th inch fiberglass sheet that I will make the flange with. As to fitting all those pieces of XPS in a loadbearing fashion, which is important in this instance, with a can of spray foam looks difficult. All around the perimeter of the hole the foam would have to be fitted underneath, and there are irregularities in the surface everywhere. If I use 4 pound or 6 pound pour foam, it will have less propensity to absorb water than 2 pound foam and will fit very well, almost perfectly, and will be easy to install.
As to longevity, that’s a subject! The boat is 40 years old this year and I wonder how many of its close brothers and sisters are receiving this amount of attention that doesn’t make much financial sense? I don’t know if it’s an indictment of our culture, but she wasn’t built to last forever. What about all those rusty Ford Escorts that never got rebuilt?

 

xps foam will completely dissolve with the resin.

 

Those boats were built for winning races.

 

You can go with 6 lb pour foam. It will be lighter than the wet foam you removed but still provide sufficient buoyancy and structural support for your CL 16 dinghy. Using 10 lb foam would add unnecessary weight without much benefit.

 

The only reason to go to a foam over 2 pound density is if the foam is doing some major work carrying the people on deck; even then; only the top few inches need to be better than 2 pound.

“closed cell” foam performs rather poorly and worse when trimmed to fit; water ingress is pretty high

Strongly recommend xps and spraying in closed cell foam as you build up.

 

Sorry I came a little late to the party. Experiments done by the Coast Guard and ABYC have shown through testing of boats for flotation that pour foam is the worst culprit in absorbing water. Block foam barely absords any water. The Coast Guard did a research study on this way back in the mid 80's. I was the project manager. Encasing the foam in a bag eliminates the problem of water absorbtion. 2lb foam is pretty much the industry standard. The only boat manufacturer that I know of that uses 6 lb is Boston Whaler, and in that case it is defintely structural. The foam is literally part of the boats structure. Using a higher density foam of course adds weight. 10 cubic feet of 2 lb density weighs 20 lbs, 10 cubic feet of 6 lb weighs 60 lbs. If your boat is weight sensitive, as many sailboats are, that can make a huge difference in it's performance.