Re: Putting Foam in your boat?
Geez here we go again;
first let me say, I am retired USCG and spent 25 years in Boating Safety, 20 of those working with boat manufacturers. All during that time I was involved with testing boats for flotation. I have also been involved with research on problems with foam in boats.
1. Yes your boat was required to have flotation. NOTICE I said flotation, not foam. Foam is just one means of achieving flotation, and is the preferred method by boat manufacturers, but is not required. There are other alternatives. But if you like foam and it will do the job by all means do it.
2. Just dumping foam in the boat will not accomplish much. The boat may float but it may not float in a level upright attitude. The whole point is for the boat to float upright and provide a rescue platform. Also most boats with level flotation alllow you to stay in the boat and the top half of your body, the part most vulnerable to hypothermia, is out of the water. Some, like Boston Whaler float so high the engien can still run with the boat fully swamped.
3. Yes there have been problems with foam absorbing water. All of those problems have been with two part pour or spray foam. The worst has been with foam made using the bucket method (mix it in a bucket and pour it in) Machine made block foam has NEVER had these problems. Why? Because block foam is made under very tightly controlled conditions. Two part is not and bad things happen.
4. Enclosing foam in plastic is not bad for the foam! Some manufacturers do this and they have never had problems. In fact it helps to preserve the foam. If you do this you must allow the foam to fully expand and cool (foam heats up, what is called exotherm, during the expansion) before you fully enclose it.
5. I have always recommended using block foam. Yes it is a little more difficult to get but you will not have the same problems. And if you encase the foam in platic or glass it in you can use any type of foam. If you glass it in you must use epoxy resin. Polyester melts it.
6. The foam that is most commonly used is polyurethane because it is not affected by gasoline, solvents, cleaners and other corrosive chemicals. But if you encase foam so that these things, plus water, can not get to it, you can use plain old styrofoam. I have used this in my boat and many boat manufacturers use it, primarily in jon boats and other small boats where the foam is not in the bilge. You can buy it at Home Depot or any hardware store. Just ask for insulation foam.
7. You should do some reading first. Look at Safety Standards for Backyard Boatbuilders
http://newboatbuilders.com/docs/backyardboatbuilders.pdf Also a page on flotation
http://newboatbuilders.com/pages/flot2.html and
http://newboatbuilders.com/pages/flotdiag.html
8. 2lb density foam weighs 2 lbs per cubic foot. This means it will support 60.4 lbs of dry weight. 4 lb density foam weighs 4 lbs per cubic foot and will support 58.4 lbs dry weight. Either will support a lot more submerged or swamped weight. You need to figure out how much flotation you need and where it should be placed on the boat. If you put it all in the bottom, the boat will float great, upside down. It needs to be distributed so that the boat floats level. Essentially you need flotation for the boat itself, for the engine, and flotation for the people. The pages I suggested will show you how to do that. None of it is rocket science.
Alternatives: (don't laugh all of these have been used by professionals) Air chambers, bladders, plastic bottles (sealed), ping pong balls, pool noodles, balsa, beer cans (sealed) and anything that will enclose and contain air. Use your imagination.
I agree with those who say the compartments should have drainage. There should be limber holes that allow water to drain aft to where the bilge pump and the boat plug are. If the water can't get out you are in a lot more trouble than just soggy foam.
By the way cutting closed cell foam that is made properly is not a problem. the only exposed cells are the ones cut. Badly made foam is not necessarily closed cell. If there is too much heat the cells expand too fast and the surface is too thin. It breaks easily and does not bond well to the other cells, so water permeates easily. If there is not enough heat it doesn't expand, you get something like bread dough and it doesn't support anything. This is why I recommend block foam. All the cells are just about perfect. We tested machine made foam for two years, submerged in water, and it absorbed 2/10% of it's weight of water and that was all in the first month. That is about one drop of water for a cubic foot of foam.
( For the ones in that age group hehe 
