You might have something there. Even though we are cat sailors, when we got our first cruising boat, we got a monohull. Sure enough, it sank -- at a dock. (It was a 37-foot monohull.)

Do you know why your boat sank? And is the entire hull and cabin underwater? Those things make a difference in how you go about raising it.

The guys trying to raise ours originally tried inflating innertubes or plastic bags or something in the boat, but that didn't work, so we had to get two tow trucks with crane booms on them, with their booms out over the boat and slings under the boat attached to the booms. At the same time they had pumps going in the boat, and they had to raise it very, very slowly, so the water could be pumped out as they were raising it. Even so, I thought those trucks were going to tip over backward from the load.

The trouble with a monohull sinking, usually it is through a slow leak that goes on for a long period of time (like through a packing gland or or a valve for a through-hull fitting), so the water can't get out fast the same way it got in slowly.

So even if you use foam, you will probably need pumps to help get the water out as the boat rises, once the gunwales are level with the water -- unless, of course, there is a big hole in the bottom to let the water out. (Actually, if there is a hole, you may have to patch or plug the hole somehow before you can completely raise the boat.)

Ours had a hole from an underwater piling, but once the boat was raised and all the water had been pumped out, the pumps were able to keep it afloat until we towed it to a marina to be pulled out and repaired. Actually, I can't remember -- maybe a temporary patch was put over the hole underwater.