I've been restoring my jon boat and I cut out a storage hole in the front seat. Enclosed in the cavity was a bloe block of foam. What is the purpose of the foam INSIDE the boat?

I removed the foam because it had a hole eaten through it and it looked like it had been occupied by a mouse through the winter. I want to replace it but I just don't understand its purpose.

I believe it is for flotation if water fills the boat.

It is floatation.  The previous poster is correct.

You cannot use just any type of foam to replace it.  Some types will absorb water like a sponge, rendering it useless as floatation and adding mucho weight to your boat.

Most of the time, boat manufacturers use a two part foam.  It is two liquids which when mixed together create an expanding foam, ideal for irregular contoured cavities.

Those compartments need to have fairly large "vent holes" in the top to allow the expanding foam a place to escape.  You should be able to find it at the larger marine supply stores.

Here's one.

http://www.jamestowndistributors.com/userportal/show_product.do?pid=2198&familyName=Floatation+Foam

It is floatation. The previous poster is correct.

You cannot use just any type of foam to replace it. Some types will absorb water like a sponge, rendering it useless as floatation and adding mucho weight to your boat.

Most of the time, boat manufacturers use a two part foam. It is two liquids which when mixed together create an expanding foam, ideal for irregular contoured cavities.

Those compartments need to have fairly large "vent holes" in the top to allow the expanding foam a place to escape. You should be able to find it at the larger marine supply stores.

Here's one.

http://www.jamestowndistributors.com/userportal/show_product.do?pid=2198&familyName=Floatation+Foam

X3

Foam is either open cell or closed cell. Use the closed cell. It is more expensive and requires that it be mixed, but will not absorbe water like the other.

Ranger used to have a picture in one of their adds (it may still be around) where they cut big chunks out of the hull to demonstrate the safety of their flotation system. With big sections missing, and several men in the boat, it still floated fine. It very clearly showed the importance of filling all the voids with floatation foam.

Ranger used to have a picture in one of their adds (it may still be around) where they cut big chunks out of the hull to demonstrate the safety of their flotation system. With big sections missing, and several men in the boat, it still floated fine. It very clearly showed the importance of filling all the voids with floatation foam.

Here is a Boston Whaler with its foam filled cavity, floating!

I know you would need a lot of it, but would that foam spray work that you spray into holes in your house (like after you run a cable in). It's meant to get wet and expands like crazy once it comes out of the can haha.

Ok, thanks guys. I figured it was just for emergency situations. I'm going to look for some closed cell spray foam. I really don't need very much and the spray would be easiest.

Another question. Once I fill in the bench, will I be able to cut the foam to size?

Ok, thanks guys. I figured it was just for emergency situations. I'm going to look for some closed cell spray foam. I really don't need very much and the spray would be easiest.

Another question. Once I fill in the bench, will I be able to cut the foam to size?

Yes.  It cuts very easily with a knife, handsaw, drywall saw, and just about any other cutting implement.  It also sands and grinds easily.

Perfect. Thanks guys. I went out and picked up some "Great Stuff" foam from Home Depot. Their website says it's closed cell and the spray foam is pretty easy to use. It was also only about $6/can