I am re doing the floor on my boat since it was all rotted and after i took the floor out the foam is full of water and really heavy. Is there a place i can buy new foam for it. is is needed? ( im sure it is because it was already in there) and does anyone know how much it would be?
It is needed if the boat is going to float as designed.
Two options:
1. 2 part blow foam
2. Sheet foam
BOTH have to be sealed cell foam or you will be right back where you started. The 2 part is commonly referred to as MARINE foam.
If you go sheet foam, you use foam sheet glues to hold the sheets in position with each other for cutting (electric turkey knife is fine). Fine shaping with a band sander/coarse (40-50 grit) works well.
Stu has it right. Yes, you need the foam IF you want to boat to float as intended when swamped and you must use closed cell foam so it won’t absorb water.
Whatever you do, do NOT use consumer spray foam designed for sealing air gaps around the house. Most of these foams are not closed-cell and therefore will absorb water like a sponge.
Personally, for a DIY application, I’d go the sheet route. If you buy thinner sheets, you can flex them to follow a contour and then build them up in layers. Also, sheets of closed cell have tremendous boyancy, so it’s not usually necessary to completely fill a cavity as the manufacturer does with spray foam.
I’d say a lot depends on your application and how much foam you had to remove to clear up the water-logged problem.
Grouse
Why would a boat manufacturer put stuff in that will absorb and hold water ??? 
Or did somebody else do this floor once already ? 
Are you aware of any manufactures of sheet foam in the metro area? I’m looking for scraps, off color stuff or 2nds. Got a project I want to attempt, but don’t want to spend retail for the pink sheets at Home Depot.
Thanks!
Quote:
Why would a boat manufacturer put stuff in that will absorb and hold water ???
Open any boat up after 10 years of use and you’ll find a lot of water – regardless of manufacture! Closed cell foam won’t permeate ambient air/moisture as it is designed for. When saturated for long periods of time in water, it permeates water and becomes water logged. The best boat designs I have seen so far has NO foam on the bottom 1/3 of the boat. But, then there is the layers of glass over plywood (older designs) that eventually fill with water and adds more weight to your rig
http://www.uscomposites.com/foam.html
I’m refurbishing an old Lund right now & this is what I’m using. The expanding foam adds structure stability to the boat besides adding flotation.
The foam I removed from the boat was water logged also. This time I’m leaving a space down the center line that is not foam covered. Hopefully this will allow water to drain back to the bilge area.
i literally lay a small ‘drain tile’ down the center of the boat for this purpose. my feeling is that it doubles the longevity of the foam. Small S&D is perfect for this. put the holes in it if it’s not already perforated.
do you need anything speacal to do the spray foam?
Everything I see on the spray is marine compatible, but not info or recommendactions on the floatation aspect????. Anyone have any info/insight?
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