New foam on an old boat

[JelloPNW]

Hey guys,

A previous owner of my '78 Gregor U-151 welded aluminum pulled all the foam out from the 3 benches (seems to be pretty common practice). I'm thinking about adding it back but I really like having the under bench storage.

I'm planning on adding a shallow deck a few inches above the bottom of the boat and figure under the deck is the only spot for new foam. I was originally thinking just 2" rigid foam insulation board loose on the aluminum covered by ACX would do it but my deck won't be nailed down so I imagine in the event of the boat taking on water the foam and deck will float away while the boat goes down. My next thought was 2 part expanding foam but I have 2 concerns about this stuff:

1. Will it stick to the aluminum so strongly that if the boat takes on water it won't break free of the hull and float away?

2. What's the best way to deal with it blocking the drainage?

Thanks guys!

 

[Scott Danforth]

1. yes
2. if you think you can control where expanding foam goes, think again.

 

[kcon]

If your deck isn't set in place and you want foam under it, put a LOT of weight on the deck before pouring the foam so it doesn't push up on the deck, like hundreds of pounds, still you'd want to be exact with how much foam you pour for that amount of space.

Also, I'd recommend you sort out the average amount of weight you'll have in the boat, and calculate out the flotation weight of the density/amount of foam you intend to use and be sure you have at least enough foam to support that weight. 2 pound foam will support 75lbs of flotation per quart.