I'm instsalling new Aluminum fuel tanks in my 27 Magnum Sedan. I need to know what bedding material to use under the tanks? When I removed the old tanks there was a pad like material but it was removed in pieces with the contaminated foam around the tanks. A product & brand name would be much apreciated....

neoprene closed-cell foam. 1/4 inch thick. all over ebay. closed cell means waterproof. doesn't soak water up like a sponge.

i would foam the tanks in,first you will need to apply a coal tar epoxy to the fuel tanks,if they are still being built have the builder apply the coal tar epoxy..next set the fuel tanks in the boat and make sure theirs at least 1/2''-1'' between the hull and the fuel tank..once the tanks are in place you will need to make sure the tanks are in place and secured so when you poar the foam in from the port and starboard sides the foam will fill the cavity under the tanks ans not lift the tanks out of their position..

have a drill with a paint mixer attached to it,once you mix the 4lb a & b together and blend it with the drill do it fast because you have vary little time to work with it...do a test mix first with a few onces to see how fast it takes for the foam to kick off and keep that number in a safe spot until it is time to poar the foam in place..after the foam cures in 24 hrs you can trim off the excess and apply a coat of good urethane paint over it to seal up the parts of the foam you trimed off..

here is a good source for the foam...remember 4lb foam and its a easy task..
good luck!

http://www.uscomposites.com/foam.html

We are reproducing the tanks in our shop. Will look into coal tar epoxy. What is the purpose of the epoxy? to prevent corrosion?
How do you keep the tank from coming up as the foam expands??

Here is a Superboat build thread. Scroll down, there are some good pictures of foaming in the tank.

http://www.offshoreonly.com/forums/s...-pictures.html

Basically what fixx said .
It's critical to properly barrier coat the tanks now while you can so they'll be sound for years to come ..even if the foam were to absorb water later down the road.

Notice also that fixx mentions 4lb foam .. That is not accidental. You must use the right density for the installation of tanks .. I never knew it before I did it , but the stuff is not all the same.

One last thing .. courtesy of MOP ... I did mine as he recommended .. using small pours first to set them in place on the bottoms . If you do a big all at once pour things can get out of control very fast and if the tank lifts , it's all over.
Because I couldn't strap mine down I weighted them with a ton of cinder blocks and was very careful .

their are chemicals in the foam that will attack the alunimum,,coal tar epoxy is really good stuff,,will be the last tanks the boat will ever need after its applyed..

cool if your building your own tanks then you will need to weld on some tabs to keep the tanks from resting on the hulls bottom..once the tanks are in place i use 2x4's across the top of the tanks..then i wedge them under the cock pit deck to hold them down...it dont take much to hold them down,you just dont want them to move when the foam is setting up.

Thanks for link.

Mrfixaal I don't believe there are any chemicals that attack aluminum in the urethane foam. I know that if you pour the foam in to fast in a closed in area that it can potentially set it self on fire as well as grow to fast & move anything in its way. I have seen Shrimpers & large Tuna boats get foamed in around there chillers which are made of aluminum & they never had corrosion concerns. Urethane is pretty benign stuff.
Slow pours also make for smaller more uniformed cells.

Thanks all for the help & suggestions.

The foam won't hurt the aluminum, but moisture, especially seawater that might find its way into the bilge and get into the foam will make short work of the tank...

manufacturers foam in tanks because it is quik and easy and it will usually outlast the warranty. it is not considered a good idea.