Fuel tank foam 2lb or 4lb
 

Which foam to use when installing a new fuel tank? Called a local supplier and he insisted on me using the 2lb, also said it was the only uscg approved. Others have stated and told me to use 4lb. What are your thoughts?

do a search on here. Others have said to use no foam, tie it down. My aluminum tanks have "L" brackets welded to the top and are thru bolted to bulk heads. no foam. They've been that way for 24 years.

I did a search. No solid answers on what foam to really use or reason behind it. I am using foam. Mine had L brackets through bolted to the bulkhead also, 3 out of 4 broke. If my tank leaked because of corrosion I'd consider not using it. However it was a uncoated raw aluminium tank with no pitting or corrision on it. There was also flotation foam around the tank in the cavity. Boat is almost 16 years old and came from florida 6 years ago. I'm sure it had seen salt.

coal tar epoxy the tank and foam it with 4 pound

New tank will be coated. The uscomposites site gives about the best explanation I could find on why to use the 4 lb. Was just looking for some better answers because I've got a supplier insisting on 2lb.

2lb is looked at more for flotation purposes and 4 lb is looked at more for strength. Mr. Glass Dave really should be asked this question as some builders completely stay away from foam in any part of the build for a couple of reasons. .

I coat the gas tanks as well - have used POR 15 in the past that stuff is some tuff stuff.

From what I have read 4lb foam and make sure you have a drain under it. The consensus why they rot out with foam was improper drainage. Foam would become waterlogged and then rot the tank. I believe I read to cut a PVC pipe in half and run it under the foam. Arc up and away from the V.

I dont actually foam the tanks in but do occasionally use four pound to set the corners or give it some sort of foundation. Yep as far as i have heard two pound for floatation and four to set tank. Make sure you give water the ability to get out if you do use foam in any capacity. It is certainly a grey area that you will get many different answers to :D

4 pound anf i always foam tanke in..espically supporting the bottom,,they can and will split if not supported on the bottom..ok 200 gallons of fuel..ruffly 8 lbs a gallon thats 1600 lbs..dont trust those l brackets with that kind of weight..make sure theirs a piece of 1'' pcv under it bulk head to bulkhead..glued in with 5200..after the foam cures for 24 hours take a grinder to it and taper it towards the back of the boat then paint over the top of the foam..put holes in the bulkhead in the engine compartment for the water to drain..glass the holes so it dont rot..

The cavity already has a 1"pvc fiberglassed into the hull to drain from bow to stern. During all the searching on this site, I found the way superboat installs there tanks and I like that method. I will probably mirror that. Also the way the manufacturer of this hull told me to do this tank is very similar to the way superboat does them.

This is why you don’t foam in an aluminum tank.

http://i21.photobucket.com/albums/b2...enname/9_2.jpg

This is from a Donzi I did last year. Not a boat you want a failed fuel tank install in.
This was a mid-west boat (fresh water). Tank was less than 10 years old. The whole thing was coated in coal tar. Then put in place and foamed in. The issue was the front bow eye leaked (another impossible thing to fix in a Donzi without taking the top off). Water rolled down the drain and over the floatation foam and on top of the tank. Between it and condensation the coal tar was pulled off the tank by the foam and then the tank was turned into swiss cheese because the tank could not breathe (air circulate around it) or expand and contract.

http://i21.photobucket.com/albums/b2...enname/3_6.jpg

The new install is done like my 1972 Allmand SuperNova was done (43 years later and the tank is as good as the day it was made, I had it out 2 years ago just for inspection). Cut up rubber strips (I used a couple found tractor trailer mud flaps) for it to sit on and for the sides between it and the stringers so there is an air space and it’s not sitting on fiberglass anywhere. Liquid nail the strips in place and a couple more dabs on top of the rubber. Squeeze tank in place and then block it in with some teak blocks and stainless steel screws. The tank is there to stay and the way it’s installed even though this boat is on its 3rd tank it should be its last for a least a few decades.

Same way my velocity tank was installed from the factory. Ill be putting it back in the same way.

ok,,next time your outside find a brick...get a piece of aluminum foil,,set brick on the foil.lift up the foil by the sides.now go up and down real fast...let me know how long the foil lasts..