Kaama Scarab Fuel Tank Installation

[Bulldog]

I am replacing the 4 saddle tanks in my Scarab. It is a full stagger setup, and the tanks sit lengthwise between the stringers and hull. There are 3 bulkheads, one at each end and one between the tanks. There is about 2 inches of clearance all around the tanks which was filled with expanding foam. This stuff is somewhat porous and held water which subsequently created pinholes.

I have the new tanks and will be installing them soon.

Is there an expanding foam that wont soak up water? I will use the original type stuff if I have to but would like to get some advice or opinions.

One idea is to cap the foam by pouring a layer of catalyzed rubber on top of the foam.

TIA (Tanks in advance!)
Bulldog aka Ronnie

[rws]

According to John Greviskis (Ship Shape TV fame) if you don't break the out skin of the poured urethane foam, it will not absorb water,He says to seal any edges that were trimmed with resin ,but Your idea of using rubber would probubly work and be more flexible.The salt water Boys coat the outside of their tanks with tar ,so I'm told.

Rob

[Bulldog]

Many of the manufacturer's state their foam is some percentage (90-95%) closed cell which means it is somewhat porous. Last year I replaced the deck on my little 17' runabout (MiniMe) which the previous owner left outside, uncovered, and the foam underneath was waterlogged to about 1/4" depth all around.

I removed 5 large contractor bags of the stuff which weighed about 50 pounds each. The very thing that was supposed to help that boat float would have also helped make it sink! I could have easily and unknowingly overloaded the boat in that condition.

Thanks!
Bulldog aka Ronnie