I think the foam as flotation as any other device (even a boat) works on displacement. With the foam in the mast it is not displacing anything except air on the inside. The mast itself is doing the displacement. While adding foam you also add weight and not volume. Look at it as adding bricks to a boat with out changing the hull size. At some point the weight to displacement ratio will go into the negative and the boat will sink. With the foam on the outside it will actually displace more volume (water) and thus add bouyancy. A previous post said to seal the mast that would be your best and first attack on the situation.



JMO



Clayton