[LoveMySeacraft]

If its foamed in place, as you said, and has moved...Then use up as much of the fuel as possible, or pump it out, move it back into position & then foam the rear, and any other void spots. I would'nt try to float it back in place with water. Using 2-part(A/B) foam will displace any existing water areas & then that tank shouldn't budge any more. Most commonly used foam is what they call "2-pound" foam. Thats because its less money. But I prefer using the more expensive "4-pound" foam, because its much denser & stronger. The tank ain't going nowhere with 4-pound.