The only unsinkable boat I know about is the Boston Whaler
www.whaler.com which is made of two fiberglass shells bonded
together with the inside filled 100% with foamed in-place
resin that makes it one solid boat. They even can be cut
into sections and the still get you to shore with dry feet.

But aluminum floats don't work well with foam inside because
of corrosion between the foam and metal. A better solution
is to fill the compartments with ping-pong balls. They
displace water, don't weigh too much and can be removed for
inspection and corrosion control.


--
James H. Macklin
ATP,CFI,A&P

Some of the small sail boats also have foam filled compartments with the
same effect. The name MacGreggor comes to mind from years ago, and there
are probably others by now.

Peter