Marine plywood is not well defined in every day life.
First, the best way to know if it is a good buy is to do a boil test. Do a
little googling and find out the British Mil specifications.
Normally a good plywood for marine use has no void and can withstand the
boil test.
I usually boil a 2" X 3" plywood sample for about 30 to 45 minutes. Then
I let it air dry for a day. After that if the sample look good and can hold
a screw and nail I take it as good boat building quality.
Start with : http://test.wbdg.org/ccb/FEDMIL/p18066c.pdf
One has to be careful, plywood used for crating is not expensive and has
little value in boat building.


"Edward Stammer" wrote in message
...
Does anyone know if cheaper birch plywood with 8 layerrs would be usable
as Marine plywood?

$50 per sheet versus paying approxiamately $100 a sheet.

Ed