Toller wrote:

Oak is about 50% heavier than mahogany, but I actually want the weight, so
that is not a problem. Besides, it is free and the cedar would be about
$50.


What you are describing is a disaster guarenteed to happen.

As someone suggested, use the oak for something else.

Might even barter it for some good foam, but these days, good white oak,
even 8/4 is cheap compared to foam, even Divinycell.

Cover the foam with some 17 oz double bias and epoxy.

SFWIW, the above describes how my rudder will be built.

Lew