Simon,
If I understand you correctly this part of the hull can experience quite high compression loads from the rig as well as coming off waves or big chop.

Given that I would also put a layer of 200gm glass over the crack after taking back to bear timber. When loaded up if the ply wants to seperate again the glass will prevent it even more affectively that injecting a resin glue mix. However I would do both.

Regards,
Phill

I know that the voices in my head aint real,
but they have some pretty good ideas.
There is no such thing as a quick fix and I've never had free lunch!