I plan on repairing a board that has creased/cracked across the bottom and half way up the rails about 40cm back from the nose. I am having trouble finding divinycell of the right size and density in my area but can get a sheet of H60 in 4mm. Is that dense enough for the area I am using it for and what about future repairs in load bearing areas? I have searched the forum and read various threads about board building and H80 was the only density I found mention of. I tried scrounging from local boat builders but they only have much thicker stuff.

If it's only a small area, in theory you should be able to make up for the lower density foam with a bit more cloth.
The problem with the type of repair you're doing, is the new foam ends up a bit thinner than the original.
(If you do the job properly and overlap the interior layer of cloth anyway).
So thinner and less dense, = less stiff, I'd be tempted to throw a bit of carbon at it to compensate. That way you aren't making it too much heavier with extra layers of glass.

Thanks decrepit, I might try harder to find the right foam then.