I keep my NorSea on a lift
and can measure or take a picture for you as soon as I get enough water
to get her back on.
I don't know the size of the aperture exactly, but I am swinging a 14-9 three blade with a 1GM10
It's a lot of prop and I'm sure that I'm paying a small price
for it under sail, but truthfully, I haven't noticed a drop off in speed. The extra torque I get in a headwind or current
is really worth it for me.