Replace C/B with Shallow Keel

It depends on your speed. At 10 knots a small fin develops 4 times as much lift as at 5 knots. If the dingy sails at 4 knots and the sailboard at 16 , that is 4 times as fast and thus 16 times more lift.
The faster you go the smaller the keel can be.
A sailboard has also very little vindage

 

The diference is, of course, that a sailboard hull has virtually no draught (so the skeg is deeper for the same draught) and they go much, much quicker. I agree about the rudder though.

Edit: You beat me to it Raggi!

 

I type woth four fingers, sometimes five!

 

Followup: If anybody really giv-a-damns;

The project is abandoned. Dirty shame its too bad.

It was sailed oncet in deep watah with the center skeg and with the centerboard in place and with only the mainsail. I don't recall if it had the twin runners too tho I think not. It was decked over and had a short bowsprit.

Couldn't talk him into setting the jib so it was hard to tack. He sat down in it, centered, facing straight forward on the bottom on a wood frame with no padding for his butt or back and he's 6'4". It shortly became very uncomfortable. It leaked, he had to bail the whole time, and came out soaking wet. The rudder was actuated by foot pedals and a cable. It rotated up.

Actually it would have sailed good enough had the jib (a decent sail) been set. The main, a very poor sail in itself, couldn't be set properly.

I had told him it would probly take just 3 attempts B4 it was under control and fun to sail but nope; its over. Just a little more effort and it woulda worked in deep water but not in the shallow water in which he'd hoped to sail.