Been thinking about fin design and the issues that arise at high speeds and am wondering if anyone in the past has explored doing away with the "traditional" fin as we know it and incorporating a series of longer but extremely shallow (and thin)blades - say 3-4mm thick, approx 500long and tapering gradually from nothing to a depth suitable for tracking stability at top end speed.
I don't have a great grasp of the forces involved (physics and laminar flow dynamics) but if the area of a traditional speed fin can be matched by a series of shallow blades then will enough lateral resistance be achieved to stop the board from losing directional stability? and if so wouldn't there be considerably less drag and potential for cavitation. Just looking at AA's speed run it was so broad that I feel a design of this nature could just be the ticket.
Of course the board couldn't be gybed and would only be good for going in a very straight line* (but if this 50knot limit is to be beaten then maybe a radical idea is in order) *Top line dragsters don't turn too well either
Maybe someone can saw 3 to 5 slots into an older speedboard and epoxy some tapering aluminium blades to the underside and fill in the fin box or maybe someone can tell me to go back to fluid dynamics 101.
starting to sound like a kite board 
i'm not saying it wouldn't work but i see a couple of issues,
1. with high winds the water surface is turbulent so you are going to need a deeper foil to achieve a good centre of lateral resistance.
2. the drag on a long and stumpy foil i would think would be to high because of the drag ratio?????? something more like a kite fin might work better??
decrepit???? i think you built something similar?????
Well sort of, I was trying to get as much fin out of our bottom growing weed as possible, so I tried a twin fin with quite small fins close to the rails.
Trouble was it has a twin concave bottom, great for single fins, but each twinny was in a concave.
That's where the air goes that's trapped by the nose.
I was also using some old surfboard thruster fins, the leading edge was much too thick.
Result, as soon as I hit 25kts I spun out, every time I tried.
Haven't given up yet, it's been on the back burner for a while now, but it needs the concaves filled in and new speed fins, before I try it again.
The trouble with long shallow fins is they have a very high induced drag, so aren't real fast.
The old Hypersonics with the 70 mm deep channels generated lift with the hull. You could sail them with a much smaller fin than you would normally use. I suspect you could modify that concept for a speed board but I would guess that you would not be able to equal the efficiency of a flat featureless bottom with a well designed speed fin. Still, if it enabled you to sail in shallow water you may get a payback from that, the fact that you could sail Hardies run say in any direction at low tide with pretty smooth water, and the fact that that particular hull design delivers an exceptionally smooth ride may get you to record speeds. What do you think of that?
