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.

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.

Or it could lift right out of the water, and you'd be left with no fin at all!