I reckon fin drag is over-rated, fins went short to balance the narrow hulls rather than for drag reduction. But the short fins with a standard aspect ratio were a little small in area for comfort. So now we have short, low-aspect speed fins. Plenty of area but the centre of lift is still at the right spot to balance narrow hulls.
Could you achieve the same with twin fins of the same length but with standard aspect ratios? Tip vortice losses vs. aspect ratio gains, who knows the technical details?
I've seen twinzer waveboards go pretty fast, that quads even go at all has to say something.
What would be the advantages? Not much. If one catches a bit of weed the other might keep you in control. But twice the chance of catching weed.
There's been a lot of backyard experimentation with single speed and weed fins because it's easy. Putting an extra fin box in a board is messy so not much experimentation goes on.
Here's one from the archives. Who remembers this?
You don't need much fin surface area at 50knots. That X2 21 of MvM is probably 150cm2.
The X2 was about 6mm thick at the base. If you had 2 fins to give that area they would probably be too thin to be strong enough and not long enough to keep the windward rail up.
I was at my peak in the '80s - 30 is still fast, but young fellas come down to the lake and clear 40. We gather on the beach and compare fins. They don't make sense to me.
No. 1 97kg 1.5:1
No.2 98kg 1.5:1
No.3 98kg 3.3:1
No.4 97kg 3.3:1
No.5 92kg 1.5:1
N0.6 95kg 3.7:1
No.7 78kg 3.2:1
No.8 106kg 2:1
No.9 92 kg 1.5:1
No.10 80kg 2:1 (go Kato !!)
No.8 is more like 111kg now, then add wetsuit, harness, helmut, weight jacket, bolt on some balls of steel, add moisture to the neanderthal and he is pushing 120kg.
The '09 record was done with record flab/weight at the time over 120kg
Mmmmmmmm Doughnuts, and 50 knots on the menu this weekend.
Twins, being shorter in depth ain't going to help for control when they lose contact with the water when your skipping over the back of rolling chop. Usually run a bigger deeper fin for chop. But hey give it a go might be be good for tighter flat course conditions.
not so significant if you are a 110kg neanderthal........
........No way to talk about the men from Pays Bas.
I think differences in sailing conditions and small sample space might "cloud" those results a bit. If you look a bit further back (say 5 years) you'd find that the "new" low aspect fins arent actually faster than the stuff we've been using for years. Just because they are the only thing available on the market doesnt mean they are a faster design. And there arent any lightweight guys going fast on these fins either 
. The fast results on these fins are coming from big guys in a flat land that has been very windy the last year. Hopefully the wind will be back down here tomorrow 
as for MvM's fin I dont recall him ever saying that it looked like that during his run... only that it was the fin he used and thats what it looked like afterwards. Its pretty easy to smash into a bank at the end of the run when its broad.
Hi guys,
That's the pic I took of Martin's C3 X2 21 after he did his record run with it in Southend 2007 with MS TR-3 5.1 and Naish Speed Pro 60 production Speedboard.
I was not there but Martin told me he first ruined it on a reef and then did the run.
Serge Beumer
The Flat Land
I sail twin fin freeride boards and have really noticed the extra control and comfort they give you thus helping you to go fast. I have snapped a few fins as well and as I have only ever lost one at a time am always able to sail back.
I have been thinking about getting a more speed orientated twin fin maybe fit it with asymmetrical fins just to see how fast it will go.
if you run 2 real small assy fins in a board would you need a port tack assy and a starboard assy in the board ?
That is how I was thinking of setting it up. I guess if you were going down a speed course you would only go with what ever tack was needed for the course.
That depends.
Is the difference in the lift to drag ratio of an asymmetric fin and a symmetric fin greater than the difference in lift to drag ratio of a symmetric fin and an asymmetric fin on the wrong tack?
Those CFD packages should be able to answer that question. If the answer is yes then one of each would be best for all round sailing.
The Lessacher weed fins get good reviews and they use a port and starboard mix of asymmetric foils so maybe the answer to the question is yes.
Hey SWS, who makes a twin fin freeride board?
