looks like MVM's fin after he broke 50 knots.....

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.

Ian K said...

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.

I reckon ya missing a few things...

fins were short and fat in the '80s then went longer to balance wider boards. The fin area was large cos we spent more time going slow, and nobody knew any better in the sport- back then 30kts was record fast. At the low lift coefficients/angles of attack we are constrained to (for various reasons) the mechanics are pretty well understood.

Xfoil (when set up correctly) has been well correlated with tank tests and gives a pretty good ballpark of actual performance. At low angles of attack/lift coefficients, the 3D effects are actually quite minimal and total lift and drag forces are relatively easy to predict.

I reckon 4-6kg of drag is a lot. Thats what ya get with lots of surface area (say one of these silly delta style fins) dragging through the water at low angles of attack... not so significant if you are a 110kg neanderthal.

I'll stick to my single, short, low surface area, thin carbon fins thanks

slowboat said...

I reckon ya missing a few things...

fins were short and fat in the '80s then went longer to balance wider boards. The fin area was large cos we spent more time going slow, and nobody knew any better in the sport- back then 30kts was record fast.

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.

So if low aspect fins compromise so much on drag are they just popular because they're more secure against spin out?

I did a bit of research on the internet, scaling with a ruler. Here's the approximate aspect ratios of the fins used by 2011 top 10 on GPS-speedsurfing

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 !!)

I'm now very curious about MvM's fin. Does he have a wicked sense of humour? I clearly remember it portrayed as the 50 knot fin. All mention of this aspect of the record run has now disappeared from the internet. I thought stuff in cyberspace stayed forever. Who else remembers?

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

Troppo said...

Spotty said...




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

You don't get to 120kg eating salad!

You do if it's Caesar Supreme

not so significant if you are a 110kg neanderthal........

........No way to talk about the men from Pays Bas.

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.

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 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?

SWS said...

I am getting one made up by OES but the ones I sail currently are hifly madd's.

Checked out their convincing web page. They do mention the relationship between footstrap position and fin depth. Hence they only have an inboard footstrap option.

Which raises another point - all performance boards have footstraps in the maximum outboard position. It's as if we always end up using the longest fin possible for that width board. So why have wingers never really caught on for windsurfers? At least in flat water you should be able to keep them clear of the water.

How would a 50 cm wide board with wingers allowing for a formula board stance go? You'd need a 50 - 70 cm fin. Might be pretty quick in moderate winds.