Fin whistling usually is because of the finish on the trailing edge (TE) of the fin.

Quoting Ian Fox’s words from the Starboard forum:

“Often if the TE is finished too symetrically, the waterflow “collides” as both sides of the flow come together off the back of TE. By angling the TE slightly, you minutely shorten the flow on one side, which disrupts the harmony of the flow/s, and they actually merge more smoothly, without the whistle, which in turn often can indicate some minor loss of efficency.”

What sought of fin do you have? I would imagine its not good to have a whistling formula fin; it doesn’t sound too efficient.

There’s a few discussions about this going on on the Starboard forum with some ideas on how to cure the problem.

http://star-board.com/forum/showthread.php?t=1466&highlight=whistle

http://star-board.com/forum/showthread.php?t=4113

Could anyone tell me why my fin keeps a high noice, sort of whistling sound. The noice doesnt disturb me but I would like to know the reason. Should I sand it, is it breaking ….

I have tried the R20 now a bit in different conditions, going from flat to chop and even big swell. Used it with 12,11 and even 9m Vapors on my exocet WF08 (the black one). The R20 I got is produced in april08 and has rake +6.
When you take this fin in your hand, you observe immediately the very very soft tip. But it is clear that it is only the top1/3 that is soft.

Sofar, I really like this fin. It is so easy to sail in all conditions. It is selfregulating the power and still delivering the lift needed to get a FW board going. Going downwind is really easy. It feels fast and controlable. I have not yet used it in a real up-down wind race, but I saw Marcus Bouman using one recently in marginal winds and he was realy far ahead of the rest (Dennis,Adri, …….).
I did put my mastbase a bit more rearwards (1cm).

The R20 feels like a very “universal” fin that was really easy to use.
Maybe also interesting: my weight is currently 90kg.

I really have no idea where I find the time either, lol!

Actually I’d be really interested to hear some feedback on the R20 if you wouldn’t mind emailing me about it or even posting a comment here. My comments regarding the R20 have been based on the photos I’ve seen of it and the very short report I was given by Michal Polanowski (POL-16) after the FW Worlds in Brazil (see above photo at end of this article). Basically, I was told it was “very soft” and “looked like a Kashy shape” and that’s about it, but I’d love to really know what it is like.

There doesn’t appear to be too many around at the moment and absolutely none here in Australia. But you’re right, if its anything like I think it is, you will need to adapt a little and get used to this fin as I’m sure it won’t feel anything like a standard R13.

Cheers!

great articles. Amazing you find all the time to do this.
I’ve just got a R20 and will try it soonon my exocet WF087. I got it 2nd hand at a, the former owner had tried it once and didn’t like it. Maybe he was expecting a classic behaviour.
With what you mentioned, it is logical that you need to addapt to a fin like R20. Understanding how it works is a good step in the right direction.

Thanks and keep up the good work.

I also haven’t tried the FRB 5B Hurricane fins. For me, I think they are too big and probably not the fastest fin out there. I prefer a bigger sail and a faster fin (ie, a 12m and R13) rather than a big sail and big fin which I feel isn’t versatile/mobile enough for pumping, gybing/tacking at good speeds.

Because of the power-to-weight ratio, a FW board is chasing ’speed’ as well as ‘lift’. With a standard R13 in 15 knots of wind a good sailor will be able to point 55 degrees upwind at a speed of 14.5 knots (VMG = 8.3 knots). If you can retain that height and travel at 15.5 knots, then that is a 5% increase in performance. This is something that I believe these newer, softer and more torsionally stiff fins (Kashy, R20 etc) are allowing sailors to do more efficiently. Nobody is pointing higher than they were 5 seasons ago, they are just travelling faster at the same upwind angles. “Speed” being the key ingredient here.

On a Yacht, you are mainly chasing ‘lift’. Hull speed is usually limited by other factors (weight, displacement etc). I’m not a yachting expert (never sailed one in my life) but as they are NON-PLANING boats I can assume that ‘pointing’ is their main focus – not speed. Various keelboats have at their disposal contraptions like canards, wing-keels etc to help but principally they are chasing point and so reducing keel drag with geometric twist is probably not on their agenda? (someone more “boat” orientated could confirm this for us?)

I don’t know a whole deal about Gliders either. Actually nothing. But I would guess they are also chasing lift at the expense of speed, just to stay in the air. I assume gliders have asymmetrical foils and trim tabs on the wings? They could even have ‘aerodynamic twist’ built into the wings.

That’s getting a little off topic of this article, but there’s a few mentions of glider wings in the article on Aerofoils and Wings which explains twist even further: http://www.auf.asn.au/groundschool/umodule4.html

Cheers.

With regard to drag I see the idea but still have some doubt. For instance the keelboats run a lot of tank time, but I don’t think they build in twist to their foils (ASFASIK) On Hang Gliders ‘VG’ is pulled to reduce twist and improve glide, at the expense of control. Whatever I’ll settle for the fact they work very well and look forward to trying one of the new designs.

a) understanding twist:
As the point, through which the resultant lift forces act on the fin, is offset to the neutral axis for bending, there is a torsional moment associated with the bending force; this torsional force produces geometric twist.
The torsional stiffness at a cross-section along the fin is determined by the weight, fibre direction and type of carbon reinforcement used in the manufacture of the fin eg 300gm/sqm double bias carbon.
The angle of attack (aoa) at various positions along the leading edge of the fin is a function of the torsional moment and sectional torsional stiffness.

b) geometric twist reduces drag:
With a fin moving through the water, some water leaks around the fin tip from the windward side to the leeward side producing a fintip vortex.
With all other parameters remaining the same, the induced drag decreases as the angle of attack decreases.
If the lift diminishes towards the fintip with a smaller aoa associated with geometric twist, there is less pressure differential near the fintip. The result is a smaller fintip vortex and a reduction in the induced drag.

Cheers