Why does a hydrofoil sing?

[tahoedirk]

What makes a hydrofoil sing?
My first foil makes occasional whalelike singing noises. My new foil sings consistently . First I thought it was kind of cool, now , not so much . What's happening?

[Hawaiis]

Vibration makes the sound.

[windfreak74]

question does the vibration come from the fron or rear wing?
maybe you need more carbon reinforcement so it vibrate less.

[Hawaiis]

It can come from anywhere, my new spots2 with very rigid Carbon also sings. I think it might come from the wing tips where it is thinner.

[Tone]

I think, tape on certain parts i.e.leading edge, can help

[NorCalNomad]

It will come from any wing surface. Happens with surfboard fins too

[revhed]

I respectfully submit that this "whistling" sound comes from a resonance caused by cavitation.
See http://eportfolio.lib.ksu.edu.tw/user/T ... i-2008.pdf
I was going to call it harmonic resonance caused by cavitation because it sounds "harmonic" to me,
although I can not verify this at all with a KBHF!
Anyone have a guess at what frequency this is?
I have flown quite a few foils that whistle, all having about the same sound.
It also seems to be speed related on my high wind, wave foil because it starts at 24 knots and no sound below that speed.
Sometimes it bothers me other times not.
Is this causing vibration on some part of the T bar and,or wings, or not, I do not know?
Does anyone?
R H

[Randahl]

Glad I'm not the only one.

[cglazier]

Years ago when I was racing catamarans we sometimes had the same singing on some boats. When we sanded the trailing edge of our daggerboards and rudders to make them sharper, it stopped the noise.

A trick to find out which trailing edge is causing the singing is to put some wide tape along the trailing edge that you suspect and leave about 1 cm extending past the edge (so it extends loosely behind the wing). If this effects the singing, then this trailing edge is the culprit. (Box packing tape works).

Having said all this, I don't think the singing really effects performance much.

CG

[BWD]

I relate it to the similar (if not same) phenomenon in sailboats.
The foils of bigger boats also hum or sing at certain speeds, or increasing with speed.
The cause has been said to be vortex shedding from the TE at resonant frequencies of the foil structure.
It is often recommended to have yacht foils end with a squared off TE, instead of a knife edge. For dinghies, a mm or so, for large boats, a cm or more. This is for ease of build, maintenance and safety, and in some cases performance.
One fix has even been to bevel the foil TE on one side so if the TE edge begins to resonate, it will not effectively generate a vortex (or sufficient elastic reflex) on the opposite side to continue the vibration.
Probably not the best solution for racing, but maybe more pleasant for fast cruising without "whale" sounds. Although I have read of cases where the foil resonated enough to deform and add drag so more drag was saved by squaring off or beveling the TE.

All this refers to larger, more vertical blades in different flow conditions.
Since kitesurf foils and surf fins are so much smaller, and usually faster, the effects and solutions will be different, but I thought the parallel perspective might be interesting to some.