Fangman ( thank you ) on another thread inspired me to following conclusions

Sound strange to talk about sound in this context ... but maybe not so.

What I very interesting to know could be acoustic profile of every fin we use.

Experiment could be following :

lets attach high range microphone/ sensor to register how our fin vibrate during very high speed run 40-50ktn .

We already could anticipate that our fin / every fin will have few characteristic harmonics - resonance frequencies.

They depend how long the fin is, how thick and wide, then from what material is build.

Now the speed at which our sound wave travel differ if you fiberglass or metal.

My hypothesis here is that wrongly vibrating fin is able to loose a lot of energy to water, causing excessive drag.

But well done fin at certain frequency could minimize that drag below level of not vibrating fin at all !!!

I propose following hypothesis / formula - to be experimentally tested one day.

" The higher is vibration frequency of our fin - the less drag is produced " .

That make absolute sens for me since at ultra sound frequencies small bubbles are created even to separate surface of the fin with water ! Our fin could run almost dry in air bubble.

I am soo excited because our mate ( Fangman ) mentioned now about making fins from metal - titanium - which make perfect sense- if we want very high frequency generated .

If my hypothesis will confirm, fin designers may now design fins to vibrate. special resonance cavity or shape will cause fin naturally vibrate promoted by the water flow.

The easiest experiment could be performed by attaching vibrator 0 -50 KHz to our tested fin ,
and measure the resistance in our artificial run. How drag changes in relation to applied frequency ( if at all ) .

Macro, I don't think a titanium fin is too far away, it's just the finances that are! Your thoughts on fin resonance frequency is something that has never occurred to me - I wonder?

I am absolutely positive .

At extreme I found that just loose fin, bit not tighten enough in the box - will instantly slow my board below 30 knots.

Simple tightening bolts and board instantly pop few knots more. Same wind, sail everything.

That will be example of very low frequency oscillation, but the rules/formula should be the same.

If the idea happen to be true then we could even follow with board design to actually amplify vibration and vibrate the bottom surface of that board too.

Like box of guitar amplify quiet string vibration - our board - works like big guitar There are already some indication that acoustic of the board and fin may play significant role.

That fastest the board - more narrow is - shorter string - higher resonance frequency - less drag.

Shorter fin - higher frequency - less drag.

Now we could start experiments using different material to artificially rise frequency for the same length of the fin.

Fin made of any metal should vibrate much higher that made of fiber glass. We could tune fin frequence adjusting how wide and width is.

Sorry Macro, I have to disagree, a fin running in bubbles may have very low drag, but it will also have very low lift, you'll just be going sideway!!!!

Similar thing may be happening with loose fin bolts, (I know it does for me) If you don't have an airtight seal on the fin bolts, air will be sucked down onto the fin and cause loss of lift to the point of ventilation.

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decrepit said..
Sorry Macro, I have to disagree, a fin running in bubbles may have very low drag, but it will also have very low lift, you'll just be going sideway!!!!

Similar thing may be happening with loose fin bolts, (I know it does for me) If you don't have an airtight seal on the fin bolts, air will be sucked down onto the fin and cause loss of lift to the point of ventilation.

This bubbles from ultrasonic waves are microscopic.
So don't have any absolutely effect on so called spinning.

Also my loose fin, didn't spin out, just free movement convert into low vibration at higher speeds consuming energy.

If somebody has any doubt if vibration may have any to do with resistance -

do following experiment - take your oscillating sander and try to drag on table.

When turn off and power on. Any difference ?

But I agree with you Decrepit that unintended vibration may cause also cavitations - spin out- otherwise hard to explain.So sometimes some fin that size wise should keep grasp spin out easy without any reason.Some others don't.

Culprit could be resonance vibration again - but the wrong one. Not the frequency we actually want.

The problem we may have that to produce this vibration / sound wave we also need energy - so there is trade of between - requirement for energy used to produce sound and benefits in lowered resistance/ drag.

Maybe some devices may help here - like a gadget whistle inbuilt into mast base/extension to produce high pitch sound by the wind passing .Sound /vibration transferred then onto board to resonance (?)

Potentially vibration is a good shark deterrent? Or could be used to turn your board into a vibration plate burning additional calories

Seriously though I've seen first hand that there is a significant amount of play in your iso97 Fin box and it always surprises me that you dont spin out more

Select Fin use to whistle once they got to the mid 30s. You could hear it when you sailed past one . Never got a Select past 38, they always got dragy and spun out

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kato said..
Select Fin use to whistle once they got to the mid 30s. You could hear it when you sailed past one . Never got a Select past 38, they always got dragy and spun out

That may indicate that lower frequencies will effect performance negatively , but higher improve.
In this case vibration - high pitch - could be beneficial - whistling sound.
But if we got into very high range/ high pitch - it will be quite difficult to hear.If I have only more time I will do following experiment:
Attach to the fin bolts piezzo electic inducer , from popular ultrasound cleaners.

Then hand switch could turn this on and off when running high speed. The observe sudden peak on the speed graph.

That for testing purposes only.

Because at the end find could be designed to vibrate by them self, without the need for artificial simulators.