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Old 10-01-2009
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Quote:
Originally Posted by Crapaud View Post
If the turbulence occurs at the trailing edge, it should not cause vibration or hum - unless the turbulence wash from the keel is effecting the rudder. I would think at the higher speeds, the fluid flow is separating (Transitioning from laminar to turbulent) slightly behind the widest part of the foil. This would then effect the trailing & thinnest section of the foil - and noise (hum) could be generated.

I think you are correct in saying the surface finish is a factor, but it helps promote the vibration not the reason for it. Because of the shear stress the hull, keel and/or rudder generates while moving through the water - any disruptions on the surface finish will cause the flow to transition - resulting in the eddies and pressure variations that cause the vibration.

The word "flex" might be misleading - think of it more like the continuous shifting from tension to compression.

I do believe the vibration can and does promote fatigue in components (how much - is debatable), but does it effect speed? When I think of vibrations as mechanical energy lost into sound waves - the thought is that it could slow a boat down. Another line of thinking is it reducing the effects of friction - like the old football game with the figures moving on the vibrating game board. Any feeling one way or the other? Not that I an suggesting adding vibration generators to sail faster. . .if that be the case.

JP
Humming is always bad - it indicates part of your rigging is not in tune and too much slack... just that simple. You can't hum a guitar string if tuned correctly nor should your rigging hum unless you want to be the next sailboat musical sensation..
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