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Go Back   SailNet Community > Out There > Racing > Boat hum
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Topic Review (Newest First)
04-12-2011 09:48 PM
Gust14882 I used to crew on a J-80 named "Uproar" because the keel hummed at speed. It started at around 8 or 10 knots, and increased in pitch the faster we went. Once the boat started humming, we ignored the knotmeter and trimmed to get the highest frequency. I'm pretty sure it was vibration of the fin keel itself that created the sound, but it was obviously caused by the water flow over the foil. If it had been the rudder, you could have clearly felt it through the tiller and that wasn't the case on this boat. Ah the sound of 15 knots running under spinnaker and a full moon ...heavenly!
06-08-2010 04:58 PM
puddinlegs
Quote:
Originally Posted by US27inKS View Post

The eddy on the back edge of the foil creates drag, and can be eliminated by reducing the trailing edge to a point. This is impractical at best, so reducing it as much as possible is the goal without sacrificing the ability to withstand a small impact. Besides, getting a pointed edge straight is a bitch.
Actually, though counter intuitive, a pointed trailing edge is slow. Go have a peek at any performance racing boat foil and you'll see that it will be squared, width about 1/4" inch or so, and perfectly faired in this manner from top to bottom the the trailing edge of both the foil and even the keel bulb.
06-08-2010 04:52 PM
puddinlegs
Quote:
Originally Posted by artbyjody View Post
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..

Not always true Jody... There's always different tension in shrouds depending on sailing load (think leeward shrouds while going to weather... then of course, there's the slapping headfoil at the dock when the backstay is off that is stopped by wrapping a pole lift or the like around the aforementioned flapping bits). One boat I sail on regularly has a runner dependent rig. When we're going to weather in a breeze and the runners are loaded to the hilt, they hum. The boat well tuned and very fast. We occasionally get some hum from a loaded check stay on my boat in higher winds as well... same thing. Boat's humming right along! But as other's have said, we're talking underwater foils, not rigging.

Haven't seen you're boat out on the Sound since you've been back in the water. Hope to see you out this summer.
06-08-2010 03:10 PM
L124C When my Yankee 30 is at speed on anything from a beam to close hauled, she makes a loud eerie (electronic sounding) whine in the cabin. If you are astern, it sounds like it's emanating forward. If you are forward, it's coming from astern. It really seems like it's omnipresent! I sail with the transmission in reverse (to avoid drive train wear). If I put the gearbox in neutral the sound goes away, so I assume the resonance is in the prop. However, the omnipresent quality and intensity of the sound is almost unbelievable.
10-23-2009 12:56 PM
grahammcg Lots of interesting theories.
The most likely cause is trailing edge harmonics where the 2 streams of water from each side of the keel or rudder 'hit' each other.
Solution is to chamfer (angle?) one side of the trailing edge so that 'collision'
doesn't occur. Works on my Hobie - & it goes fast! (not always with me on it!)
10-02-2009 11:00 PM
fullkeel7 Not sure of all the science here, but I loved that 'hum' in my Laser days. I just thought of the hum as an 'earily warning system' that one or possibly two things were about to happen. 1: That the real fun had just started as the boat got up on plane or 2: That I was probably going to fall out of the boat again. If the hum stopped, that was the indicator to start back to the launch area and go home.
10-01-2009 11:46 PM
artbyjody
Quote:
Originally Posted by US27inKS View Post
I think we're talking mainly about keel or rudder hum at high speed. This is completely different than the rig humming.

Only if you have centerboard keel that you can lift.. rigging is something different..Cause and effect..depends on the boat..
10-01-2009 11:43 PM
US27inKS
Quote:
Originally Posted by artbyjody View Post
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..
I think we're talking mainly about keel or rudder hum at high speed. This is completely different than the rig humming.
10-01-2009 11:16 PM
artbyjody
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..
10-01-2009 11:04 PM
Crapaud
Hum vs. Speed?

Quote:
Originally Posted by zz4gta View Post
I agree, everything does flex to some extent. However, I think that the finish on the foils itself and the trailing edges (non-laminar flow) will cause the hum before a "flex" or vibration hits it's natural harmonic frequency.
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
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