Vortex shedding-certainly real - Page 2 - SailNet Community
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post #11 of 14 Old 1 Week Ago
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Re: Vortex shedding-certainly real

Referring back to post #1, the OP mentioned “vibration” that was damped by wrapping the mast with a halyard. Give that the wind was coming from the side, it is likely that the mast groove (for the sail slides), assuming his mast has a groove rather than an external track, could have been “whistling”. Think of the way a flute produced sound. This effect can be more pronounced with boats that have a deeper “groove” for in-mast furling. By wrapping the mast with a halyard, the OP disrupted the airflow across the (assumed) groove and minimizing the tendency for vibration.

The in-mast furlers can be quieted by closing the opening and there are devices designed to do just that. Without such a device, a side wind can produce an eerie, low-pitched moaning noise that carries quite a distance. This is a concern for docked boats that are not pointing into the wind, and would not normally be the case at anchor or on a mooring. BTW, you can get this with in-boom furlers as well, but that can be mitigated by the narrow sail cover that Leisure Furl, for example, provides to close the gap and protect the sail.

For several years Mystic Seaport has had the large sailing vessel “Wireless” at a dock that is athwart the NW wind flow that we often get in the winter. With in-mast furling on 2 masts, the noise generated a number of complaints by residents that the Seaport took to heart, by employing a device the closed the furler gap and successfully mitigated the problem.

The “whistle” effect is very different from vortex shedding from the mast itself, which is what I experienced 30 years ago on my catboat.
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post #12 of 14 Old 1 Week Ago
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Re: Vortex shedding-certainly real

Quote:
Originally Posted by alanr77 View Post
I think the wind angle and surrounding “funnels” had a lot to do with it. There’s a 35’+ IP next to me with a giant tarp wrap around it and a large building in front of me. A large hill is behind me. I didn’t notice the violence effecting any boats around me but it’s possible. It’s one of those things I guess you don’t research unless it’s happening to you. I’ve had mast resonance happen and sometimes even a slight vibration in other boats. This was the first time it was so violent as to move a 12 ton boat in its cradle. I’m not kidding when I say my sea swing and various other gimbaled items were swinging 4-5” athwartship and this went on for hours. Then again, I’m not usually out of the water for a couple months so the previous reply regarding the boat not being able to move in the water may be the answer.
We’ve been storing our boats in a yard with gravel for decades. Since I store with my keel-stepped mast up, there is always some rainwater that comes in the holes for halyard entry and exit, so I periodically (at least every week or so, make a trip to the yard to manually pump out the slack bilge area by the mast step.

When I visit the yard, I ALWAYS check the poppets on my boat and my neighbors, as well, to make sure they haven’t loosened with the ground moving (freeze-thaw cycle?). Almost every visit there are minor adjustments to snug things up and sometimes there are serious adjustments. You would hope the yard does this kind of check on a frequent basis, but don’t count on it being thorough. At least we are near enough to make frequent visits ourselves.

So, it’s hard to imagine a boat moving in its cradle: perhaps we are talking about individual poppets that are settling, with the wind loading not helping. Again, we’ve had no problems in the 22 yrs my 35’ sailboat has been stored with the mast up on the hard.

P.S. FWIW, I can feel and hear the wind-induced vibration with the boat in the water and don’t sense there is any significant energy dissipation into the water at those higher frequencies.
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Re: Vortex shedding-certainly real

I prefer to winter store my boat just for the energy dissipation in the water.
One afternoon working on my boat in the winter on jack stands , mast up, when it was blowing 30 the mast was humming like a tuning fork. I’d never heard that sound when in the water tied in the slip.

With the boat being on 10 jack stands that’s where the energy dissapated while in the water it had a soft heel and easy energy dissipation. The jack stands are chained together for a reason, the energy can move them.


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Re: Vortex shedding-certainly real

Guesss that's why flags flutter and sails luff?
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