Join Date: Nov 2009
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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.