Vibrating Mainsail

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Art Femenella

I have a Catalina 30 TRBS with harken "0" furler set behind the mast to furl the mainsail. As the wind gets to 14 knots and above, my furled mainsail begins to oscillate causing a vbration that goes through the mast, down the stays and throughout the boat. I have been told this is due to the wind passing around the mast, over the open space and then around the furler. Anyone have any thoughts on how to minimize or get rid of the vibration? My rigger said the tension is as great as it should be, so its not due to that. Thanks.
 
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Allen

One possible cure...

Art, The oscillation of your mast is due to the fact that round or oval spars that are straight will respond to the wind that way. It's just plain physics. There are 2 things you can do to minimize the "pumping" action: 1. Make the spar "less round". 2. Make the spar "less straight". To make it less round, wrap your main halyard around it. The halyard will interrupt the normal wind flow & reduce the oscillation. Check out the non-retractable antenna on many cars (like a Chevy Tahoe) and you'll see that there appears to be a wire wrapped around the antenna. This is there to reduce the same motion you're talking about when the car is in motion. Your halyard will have a similar effect. To make it less straight, tension your backstay so the mast is slightly bent in the middle. Our rigs aren't meant to be bent like a fractional rig is, but it does help at least on my boat it does. The same thing happens on my boat, especially when the wind is on the nose, like when at anchor. It can be annoying, but maybe those tips will help. Good Luck, Allen Schweitzer s/v Falstaff C-30 Hull# 632
 
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Art Femenella

Possible solution

Allen, Thanks for the clear explanation and the possible solutions. Two days ago I tried something and it looks like it works. I have a second jib halyard. I wrapped the halyard loosely around the mast and the furled sail and tied a bowline. To the bowline i tied a downhaul. I hauled the halyard up until it engaged the spreaders, and then just tight enough to capture the sail. I have experienced 20 knot winds at the mooring since then with no oscillation. But I will try your methods as well. Thanks, Art Femenella
 
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