Mast luff track, aerodynamics and mast judder.

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jonjo

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It has been suggested to me that in addition to the well documented benefits of an external mainsail luff track, a Tides Marine track might also allieviate the mast judder that affects my treaky mast in a medium cross wind. I am talking about the type of judder that occurs in harbour when a medium strength wind strikes the mast at an angle.

Online research indicates that such judders are caused by vorticies forming and collapsing on the lee side of the mast.

Is there hope that an external mast luff track could disupt the formation of such vorticies?
 
I experienced mast judder due to vortices on a Westerly Corsair I bought new. As I recall, Westerly supplied me with a bit of Selden kit, a long plastic strip about 9 or 10cm wide, which was hauled up the mast and acted to shed the vortices, thus solving the problem.
 
Many metal chimneys on factories have a spiral of metal on them. I believe this is a vortex shedder to break up the vortices and prevent vibration build up.
 
crewman said:
Many metal chimneys on factories have a spiral of metal on them. I believe this is a vortex shedder to break up the vortices and prevent vibration build up.
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An interesting subject I knew nothing about untiil a prolonged period of light northerlies striking the marina triggered lots of mast judder. My main concern is progressive fatigue on the standing rigging, atleast it goes away once wind speed exceeds 20 knots and it is not an issue when a sail is hoisted.

The luff track is on my shopping list in a quest for easy mainsail handling, fixing the vortex judder would be a bonus. The issue is affecting my choice of summer mooring, currently it is down to a sheltered river mooring or wind exposed marina berth. The benefit of a mooring is that the yacht will tend to pivot around to the wind and the wind has to be 30 degrees off the bow before the judder starts.
 
Some forestay foils on race boats vibrate violently in a breeze with no sail in place. They normally come with a triangle of cloth with a bolt rope on one edge. This is hoisted about a third of the way up the foil and tied down to the stemhead and the base of the mast to stop the vibration. Could you fit something similar and tie it back to the end of the boom or a stern cleat?
 
DJE said:
Some forestay foils on race boats vibrate violently in a breeze with no sail in place. They normally come with a triangle of cloth with a bolt rope on one edge. This is hoisted about a third of the way up the foil and tied down to the stemhead and the base of the mast to stop the vibration. Could you fit something similar and tie it back to the end of the boom or a stern cleat?
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I have tried extra bracing by looping a halyard tight under the first spreader, one turn around the mast then out to an eye pad on the fordeck, even with lots of winched on halyard tension the problem is nearly as bad. Someone in the internet recommended fitting an extra mast slide above the mainsail headboard sliders, hoisting this with some low stretch dynema tied off to a sidedeck anchor. My halyard experminment last night was using a standard braid on braid rope which is probably too elastic to brace against the judders. The proper solution is to prevent vortex formation in the first place.

I shall try spiraling the halyard around the lower 3rd of the mast from the first spreader downwards but right now the mast is quiet as the wind is not exceeding 20 degrees off the bow.
 
jonjo5 said:
I shall try spiraling the halyard around the lower 3rd of the mast from the first spreader downwards but right now the mast is quiet as the wind is not exceeding 20 degrees off the bow.
Click to expand...

I was going to suggest that, imitating the spirals on factory chimneys. Hauling up a length of fatter mooring line and wrapping that instead might be even more effective.

Mike.
 
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