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Old 15-02-2011, 22:47   #1
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Roller Furler Tensions

How does one set up the forestay to the correct tension? How much forestay sag is normal/expected?
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Old 16-02-2011, 00:22   #2
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Depends on the rig. On the typical masthead rig the forestay tension is controlled primarily with the backstay, and somewhat with the mainsheet and vang. Hopefully the backstay has some kind of easy adjustment provided.

You need just enough backstay tension to 'get the job done', and no more. Helpful, huh? That's what the pro's say. Or a few pounds shy of popping the bulkhead tabbing.
Ur, not quite enough to drive the mast thru the keel.

Sails are cut the accommodate the expected forestay sag. If it's flopping around it's probably too loose. Big boats have a hydraulic gauge to set the tension.

Sorry, there is no good answer. Take your sailmaker out for a sail. She will know.
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Old 16-02-2011, 00:29   #3
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I'd imagine that most installation manuals for furlers will have some kind of instruction. Since I'm familiar with Harken, the Harken manual merely says it works better with tight headstay tension. How tight is tight depends on your boat. Either a manual for you boat will say, or rigging guides will have tensions based on assumed loads based on wire diameter and will have techniques for measuring the tension. i.e. % stretch of the wire will tell you how much you have preloaded the wire.

I can see from a mechanical viewpoint, trying to rotate a curved foil will be harder than a straighter one and will try to pry apart joints.

From: http://www.harken.com/pdf/4416.pdf page 27


Headstay Tension
A furling system will work best if headstay is tight.
A loose headstay is difficult to rotate and can cause
unusual wear on foil joints.


Harken's manual also says a detensioned halyard unloads the swivel bearings making it easier to furl.

John
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Old 16-02-2011, 02:34   #4
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My boat manufacturer provided rig tension specifications. I used a Loos gauge to tune the rigging. Then setting the foresail halyard tension was a bit of trial and error until I got a good combination of easy foil rotation and good sail shape.
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