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  #1  
Old 12-16-2006
bkw bkw is offline
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bending the mast

bending the mast is one of the ways to flatten a sail. very light air and heavy air.
on a mast head rig how can the mast bend? seems that tightening the backstay would only pull the mast straight back and also tighten the forestay. not have any affect on the shape of the sail.
would this be correct?
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Old 12-16-2006
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As you say, applying backstay tension on stiff masthead rigs tends to tighten the forestay.

However, on boats with lighter, more flexible mast sections the backstay adjustment can put enough compressive loads on the rig to bend the mast (imagine compressing a toothpick between your fingertips). This is esp. true with powerful adjustments like hydraulics.

On such rigs checkstays are required to limit mast bend so that further tension does indeed tension the headstay, after the main has been flattened with bend.

You'll likely find such rigs only on boats that were intended to be raced.

Last edited by Faster; 12-16-2006 at 05:56 PM.
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Old 12-16-2006
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On a masthead rig, the forward lowers have to be taut, so that, when you add tension to the backstay, they won't let the lower section of the mast move aft. Also, you have to loosen the tension of the aft lowers, so that, when you apply tension to the top of the mast, through the backstay, the middle of the mast is able to bow forward. You should adjust the aft lowers so that they become taut when the mast bends as far forward as you want it to. Properly adjusted, the aft lowers prevent you from over-bending the mast.

You can also loosen the headstay a little, so that, in light air, with backstay tension off, the mast is straight and the headstay has a slight sag, but, when you increase the backstay tension, the headstay becomes taut, the middle of the mast can bow forward, and the top of the mast can bend aft a bit.

If you adjust all the shrouds and stays to approximately equal tension, they won't permit the mast to bend in any direction.

Last edited by Sailormon6; 12-16-2006 at 07:01 PM.
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Old 12-16-2006
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by forward lowers you mean the shrouds?
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Old 12-16-2006
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Yes he means the shrouds however not all sailboats have two sets of lowers. But the basic idea applies in any case. If you have a keel stepped mast then you can induce prebend in the mast depending on where you position the base. They are many variables.

Gary
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Old 12-16-2006
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Quote:
by forward lowers you mean the shrouds?
Believe it or not, the software for this forum won't let me use less than 10 characters to answer your question. I'm sure I've met my quota by now, so the answer to your question is "Yes."
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Old 12-16-2006
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