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Old 05-05-2014
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Appropriate mast bend?



Hi All,

I read through Seldon's mast tuning guide, as well as some other less formal guides when tuning my mast recently, and I got all the shrouds/stays tensioned correctly. this being my first time tuning a mast, however, I'm second guessing myself. The mast is in column. Is this amount of mast bend appropriate?

The boat is a Beneteau 361.

Any input is greatly appreciated.
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Old 05-05-2014
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Re: Appropriate mast bend?

Looks reasonable to me, what does the manual say about pre-bend, 8" or something like that? I assume the backstay was not tensioned for the picture?
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Re: Appropriate mast bend?

Forgive my ignorance, but is mast rake (mast raked back just a bit) accomplishing basically the same thing?
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Re: Appropriate mast bend?

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Originally Posted by krisscross View Post
Forgive my ignorance, but is mast rake (mast raked back just a bit) accomplishing basically the same thing?
No. When the mast bends the center of the luff moves forward, pulling sail cloth from the sail and making it flatter. An obvious corollary is that any sail to be used with a pre-bent or bendy mast is cut with this in mind.

Simplified, but the point is mast bend affects fullness, while rake primarily affects COE (also lift if extreme).
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Re: Appropriate mast bend?

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Originally Posted by krisscross View Post
Forgive my ignorance, but is mast rake (mast raked back just a bit) accomplishing basically the same thing?
Mast rake will primarily affect your rig balance and the amount of weather helm you may or may not have since it moves your CE fore and aft. Mast bend generally is set to match the luff curve of your mainsail so that the draft position is optimal for the cut of the sail. More bend pulls material forward and 'flattens' the sail somewhat. A sail meant for significant prebend will have a very full shape set up a dead straight mast.
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Re: Appropriate mast bend?

The exact Pre-bend really depends on how the sail was cut as there are some pretty big difference's from one sailmaker to another

It is why there are 27 tuning guides for the J24 which vary from perfectly straight to really bent
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Re: Appropriate mast bend?

Thanks guys for the insight.
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Re: Appropriate mast bend?

Try the mast bend where you have it and see if you like how the sail sets. It looks like you have about 3~4" of bend or half a section. You're limited with a swept rig as to how much bend you can achieve.
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