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post #1 of 8 Old 03-25-2012 Thread Starter
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Backstay and forestay

I have read a lot about standing rigging both on the forums here, books, other articles, etc. I still don't completely understand the interaction of the back and forestays on the rigging. i have read several articles on sail trim that talk about slacking the forestay under certain conditions. I also understand the the backstay is on many boats (not mine yet) adjustable. So my question really is- do the backstay and forestay only affect mast rake, or do they play an integral part in holding up the mast? Based on what I've read, I would guess that they are really not for holding the mast up, but for setting the mast angle. I am in the process of replacing the shrouds and both stays and would really like to understand the standing rigging better before the project is complete. Thanks for any input you have.
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post #2 of 8 Old 03-25-2012
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Re: Backstay and forestay

Thier function is to hold up the mast. By adjusting them you can change the rake or fore ans aft tilt of the mast. Most production boats have specifications for your stays that put the mast where it's supposed to be for your boat to be properly balanced. If for example with your normal working sails you boat has a lee helm that is tends to fall off the wind you would loosen the forestay and tighten the back stay so that the top of the mast moves aft, hence moving the mainsail aft and thus correcting the lee helm. For boats where the head stay attaches only partly up the mast while the back stay is the top, tightening the backstay with the headstay fixed puts a slight bow in the mast reducing the draft of the mainsail. I've only seen this being done on racing class boats. in general you want the headstay tight enough so that it doesn't sag off to leeward significantly. The tension needed to do this depends on the wind strength. So many cruiser racers have a backstay tension adjuster. You can crank it down in higher winds. As the tension increases the compressive force on the mast, you can ease it off when the high tension isn't needed. It can also be used to adjust the mast bend as discussed before.

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post #3 of 8 Old 03-25-2012
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Re: Backstay and forestay

The backstay-forestay combo do THREE things simultaneously

1. by length adjustment of the forestay determines mast rake.
2. both help to hold the mast up
3. (most important) provide a means for the PROPER leading edge and overall aerodynamic shape of the jib. http://www.ftp.tognews.com/GoogleFil...f%20Hollow.pdf

... and you adjust the backstay tension - 'as needed' when sailing ... or alternatively simply set tension in the backstay so the forestay is at about ~15% tension when sailing in 12-15kts. windstrength; the backstay reacts with and 'controls' the forestay tension.

Most 'stock' jibs are cut by the sailmaker 'expecting' that the forestay will be at approx. 15% tension and the boat will be sailed in 12-15kts of wind.

Last edited by RichH; 03-25-2012 at 06:03 PM.
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post #4 of 8 Old 03-25-2012
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Re: Backstay and forestay

they do of course hold the mast up, especially if it is a deck stepped mast. the forestay determines the mast rake, the backstay determines the amount of tension on the forestay which sets the amount luff curve in the foresail. while sailing the forestay will never be perfectly straight so the sails luff is cut curved to match the curve or sag in the stay. the backstay is set to match the curve of the forestay to the curve of the sail. as the winds builds the forestay will sag more and you will need to tighten the backstay.

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post #5 of 8 Old 03-26-2012 Thread Starter
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Re: Backstay and forestay

Thanks for the explanations! It all makes much more sense to me now.
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post #6 of 8 Old 03-26-2012
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Re: Backstay and forestay

Hey,

So far no one has mentioned a few important facts.

Is the boat in question a masthead rig or a fractional rig? A masthead rig, where the forestay goes to the top of the mast is not usually as adjustable as a fractional rig, where the forestay connects to the mast below the top of the mast. On a fractional rig, since the backstay and forestay are separated, increasing the backstay tension will bend the mast (this is done on purpose) and is used to flatten the sail in higher winds, and to ease the mast forward on downwind run to allow the spinnaker to project more to windward.

You can do the same thing on a masthead rig, but it is not as effective. You can still adjust the forestay tension to remove the curve, but you can't really bend the mast.


Good luck,
Barry

Barry Lenoble
Deep Blue C, 2002 C&C 110
Mt. Sinai, NY

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Last edited by BarryL; 03-27-2012 at 10:11 AM.
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post #7 of 8 Old 03-26-2012 Thread Starter
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Re: Backstay and forestay

The Cat 22 is a masthead rig. But it seems many ppl use an adjustable backstay on this boat.
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post #8 of 8 Old 03-26-2012
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Re: Backstay and forestay

While a masthead rig gives less adjustment than a fractional rig an adjustable backstay still allows changing the forestay tension for different conditions.

Brian
Living aboard in Victoria Harbour
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