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ellistine View Drop Down
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Post Options Post Options   Quote ellistine Quote  Post ReplyReply Direct Link To This Post Topic: Sail Twist
    Posted: 21 Oct 08 at 9:57am

Is an open or twisted leech a good thing or a bad thing?

I had always assumed it wasn't good but can it used for depowering? When we've been overpowered I usually put on lots of kicker and cunningham but that would straighten the leech when perhaps we're supposed to be letting the wind spill out?

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JimC View Drop Down
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 08 at 10:08am
This sort of thing is really very boat specific.

Lasers, for instance, are special cases and have quite different treatment for depowering than most other craft...
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ellistine View Drop Down
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Post Options Post Options   Quote ellistine Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 08 at 10:22am

Laser Vago in this case.

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Chew my RS View Drop Down
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Post Options Post Options   Quote Chew my RS Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 08 at 10:29am

In general you want an untwisted leach so that the air flows across the sail in a uniform way at all heights up the mast. In light winds some twist can be good, as the wind gradient means that the angle of the wind is different at different heights (due to friction with the rotating earth). Therefore twisting the sail to suit the wind direction maintains the uniform flow. You are right, twisting the sail in strong winds is one way of spilling excess power, but it is not generally the best way.  It is usually faster to flatten the sail as much as possible (lots of kicker, downhaul and outhaul), lift the daggerboard, hike like hell and ease the sails if needed.

In my experience it is better to have a flat, flogging sail than a full twisted sail (it is not really possible to have a flat twisted sail, 'cos the kicker must be eased to get twist, but easing the kicker straightens the mast and therefore powers up the sail). 

I've not sailed a Vago, but you have an untapered (and therefore stiff) mast I think.  This probably makes it hard to get enough mast bend to flatten the sail fully by pulling on the controls. 

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ellistine View Drop Down
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Post Options Post Options   Quote ellistine Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 08 at 10:43am

So if the mast is stiff then would twist be better suited it we're never going to get the sail particularly flat?

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JimC View Drop Down
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 08 at 10:44am
> (it is not really possible to have a flat twisted
> sail, 'cos the kicker must be eased to get twist, but
> easing the kicker straightens the mast

Note for other folk, this is not really the case with modern full batten/large roach stable mylar rigs, where the downhaul is the key control for bending the mast. Different rigs really do march to quite different drummers.
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Post Options Post Options   Quote Chew my RS Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 08 at 11:34am
Originally posted by ellistine

So if the mast is stiff then would twist be better suited it we're never going to get the sail particularly flat?

Maybe, but only as a last resort.  Its still probably better to get the sail as flat as possible and let the main out. 

And, of course, Jim's right. Rigs with full length battens and large roaches work differently. 

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ellistine View Drop Down
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Post Options Post Options   Quote ellistine Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 08 at 11:41am

Thanks all.

At Rutland at the weekend (very windy), while beating the wind was hitting the back of the sail so hard that it was popping the battens the wrong way.

Presumbaly in this case the sail was no where near flat enough?

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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 08 at 12:02pm
Originally posted by ellistine

Thanks all.


At Rutland at the weekend (very windy), while beating the wind was hitting the back of the sail so hard that it was popping the battens the wrong way.


Presumbaly in this case the sail was no where near flat enough?



Sometimes that's inevitable if its windy enough, but the more you flatten the better off you'll be, especially at the top. Its a fairly conventional sort of UK rig with short battens lower down and long ones at the top. Tuning guides for other boats with similar rigs would be worth reading if there are no Vago ones available. I'm not the right person to advise on setting up such rigs.
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Post Options Post Options   Quote Jamesd Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 08 at 2:57pm
Originally posted by ellistine

At Rutland at the weekend (very windy), while beating the wind was hitting the back of the sail so hard that it was popping the battens the wrong way.

Presumbaly in this case the sail was no where near flat enough?

It probably wasnt flat enough. but i know in some classes if you over tighten the kicker the batterns will invert. so perhaps it needed to be eased a few inches.

also when dropping the mainsheet the jib should be going down as well to stop the front of the main backing. it keeps the slot open as well. Its far faster in those conditions in all venues (well all the ones ive visited) to keep the bow down ease jib and main together and power on through the gusts and watch the guys that pinch and rag their sails go backwards. only problen is that it is seriously physically demanding.

btw this is just something that ive found in the RS classes, it does vary as Jim has said between boats, and sailors

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