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light wind rigging quandary
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ittiandro



Joined: 22 Nov 2009
Posts: 267

PostPosted: Thu Jan 22, 2015 11:25 am    Post subject: light wind rigging quandary Reply with quote

I am mostly subplaning because of the prevailing conditions here and my aim is to maximise the lightwind capability of my gear , by compensating, if at all feasible, the inherent bias of modern equipment towards strong winds sailing, speed and, ultimately, planing.

Regarding the sail, I had always thought that, for maximum power, it should have a fuller profile ( a deeper pocket) in its the lower part and forward of it, towards the mast. . Here is supposedly where the center of effort of the sail should be located for optimal (light wind) performance and this fuller profile would be attained by increasing the DH tension, in combination, of course, with the OUTHAUL adjustment. .

I am however a bit puzzled, because http://www.boardseekermag.com/news/awt-day-2-light-wind-rigging-josh-stone/6/#0oBRULi7HTVScPDt.97 gives a different story. It is said there that in order to give a fulller ( deeper shape ) to the sail, the DH should be slightly DECREASED, not increased!

I also read in one of the forums that one way to deepen the profile in the lower sail (and to shift the center of effort even more forward, closer to the mast ) would be to stiffen the batten above the boom) by inserting a 2nd shorter half batten in the pocket, at the leech end. The flattening of the sail on the leech side would amplify and shift even more forward the full profile of the sail.

I wonder if you or anybody can comment on all this.

Thanks

Ittiandro
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gvogelsang



Joined: 09 Nov 1988
Posts: 433

PostPosted: Thu Jan 22, 2015 12:53 pm    Post subject: Reply with quote

The boardseeker article is correct.

Ease up on the downhaul, perhaps until there are "almost" wrinkles on the luff of the sail.

Ease up on the outhaul to put more pocket in the sail.

I sure wouldn't put a stiffer batten in the sail. The battens are stiff enough, and you want everything softer for light wind.
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ittiandro



Joined: 22 Nov 2009
Posts: 267

PostPosted: Thu Jan 22, 2015 2:02 pm    Post subject: Reply with quote

gvogelsang wrote:
The boardseeker article is correct.

Ease up on the downhaul, perhaps until there are "almost" wrinkles on the luff of the sail.

Ease up on the outhaul to put more pocket in the sail.

I sure wouldn't put a stiffer batten in the sail. The battens are stiff enough, and you want everything softer for light wind.


Thank you for the clarification

Ittiandro
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PeconicPuffin



Joined: 07 Jun 2004
Posts: 1807

PostPosted: Sat Jan 24, 2015 9:42 am    Post subject: Reply with quote

Note that if your intention is to plane, your sail must still have a floppy leach in order to plane in the lightest winds. The full pocket is great, but the wind still needs to be able to slip off the sail easily to develop lift. It's a common mistake to kill the floppy leach (your exhaust, if you will) in pursuit of power. If you're not looking to plane but instead are simply nonplaning sailing (ie longboard on a lake for fun) then don't worry about the leach.

Without the leach venting you'll feel a lot of tug from the sail, but it will take much more wind to shove you onto a plane.

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U2U2U2



Joined: 06 Jul 2001
Posts: 5467
Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Sat Jan 24, 2015 9:59 am    Post subject: Reply with quote

100% agrree with those who posted above. I would not try to improve performance with a batten change, on any sail that is modern and try to outengineer the maker/shaper

There will be a point where down/outhaul adjustments will have diminished return, the sail will not perform.

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isobars



Joined: 12 Dec 1999
Posts: 20128

PostPosted: Sat Jan 24, 2015 10:04 am    Post subject: Reply with quote

I use the DH to tune foil stability, my sail size to macrotune sail power, and my OH to microtune sail power. Long before I'd start changing battens to overcome the sail designer's expertise, I'd just buy a bigger sail, buy more neoprene if my wind were better in the winter, buy a Jetski, and/or move to a windier location. There are plenty of sails out there designed by experts for maximum low end power.
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ittiandro



Joined: 22 Nov 2009
Posts: 267

PostPosted: Sat Jan 24, 2015 11:32 am    Post subject: Reply with quote

PeconicPuffin wrote:
Note that if your intention is to plane, your sail must still have a floppy leach in order to plane in the lightest winds. The full pocket is great, but the wind still needs to be able to slip off the sail easily to develop lift. It's a common mistake to kill the floppy leach (your exhaust, if you will) in pursuit of power. If you're not looking to plane but instead are simply nonplaning sailing (ie longboard on a lake for fun) then don't worry about the leach.

Without the leach venting you'll feel a lot of tug from the sail, but it will take much more wind to shove you onto a plane.


Thank you for your input.

You are right, maybe I shouldn’t worry about keeping a tight leech in light winds, because at 12 knts one has perhaps reached the threshold beyond which the door must be closed and the” exhaust” kept to a minimum in order to maximize whatever little wind we have. The only thing is that, from my experience, such a tight leech prevents the rotation of the sail. This is why I was thinking of slightly shortening the batten. Unless... there is no problem in helping the rotation by pushing the recalcitrant sail with the hand or the foot. Even so, sometimes it takes more than a little push..
The stock suggestion is to use larger sails I already have an 8.5 and I am reluctant to use a larger one, because of the cost and also because large sails tend to become heavier and harder to handle, especially for uphauling..

Thanks

Ittiandro
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adywind



Joined: 08 Jan 2012
Posts: 665

PostPosted: Sat Jan 24, 2015 12:25 pm    Post subject: Reply with quote

Hi Ittiandro , take a look if you want at the last 4 comments in this discussion and tell me if your case is similar.
http://www.iwindsurf.com/forums/viewtopic.php?t=29450&start=10
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coachg



Joined: 10 Sep 2000
Posts: 3065

PostPosted: Sat Jan 24, 2015 1:44 pm    Post subject: Re: light wind rigging quandary Reply with quote

ittiandro wrote:
I am however a bit puzzled, because http://www.boardseekermag.com/news/awt-day-2-light-wind-rigging-josh-stone/6/#0oBRULi7HTVScPDt.97 gives a different story. It is said there that in order to give a fulller ( deeper shape ) to the sail, the DH should be slightly DECREASED, not increased!


Yes, this is because as you increase down haul the mast bends and effectively moves the leading edge of the mast farther away from the clew which flattens the sail similar to increasing out haul. As you decrease down haul the mast moves back, shortening the boom length & deepening the draft.

As stated earlier you would be better off getting a longboard specific sail rather than trying to make the sail you have work outside its range.

For under 12 knots it seems like a lot of work for very little gain.

Coachg
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isobars



Joined: 12 Dec 1999
Posts: 20128

PostPosted: Sat Jan 24, 2015 1:53 pm    Post subject: Re: light wind rigging quandary Reply with quote

Amen.

How about rather than cruising, fit your goals to your conditions and go instead for light air freestyle with a big platform and smaller sails?
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