Batten Tension Article

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Rick
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Re: Batten Tension Article

Postby Rick » Wed Jan 21, 2009 10:43 am

See below; I'd say the sail on the right had overdone it as the lower batten is S bending (snaking).

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Re: Batten Tension Article

Postby Grahame Smith » Wed Jan 21, 2009 10:58 am

Rick

this good example of what I was trying do describe this shape is becomming a common sight in the fleet and often more exagerated than the photo you have found.
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Re: Batten Tension Article

Postby Rick » Wed Jan 21, 2009 11:08 am

Well imho that is too much, I'd welcome the comments of others ....
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Re: Batten Tension Article

Postby Rick » Wed Jan 21, 2009 11:34 am

Here is a photo of my sail set ...

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Re: Batten Tension Article

Postby DanV193 » Wed Jan 21, 2009 12:42 pm

Grahame(s)/ Rick

I don't know if that picture at the top of the page is a common sight. Whereas I have seen many people with S- shaped battens when the sail is unloaded (i.e. before the start as Rick describes) I can't remember seeing a sheeted in sail with such a horrible S-bend before.

Admittedly I haven't been looking for it. Whatever, it looks terrible and surely can't be fast.

However, I guess if people are doing this it must be because they believe it will make them quicker, and perhaps they have done the 2-boat tuning to get the evidence. Until recently I have been sailing with just enough tension to remove the wrinkles, and on good advice i have wound them up a bit( but not to the extremes being talked about), but to be honest I have not noticed any tremendous change in performance.
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Re: Batten Tension Article

Postby Grahame Smith » Wed Jan 21, 2009 1:44 pm

Dan You are correct it is always more evident in an unloaded sail ie in light airs or as you say before the start. In any reasonable breeze this snake will not show either because the kicker is applied or the main sheet tension come in to play and will allow the batten to set in a more normal shape.

I have set mine so that this s shape will only occur under max cunno and little/no kicker and little or no pressure in the sail to remove the effect I can either ease cunno or increase the Kicker/main sheet tension or hope for breeze. are my battens too tight !!! thats the question.
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Re: Batten Tension Article

Postby paul manning » Mon Jan 26, 2009 4:40 pm

Just to clarify, the sail shape of Yaroslav "Arkas" sailing upwing at Silvaplana is most likely caused by two issues.

1. The outhaul is too tight, which is a common feature noticed when watching the class sail. The outhaul gets pulled on a lot from the beach setting as the boom drops under mainsheet tension and the middle of the mast bending forward.

2. There is too much batten tension on the lower batten causing it to S bend.

The over tensioned outhaul has removed all depth from the lower leech causing it to collapse.

If you look at the relationship between the distance of the middle of the foot and the middle of the boom on the photo's above you'll see how much difference there is.

The boat to windward of "Arkas" will end up with a very similar shape, but he has not yet pulled his main on fully. Note the creasing from the clew through the Hyde Sail logo, and then look at the foot of GBR293 "Harken" there is no sign of creasing at all.

By pulling on so much outhaul you are putting a lot of tension through the bottom of the sail, and I always recommend the outhaul needs easing far more than people think.



I hope this helps.
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Re: Batten Tension Article

Postby SELSBowbitch » Tue Jan 27, 2009 12:51 pm

I'd agree with Paul on this one, he still has no kicker on either which will make the issue even worse.

The best bit of advice I could give is to set the batten tension without the boom on to as much as you can on the bottom 2 battens without creating the snake as per that photo and jsut take the wrinkles out of the top 2 battens.

The outhaul setup is really critical as it controls the lower leech curve of the sail and affects your pointing ability a lot if it's set wrong. I usually tell people to set it up so that when sheeted on with max kicker there is no crease in the bottom of the sail. This obviously changes as the wind decreases, the kicker is eased and the boom rises creating too much belly in the sail, therefore you need to add more outhaul to compensate for this. In the lightest of airs it is almost full outhaul.

Hope this helps!

cheers
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Re: Batten Tension Article

Postby Rick » Tue Jan 27, 2009 1:18 pm

One thing to note is that as the boom has an accute angle with the mast the distance between the mast track and the clew cringle increases as kicker is applied; this is unique to the MPS.

This means that you can literally rip your window apart if you have too much outhaul then apply loads of vang putting huge tension in the cloth accross the window.

I am sure that some people who have had seams fail over the window area have probably ripped the seams apart by using tight outhaul then vanging up ... this is a quirk of the MPS, a good quirk because it eases the outhaul when you release the vang to go downwind.

Best thing to do is to try the settings ashore and see how the foot depth reduces as the vang is applied; also try putting loads of outhal on then vanging up slowley, you will soon see the cloth becoming highly loaded so take it easy and learn what max outhaul is for max vang.
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Re: Batten Tension Article

Postby Grahame Smith » Tue Jan 27, 2009 1:48 pm

A new variation on the tread is it possible to begin to quantify some of this if we cant reduce it to a number then it cant exist is an old addage so Rick could you give some guide line measurment for the out haul may be in terms of distance from the out haul block to the boom band on the sail tack in relation to max normal kicker position or depth of the foot from the boom this would be a great help for light 1 - 2 medium 3 - 4 and above 5+ might also help prevent unnessesary sail damage although this is not the only cause of seam failure

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Re: Batten Tension Article

Postby Rick » Tue Jan 27, 2009 2:04 pm

When my boat comes out of winter hibernation I will take some snaps.

But of course old sails shrink over time and so any absolute measurements will not be that helpful; more a point of understanding what is going on and looking at the sail; if there is a crease over the window then the outhaul is probably too tight.
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Re: Batten Tension Article

Postby SELSBowbitch » Tue Jan 27, 2009 3:39 pm

This also has it's roots in the mast set up. If you have too much bend in the mast you get a diagonal crease from the outhaul to the spreaders (usually caused by a lack of lower tension) If the outhaul is too tight and the mast overbends it will cause extra loading across the window seam and therefore possibly cause the failiures.

I suggest that we put a more comprehensive (and up to date) tuning guide together early this season to include some details on sail setup as well as rake, spreaders etc as well as some general rules of thumb.
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Re: Batten Tension Article

Postby Rick » Tue Jan 27, 2009 3:51 pm

SELSBowbitch wrote:This also has it's roots in the mast set up. If you have too much bend in the mast you get a diagonal crease from the outhaul to the spreaders (usually caused by a lack of lower tension) If the outhaul is too tight and the mast overbends it will cause extra loading across the window seam and therefore possibly cause the failiures.

I suggest that we put a more comprehensive (and up to date) tuning guide together early this season to include some details on sail setup as well as rake, spreaders etc as well as some general rules of thumb.


Well volenteered; you pull together the text and photos and I'll put it all up on the website & eNewsletter :D
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Re: Batten Tension Article

Postby SELSBowbitch » Tue Jan 27, 2009 5:16 pm

d'oh! :lol:
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Re: Batten Tension Article

Postby Bruce » Thu Jan 29, 2009 10:53 pm

I sail with much less batten tension than Graeme seems to ... perhaps that's why he beat me in the Worlds! :)
Even so, I have still had to have 3 of the plastic end caps on the luff replaced on my old sail. All the ones on my new sail were kindly replaced by Chris at Silvaplana! I try to use as little batten tension as possible without getting creases, otherwise I have problems getting the main up and tacking/gybing in light winds becomes more difficult.

I find the easiest way to set the batten tension is to pull the main up, flip the boat on it's side and then pull on the cunningham. You will normally get creases about 1-2 feet from the mast where there is maximum curvature. I tighten the battens up until there are no obvious creases on the batten pocket.
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