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post #1 of 19 Old 4 Weeks Ago Thread Starter
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Jib Sail Twist

The book says that moving the car forward decreases twist because the sail is being pulled down more tightening the leach.

This of course also slacks the foot increasing draft.

In real world racing under what circumstances to you adjust the car with what theory in mind?

I have always always just pulled the car back to flatten the sail in heavy air not really thinking to much about that increasing the twist.

I'm probably missing some nuances?

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post #2 of 19 Old 4 Weeks Ago
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Re: Jib Sail Twist

As you fall off the wind move the car forward and if you have a snatch block use it to move your sheeting location as far out as you can. This will improve the power of the sail. If you want to depower the sail move the car aft which will twist off the top half of the sail.
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post #3 of 19 Old 4 Weeks Ago
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Re: Jib Sail Twist

Moving the car forward powers up the jib, which is helpful in light air and sailing off the wind.
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Re: Jib Sail Twist

Also for you newer sailors that have a furling headsail...make sure when you reef the headsail to move the fairlead forward because if you don't you will have real lousy sail trim.
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post #5 of 19 Old 4 Weeks Ago
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Re: Jib Sail Twist

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Originally Posted by robert sailor View Post
As you fall off the wind move the car forward and if you have a snatch block use it to move your sheeting location as far out as you can. This will improve the power of the sail. If you want to depower the sail move the car aft which will twist off the top half of the sail.
..unless you're really using a Genoa, not a jib, and the top of the thing is fouling on the spreaders - in which case moving the car forward isn't going to help you one iota.

Rule of thumb when trimming the headsail: LOOK UP!!
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post #6 of 19 Old 4 Weeks Ago
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Re: Jib Sail Twist

Sail twist is mostly an academic exercise ... as the sailmaker has inbuilt most of the 'twist' in the design of the sail for is usual flown wind ranges - IMO Only when in very light wind does wind gradient become a real issue 99.5% of the time.
Especially when in the higher wind ranges where the wind gradient all but disappears, there is no valid reason to twist-off a jib ... and one has a reefing-furler for the jib/genoa .... or knows how to flatten/reef the main.

Depowering via 'twist'.
Sails are 3 dimensional and so is wind flow. A twisted off jib will have its head panels subject to flow detachment, oscillating flow detachment at the head as the boat pitches in increasingly larger waves, the foot section will invariably be well over-trimmed, and only the midsection panels 'drawing' well. With increasing wind and sea-states, depowering by 'twisting off' will literally destroy most of the sail shape that was designed-in the sail - why? Why do this when one can simply, drop the traveller down a bit, reef the jib a bit (down to ~30% max. reduction) with a reefing-furler, and then if needed consider to flatten/reef the main.
In most cases by firstly flattening the main or dropping the traveller down a bit will create less 'upwash' being sent forward to the jib ... an automatic de-powering without sail distortion. Ditto when reefing the main. Both cases will also 'open the slot distance' for further 'de-powering'.
A further advantage of reefing down a jib, etc. instead of grossly destroying aerodynamic sail shape, is the ability to be able to 'blade out' consistently and under precise control. Blading-out (by either sheet easing or helm control) to control heel, etc. with a grossly twisted off sail can result in a surprise power-ups during unstable wind flow. Blading out with a properly set and shaped sail (with no additional twist) is easy.

In real world racing, when over-powered or the boat is being stopped/slowed by increased wave action - either change/peel to a different/smaller jib (or roller reef the jib down); but then, trim it 'perfectly' (w/r 'fore/aft' on the fairlead car) is in order; followed by POWERING-UP the sail to be able to 'punch' through increasing wave height. The smaller luff size will take care of the heeling moment, the increase in draft will power up to be able to 'drive'/punch into waves.


For a cruiser with a reefing-furler, the best probable way to de-power is to simply reef down the jib sail area a bit; and then set the fairlead cars to whatever it takes to 'perfect' with respect to the luff tell tales --- NO Twist added. Then, to satisfy the need to 'open the slot' due to the higher wind flow, simply keep the jib leech off the spreader tip a few more inches further than when 'tight'/normal.
Most headsails on cruising boats without a big sail inventory are probably waaaaay too large in most cases; when overpowered, just roller reef them down a bit to normal size and eliminate all the twisting-off errors, slow boat, shaking sails and splitting sail seams.

A perfectly set/trimmed sail can easily be bladed-out for the short term. If that doesnt restore one's comfort level (heeling), then reef down a bit on the jib. etc. ..... but restore that perfect tell tale flow by precisely setting those fairlead cars to 'perfect' - NO added TWIST. Set up the fairlead cars so that the luff tell tales are flying 'perfect', always.

Last edited by RichH; 3 Weeks Ago at 09:43 AM.
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post #7 of 19 Old 3 Weeks Ago
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Re: Jib Sail Twist

Thanks Rich... I've struggled with why people always talk about genoa car movement, and I can see it if you can get REAL granular control (say infinitely adjustable cars), but if you got the slotted 1 inch adjustment cars, the change in car placement releases too much.

What I've found is objective is to SET the car so that upwind you get even draw, with flow, top/middle/bottom... that's been my experience. Sure, if you are sailing off wind, especially on a reach or deep reach, play with the car to get those tails drawing correctly again.

With my S2 the racing genoa 155 has had me struggling with this a bit, as the cut is much higher off deck by the genoa cars, and I've struggled to find the best position upwind that has the bottom pulling at roughly 45 degrees, but also doesn't harshly close the leech at the spreaders. I think I finally have it.

I will admit when I was short of crew, that we started one race in 5-8kt winds and ended it in 12-15kt, and we moved the cars aft a notch, to help twist off the oversized genoa (we were still on our ear)...
Example:

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Last edited by SHNOOL; 3 Weeks Ago at 07:40 AM.
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Re: Jib Sail Twist

Think some of this discussion depends on boat size and sea state.
When you are on something that parks in the red light district wind at top of sails is clearly different then wind on deck.
When there is a 4' chop there is enough parasitic drag to slow wind on deck.

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Re: Jib Sail Twist

I've found that the extra power from moving the cars forward, is useful when sailing in light air, through powerboat chop.

SCHNOOL is fairly correct in that it's granular, but I don't find slotted jib tracks to be useless.
I use hank-on jibs, which require significant car movements when changing sails. Once a sail has been chosen though, moving the car one slot fwd/backwards from its "base" position usually achieves the desired result.

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post #10 of 19 Old 3 Weeks Ago
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Re: Jib Sail Twist

Quote:
Originally Posted by SHNOOL View Post
Thanks Rich... I've struggled with why people always talk about genoa car movement, and I can see it if you can get REAL granular control (say infinitely adjustable cars), but if you got the slotted 1 inch adjustment cars, the change in car placement releases too much.

What I've found is objective is to SET the car so that upwind you get even draw, with flow, top/middle/bottom... that's been my experience. Sure, if you are sailing off wind, especially on a reach or deep reach, play with the car to get those tails drawing correctly again.

With my S2 the racing genoa 155 has had me struggling with this a bit, as the cut is much higher off deck by the genoa cars, and I've struggled to find the best position upwind that has the bottom pulling at roughly 45 degrees, but also doesn't harshly close the leech at the spreaders. I think I finally have it.

I will admit when I was short of crew, that we started one race in 5-8kt winds and ended it in 12-15kt, and we moved the cars aft a notch, to help twist off the oversized genoa (we were still on our ear)...
Example:

I've found in light wind and heavier wind the pin tracks to be helpful, but the majority of the in betweens, not so much.
I'm actually considering a set of Garhauer Genoa cars for next season to add this 'granularity' as they seem to be a relatively cheap upgrade (500US total). Thoughts?

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