The following text taken from the Laser SB3 web site..... Can anyone explain why this happens and why is it accepatble that it happens in 2007, when we are bombarded with sailmakers claims about shape retention, dimensionally stable sailcloths and all the other puff we read when deciding who should get our hard earned cash for new sails?

"If you lay a new main on top of an old main, you will see the luff is 6-10 inches longer on a new one, than an old one. This is because after about a year, the bolt rope in the luff shrinks, and they all end up roughly the same."

QED if anyone sails with anything other than a brand new sail at any major competitions they are at a distinct handicap!

All hi tec sails do that - I don't think it's luff rope shrinkage but the creases that use causes.

If you screw up a bit of paper then straignten it out it's not as big as the creases consume material.

It's nothing to do with sail quality - it's just what happens when flat meterials get creased.

Known issue in the 300 class. Our class rules allow you to fix the sail to the boom withoout using a shakle. So you can then use a bit of odd string instead to reliease the tension. This stops too much luff tension. In some cases the sails have strank so much tenstion is the same as cranking on the cunningham! See Mr Baille's "Jock Strap"

http://www.rs300.com/Features/ian_baillie_tells_us_how_he_has_.htm - http://www.rs300.com/Features/ian_baillie_tells_us_how_he_ha s_.htm

Doesn't every class?

Yes. Did someone tell you sailing was a cheap sport?

I don't think this is just about the bolt-rope. Mylar headsails also shrink. 

I have a Finn as well but I haven't tried applying any rig tension yet, I leave that to the boats I sail with stays.

I don't think it's just the sail creasing, on older sails the bolt ropes can be very short and no amount of tension will pull them back into shape.

I have already said the bolt rope shrinkage is a red herring ... the film sails lose size in all dimension due to creasing ...

So, Im trying to work out why it helps to unpick the stitching and slide the sail down the bolt rope as others have suggested? Surely that means the bolt rope has shrunk, whatever has happened with the cloth creasing?

To those who have unpicked the stitches: when you've freed it, does the sail luff elongate relative to the bolt rope, or vice versa?

Ok i should of said luff tension, i knew what i meant at least.

I spoke today with a sailmaker of many years experince and wisdom. He suggested that bolt ropes will indeed shrink. Especially iIf a sailmaker (who is in business to make money) uses inferior quality rope for his bolt ropes. dodgy cheap ropes are quite hard to detect as such until they have indeed shrunk! 

The cost of similar diameter ropes can vary by up to a hundred times......if you could get away with using a material that was  costing say 5p a meter rather than spending £5 a meter would not you?  (ethics don't come into this, as by the time the rope has shrunk chances are other factors will have worn out the sail in any case.) 

I certainly do not buy into the creasing theory.....film sails are usually carefully rolled by most crews and any how 10 inches is a hell of a lot of creases in a 30ft luff. That is nearly 3%!   In IRC racing let alone one design 3% on a finishing time can mean quite a few places lost!

As usual it is a case of buyer beware!

If you have any control over what materials go into your sails make sure you ask about what type of rope your sail maker uses for bolt ropes......Pre-shrunk, pre stretched dimensionally stable ropes must be clearly specified....even if the cost is marginally more, at least you will reduce the onset of shrinking luff lengths!

If you are stuck with a MOD supplied sail and locked in by class rules (written by the manufactuer/integrator in most cases) they hard luck.....unless you get a class association committee with some big gonads to sort out this sort of issue with the manufacturer....

I believe both theories - I think film sails do shrink slightly from creasing, but only slightly and I'm sure the bolt ropes do shrink, why else do some sailmakers add an extra length to allow for re-stitching.

HOWEVER I've never worried about this.

Surely the effect of the shrunken bolt rope is simply to put on some negative cunningham tension.  The actual sail fabric isn't affected by this.  Therefore you can easily redress the effect by applying some positive tension to pull the bolt rope back to it's original length, returning the sail to it's designed shape.

Or am I missing something?

Ian

The rope does shrink but the effect from creasing is in all dimensions of the sail ... UV also plays it's part.

Bolt rope shrinkage definitely occurs.

I have an elderly solo sail where the bolt rope has shrunk so much that the sail is bunched up like a curtain on the rope and near impossible to get up the mast track.The bolt rope is shorter than the luff of the sail. If it was cloth creasing then the luff of the sail would be shorter than the bolt rope!

Or am I missing something here.........

Film sails have boltropes too.

I dont see why they should be any less prone to shrinkage if they're cheap rope (see earlier entry).

I'm sure sail creasing reduces the overall dimensions of many sails but I don't see why you're (Rick) so against the notion that bolt ropes shrink.

Why do some sail makers put tails on the bolt ropes if it's not because bolt ropes shrink?

This all came into sharp focus yesterday when a club-mate said the stitching at the bottom of his luff had come undone, so it was a question of re-stitching it. We've all talked about unpicking the stitching when the bolt rope shrinks, but then what? How far/hard do you pull the sail down over it?

The question thus became how to get the relative tensions right in the sail and the bolt rope, e.g. should you tension the bolt rope to straighten it out a bit and then pull the sail less-so, equally or more-so before stitching?

Does anyone have a sailmaker-approved method of doing it?

 I cant comment on film sails as the only ones I made were for windsurfers and didnt have a bolt rope.

As for nomal (dacron ) sails the bolt rope should be just a little tighter than the cloth but not by much, Its one of those dark arts.

As for resewing its out with the palm and needle and some waxed thread, sewing through the cloth and rope then round the rope and throught the cloth to keep it tight to the bolt rope where it goes into the mast slot.

Hope this helps as  its a long time since i have made sails. 

I always thought it was to give something to grap to pull the sail down

The extra tail on the boltrope is to allow you to adjust the tension after a while.

After some use the sail cloth stretches (even the film ones) so to get the desired sail shape back you adjust the sail in relation to the bolt rope.

Think of it this way the bolt rope is fastened at the head and the tack of the sail and is floating for the rest of the luff length. When you apply downhaul/ cuningham tension you are pulling down on the sail cloth and not the bolt rope. The sail cloth has a certain amount of elasticity and even the seams get pulled slightly so the cloth in effect stretches and there is some shrinkage of the bolt rope but only minimal compared to sail cloth stretch.

Sceptical ? check how much downhaul a cat uses to flatten the main. We use the downhaul to compress the mast and cause it to bend in the middle to increase the curve in the mast and thus flatten the sail- this requires a huge amount of tension. Almost all cat mains wear out at the luff first.

I have to start with the caveat that my experience of sailmaking is limited, but I did it pretty solidly for two years.

With regard to manufacture in most cases the bolt rope is made up separately with its dacron casing and is then stretched out by pinning to the loft floor. It is then attached to the unstretched sail. My understanding is that this adds fullness to the luff as the boltrope returns to its original length which can then be taken out as required by halyard tension/ downhaul. It's the elasticity of the boltrope that allows for this, I don't think that using prestretched ropes as suggested earlier would be helpful!

I'm sure that they do shrink or at least lose their elasticity. If there's a tail it's a relatively easy job to make an adjustment, however most boltrope replacements I have done have been because of the worn casing jamming in the track and not for shrinkage...

If you're lucky you can pull a new boltrope up through the existing casing whilst it's still attached to the sail - it does depend how tightly the original has been made, though!

Like dacron laminate cloth is also susceptible to UV, particularly if it has a kevlar scrim. The mylar film becomes brittle with age (read UV damage and flogging) and I'm certain that this also involves some shrinkage.

More of an issue in one design / PY than a measured handicap rule I guess. I get my sails re-measured for IRC so any shrinking is compensated for by a rating drop.

No, replacing the boltrope is not an easy job. In some cases it can be (see my previous post), but it does depend on a number of factors. Most boltropes I have replaced are made from nylon or polyester 3-core, depending on the stretch required.

Before putting your sail in to your sailmaker to have a replacement boltrope be sure that the sail is in good condition and is worthy of the repair - it can be expensive!