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Mainsail luff shrinkage---acceptable?

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iwsmithuk View Drop Down
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Post Options Post Options   Quote iwsmithuk Quote  Post ReplyReply Direct Link To This Post Posted: 09 Mar 07 at 3:50pm

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.........

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Post Options Post Options   Quote Guest Quote  Post ReplyReply Direct Link To This Post Posted: 09 Mar 07 at 4:08pm
I think we are talking about film sails here ...
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Post Options Post Options   Quote iwsmithuk Quote  Post ReplyReply Direct Link To This Post Posted: 09 Mar 07 at 4:23pm

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?

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Post Options Post Options   Quote Medway Maniac Quote  Post ReplyReply Direct Link To This Post Posted: 12 Mar 07 at 1:06pm

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?

 

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Post Options Post Options   Quote FireballNeil Quote  Post ReplyReply Direct Link To This Post Posted: 30 Mar 07 at 5:29pm
If you unpick your luff rope because it has obviously shrunk (creased up excess sailcloth all the way up it) how much do you need to unpick and do you have to resticthit? If re-stitching is required what is the best method?
Neil

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Post Options Post Options   Quote scottish_tornad Quote  Post ReplyReply Direct Link To This Post Posted: 30 Mar 07 at 8:06pm

 

 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. 



Edited by scottish_tornad
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FireballNeil View Drop Down
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Post Options Post Options   Quote FireballNeil Quote  Post ReplyReply Direct Link To This Post Posted: 30 Mar 07 at 10:55pm
Thanks for the input!
Neil

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Post Options Post Options   Quote Matt Jackson Quote  Post ReplyReply Direct Link To This Post Posted: 30 Mar 07 at 11:13pm
Originally posted by iwsmithuk

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

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

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Post Options Post Options   Quote scottish_tornad Quote  Post ReplyReply Direct Link To This Post Posted: 31 Mar 07 at 11:01pm

 

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.



Edited by scottish_tornad
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chic View Drop Down
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Post Options Post Options   Quote chic Quote  Post ReplyReply Direct Link To This Post Posted: 30 Apr 07 at 9:06am

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.

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