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post #1 of 8 Old 06-25-2011 Thread Starter
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Trimming old Dacron sails

Hello all, I've been lurking for some time now and I love the forums. Thanks for all the great advice.

I have a question about trimming old Dacron sails. I'm the main sail trimmer on my boat, and I'm usually trimming for very light winds (less than 10 knots). Initially, I did all the things I thought you were supposed to do - traveler up for twist, outhaul loosened 2/3 inches, no backstay. But when I trim the sails this way, it gets a huge belly, and sometimes the luff will actually backwind. After thinking about it, I'm guessing that the old (3 or 4 years) sails are stretched out; so sailling with everything so loose is not giving the right shape. I've begun leaving the traveler a little lower (and sheeting in) and keeping the outhaul very tight, and I think it sails a little better. I'm still not sure how to stop the luff from backwinding. I know that is killing our speed.

Any help is appreciated.
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post #2 of 8 Old 06-25-2011
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Yes - as sails stretch they will be subtle differences in trim, that being said your sails may have been originally cut for light airs and have more draft to start off with.


Used racing sails are surprisingly inexpensive, hotshots use their sails for one season ( or less ), there are a couple of shops that specialize in this.

A buddy of mine bought a brand new looking Kevlar race sail which fit his late 1980's Danish cruiser for $300 !
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post #3 of 8 Old 06-25-2011
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From your description it is a good possibility that the luff boltrope needs to be 'eased' or adjusted (by a sailmaker). Boltropes change dimension over time due to the constant stretching (they get progressively shorter over time) and that leads to increased draft, draft aft and with a hooked up leech. Also, a boltroped sail unless otherwise specified when built will be designed for ~15kts. of wind strength and if you sail at ~5kts the luff section will be too 'rounded' ... and you will easily get so-called 'backwind' because of the deep draft shape.

Go to How to properly RAISE a woven dacron mainsail - SailboatOwners.com and go to the section on checking the boltrope near the end of the article by checking the angle that the boom makes with the mast when the sail is raised, etc. If that angle isnt 'right' then take the sail to a sailmaker and have the boltrope 'eased' .... pretty cheap alteration. Note - a woven dacron mainsail that is typically flown/used in 'light' winds should have less 'boltrope preload' so that the luff entry shape is more or less FLAT.

The most common cause of shape distortion in a woven dacron mainsail is not 'stretched out' but rather a 'shrunken boltrope' ...... OR the sail isnt being properly 'stretched out' with proper halyard tension when being raised.

hope this helps.
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post #4 of 8 Old 06-25-2011
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One more reason to like loose footed mains.

But what do I know (according to some people in my sailing club)
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post #5 of 8 Old 06-25-2011
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FWIW a loose foot or shelf foot makes no difference as the point of maximum draft is 'set' by the amount of 'broadseaming' (tapered seams from midcord forward).

A 'racing cut' sail has a flattish 'entry' roundness (about the first 1/3 of the cord length) but requires *precise* steering/trimming; a 'cruising cut' has a 'rounded' luff shape and is 'forgiving' for the helmsman but is vulnerable to so-called 'backwinding' if the amount of draft, etc. is too great.
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post #6 of 8 Old 06-25-2011 Thread Starter
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Quote:
Originally Posted by RichH View Post
From your description it is a good possibility that the luff boltrope needs to be 'eased' or adjusted (by a sailmaker). Boltropes change dimension over time due to the constant stretching (they get progressively shorter over time) and that leads to increased draft, draft aft and with a hooked up leech. Also, a boltroped sail unless otherwise specified when built will be designed for ~15kts. of wind strength and if you sail at ~5kts the luff section will be too 'rounded' ... and you will easily get so-called 'backwind' because of the deep draft shape.

Go to... and go to the section on checking the boltrope near the end of the article by checking the angle that the boom makes with the mast when the sail is raised, etc. If that angle isnt 'right' then take the sail to a sailmaker and have the boltrope 'eased' .... pretty cheap alteration. Note - a woven dacron mainsail that is typically flown/used in 'light' winds should have less 'boltrope preload' so that the luff entry shape is more or less FLAT.

The most common cause of shape distortion in a woven dacron mainsail is not 'stretched out' but rather a 'shrunken boltrope' ...... OR the sail isnt being properly 'stretched out' with proper halyard tension when being raised.

hope this helps.
Thanks, that is great stuff. I've never even heard of a boltrope.
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post #7 of 8 Old 06-25-2011
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Originally Posted by Blackjack2000 View Post
Thanks, that is great stuff. I've never even heard of a boltrope.
Its the three strand dacron 'rope' inside the 'sleeve' at the luff (and foot if the sail is 'shelf footed')
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"old Dacron sails. ... it gets a huge belly,"

Personal rule of thumb, five years of any regular use and the sails are blown out and cannot be trimmed anyway. Ten years, and FOR SURE they're blown out if they've been used.

Is there any plastic coating (calendaring) left on the sails? Do they feel like, well, new sails? Or cheap hotel bedsheets? If they're soft enough and flexible enough to feel like any kind of bedsheets, they're blown out.

If there are any lofts local to you, they'll send someone out to stop by and look at your boat for FREE, because they know that if you need new sails--that's their business. Obviously they've got some incentive to say you need new sails...but most will tell you if you can get another year or two out of what you've got, or if they can recut it. Always worth a call.
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