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post #17 of Old 03-23-2012
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Re: New sail Dacron characteristics

You really have to be aware that the advantage of woven (even high modulus) dacron is its 'adjustability' of the all important shape of the sail ... ie. the adjustability of where the position of maximum draft (POMD) occurs and the relationship of the position in response to the 'stretchability' of the luff (boltrope, etc) which continues to make woven dacron the CHOICE material for cruising and occasional racing. Laminates whether sewn or glued or mold formed are essentially 'locked' in shape and are FAR less 'shape adjustable- - the shape you buy is the shape you get.

As in the case of POMD on a boltroped dacron sail, its the amount of halyard (and/or cunningham) tension that determines where the POMD is located. Most sailors with woven dacron hardly ever get this 'pre-load' from the boltrope correct when raising such a sail ... and then complain of 'weather helm'. Tape luffed sails are entirely 'different' and do not have the requirement of 'pre-load' when raising ... and since they dont have the 'boltrope' can stretchout all over the place in dynamically changeable windstrengths, etc.

When a sailmaker cuts/designs a woven dacron sail (all configurations - cross cut, radial, etc.) WITH a boltrope, that boltrope is purposely shortened (typically by 1" for every 10-11 ft. of luff/foot dimension) and if you 'just raise' and never stretch out that boltrope 'preload', the sail shape will be draft aft, over draft, and leech hooked to weather. With boltroped woven dacron you MUST stretch out that boltrope so that the sail can take on its 'AS DESIGNED' luff / foot dimension ... otherwise those described mal-shapes will occur AND the tack angle will be well beyond 'designed' (typically greater than ~89 degrees) and with the clew/boom in a drooped-into-the-cockpit shape.
Here's how to PROPERLY RAISE of a boltroped dacron sail, and what to do when the sail because of 'hysterisis' of the boltrope causes it to eventually become shorter than its OEM length and how to set up for PROPER 'weather helm' each and every time you raise such a sail. Probably 95% of ALL sailors using boltroped woven dacron NEVER do this, they just 'raise' and never 'tension' that luff !!!!!!!!: How to properly RAISE a woven dacron mainsail -

RX: So, if you are getting 'variable' shape out of your new woven dacron boltroped sail, you probably arent applying CORRECT but variable luff, etc. tension on that boltrope when you are 'raising' it.

Woven dacron does become 'stretched' over time and hard usage. HOWEVER you 'can' readjust the boltrope 'preload dimension' by 'easing the preload tension on it' to restore the proper sail shape - thats why woven dacron 'lasts longer' because you 'can' easily 'reshape' such a sail back to 'as designed'! The downside of woven dacron is that there no means to compensate for a leech (length) that has become permanently stretched (other than reseaming the leech back to 'flat' - expensive), just about all other 'deformations' can be inexpensively corrected.

Last edited by RichH; 03-23-2012 at 01:39 PM.
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