Sail bolt rope shrinking

[davidpm]

This is a question prompted by Sqidd's excellent post about ironing sails.

Apparently there is a common problem with older sails where the bolt rope can shrink causing the sail to become more baggy.
http://www.neil.fuller.dsl.pipex.com...s/boltrope.pdf

I have seen sails like this myself and figured they were shot but maybe they can be fixed.

As to why the rope would shrink rather than stretch I'm not sure.

[RichH]

That which causes 3 strand rope, dacron rope in the case of a sail's boltrope, is called mechanical hysterisis or permanent dimensional changes due to constant 'stretching'. The same thing happens with 3 strand dock lines that are put under repetitive strain .... they get 'harder', fatter and shorter.

Here's how what happens in boltropes, how to test your boltroped sail to see if the boltrope needs replacement or 'adjustment': How to properly RAISE a woven dacron mainsail - SailboatOwners.com

[Squidd]

Rich H was a great help in explaining/confirming the process of splicing in additional bolt rope to the luff line and then calculating the bolt rope "preload" to obtain/regain standard luff dimension...

I did it on an older MacGregor Venture Cat 15 sail that was baggy, hard to raise (bolt rope in track) and had a droopy boom (over 90*) unfortunatly I don't have any "before" pics and it's too cold to set up "after" pics, but here is the sail luff before adjustment...



You can see the shrinkage in the "bunching up" of the luff sleeve which made it hard to slide up the mast and did'nt allow the sail to properly tension/shape itself on the rope.

Measured "as/was" the luff was 17'8" and the recommended length is 18' 5" so you can tell the rope had shrunk close to a foot in length..!!

I cut the sleeve near the tack, pulled the bolt end free and step spliced in an additional 1'6" of 3 strand bolt rope...I also "cross stiched" the strands and bound the splice ends before sliding the additional length back into the luff sleeve...

Here you can see the luff sleeve is been relieved quite a bit as it relaxed and now I just need to set the preload dimension and reattach the bolt rope to tack...



Mast track from tack pin to halyard pulley is 19' and before the sail even when pulled excessively tight was a good foot short of top of mast...now with the restored length in luff I should be able to raise the head to height effectively raising the leach/clew and boom end as well as restoring "flatter" airfoil shape to a 40 yr old sail... If this works as well as I believe it will I'll be doing this to my PY sails next...

Full thread here...Iron your Sails...? - SailboatOwners.com