Adjusting for a shrinking bolt rope?

02/01/2014 15:12:18
I have a 2008 Speed mainsail made from a laminate type cloth. The sail has a ‘bolt rope’ that looks like/is a solid white plastic tube enclosed in a Dacron sleeve. Can someone confirm, so these pieces of rubber/plastic shrink? ….and if so do they shrink faster than the sail cloth?

I ask because I have noticed quite a bit of bunching in the white luff material/Dacron) that encloses the rope and I have also noticed that the tack of the sail and the bottom of the boltrope appears to be securely captured/trapped, such that if the bolt rope were to shrink it would have the affect of causing the sail to shorten and bunch up with it.

Can someone confirm, should I be freeing the bolt rope at the tack and allowing the sail to slide down, or do people not do this?

Is the bunching something that the sail maker incorporated when they originally trapped the bolt rope and sail….ie to make the sail fuller in the absence of an Cunningham?

Can this bunching get excessive and thereby cause the sail to set too full?
….is this when speed creases come from???

Or is it the mylar of the sail laminate shrinking which is then visible as a gathering of the bolt rope mylar material?

Do the guys at the front of the fleet not know what the hack I am talking about i.e. new sails 2x a year ;-)

Many thanks for the explanation.


02/01/2014 18:30:34
Hi Chris,

The cord in your mainsail isn't supposed to shrink but it does. Releasing the cord at the bottom and letting the cord move up inside the luff tape will help bring the draft forward in the mainsail.

When the cord is sewn into the sail the cord is pulled ever so slightly tighter, this allows you to control the position of the draft a little easier, certainly when sailing downwind the sail can suck up the mast to help move the draft back and help the leech to stand up. When sailing to windward a little cunningham can be added to allow the draft to move forwards again.

All laminate mainsails shrink and most bolt ropes/cords shrink as well. Always allowing the sail to dry after use and rolling sails carefully once finished with, will help prolong this effect.

A sail that is over a year old and seen quite a bit of racing may need the bolt rope/cord letting back into the sail. If more than 2-3 inches is let in I would recommend taking the sail to your nearest sailmaker to have some extra rope/cord added. A useful sign to indicate wether the rope/cord or sail has shrunk is by pulling the mainsail to the black band at the top of the mast, the tack of the sail will be hard to get close to the lower band.

If you want to talk about speed creases probably best giving me a call as there are quite a few variables and it would be easier and quicker to talk you through it.

Hope that answers your question.

Cheers Taxi

02/01/2014 18:30:48
Chris M
They do seem to shrink. They shrink less than rope, but still enough to cause what you describe.

I'd ring Taxi ay HD sails and ask him what's best to do. If there is a bit of bolt rope left sticking out it can usually be adjusted using that bit, if not it may need a new rope.

03/01/2014 14:02:56
Thank you Taxi for the explanation, the above is very helpful.


Your Name
YouTube Clip
Paste the link provided by youtube under the "Share" button, looks like this ""
Type a Number under 40: