I don't know if anyone else has this problem but the main halyard(s) on my daughters 29er seem to shrink! The last one has become the jib halyard on my Merlin but the new one made 25mm longer is going the same way (and I don't need another Merlin jib halyard just yet!). Am I the only only person to have this problem? Does anyone have any ideas on a better product? Maybe because it goes on a rack, it is easier to notice this "shrinkage". 
Cheers Dave

Dyneema dies shrink under uv. The poorer quality ropes suffer more than others due to their coating but my Chinese pole vangs "lost" nearly 4 inches in a season.

Sk78 dyneema is a premium product so should be better. English braids version is called dynamic line. Ill look up the specs for it later for you if you like?

Hi, First a disclosure, I'm the technical manager at Marlow so I have a vested interest.

We produce hundreds of thousands of metres of D12 type rope each year and the feedback for 99% of it is good. However we have have had rare reports like this one spanning perhaps 10 years, only 2-3 per year though. With such few reports it's difficult to pin down exactly what's happening.  These reports cover several different industry areas and applications, D12 and D12 MAX, covered and uncovered ropes.   We've never found a fault in the material or the construction suggesting that this shrinkage is due to the environment in which the rope is used/stored.  The common factor appears to be that the ropes reduce in length while in an unloaded condition rather than when in use or even when new.  What we can definitly say is: 
-All the ropes are made from DSM Dyneema fibre, either SK75 or SK78.
-This phenomenon has been reported on both D12 and D12 MAX which undergo different stretching conditions.
-Dyneema does not shrink in water like some other fibres.
-Dyneema will shrink if it gets hot when under no tension.

As this can affect both D12 and D12 MAX I don't think the stretching process we put the rope through here at the factory is the cause.  Some of the ropes have not been used until months after stretching so residual 'shrink back' is unlikely.  We've also not seen this occur with rope in our factory. 

DSM Dyneema (the fibre producer) have been informed of this in the past and heat is the only explanation they've been able to offer.

Therefore the most likely cause and the only one we've been able to re-produce in the factory here is that the ropes have been exposed to elevated temperatures while they are stored, the sort of temperatures required would be possible if they were in a mast in the sun for instance.  Unfortunately this can only really be proved or disproved by feedback from people who have seen this issue and can report on the conditions the rope was under when it happened.  Until then it just remains the leading theory.  I also see from the previous post that it's happened to the Chinese UHPME fibre as well So it's not just us!

BTW:  For the record:  EB's Dynamic range is made from exactly the same fibres and has very similar construction and stretching process as the D12 so is unlikely to behave any differently in this respect :-)  

Sorry about the long post, hopefully it's helpful!

My Chinese stuff "lost" around 4 inches from a 3 metre (excuse the mixed systems!!) length and I was shocked to find that this was actually within spec!

I haven't been able to find a specified shrink rate for the EB dynamic line, it would appear that none is expected and Paul's post really confirms that. It could - I suppose - be due to minor inconsistancies in the PU coating? UV must have an effect.

Interestingly I've just changed a set of Vectran (V12) pole vangs - they've shrunk!! So dyneema it is from now on

My Chinese stuff "lost" around 4 inches from a 3 metre (excuse the mixed systems!!) length and I was shocked to find that this was actually within spec!

I haven't been able to find a specified shrink rate for the EB dynamic line, it would appear that none is expected and Paul's post really confirms that. My working theory was that it could be due to minor inconsistancies in the PU coating. UV is not all that good to most fibres.

Interestingly I've just changed a set of Vectran (V12) pole vangs - they've shrunk!! So dyneema it is from now on

I've seen some people using an old halyard which they tie to the main halyard after dropping sails and then pull the main halyard back into the mast leaving only the knot and the sacrificial old line exposed to UV. Same with jib and kite lines if not wire. As long it's UV that is the problem rather than heat, this should work for your dyneema or vectran.

Hi guys,

I just noticed this thread on the forum and found it interesting reading. I have worked with Paul, Marolw, a great deal and their product is top notch. I would be very surprised if his assumptions were not incredibly accurate.

One thought I had with assumed shrinkage on Dynema or Vectran halyards is that in between use the halyard can relax , not shrink but would need tension to re-stabalise itself.

I used Marlows excellent sK90, top of the range dyneema, for making jib stay/halyards and trapeze cables for many of the 470 sailors competing in last years olympics and also for the first part of the Laser vangs and we noticed that if not used there was an assumed shrinkage but if kept under a reasonable load there was not.

Hope that is helpful in some way to any of you reading this...

I would be very grateful, as I am sure Paul would too, for any feed back from sailors on rigging, rope work and such like matters. Please feel free to contact me at my email address above or on my facebook page.

https://www.facebook.com/THENOTTINGHILLRIGGINGCOMPANY

cheers 

G

Just seen this. What would be very interesting is to hear what sort of loads are required to prevent this shrinkage occurring.

Loads to prevent the line from retracting/shrinking don't have to be big. 

Say you had a Jib or main halyard that you wanted to keep at a specific length, hand tight, a good pull, should be adequate.