Is it worth using Dyneema for running rigging on a crusing boat?

[Rossynant]

For wear I would not be concerned by going to 8mm, the big difference between dyneema with polyester cover and dbl braid polyester is that in dyneema it is only the core giving strength to the rope.
The cover is far more stretchy than the core so it will not start to take any substantial load before the core is overloaded.
So you can wear the cover down to nothing before chafe is becoming an issue.

This is right, but what I want to say is 8 mm diam line has actually much less core (in area) so it will wear to nothing rather sooner...
As for strength - there was a boat having old cotton halyard, some 10 years old, for main, and polyester same size was installed for jib (twice smaller than main) - polyester probably has 5 times breaking strength. But it broke in two years or so, while cotton still served. Breaking strength is not so much an issue with lines as wear, unless someone gets to really small size.

 

[knuterikt]

This is right, but what I want to say is 8 mm diam line has actually much less core (in area) so it will wear to nothing rather sooner...
As for strength - there was a boat having old cotton halyard, some 10 years old, for main, and polyester same size was installed for jib (twice smaller than main) - polyester probably has 5 times breaking strength. But it broke in two years or so, while cotton still served. Breaking strength is not so much an issue with lines as wear, unless someone gets to really small size.

The difference is that when the cover on a polyester dbl braid is chaffed 1/2 way through the strength of the rope is reduced.
You can remove the cover on a dyneema rope without reducing the strenght at all.

A 10mm dyneema rope has the same thickness of the cover as 8mm dyneema so you don't get any more fibre to "chew" on if you increase the diameter.
Rope construction is different so there are different considerations.

One single case study of cotton vs polyester is not good for comparing an all different type of rope.

 

[Rossynant]

Cotton vs polyester was to show rope failed from wear, having a lot more strength than necessary.
As for core chafing - friction falls on area - circumference of 8 mm rope is rather different from 10 mm... naturally internal chafe, in core, also takes place when rope goes bending over something and also has nothing to do with breaking loads.
But of course it's all theoretic, each rope has some particular traits. Just to point that there is more to rope size choice then breaking strength - this is usually in excess anyway.

 

[knuterikt]

Cotton vs polyester was to show rope failed from wear, having a lot more strength than necessary.
As for core chafing - friction falls on area - circumference of 8 mm rope is rather different from 10 mm... naturally internal chafe, in core, also takes place when rope goes bending over something and also has nothing to do with breaking loads.
But of course it's all theoretic, each rope has some particular traits. Just to point that there is more to rope size choice then breaking strength - this is usually in excess anyway.

If you have a rig where this is a real problem - you are in big trouble (we are talking halyards here)
1) There is something wrong with your rig - creating excessive chafe
or
2) Your inspection / maintenance routines is non existent or conducted to seldom.

 

[William_H]

Wear of a halyard can be reduced by the simple expedient of using a bowline at the sail head rather than slice and shackle. This way every time you hoist the sail you put the wear spot in a different location. Not so useful for furling jib where halyard is left on for the season. But useful in my case with hank on jibs.
Dyneema /spectra really has less stretch than polyester. If you are using polyester on furling jib you may not mind having to tighten the halyard a few times when the sail is fitted to take out stretch. I found on my little 21fter that with hank on jibs that even with 6mm spectra there was an annoying stretch after hoist and it had to be retensioned for proper luff tension. 8mm spectra is a vast improvement but still sometimes needs to be retensioned.
I still use wire/polyester for main halyard. It does seem to me that no stretch here is even more vital as your load on the mainsheet tends to try to pull the main sail down.
I don't think stretch in a back stay system will matter much. So yes use dyneema/ spectra (10mm) on main halyard and also on jib if you change jib often. good luck olewill

 

[Plevier]

If your (OP's) existing halyards are polyester braid on braid you can get quite an improvement by changing to braid on 3 core polyester. Not as good as Dyneema but will halve your present stretch for much less cost.