tomframe
Well-Known Member
Hi, I have picked up some 10mm rope, Kevlar core with a polyester outer - seems overkill to make halyards from Kevlar - do you thinks its advisable to use this, what are the negatives?
Kevlar ropes
- Thread starter tomframe
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charles_reed
Well-Known Member
Kevlar Halyards
Not at all overkill, Kevlar has probably the least hysteresis of any of the textile ropes.
It does have two major disadvantages:- It is very prone to uv degradation and to fatigue failure.
My boat had kevlar halyards on it when I first had it - all three fatigue failed within 3 seasons - I've replaced them with dyneema/spectra. Far more springy than Kevlar or Vectran, but slightly stronger than Vectran, it's about the cheapest of the three, and weight for weight about twice as strong as stainless wire.
By all means use Kevlar where it goes round no pulleys and isn't exposed to the light of day. Or change it annually as the dinghy-racing boys used to before the advent of Spectra/Dyneema.
Not at all overkill, Kevlar has probably the least hysteresis of any of the textile ropes.
It does have two major disadvantages:- It is very prone to uv degradation and to fatigue failure.
My boat had kevlar halyards on it when I first had it - all three fatigue failed within 3 seasons - I've replaced them with dyneema/spectra. Far more springy than Kevlar or Vectran, but slightly stronger than Vectran, it's about the cheapest of the three, and weight for weight about twice as strong as stainless wire.
By all means use Kevlar where it goes round no pulleys and isn't exposed to the light of day. Or change it annually as the dinghy-racing boys used to before the advent of Spectra/Dyneema.
forethought
Member
Kevlar Halyard
It is OK provided the sheaves are large diameter wide and specially flat for Kevlar - the typical failure is the racing poseur with the Kevlar Halyard replacing wire or other rope that has them blow up in the first good slog to windward.
The reason being the extremely low stretch means that all the load is taken by the strand which goes the longest path round the sheave. U profiled sheaves dont let the rope flatten enough, and until the boat begins to pound , the few strands taking the load suffice. Once they break, the chain reaction starts and you end up with two separate fluffy rope ends.
Leave them to people with budgets to design the boat systems for kevlar.
It is OK provided the sheaves are large diameter wide and specially flat for Kevlar - the typical failure is the racing poseur with the Kevlar Halyard replacing wire or other rope that has them blow up in the first good slog to windward.
The reason being the extremely low stretch means that all the load is taken by the strand which goes the longest path round the sheave. U profiled sheaves dont let the rope flatten enough, and until the boat begins to pound , the few strands taking the load suffice. Once they break, the chain reaction starts and you end up with two separate fluffy rope ends.
Leave them to people with budgets to design the boat systems for kevlar.
William_H
Well-Known Member
Halyards
My experience with halyards is that you need the least possible stretch to keep a decent sail shape.
If you consider that with the mainsail your main sheet with at least 4 purchase probably 6 purchase is pulling on the halyard with no purchase then any stretch of the halyard is going ot allow the boom to droop.
So while a thin halyard inn specra or kevlar will be adequately strong it will still stretch. If you go for spectra/Kevlar halyard which is obviously cheaper than wire/ropetail then go for the thickest you can fit in the pulleys
Not so obvious with the jib halyard any stretch will put more camber in the jib so making it less efficient in the stronger winds.
I have a spectra jib halyard on a smallish 21fter and found the 6mm was still too stretchy so have gone to 8mm which is better. (acceptable) I still have wire /rope tail for the main and hope it lasts a long time as I don't want to go to spectra. good luck olewill
My experience with halyards is that you need the least possible stretch to keep a decent sail shape.
If you consider that with the mainsail your main sheet with at least 4 purchase probably 6 purchase is pulling on the halyard with no purchase then any stretch of the halyard is going ot allow the boom to droop.
So while a thin halyard inn specra or kevlar will be adequately strong it will still stretch. If you go for spectra/Kevlar halyard which is obviously cheaper than wire/ropetail then go for the thickest you can fit in the pulleys
Not so obvious with the jib halyard any stretch will put more camber in the jib so making it less efficient in the stronger winds.
I have a spectra jib halyard on a smallish 21fter and found the 6mm was still too stretchy so have gone to 8mm which is better. (acceptable) I still have wire /rope tail for the main and hope it lasts a long time as I don't want to go to spectra. good luck olewill
