Being happy with the original Lewmar winch system for our mainsail we would like to keep it. But the stainless steel wire being rather heavy and worn out we are thinking of replacing it by pure dyneema, without needing to replace the top mast sheave.
Our existing stainess steel halyard is 6mm, with 2000 Kg resistance. A 5mm pure dyneema halyard would have a 2600 Kg resistance.
Has anybody done this?
What would be your recommendation?
Any problem to be expected??
A complementary question is the type of terminal recommended at the top of the mainsail: splice (but the additional thickness might cause problems in the sheave?) norseman type terminal(does this exist for dyneema?), or talurit (aluminium, or copper) as on the existing wire???
Safety question - assume you have discovered that the winch handle should always better be removed from a halyard reel winch?
Has been pointed out earlier on the Forum that fiber halyards replacing wire must not be chosen on equal breaking strength, but instead based on Safe Working Load, which is taken as 20% of the breaking strength.
Your maximum main sheet load, which is closely the same as the halyard load, was luckily specified recently, and using the SWL approach the fiber halyard should then have a breaking strength of minimum 3000 kg. This means 6 or 7 mm diameter depending on manufacturer.
6 mm fits on the winch drum, maybe also 7 mm, but it needs to be checked if 7 mm fits the halyard sheave groove. If not, a simple remedy to the sheave is to put in an O-ring filling the groove. This requires that the sheave is removed though.
Referring to the termination, use the halyard knot recommended by Rod Stephens, found in the Forum Maintenance section. The knot can take about 1/2 of the line breaking strength, while you use 1/5 per SWL definition, so there is a good margin.