main halyard help needed

[amoret]

Hi, I recently changed the wire main halyard for a 6mm dyneema rope. But the masthead doesn't take a sheave big enough for the 6mm rope. The largest diameter sheave it takes is 8mm, not really big enough for the rope. I've thought about removing the sheave and just running the rope around the clevis pin, or using 4mm dyneema rope for halyard.

The boat is a 22ft trailer sailer used for cruising in light to moderate conditions in mostly sheltered areas.

I notice that some boats have rope halyards, but cant see the masthead clearly in photos, I wonder how others get round the problem. Any help or comments is much appreciated.

Many thanks

[RainDog]

4mm is certainly plenty strong. You would not want to pull on it worth your hands. I assume you are replacing a wire to rope halyard? Could use 4mm Dyneema for the part that was wire, and a more hand friendly line for the pay you pull on and cleat off.

[roverhi]

6mm is smaller than 8mm. Was there a typo in your posting?? If the old halyard was wire spliced to rope, the Mast head sheave should take the same diameter line as the old rope portion of the former halyard. Unless you had a wire reel winch, which is doubtful on a boat your size, the sheave has got to be able to take more than 4mm line which is something like 3/16". In any case, 4mm Dyneema is more than strong enough.

[amoret]

thanks for the suggestion Raindog. Probably the best thing to do. What do you think about the idea of removing the sheave and just running the 6mm rope around the clevis pin? ( I've already bought and installed the 6mm rope)

[Tempo Spars]

Make a tip splice in the halyard. That is removing the cover of the rope so that at max hoist the cover is just through the jammer. This will reduce the line size around the sheave and run much better. Removing the sheave totally is not recommended. I would replace the sheave with an acetyl one and clean the axel. A sheave is worth about $40.


Roland

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[amoret]

Hi Peter, thanks for the reply. 8mm is the outer width of the sheave, ( 6mm on the inside ) the 6mm rope pinches in the sheave which is really only recommended for 2-4mm rope. The rope part of the old rope/wire halyard was 8mm and never got out of the mast head. (so big at the join it wouldn't pass through the top of the tapered mast)

[RainDog]

Originally Posted by amoret

thanks for the suggestion Raindog. Probably the best thing to do. What do you think about the idea of removing the sheave and just running the 6mm rope around the clevis pin? ( I've already bought and installed the 6mm rope)

No harm in trying it. Dyneema can handle the extreme bend and is very slippery. Just keep an eye out for chafe.

[CRANBERRY]

Sorry I am a rope maker and Dyneema DOES NOT like tight bends. leave the sheave in place. Yes its slippery but the loss in strength just going around a sheave would be greater then 50%

[RainDog]

6mm dyneema at 50% strength will still be strong enough to lift his entire boat out of the water with room to spare.

[roland stockham]

Sorry but this makes no sense 8mm diameter sheave??? that would take a wire size of 1mm and rope less than 1.5mm. 6mm low stretch ropes like a sheave diameter of 5-7x the rope diameter. Bigger is better. Running a rope over the spindle will trash everything and have the same effect as running over a blunt knife.
Sizing hallyard is about handling so the don't cut your fingers off, wear at the blocks and 'creep' - to light and stretchy and the luff will keep going slack. The load on a small boat is minimal but is bases on sail area 3-4mm rope should be fine. To big a diameter is going to make it much harder to hoist

[jongleur]

Can you get a wider delrin sheeve and sand it
narrower to fit?

[savoir]

The old halyard would probably have included either 3mm or 4mm 7x19 SS wire. The 3mm has a break load around 500kg and the 4mm around 900kg. 5mm Amsteel Blue has a BL around 2200kg while 4mm is around 1700kg.

I suggest using the 5mm because it will stretch less but the 4mm would certainly work. The weight difference is inconsequential.


You might consider stripping the cover from a thicker Dyneema SK75 rope of 7 or 8mm.

[savoir]

Originally Posted by roland stockham

Sorry but this makes no sense 8mm diameter sheave??? that would take a wire size of 1mm and rope less than 1.5mm. 6mm low stretch ropes like a sheave diameter of 5-7x the rope diameter. Bigger is better. Running a rope over the spindle will trash everything and have the same effect as running over a blunt knife.
Sizing hallyard is about handling so the don't cut your fingers off, wear at the blocks and 'creep' - to light and stretchy and the luff will keep going slack. The load on a small boat is minimal but is bases on sail area 3-4mm rope should be fine. To big a diameter is going to make it much harder to hoist

He means " width ".

[fkittson]

We have a Alberg 30 that had wire rope halyards. We have just done the switch to amsteel rope 3/16 spliced to a 3/8 tail. We measured the old halyard when stores at the bow pulpit and added 16" to that. Then spliced 3/8 the rest of the way to the clutch. The 3/16 Amsteel rope is actually stronger the SS Wire and you can still use the old wire V shives. Just make Shute whoever splices it knows what they are doing. At .90 per foot is not that cheep.


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[amoret]

Umm yes, sorry 8mm width sheave