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How a 2:1 halyard works

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I will chip in and I know it is slightly thread drift but our boat has 16m luff and had double purchase when we bought it but we found it slow to hoist and lots of rope so we got rid of it. I don't think it any harder to hoist the sail without the purchase.

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On some performance dinghies they rig it the other way, small block in the mast, halyard attached inside, through internal block and out the exit box. The tail comes out the mast and that's what you haul. Double the weight as Chic says but for every 1m of hauling you pull up 2m of sail. Good for super fast hoists. Probably more playing around to set up.

Grant, that's a 1:2 set up and only someone on bad bad drugs would use that.

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Here is a photo...

 

http://www.flying15.org.uk/news/flying- ... in-halyard

 

By virtue that the head board of the sail is supported by two ropes equates to a 50% reduction of load on the blue halyard down the mast.

 

 

Thus - the compression on the mast between the hound and masthead (3/4 rig) is reduced. The percentage of reduction on the rope is 50% but the reduction on the mast varies from mast to mast.

 

Having the 2:1 in the mast is a complete waste of time as the compression is still there and the headboard is only supported by one fixed point. Not 2 as in this setup attached.

 

Having this setup also stops any creep as the most loading is Always between the headboard and sheave in the masthead crane.

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Tim is right. Reduces by 25%.

 

If the mainsail luff load is 100kg say. Then your main luff is inducing 100kg of compression in the rig downwards.

Likewise a 1:1 halyard is pulling up and around the sheave and back down again- 100kg so the over all load is 200kg. (Halyard load plus sail)

 

If you have a 2:1 quite right it halves the load on the halyard. But the halyard load is only half the compression of the system- so you end up with 100kg mainsail compression, and the halyard compression is half so 50kg. =150kg or 25% less over all compression on the rig.

Not quite.

 

In a vector load diagram you have down ward forces imposed by luff and halyard that are in equilibrium ( or the sail would fall down or go up) the force imposed on the Halyard ( luff as well) is one downward force.

 

The compression on the mast is one force from these. The bend from this compression is dependent on the mast section.

 

But the most compression, or downward force is the effect from the main sheet ( or kicker/Vang if using to tension the leech). That is a downward and aft pull.

 

Remember the boom is a big lever of fulcrum acting on the mast with great load.

 

Then we have the wind effect to consider.

 

The best way to reduce compression on a 3/4 rig mast (above the hounds) is to have a mainsail that needs the least amount of mainsheet tension to get optimal shape and twist.

 

Or a stiffer mast.

 

Which is why flatter (upper third) shaped sails are faster on these soft rigs in most cases.

 

Remember every mm of compressional bend in a mast (from step to head) alters every setting you have on your sail...

 

The stays, sheets, luff, fore stay, kicker, spreader angle etc... all go slack proportionally, which in turn alters your sail shape for the worse.

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From my experience the driving factors in mast compression is chainplate width, righting moment and tight luffed upwind code zero type sails. So you need to get the chainplates as far outboard as possible, much like the open 60's are doing with deck spreaders. Then have all highly loaded halyards on halyard locks.

 

Mainsheet doesn't contribute very much to compression in the grander scheme of things. Maybe in an A class cat it would, but not on most boats.

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Grant, I'll do you a diagram, but got to go out now. Tomorrow. For a given halyard tension, it is not possible to reduce mast compression. For every force, there is an equal and opposite force to achieve equilibrium. Otherwise sail goes up or down... Simple explanation tomorrow with pics and force diagram.

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Grant, I'll do you a diagram, but got to go out now. Tomorrow. For a given halyard tension, it is not possible to reduce mast compression. For every force, there is an equal and opposite force to achieve equilibrium. Otherwise sail goes up or down... Simple explanation tomorrow with pics and force diagram.

 

Sure you can reduce mast base compression for loads induced by a halyard. I bet you a bottle of rum I can prove it. 8)

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2:1 does not decrease mast compression, if the luff is tensioned to x between crane and head then the mast is compressed by x. It does not matter if its 1:1 or 100:1 the sum is still x, its just that the string is easier to pull.

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2:1 does not decrease mast compression, if the luff is tensioned to x between crane and head then the mast is compressed by x. It does not matter if its 1:1 or 100:1 the sum is still x, its just that the string is easier to pull.

 

This is true if you hoist your main by standing on top of the masthead crane and pulling up.

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I know the theory IT but I just can't explain it quite right.

 

If my mast section was as limp as it would have to be to knot cope with my main halyard loads I'd be filling me undies with brown stuff as I left the marina knowing it was all gonna come knot long after I hoisted the sail. Yes I do know exactly what loads my halyards have on them when in use.

 

I suspect a lot of 2:1's on boats like mine are more monkey see = monkey do rather than anything significantly structural but if it make people think the boat is faster they will sail it faster, so the 2:1 may do little in a structural sense it could be a good mind tweaker.

 

Right, off to me cave for some experimentation. Back soon.

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