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How a 2:1 halyard works

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

 

Incorrect, it does not matter. The luff is tensioned from tack to head by X, you cannot change it by using a halyard lock or 2:1 purchase. If you got 2 spring balances and attached one to the foot and one to the tail of the halyard, hoisted the main wth a 1:1 purchase there would be an equal force (assuming no friction for the sake of discussion) on both. If you repeated with a 2:1 the sum total of the load is still the same but divided between the head, the block, the deadend and the bitter end. Im other words the luff retains the tension but above the head each part of the purchase where it attached to the crane divides the load so 1/3rd ends up in your hands but the total load is the same otherwise your luff would sag.

 

Your diagram does not make sense

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Your error is in not calculating from the tension required for the sail which is 100kg not 200.

 

In the first diagram it requires 100 kg to tension the sail. That means the axle on the sheave is transferring the same 100kg downwards not dividing it.

 

In 2, you still have 100kg so each part is approx 33kg not 50

 

In 3 you still have 100kg but now its pinned to the masthead

 

Slice it and dice it any way you want but the tension on the spar is the same, its transferred in different propportions according to purchase but its still 100kg.

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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.

Compression on a mast is in more than one sector.

 

Below the stay/stays attachment

 

And above the stay attachment (hounds)

 

The angle of the stays has no bearing on compression. The tension you put on stays does.

In a 2:1 main halyard its most advantage is the Mast head to hounds compression.

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KM:

 

 

To simplify...

 

There is halyard compression and mast compression acting in a downward force on the mast

 

All have 100kg of compression on the mast. (On the sheave pin/splice pin)

 

The 2:1 has 50% less loading on the halyard than a 1:1 system.-

 

The lock system has the least amount of halyard stretch potential and no halyard loading

 

The 1:1 halyard has 100kg less the friction deduction of the sheave it passes

Plus the 100kg of. Mast loading loading =200 kg

 

The 2:1 has 100kg mast plus 50kg halyard

 

The halyard lock has 100kg mast.

 

No myth just maths and physics.

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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.

Compression on a mast is in more than one sector.

 

Below the stay/stays attachment

 

And above the stay attachment (hounds)

 

The angle of the stays has no bearing on compression. The tension you put on stays does.

In a 2:1 main halyard its most advantage is the Mast head to hounds compression.

 

 

Of course the angle of the stays matters! :lol: That is why a mast has spreaders! If your argument is true then we can all take our spreaders off have save a lot of weight!

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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.

Compression on a mast is in more than one sector.

 

Below the stay/stays attachment

 

And above the stay attachment (hounds)

 

The angle of the stays has no bearing on compression. The tension you put on stays does.

In a 2:1 main halyard its most advantage is the Mast head to hounds compression.

 

 

Of course the angle of the stays matters! :lol: That is why a mast has spreaders! If your argument is true then we can all take our spreaders off have save a lot of weight!

 

Incorrect. Compression on a mast is a downwards force not a sideways force.

 

All the spreaders do is keep the mast in column.

 

10 tonnes of stay loadings is ten tonnes no matter how many spreaders.

 

All the spreaders do is stop the mast bending.

 

Wider stay angles mean nothing. Its the loading at the attachment to the mast that the compression is measured at. Not the angle they approach at or the spreader that they are deflected by.

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Im with WT here for sure. Its a fact and a well known fact too.

Having a friction sheeve/ferrule or shackle as the 2:1 block (on the sail attachment )is even better as it further reduces compression when compared to a low friction block.

It all sounds farr fetched but if you actually sat down with someone who could explain it and draw some pictures you would understand and see how simple it actually is.

 

I guess the most simple way I could discribe it is imagine getting your fishing rod, then tying a bit of string to the flexy end of it in addition to the line that runs from the reel out to the end and back with a hook on it.

Now grab the hook end and pull it towards the reel you- can bend the rod easily. Pull the direct 1:1 string that is tied to the end and its much harder to bend the rod. This is the difference in compression between a halyard lock and 1:1 halyard.

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Again im with WT here. He designs rigs for a living.....

if you moved your backstay from the transom to 1m behind the mast you would be adding a huge amount of compression when it was fully loaded. The further back away from the rig it went the less compression.

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