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2:1 halyard hardware

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I've heard a few explanations of the need for 2:1 main halyard  systems. Apart from ease of hoisting can one of you experts ( e.g. KM or Wheels )explain just how it allegedly affects the compression on the mast. Seems to me that no matter what system there are two attachment points ,top and bottom of mast, so the only effect is miles more  halyard to buy and stow ? But round the bar others say it reduces compression ? How ?

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1 hour ago, armchairadmiral said:

I've heard a few explanations of the need for 2:1 main halyard  systems. Apart from ease of hoisting can one of you experts ( e.g. KM or Wheels )explain just how it allegedly affects the compression on the mast. Seems to me that no matter what system there are two attachment points ,top and bottom of mast, so the only effect is miles more  halyard to buy and stow ? But round the bar others say it reduces compression ? How ?

All 2:1 halyards I've used and seen terminate on the masthead fitting.

The mainsail on SV Hypothetical takes 50kg of load to hold it up there in just the shape the crew are happy with.

If that 50kg is on a 1:1 halyard it is on one sheave and the that sheave is handling the 50kg. The masthead fitting, containing the loaded sheave, is now applying 50kg of force downwards.

If that 50kg is on a 2:1 halyard then the sheave now has only 25kg on it but the tang where the end of the halyard is terminated has the other 25kg, between the 2 they share the 50kg load required. The masthead fitting is now applying 25kg x 2 of force downwards.

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1 hour ago, Knot Me... maybe said:

All 2:1 halyards I've used and seen terminate on the masthead fitting.

The mainsail on SV Hypothetical takes 50kg of load to hold it up there in just the shape the crew are happy with.

If that 50kg is on a 1:1 halyard it is on one sheave and the that sheave is handling the 50kg. The masthead fitting, containing the loaded sheave, is now applying 50kg of force downwards.

If that 50kg is on a 2:1 halyard then the sheave now has only 25kg on it but the tang where the end of the halyard is terminated has the other 25kg, between the 2 they share the 50kg load required. The masthead fitting is now applying 25kg x 2 of force downwards.

Dont think thats right? 

Bit worried to have a go at this, but in the 1:1 case, the sail applies a 50kg load down, the halyard the same vaule to hold it up there, therefore masthead has 100kg of compression.

In the 2:1 case, the load required in the halyard becomes 25kg each side of the main, and another 25kg tension, so maybe 75kg compression?

Im ssure ScottiE or Ed will correct me if Im wrong.

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3 hours ago, Knot Me... maybe said:

A soft shackle with attached LF eye for use in 2:1 halyards.

m_20200202181001501.png

Exactly Knot Me

We run this sort of arrangement on the main for Oliver Sudden, Young 10/34. A fairly large square top.  Made the Soft Shackle as small as possible to ensure full hoist.  

The 2:1 is fantastic.  Easier to hoist and reduced any clutch slippage.  

Only downside is the mass of rope when hoisted.   

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We use something like this on Bad Kitty, works well & keeps the length of the 2:1 down. Not sure which flavour ours is, refer to Bart at NZ Rigging, came from him. 

block_LOOP_kohlhoff.jpg

l-lb60nb-4_7.jpg

Edited by Bad Kitty

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6 hours ago, Black Panther said:

I thought the reason was to make it easier for an old gitto pull the sail up. Nothing to do with compression.  Am i wrong? 

Yep. See this old thread for details....

 

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