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How a 2:1 halyard works


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No !!!!!! The 100Kg of Sail load on halyard DOES NOT SUM to make 200Kg. 1 x 100 = 100. 1:1 is the same as writing 1x1. It equals 1.

Having a 2:1 does not magically halve the load. The 100Kg will always be 100Kg. Think about it. It is only the effort seen on the Tail of the Halyard that changes, but the 100Kg is still between the two blocks which is still 100kg at 1:1 or 1x1 which equals 1.

In fact there is a detrimental point to going multiple purchases. You are adding a weight of extra blocks and halyard to the mast. Granted that the Halyard reduces as you pull it down, but it's still weight in the boat.

And if you still don't want to believe me, come and see me at work as I have a set up that I can demonstrate it. Which I did yesterday to prove it.

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Wow I can't believe this is still going on.

Guys the load or weight on the sail side of the pulley/sheave always stays the same no matter what the reduction, but the weight on the cleat/clutch winch side of the line is reduced when using a reduction ratio. It's not complicated.

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Wheels, you are forgetting about the invisibile part- I agree with you if you are talking luff load on the mainsail. But you really are missing the obvious, For every 100kg of luff load you pull into the main, there is an equal load of 100kg translated into the main halyard, which then goes around the sheave, and pulls the rig down too, The Main halyard sheave isnt a fixed skyhook in the sky so the load going 180 around the block doubles the load induced on the rig - just like any other turning block...

 

So for a 100kg luff load (Cunningham load say) the mast see's 200kg of downward pressure, or compression if the halyard is a direct link or 1:1.

 

Now do the same maths if you can reduce the halyard load on the part inside the rig by half then it works out as 150kg of downward load.

147242-Halyardcompression.GIF

pulley-1-1.jpg

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costaN I was just doing the same diagram, but yours is better! to have 100 kg on a halyard, one side of a block, you have to have the same on the other side or something moves. 100 Plus 100 = 200!. the 200 is on the sheave pin.

wheels, a PIC of your test rig? I'm intrigued.... :D

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Hi Wheels,

the issue is that a single block is not 1:1. If the sheave could move, it would move 1/2 the distance of the halyard recovered. That is 2:1. Like this..

 

 

Single Block 2 to 1.jpg

 

This better be right, or I've done some really crap physics over the years :lol:

 

It is NOT THE HALYARD LOAD that we are talking about here - of course that is still 100Kg at the tail. It is the compression load applied from the sheave, gooseneck fitting, and halyard termination fitting. That compression load may or may not be transmitted into the hull, depending on the positioning of the fittings. It will be taken by the mast.

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It's not 1 + 1. That is where you guys are all going wrong. It is 1 x 1. 1:1 is that same as saying 1X1. 1:2 is 1X2. 2:1 is the same as saying 2 divide by 1. But whatever the mechanical advantage, the reduction is in what a person has to pull on the halyard tail ONLY. The actual mechanical pull is not seen as tail to mast head sheave, but block terminal to masthead sheave.

Guys, we are pulling lines on the test bed almost daily. When we are working in tons and have to proof load lines, we need to be correct. It ain't a game for us, as much as we like playing with the Test Bed. We have to be accurate or someone ends up getting hurt.

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THAT Wheels, is the crux of the issue. The Halyard certainly still has 100kg on it. No argument. The discussion was about the compressive loads taken by the rig, which absolutely can be reduced by running a 2:1 halyard... Looks like we were coming at that from two different perspectives!!

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Because you do not have two 100Kg weights. The Halyard is creating 100Kg of tension on the sail, it is not an extra 100Kg of weight. If you placed a weight of 100Kg on the halyard, then yes you would have a sum of 200Kg. All the Halyard is doing is "transfering" the load of the Sail to the Halyard cleat. It is not a weight in itself.

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Yep I can show you really easily. One load cell on the "mast head" so to speak (top of the bed) and one cell on the "load" and scales on the halyard tail. Pull the Scale to read what ever and you see the same load displayed on both load cell readouts.

 

I think the important point to understand is that the Halyard is only transferring. It is not adding anything apart from it's own weight in rope of course. It simply transfers the Sail load to where ever you wish to terminate it. If the halyard was straight and terminated at the Mast head, the mast head is taking the 100Kg. The sheave is simply a point which you bend that halyard around 180degree's.

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A 2:1 system Increases Load at the mast head - while the halyard is being pulled

 

Once the halyard is cleated off, the load at the mast head reduces to the original load being lifted

 

 

How about that

 

D.

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Warlord, only the friction in the blocks and line running around the blocks and I suppose a minute amount of inertia would do that. But if we are looking at just the Sail load and assume no losses for the point of the exercise, then no. The Halyard Line is simply a transference of Sail load.

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Wheels

The load cell at the mast head should be a fixed point. It is a constant in both examples.

 

Put your load cells on the halyard section either side of the fixed point and see if the readings are the same. Then add the 2:1 on the sail side and measure again.

 

The measurement you are trying to obtain is the compression on the mast by the halyard, all other forces are the same and should be ignored for the sake of this discussion and BOOBOO's sanity.

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We have a terminology or definition break down going on here people.

 

No ones wrong but then knot everyone is talking about the same thing... or the same 'load' in this case.

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:oops: I think in my excitment I have misunderstood what you guys are trying to describe. :oops:

That pic IT now shows me what you are trying to describe and you are indeed correct.

Sorry for the misunderstanding and argument.

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