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Best rope for main halyard

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Medway Maniac View Drop Down
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Post Options Post Options   Quote Medway Maniac Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 09 at 1:22pm

How can I put this?

Farc anal, imagine you are an angel holding up the sail by its head. You are supporting only the loads in the sail, which as you say are induced by kicker, mainsheet & cunningham. This is the halyard lock situation. Mast locks do reduce compression (as well as stretch as you say)

Now, instead of holding the sail-head, you're holding a pulley which has a main halyard running from the sail head and back down to the ground. You will have to pull twice as hard as before as the sail now has a 2:1 purchase on you.

Reduce the halyard tension by putting a block on the sail head and dead-ending the halyard end at your hand, and the overall load on you will go down as there will be less total loading in the elements connecting you and the ground (sail + halyard).

I call a halyard 2:1 if I have to pull the halyard twice as fast as the sail goes up the mast. This is what most people mean, but it is a matter of definition, as you demonstrate.

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Post Options Post Options   Quote farc anal Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 09 at 1:37pm

Thank god Craiggo,  thought I was bashing my head on a wall there .

EDIT oops just read above ----   apparantly after reading the maniacs reply I am ,

 

Not to worry I'll leave the maniac alone with his Angels

 

think the rest of the world knows what we are on about .

 

 

 



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Medway Maniac View Drop Down
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Post Options Post Options   Quote Medway Maniac Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 09 at 1:39pm
Like flat earthers, you guys are entitlted to your views. Just be sure to let me know if you build any aeroplanes or bridges...
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Post Options Post Options   Quote farc anal Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 09 at 1:43pm

Hey buddy ,

 

we are the folks that build planes and bridges

 

enjoy the ride .

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Medway Maniac View Drop Down
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Post Options Post Options   Quote Medway Maniac Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 09 at 1:45pm

Heaven help us all.

For what it's worth, I'll probably use 4mm Excel Vectran on the 3k when the current Selden Kevlar runs out. Presently it's doing very nicely having an inch or so cut off the top before each Nationals!



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Post Options Post Options   Quote farc anal Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 09 at 1:50pm

Heaven ------   Angels

 

 

you having a divine moment ???

 

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Post Options Post Options   Quote Medway Maniac Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 09 at 1:54pm
Apparently I'm turning religious in desperation. But this is getting too much like a banter thread - we need some more tech input, preferably from someone who designed the existing generation of bridges and planes.
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Post Options Post Options   Quote Medway Maniac Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 09 at 3:43pm

Alright guys, here's another exercise to free up your thinking.

If I put a multi-block at the top and bottom of the mast, and instead of cleating the halyard at the foot of the mast as usual, I ran the halyard betwen the multiblocks N times then cleated it. Do you think that might increase compression on the mast?

Now go back to our earlier examples and have another think. The mast lock means there need be substantially no tension in the run of halyard coming down the mast from the mast lock, remember...

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Post Options Post Options   Quote craiggo Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 09 at 5:12pm
Medway, sorry to go back to what I was saying before.

Your analogy that an angel is holding the head of the sail up, and then you provide a pulley is all very well and good when you assume that the other end of the line is terminated at a rigid and isolated point with no degrees of freedom.

In the real case of a halyard the other end is terminated on the mast tip, and usually on the same pivot/pin that the tail runs over, and therefore it is all tied into the system which has degrees of freedom and is not ideally constrained.
As such regardless of how many blocks you have at the top of the mast ultimatly the total compressive forces are being reacted by the mast and the rigging, they are not miracleously halved by a pulley.

The load transmitted between the bulkhead and the boom in the kicker arrangement is not reduced by the purchases, simply the effort needed to increase the force is reduced.

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Post Options Post Options   Quote craiggo Quote  Post ReplyReply Direct Link To This Post Posted: 17 Mar 09 at 5:21pm
Medway, referring now to your latest question, the overall compression in the mast would increase if you ran the halyard back up to a multiple purchase on the mast because you have reduced the amount off effort required to install tension in the halyard.

I can sort of see where you are going on this therefore I will provide my answer.

Having a halyard which runs down the length of the mast will lead to compressive force acting on the mast, when no other controls are applied, however this force will be small when compared to cunningham and kicker loads applied when sailing. Changing from a 1:1 to 2:1 halyard will not change the compression forces acting on the mast, as ultimately the fully tensioned halyard will run down the mast, and once the sail is fully up the mechanical advantage is all gone, you have the same force tension in the line as a 1:1.

Obviously the luff curve on many classes is cut to allow for a given amount of mast compression caused by halyard tension. To remove the static mast compression from the equation the sails can be shackled to the top of the mast or use a halyard lock.
But as said above the compressive loads will ultimately be driven by cunningham and kicker controls not halyard.

Aaarrgggg my head hurts.

Back to designing aircraft I suppose!
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