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How a 2:1 halyard works


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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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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.

 

Correct. The lock system is best followed by 2:1.

 

I was with WT diagram 100% until the chain plate point.

 

Chain plate angel, spreader angle and length on serve to support the mast, pre bend the mast, fore and aft and side ways.

 

Compression of a mast from the stays only come from the loadings we put on the stays.... until we hoist a sail and fill the sails then the forces of wind, keel, wave loadings, stiffness of sail cloth, sail shape, crew weight, rigging and running rigging strenght and stretch comes into play.

 

Maybe mythbusters would be a good demo.

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Ok so you are saying that a shroud base 1m wide puts the same compression as one thats 3m wide when the boats at max stability?

if that was the case everyone would have their chainplates 0.5m from the mast!

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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.

 

Not in a masthead rig booboo. But yes in a fractional rig (as the force has gone from a more aft "pull" to a downward pull)

 

This is where you are confused. Side stays always have an opposing stay working against them. So all forces equalise and transferred to the mast.

 

For a masthead rig - 10 tonnes of back stay load 1 inch behind the mast is the same as 10 tonnes thirty feet back when there is a fore stay acting in a opposing force. So all forces are transferred down the mast.

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Ok so you are saying that a shroud base 1m wide puts the same compression as one thats 3m wide when the boats at max stability?

if that was the case everyone would have their chainplates 0.5m from the mast!

Well yes. But the 3m will offer more sideways resistance.

 

Compression on the mast will be the same. But boats have gone wider to offer more sideways support.

 

They have also gone to longer spreaders for the same reason... to hold the mast up and in column.

What do think the loadings are on the mast step of a unstayed cat rig.

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so snouting into the back of a wave at 20kts with the forestay lying on the foredeck, you are saying that you would be happy with the backstay 1inch back from the mast?

I fail to see what diference it makes masthead or fractional.....

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Ok so you are saying that a shroud base 1m wide puts the same compression as one thats 3m wide when the boats at max stability?

if that was the case everyone would have their chainplates 0.5m from the mast!

Well yes. But the 3m will offer more sideways resistance.

 

Compression on the mast will be the same. But boats have gone wider to offer more sideways support.

 

They have also gone to longer spreaders for the same reason... to hold the mast up and in column.

What do think the loadings are on the mast step of a unstayed cat rig.

 

well yes they are going wider so they can go with lighter mast sections......

a unstayed rig has less compression but is a very heavy section, its all a compromise between support, compression and mast section weight....

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so snouting into the back of a wave at 20kts with the forestay lying on the foredeck, you are saying that you would be happy with the backstay 1inch back from the mast?

I fail to see what diference it makes masthead or fractional.....

 

 

Just let him do it. It's good business for the spar makers.

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This is in a static scenario. And all this changes when sailing and the leeward stay goes slack.

 

Compression comes from downward forces imposed by stays, halyards etc.

 

Fore and aft and sideways support comes from angle of stays and spreaders.

 

A mast will break as soon as sideways or fore and aft support is lost.

 

With no spreaders the compression bends the mast and chord distance from mast base to mast head is lost so the mast bends and stays go slack and bang.

 

I think we are agreeing but being lost in the explanations

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so snouting into the back of a wave at 20kts with the forestay lying on the foredeck, you are saying that you would be happy with the backstay 1inch back from the mast?

I fail to see what diference it makes masthead or fractional.....

 

 

Just let him do it. It's good business for the spar makers.

 

Do what?.

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In an ideal world a stay would intersect the mast at 90deg. But then the boat would have to be infinitely wide. If this was possible there would be no mast compression induced by this stay. It would only offer sideways support. So if you want to have a super light mast then you need to have the chain plates a long way out from the yachts center line. like on an open 60. Their rules let them have deck spreaders, so they effectively end up with the load scenario of a very very wide boat and significantly less mast compression, this is all in the name of a light mast and low CoG. Because that's what the Open 60's want.

 

Compare the open 60 situation to a V5 IACC yacht, where the boat must be heavy for the rule, but they want to sheet the jib in to 5 degrees to sail high in the wind. So they end up with very short spreaders and the stays only a meter from CL to let the jib come in. So they get massively highly loaded stays, horrific compression and very heavy masts. But they get the pointing height that lets them perform to windward. Which was what IACC boats were all about.

 

The net effect is that the Open 60 mast is 70% lighter than the IACC mast for only a couple meters less height. This is solely because of a wider (more ideal) stay angle.

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Totally agree WT. But we weer talking NZ club racing boats and lamp posts.

 

I don't agree that more width and smaller sections is the right solution. Its just the current thinking and where all the money and energy has gone. If they spent as much time and effort on cat rigs then...who knows.

 

ETNZ would be dog tucker with current thin stick many stays thinking.

 

There is a lot to be said for large rotating mast sections with minimal

Stays or no stays.

 

Greg Elliot played with this and many fast cat boats in America swear by it.

 

Compression is the enemy. Cat boats suffer no issues with this. A cat boat done properly with extras would be a scary opposition.

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I don't want to sound too negative as cat rigs do have their advantages for cruising. But they don't scale very well. Over about 10m of mast height the structure in the hull to handle the massive deck collar torque ends up being very heavy. The rig also needs to be very stiff to resist too much fall off to leeward. Over a certain size you get into a never ending loop of diminishing returns with an un-stayed rig. On light weight yachts under 30ft it is economic, however unfortunately the boat will never compete in performance terms with a conventionally rigged boat. Which is a shame, cause a scaled up version of a Finn rig would look really cool.

 

Weight will always be the killer of an unstayed rig. You may be able to pull something back with a super high modulus carbon (+450Gpa) tube, but that fibre is significantly more expensive than normal standard modulus (230Gpa) carbon. So unfortunately the cat rig owner might end up spending a lot of money to prove a point and still get beaten by an identical boat with a stayed alloy rig, who spent half as much money as they did.

 

For the concept to ultimately scale, you'd want a new type of material, maybe 2 or 3 times stiffer (for the same weight) the stiffest carbon fibre currently available. But it couldn't be brittle like UHM carbon is. And it would have to be commercially available and cost effective. Invent that and I'll put a cat rig in Wild Thing.

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Yes we were talking about a local club racer, but do you really think KMs ross 930 rig is a lamp post? I think not.....

 

I dont know what boats you are taking about dude? Maybe 20 years ago they had small sections with loads of stays (Inline IOR 50 rig) but these days its all about bigger diameter lighter sections with less stays and wider shroud bases.

Bigger squaretop mains and no overlapping jibs that are not effected by the wide shroud base.

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