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Old 01-04-2011, 20:58   #16
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Re: 42' Leopard - do I really need a double halyard?

Funny, I have a single part halyard, have been considering switching to a two part...

I have a 55m2 fully battened main, which weighs around 80kg. I can hoist it by hand to around the first reefing point, then have to winch.

Raising the sail isn't really the reason I'm thinking of going two part though - its getting sufficient luff tension when the breeze is fresh. Sometimes I really have to put some weight on the winch, to the extent I wonder about how long it will last.

Might be something else to consider.
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Old 02-04-2011, 08:22   #17
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Re: 42' Leopard - do I really need a double halyard?

Good point about the luff tension in a blow. Haven't tried it in any real wind yet - don't get much of that around the BVI's!

The other alternative would be to put the 2:1 purchase on the reefing points rather than the sail head (kind of like a Cunningham). At least it is more accessible if it decides to go wrong, which you definitely don't want in a blow!
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Old 10-11-2011, 07:18   #18
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Re: 42' Leopard - do I really need a double halyard?

I've used the standard 2:1 halyard on our Leopard 42 for 8 years now and never a problem with the blocks or twist in the halyard. The fully battened main is quite heavy - I want the 2:1 purchase. In fact, I've bought a WinchRite to make raising the main less of a workout.
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Old 14-11-2011, 10:41   #19
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Re: 42' Leopard - Do I Really Need a Double Halyard ?

Hi JamuJoe,

Interesting. I wonder if either you are using smaller blocks than I did, or else maybe your main luff is cut shorter. Though ours was built by Doyle Barbados, so should be the standard size with which they supply all the Moorings' boats.

Actually, we quite like the single purchase. Main goes up much quicker, making it easier to time it to get through the lazyjacks, and then it is only a bit of winching to get the rest of the way.

BUT, on a reach with full main, we are now getting problems with the halyard chafing against the side plates at the top of the mast. I guess with the block up there, it held the halyard more centrally and, in any case, the block was there preventing chafe.

So, seems we can't win. Still trying to figure out a solution to the chafe as I actually would prefer to not go back to the 2:1.

Any chance of you posting a picture of what block you are using on the head of your main? Would be interesting to see if it is in fact smaller than what we had, which was, if I remember right, a Barton series 7.
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Old 18-11-2011, 15:33   #20
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Re: 42' Leopard - Do I Really Need a Double Halyard ?

Be careful about your mast, the compression that the pull from the mainsail contributes with is increased by 30% if you remove the 2:1 purchase!

On smaller beach cats you use a halyard stop for the main sail and sometimes 3:1 purchase on the jib to reduce compression on the mast.

/hakan
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Old 18-11-2011, 17:14   #21
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Re: 42' Leopard - Do I Really Need a Double Halyard ?

Noel,
I just don't recall the size of the head block, and won't get to the boat in Isla Mujeres until January. I haven't changed it since phase-out, so it should be the 'standard' for a Moorings 4200. I understand wanting to hurry the hoist past the lazyjacks - our solution for that annoying hangup on the batten ends is to raise the main while at anchor and slack the lazyjacks and pull those lines to the mast.
Like your web site. I've been pestering you with the questions re: rigging for a spinnaker.
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Old 19-11-2011, 02:41   #22
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Re: 42' Leopard - Do I Really Need a Double Halyard ?

Herkam,

Can you please explain the physics for why you think the compression will be higher? The compression on the mast is equal to the tension in the main luff - plus, or course, the tensions from the shrouds, stays, and forestay.

Having a purchase in the main halyard decreases the tension in the halyard rope, but it does not decrease the tension on the mainsail luff. It does decrease the tension (force) on the masthead sheave, but that is because the tension is spit between that sheave and the point at which the top end of the halyard is tied off. Add them together and you get the same downward force as you would with a single purchase. The 2:1 does admittedly put less tension on the halyard clutch, but so far it seems to handle it fine.

JamuJoe - ah, it is you with the spinnaker, eh? Hope I am being of some help. I think ours was probably the standard block too, so I can only think that maybe our luff is just an inch or two longer. Yes, I could loosen the lazyjacks, but I am too lazy to do that! If I could find a smaller diameter block, it would probably work on the 2:1 again - but as I said, I rather like the 1:1 now!
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Old 19-11-2011, 15:45   #23
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Re: 42' Leopard - Do I Really Need a Double Halyard ?

If you look a bit further down the mast with a 2:1 purchase on the halyard you end up with one sail luff with force F and then one halyard with force F/2, the sum that compresses the mast is 1.5F. If you remove the purchase you end up with sail luff with force F and a halyard with force F, the sum of forces that compresses the mast is 2F.
But as you said, this is just one of many forces that tries to compress the mast so changing from a 2:1 purchase to no purchase will not make that big differance on a cruisng multihull.

On small racing cats, for example the A-class I race, we use a 12:1 downhaul that I pull all I can manage from trapeze to bend the mast and alter the shape of the sail and then a 8:1 mainsheet to get the sail sheeted proberly. This loads this thin walled carbon mast (9.5 meters long and 12 kg weight) alot! If I would use a halyard instead of a halyard lock the mast would for sure break due to compression. The A-class don't use jib or gennaker, just one mainsail.

/hakan
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Old 19-11-2011, 19:19   #24
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Quote:
Originally Posted by herkam
If you look a bit further down the mast with a 2:1 purchase on the halyard you end up with one sail luff with force F and then one halyard with force F/2, the sum that compresses the mast is 1.5F. If you remove the purchase you end up with sail luff with force F and a halyard with force F, the sum of forces that compresses the mast is 2F.
But as you said, this is just one of many forces that tries to compress the mast so changing from a 2:1 purchase to no purchase will not make that big differance on a cruisng multihull.

/hakan
The "F" on the luff remains unchanged. With a 2:1 you have F/2 on two lines which when combined = F. You don't eliminate forces with extra purchase. Imagine you and I standing on top of the mast. You hold one line and I hold the other. There is no way I am holding F=1 and you are holding F=1/2. We each hold F=1/2. The sail headplate shackle or turning block holds F. The mast holds (F/2)*2=F.

It may be obvious to point out that the compression we are talking about is limited to the mast between the luff ring, and the mast head and the mast base sheeve. i.e it is not transferred to the deck except the horizontal load on the winch and clutch. Because this force is aligned with the aft of the mast there is almost no bending force - ok the moment arm is equal to the sheeve diameter. With a 2 inch sheave probably around 400 inch pounds with a 120lb main hauled tight. Of course this is different than shrouds, forestay and backstay which all contribute significant bending moment. In other words I don't see a scenario where halyard tension will bend or break a mast. Deck hardware and sheeves will break first.

By changing from 2:1 to 1:1 you increase F on the halyard clutch and also on the masthead sheave, mast base sheave and winch, which may be a consideration depending on the size and quality of this hardware. If you like 1:1 and the hardware can handle it and you can solve the chafe then go for it.

Personally I would figure out what was wrong with the previous setup and my gut tells me that when the luff dimension was taken for the new main, they forgot to allow for the block and the luff is too long. In this case you are probably stuck with the 1:1 until next sail change.

Rgds
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Old 20-11-2011, 06:04   #25
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Re: 42' Leopard - Do I Really Need a Double Halyard ?

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Originally Posted by Ex-Calif View Post
The "F" on the luff remains unchanged. With a 2:1 you have F/2 on two lines which when combined = F. You don't eliminate forces with extra purchase. Imagine you and I standing on top of the mast. You hold one line and I hold the other. There is no way I am holding F=1 and you are holding F=1/2. We each hold F=1/2. The sail headplate shackle or turning block holds F. The mast holds (F/2)*2=F.
Rgds
You do eliminate forces by using purchase, why would we otherwhise use these massive block systems for the main sheet?
Compression is a big thing for masts and reducing it makes the mast happier! Why would Hobie bother to put halyard lock on the main and a 3:1 purchase on the jib halyard on a simple boat as the Hobie 16? answer to get the mast to survive! Sometimes they break anyway....

If the force is F that is needed to keep the sail in place at the mast head, the compression on the mast will be 2xF with no purchase and 1.5xF with 2:1 purchase and only 1xF with a halyard lock (which is quite messy to deal with on a cruising multihull when it gets stuck....)

Don't bother with the mess at the mast head, focus on the lines a bit further down and calculate the forces there.
There is only one line going down along the mast and with a 2:1 purchase it has the force F/2 instead of F where F is the force on the luff, so you get a reduction of compression.

If you want to test this with an experiment, take a scale for fishing and tie it to something at 1.5 meters height to get a godd reading height. Put one block on the scale, tie a line on a weight on the ground and through the block and then pull dowwards until the weight is lifted, check the reading on the scale, it should be 2 times the weight that you just lifted from the ground.
If you put another block at the weight and then tie one end of the line at the scale and lead it down to the block at the weight and then up to the scale and through that block and then pull downwards until the weigh is llifted you will only need to pull with half the weight due to the purchase of 2:1 and the scale will read 1.5 time the weight. The only forces pulling at the scale is the weight and your pull in the line of 0.5 times the weight.
You can make the final test and tie a loop on the line and just hang the weight on the scale, it will then read the same as the weight (this is a halyard lock)
/hakan
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Old 20-11-2011, 16:04   #26
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Quote:
Originally Posted by herkam

You do eliminate forces by using purchase, why would we otherwhise use these massive block systems for the main sheet?
Compression is a big thing for masts and reducing it makes the mast happier! Why would Hobie bother to put halyard lock on the main and a 3:1 purchase on the jib halyard on a simple boat as the Hobie 16? answer to get the mast to survive! Sometimes they break anyway....

If the force is F that is needed to keep the sail in place at the mast head, the compression on the mast will be 2xF with no purchase and 1.5xF with 2:1 purchase and only 1xF with a halyard lock (which is quite messy to deal with on a cruising multihull when it gets stuck....)

Don't bother with the mess at the mast head, focus on the lines a bit further down and calculate the forces there.
There is only one line going down along the mast and with a 2:1 purchase it has the force F/2 instead of F where F is the force on the luff, so you get a reduction of compression.

If you want to test this with an experiment, take a scale for fishing and tie it to something at 1.5 meters height to get a godd reading height. Put one block on the scale, tie a line on a weight on the ground and through the block and then pull dowwards until the weight is lifted, check the reading on the scale, it should be 2 times the weight that you just lifted from the ground.
If you put another block at the weight and then tie one end of the line at the scale and lead it down to the block at the weight and then up to the scale and through that block and then pull downwards until the weigh is llifted you will only need to pull with half the weight due to the purchase of 2:1 and the scale will read 1.5 time the weight. The only forces pulling at the scale is the weight and your pull in the line of 0.5 times the weight.
You can make the final test and tie a loop on the line and just hang the weight on the scale, it will then read the same as the weight (this is a halyard lock)
/hakan
Of course if you attach the scale inline between the block and the working line you will read the tension on the line. We are talking about the mast compression loads so you must insert any scale between the shackle and the head plate of the sail (i.e. Outside the block system) to read the compression force on the mast.

The A class you mentioned does have a 16:1 cuningham. The blocks are contained in the mast near the base. The reason there is a 16:1 system is so the driver can gain mechanical advantage and specifically pull a lot more tension on the sail than he otherwise normally could - its hard to reach a winch from the trapeze. The sail on the A Class is a lot lighter than the sail we are talking about here so why would the a class need a 16:1 purchase - ans) specifically to pull a hell of a lot more load and bend the mast. Similar story for the 8:1 mainsheet, however the mainsheet has the advantage of being several feet aft of the mast centerline.

You are confusing what you feel when you apply mevhanical advantage be it 2:1, 8:1 or 16:1 with what loads are actually going into the system.

Pop quiz - I pull the lazy end with 100lbs of F - what force is felt on the working end with 2:1? 8:1? And 16:1?

Once again you don't eliminate forces with a block system. In fact you multiply them.
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Old 20-11-2011, 18:01   #27
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Re: 42' Leopard - Do I Really Need a Double Halyard ?

Herkam,

You have blinded me with science, but I always assumed the halyard lock at the top of my mast was to eliminate halyard stretch rather than decrease mast compression?

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Old 21-11-2011, 00:51   #28
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Re: 42' Leopard - Do I Really Need a Double Halyard ?

Sorry about all sciense...
You are absolutely right that you gain remove stretch by using a halyard lock, but you also remove 50% of the compression on the mast.

/hakan
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Old 21-11-2011, 00:57   #29
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Re: 42' Leopard - Do I Really Need a Double Halyard ?

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Of course if you attach the scale inline between the block and the working line you will read the tension on the line. We are talking about the mast compression loads so you must insert any scale between the shackle and the head plate of the sail (i.e. Outside the block system) to read the compression force on the mast.
As I said earlier, look a couple of meters (feet) down the mast and there you can easily identify what forces that compress the mast. If you insert the scale between the head plate and the mast head you only get the forces from the sail, you must add the force you have on the halyard line also (which can be the same as the force from the sail or lower if you use purchace)

/hakan
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Old 21-11-2011, 16:58   #30
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Originally Posted by herkam

As I said earlier, look a couple of meters (feet) down the mast and there you can easily identify what forces that compress the mast. If you insert the scale between the head plate and the mast head you only get the forces from the sail, you must add the force you have on the halyard line also (which can be the same as the force from the sail or lower if you use purchace)

/hakan
Having shared the math twice I will retire. However I suggest you get with a math and physics guy.

The answers are 200, 800 and 1600 pounds at the head of the sail which is transferred to the tack and depending on the the shape and stifness of the mast will bend it or not.

Conversely to get 400 lbs of luff tension you would pull 200, 50 and 25 lbs respectively. Really, its how this stuff works.
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