Operation of 2:1 purchase on spinnaker halyard

S

srah1953

Well-Known Member
Joined
21 Jun 2007
Messages
493
Location
Ireland, Carlingford
Visit site
I'm trying to understand something but failing. I have a code 0/gennaker on a torsion rope. It was recommended that I use a 2:1 purchase on the halyard to really tension up the luff – which I haven't done. I understand the function of a block and tackle on a backstay or mainsheet, in that it allows you to tension the line as if you were using a winch. But if, using a winch I have the halyard bar taut, would a 2:1 purchase make any difference to the tension of the torsion rope? Unfortunately although the halyard is bar taut near the winch, there's still a lot of play in the luff.
Any clarifications would be much appreciated.
Thanks.
 
How much is "a lot of play in the luff"? Is it enough to cause you problems when furling the Code 0? Have you actually tried to see how good/bad it is?
I would have guessed that a 10" handle on a single-speed winch would give more than enough tension. Yes, of course putting a 2:1 tackle onto the same winch would give you potentially more tension but, is it absolutely necessary (assuming that your halyard is not too elastic)?
 
PuffTheMagicDragon said:
How much is "a lot of play in the luff"? Is it enough to cause you problems when furling the Code 0? Have you actually tried to see how good/bad it is?
I would have guessed that a 10" handle on a single-speed winch would give more than enough tension. Yes, of course putting a 2:1 tackle onto the same winch would give you potentially more tension but, is it absolutely necessary (assuming that your halyard is not too elastic)?
Click to expand...
The tighter the luff, the higher I can point with the code 0. It's still new so I haven't practiced enough but whereas the halyard is bar taut (to my eye) I can bounce the luff around. I have replaced the halyard with a dyneema mix.
 
srah1953 said:
I'm trying to understand something but failing. I have a code 0/gennaker on a torsion rope. It was recommended that I use a 2:1 purchase on the halyard to really tension up the luff – which I haven't done. I understand the function of a block and tackle on a backstay or mainsheet, in that it allows you to tension the line as if you were using a winch. But if, using a winch I have the halyard bar taut, would a 2:1 purchase make any difference to the tension of the torsion rope? Unfortunately although the halyard is bar taut near the winch, there's still a lot of play in the luff.
Any clarifications would be much appreciated.
Thanks.
Click to expand...

Going from 1:1 to 2:1 will give a noticeable effect, I will try to explain.

Dyneema rope (and wire) have what is called elastic elongation http://www.samsonrope.com/Pages/DemystifyingElongationandCreep.aspx also called stretch.

The rope will stretch under load and go back when the load is removed, elongation increases with increasing load.

A 2:1 halyard have the standing part attached to the spinnaker crane through a block attached to top swivel back to the spinnaker block and down the mast.
With this system the two parts carry 50% of the load each.

There are two important gains with the 2:1 system
1)The pull on the sails head and the torsion rope can be doubled using the same force on the halyard (winch).
2)With the same force on the head of the sail the load on the rope is halved and you get less elongation when loaded up by wind
Or a combination increasing the force on the head of the sail and reducing elongation

If you install a 2:1 system the compound load on the halyard block and standing part attachment can be doubled - make sure your spinnaker crane is strong enough.

You have another option you can use - not as effective but easier to implement (I use this on my code 0 and asymmetric spinnaker)- this will also increase the load on the spinnaker crane/halyard.
A 2:1 adjustable tack easy to rig and adjust, but it you will not get the reduced stretch on the halyard this way.

I set the tack with a little bit of slack, hoist the furled sail winching it tight, winch in on the tack before unfurling.

A picture of my furler with the adjustable tack line that is going back to clutch and winch.
6844D03B-FDF0-4458-8589-DABAFE783F88_zpsjxj7bmgi.jpg
 
They do make a real and useful difference for most "code zero" style sails, reducing the load on the halyard and winch and clutch to half for the same (roughly ignoring friction) luff tension.

As an aside 2:1's also reduce compression loads on the mast.

And as a second aside, the 2:1 halyard generates noticeable windage when sailing upwind with the normal jib, so I have a thin messenger line that I hook to the 2:1 block and hoist, so that is what is exposed to the breeze rather than the 2 halyard strands.
 
Last edited:
srah1953 said:
Looking again at the picture, I notice that you are not using a block at the tack. Does that not create a lot of friction?
Click to expand...
When I made this setup 5 years ago - low friction thimbles was not that common so i used the stainless you can see in the picture.
I was most concerned with chafe from the snap shackle on the rope, than friction.

The original idea from Selden is to have the tack line going into the center of the bowsprit - there are no sheaves there either and use the lower hole as attachment for a bobstay.
I use the center hole for an adjustable bobstay (as I can set the bowsprit in tree different positions).
The distance between the tack line attachment point and the dyneeema strop prevent the furler from turning.
I use the adjustable tack also for my furling asymmetric sail.

One of task on my work list is to make a new dyneema strop with a low friction thimble - but it's not a priority task as it's working ok.

There are of course more friction here than if i had used blocks, but I have not experienced that to be a problem.
The tack line is led back to clutch and halyard winch (ST28) on a 38 feet boat
 
srah1953 said:
What I'm trying to understand (and I'm not saying it isn't the case) is if the halyard is bar taut how would a 2:1 tackle increase luff tension.
Click to expand...
A 2:1 purchase would double the luff tension for a given halyard tension - ignoring the issue of friction losses. That is what 2:1 means. If the tension in the halyard is say 500kg you have two parts of the halyard attached to the luff given a luff tension of 1000kg
 
srah1953 said:
knuterikt said:
The distance between the tack line attachment point and the dyneeema strop prevent the furler from turning.
Click to expand...
Sorry, back again. Can you explain the above comment, please.
Thanks
Click to expand...
:)
Some people claim that you can't have an adjustable tackline with a furler.
That would be true for a 1:1 tack line as the rotation of the furler would twist the tackline (instead of standing still).
With the setup I have a tight tackline form an upside down V that is preventing the furler from rotating.

I could have replaced the snapshackle under the furler with a block to reduce friction but the snapshackle give me the flexibility to use the same furler in different roles/places.
It's used for:
Code 0
Asymmetric spinnaker (with the AFX kit you see in the picture)
A small solent sail set inside the head stay, set on a pad eye on deck (with a turnbuckle below deck to transfer load to the head stay chainplate) and 2:1 halyard.

I upgraded my furler this year with new anti torsion rope and new furling line
It was a noticeable improvement, it has been a great development in anti torsion rope since i bought the AFX kit.
The furling line is a new developed line for this purpose, the old one (three yo) had "grown" in size since new adding friction when furling/unfurling, time will show how it is new rope stands with age.

6844D03B-FDF0-4458-8589-DABAFE783F88_zpsjxj7bmgi.jpg
 
estarzinger said:
And as a second aside, the 2:1 halyard generates noticeable windage when sailing upwind with the normal jib, so I have a thin messenger line that I hook to the 2:1 block and hoist, so that is what is exposed to the breeze rather than the 2 halyard strands.
Click to expand...
Can you explain how you have the 2:1 halyard set up. I would have thought that the end of the halyard would be fixed permanently at the top of the mast then run down to a block fixed at the top of the sail, then back up, through the masthead sheave and back down inside the mast to the winch. A system like this wouldn't allow for a messenger line.
Thanks
 
srah1953 said:
I'm trying to understand something but failing. I have a code 0/gennaker on a torsion rope. It was recommended that I use a 2:1 purchase on the halyard to really tension up the luff – which I haven't done. I understand the function of a block and tackle on a backstay or mainsheet, in that it allows you to tension the line as if you were using a winch. But if, using a winch I have the halyard bar taut, would a 2:1 purchase make any difference to the tension of the torsion rope? Unfortunately although the halyard is bar taut near the winch, there's still a lot of play in the luff.
Any clarifications would be much appreciated.
Thanks.
Click to expand...

If the halyard is winched bar taut, and the luff is slack, perhaps the splice on the halyard is jamming on the sheave, so you are not tensioning the luff?
 
srah1953 said:
Can you explain how you have the 2:1 halyard set up. I would have thought that the end of the halyard would be fixed permanently at the top of the mast then run down to a block fixed at the top of the sail, then back up, through the masthead sheave and back down inside the mast to the winch. A system like this wouldn't allow for a messenger line.
Thanks
Click to expand...

Code zero type sails are easily removable, and when not in use often stowed below of in a deck bag. The block "fixed" to the head of the sail, actually clips to the sail with a tylaska's shackle. So if you have any upwind work, or want to save the sail from UV exposure, you drop it and stow it. Then most people leave the 2:1 block clipped somewhere down near the deck, and you have windage from both strands of the halyard. Instead I essential replace the sail with my messenger line. I clip it to the 2:1 block and hoist the block to the masthead and tie down the other end, so I only have a very thin piece of windage. It also saves the halyard from UV exposure.

On another issue discussed above . . . The rotating of the furling drum. mine is set on a single tack line. To stop it from rotating around that line, instead of the triangulation underneath, I simple tied a piece of bungee cord to the side of the drum, which I clip to the pulpit. That properly orients the drum and prevents it from rotating (around the tack line . . . you obviously want it to 'rotate internally').

I might comment that I have three of these style sails - a 'real' code zero (actually it is not 'real' as it does not measure in for racing, but is the same size and set for the same purpose), a 'blast reacher', which I more often use as a downwind 'twin' to my working jib than actually as a blast reacher, and a nylon downwind 'gennaker' cut sail (except the leach is straighter). I have a fractional rig and this system is really really convenient for getting extra headsails out there.
 
Last edited:
You must log in or register to reply here.

Share this page

Top