Does 2:1 halyard lessen load on mast head sheave?

[mrybas]

My screacher uses a 2:1 halyard that is not needed for the purpose of hauling the sail up. The tack line is also 2:1 so proper luff tension can be applied with the tack line. If possible I'd like to use a 1:1 halyard.
My question is the 2:1 halyard lessening load on the mast head sheave? The sheave and axle for the screacher is much smaller than the main sails (which is also 2:1 halyard)

Screacher halyard- white red/blue fleck


Compared to main halyard red/yellow

[TJ D]

Hi, the load on the sheave is cut in half with a 2:1, essentially. If you're concerned about loading, it would be good to keep it. Most rigs seem to be 2:1 these days for that application, probably a good idea in any case, if it's already rigged that way. Just some extra line to stow, after all.

TJ

[BobHorn]

I think the load on the line is cut in half but the load on the sheave is the full load.

[sailjumanji]

The load on the sheave is reduced (halved) as the tang at the terminal end of the halyard is taking up load as well. We converted to 2:1 screacher and mainsail halyards on our Corsair tris to reduce the load on clutches. Helped alleviate slippage. Just have to make sure the terminal end at tip of mast is strong enough.

[a64pilot]

Funny, I'd like a 2 to 1 on my code zero, to reduce the forces on the halyard. I believe a 2 to 1 is optimal, you may not like the result of you get rid of it?

[atmartin]

As stated, that set-up halves the load on the sheave.

What's up with that tang though? Now that you have the mast down, any chance you could switch out those sheet metal screws with bolts or, barring that, blind rivets?

[mrybas]

Originally Posted by atmartin

As stated, that set-up halves the load on the sheave.



What's up with that tang though? Now that you have the mast down, any chance you could switch out those sheet metal screws with bolts or, barring that, blind rivets?

I agree the tang is not a great set up. At the least I'll try and get the cap off and through bolt.

Also the tang being on the port side of the mast, when on port tack the swivel chafes against the mast. I guess extending the tang a bit would help, but also shorten the luff. Maybe glue a uhmw patch in the chafe area?



Maybe some kind of soft shackle/swivel to replace the current one?

[savoir]

Why not remove the tang and 2:1 system entirely ?

If the masthead fitting can handle main halyard loads then screecher loads should be easy. The 2:1 tack line can be used to set luff tension.

[atmartin]

It looks like a tricky situation.

If you extend the tang much further, it'll probably just bend and then you're back where you started. I don't see a forestay attachment, so it's a fractional rig? You could put a new tang off of the sheave bolt (may need a longer bolt) for a cleaner lead. That doesn't take the load off the bolt, but it still keeps it off the sheave.

Maybe attach your swivel snap/trigger shackle to something like this:



And things might go easier on your mast. A plastic chafe pad is a good idea. You could also try Protect Tape, if you can find it!

PROtect tapes Nastri e film protettivi Polymer film protective adhesive

[Kiwi.]

Originally Posted by mrybas

My screacher uses a 2:1 halyard that is not needed for the purpose of hauling the sail up. The tack line is also 2:1 so proper luff tension can be applied with the tack line. If possible I'd like to use a 1:1 halyard.
My question is the 2:1 halyard lessening load on the mast head sheave? The sheave and axle for the screacher is much smaller than the main sails (which is also 2:1 halyard)

There are two loads involved, the dynamic load whilst the sail is being hoisted and the static load whilst the sail is up and pulling. Unless you are using a very stretchy halyard (such as nylon instead of dyneema) the only load once the sail is up is a static load that is exactly the same (minus any halyard stretch) as a 1:1 halyard. So no, the 2:1 halyard is not lessening the load on the mast head sheave.

Using a stretchy halyard is always as silly as its sounds. When a halyard stretches under high loads it normally "powers up" the sail, which is exactly not what us cruisers want when we are hit by a big gust. Sheets with a bit of give in them are quite a good idea (don't use nylon!) as when they stretch they "power down" the sail in a gust.

Multi-part halyards have only become popular since the advent of near zero-stretch cordage. (Apologies to the old timers that have been hoisting their gaffs on multi-part halyards since Adam was a boy.) With a 2:1 halyard you can half the cost of the winch pulling the sail up (dynamic load) but once it's up (static load) the top sheave and cleat are getting the full pain.

[TJ D]

Originally Posted by Kiwi.

There are two loads involved, the dynamic load whilst the sail is being hoisted and the static load whilst the sail is up and pulling. Unless you are using a very stretchy halyard (such as nylon instead of dyneema) the only load once the sail is up is a static load that is exactly the same (minus any halyard stretch) as a 1:1 halyard. So no, the 2:1 halyard is not lessening the load on the mast head sheave.

Using a stretchy halyard is always as silly as its sounds. When a halyard stretches under high loads it normally "powers up" the sail, which is exactly not what us cruisers want when we are hit by a big gust. Sheets with a bit of give in them are quite a good idea (don't use nylon!) as when they stretch they "power down" the sail in a gust.

Multi-part halyards have only become popular since the advent of near zero-stretch cordage. (Apologies to the old timers that have been hoisting their gaffs on multi-part halyards since Adam was a boy.) With a 2:1 halyard you can half the cost of the winch pulling the sail up (dynamic load) but once it's up (static load) the top sheave and cleat are getting the full pain.

I'm not an expert, but I don't think that the sheave load is identical regardless of the purchase used. For the sheave load to be identical, the tang would have to take zero load. This is obviously not the case, the tang does take half of the load, or thereabouts, so how is it possible that the sheave still takes exactly the same load as if it were a 1:1 halyard? I'm not a rigger, but this contention does not make sense to me where the attachment point is on the mast.

Willing to be educated...

[thinwater]

High School physics. Very simple.

The load on the sheave is halved. Period. Half the load is on the masthead sheave and half the load is on the dead-end eye or pin. This is true both sailing and hoisting. The head sheave, of course, takes the full load.

Mast compression is also reduced, both hoisting and sailing. In stead of ~ 2x halyard tension it is ~ 1.5 x halyard tension (some adjustment for the trig, which have disregarded). Many performance boats use halyard locks for this later reason, which reduce it to 1x halyard tension (this is not including shroud loads, which are much greater).

Yes, I've had all three sorts.

[Kiwi.]

Originally Posted by TJ D

I'm not an expert, but I don't think that the sheave load is identical regardless of the purchase used. For the sheave load to be identical, the tang would have to take zero load. This is obviously not the case, the tang does take half of the load, or thereabouts, so how is it possible that the sheave still takes exactly the same load as if it were a 1:1 halyard? I'm not a rigger, but this contention does not make sense to me where the attachment point is on the mast.

Willing to be educated...

Yes, it’s not obvious. The key point is the difference between static and dynamic loads. Once everything stops moving in a multipart system the loads are not shared, they are the same. (This does assume zero stretch in the halyard and zero friction in the sheaves.)
If you’re better at electricity than mechanics then the equivalent situation is when a circuit, lets say a 12 volt battery with a 100 ohm resistor wiried between the positive and negative terminals if you measure the voltage on either side of the resistor, one side will be 12 volts and the other side will be zero volts, this is the dynamic situation. If you disconnect the resistor from the negative terminal and re-measure then you will have 12 volts on both sides of the resistor. (The static situation.)
The other example I can give is the difference between torque and horsepower. When motion stops there is no horsepower but there can still be torque and lots of it.

[Kiwi.]

I just thought of another way of explaining it. The force on the sail side of the sheave is whatever the force that the sail is applying, otherwise where is that force going? So the other side of the sheave must have an equal force, otherwise the halyard must be moving.

[Kiwi.]

Originally Posted by Kiwi.

I just thought of another way of explaining it. The force on the sail side of the sheave is whatever the force that the sail is applying, otherwise where is that force going? So the other side of the sheave must have an equal force, otherwise the halyard must be moving.

Remember there is only one halyard going over the sheave,; the multipart is all on the sail side. So the full load of the sail is on the sheave, what else is up there to take the load?