2:1 halyard reduces the load on the mast?

[Merit 25]

I'm trying to figure out how a 2:1 halyard reduces the load on the stick. For the life of me, I can't see how. On another site the diagram below was offered, but the diagram still shows 100 lbs on the rig.

Can someone explain how a 2:1 reduces the load on the stick?

 

[The Advocate]

Oh no..........

 

[CasualObserver]

Seriously????..................

 

[barnone]

Has this been addressed ad nauseam already?

Alright I'll bite.

Visualize a halyard lock at the top of the mast. With halyard locked it's 1:1 compression on mast to down force on halyard from Main.

Now with a 1:1 halyard, the halyard sheeve is a block and this creates a 2:1 purchase, so you actually have twice the compression force on the stick as halyard tension.

With a 2:1 halyard, the key point is that the tail of the halyard is tied up top at the halyard sheeve. So that means that the moveable part going over the sheeve is creating Double the compression force of half the load it takes to haul the halyard at deck level. So basically you get a 1/4 (25%) reduction in compression in the mast. Shit is that right? Someone correct me. I want to say 1/3 reduction but math says 1/4. Yeah it's 25% reduction.

(.5 x 2) + .5 = 1.5 (2:1 halyard) vs 2 for (1:1 Halyard)

Way less dramatic than a halyard lock or an internal halyard lock like on the Volvos, but it makes a difference for sure in performance rigs.

So Halyard lock is 50% reduction in compression

2:1 Halyard is 25% reduction.

If the second part of the 2:1 also went over the sheeve and down to the mast base then it would be the exact same compression as a 1:1 halyard.

 

[kokosir]

solid.. draw it for your self if you need

 

[P_Wop]

2:1 halyard, PLUS a lock, almost halves the weight of that piece of string dangling down inside the stick when you're sailing, as you can make most of the halyard smaller and/or naked.

And yes, we've done this before. But I feel like being nice today.

 

[knobblyoldjimbo]

barnone, NO a single block means that for every foot you pull the halyard the sail goes up a foot, therefore it's a 1:1.

 

[Finals Dodger]

If the mainsail is exerting a 100kg force on the halyard, and it is a 2:1 system with one end terminating at the masthead, each external part of the halyard is experiencing 50kg of vertical load (total 100kg). The internal part of the halyard is also experiencing 50kg of vertical load, making the total compression force 150kg.

If you just had a 1:1 halyard, or a 2:1, but with both ends of the halyard terminating at the base of the mast, the external and internal part are both experiencing 100kg, making a total compressive force of 200kg.

If you have any sort of lock at the top of the mast, the external halyard will still carry 100kg, but the internal halyard is untensioned, making the total compressive force just 100kg.

 

[Presuming Ed]

barnone, NO a single block means that for every foot you pull the halyard the sail goes up a foot, therefore it's a 1:1.

From the point of view of hauling up the sail, yes, a single block and dead ending the halyard to the sail is a 1:1 purchase.

However, from the point of view of trying to pull the top of the mast down towards the heel, a single block at the masthead gives a 2:1 purchase - the total compression on the mast is the sum of the tension in the halyard and the tension in the sail.

 

[bgytr]

I'm trying to figure out how a 2:1 halyard reduces the load on the stick. For the life of me, I can't see how. On another site the diagram below was offered, but the diagram still shows 100 lbs on the rig.

Can someone explain how a 2:1 reduces the load on the stick?

Draw the free-body diagram, simple statics question from Physics 1, or engineering statics class.

If P is the downward force generated by the mainsail head, then a 2:1 halyard setup with the halyard cleat down on the deck causes a compression force of 1.5P. A standard 1:1 with halyard cleat on deck causes a total compression force of 2P. So yes, the 2:1 lightens the compression by 25%.

 

[UniGor]

Draw the free-body diagram, simple statics question from Physics 1, or engineering statics class.

If P is the downward force generated by the mainsail head, then a 2:1 halyard setup with the halyard cleat down on the deck causes a compression force of 1.5P. A standard 1:1 with halyard cleat on deck causes a total compression force of 2P. So yes, the 2:1 lightens the compression by 25%.

And to take it a step further: a 2:1 with a lock will reduce the compression force to P (0.5P from the dead end of the halyard + 0.5P from the masthead sheave)

The real advantage for the 2:1 comes from the reduced load (0.5P) in the halyard itself and the deck level blocks, winches etc.

 

[Merit 25]

I see, I was forgetting that the load making a 180* turn around the masthead sheeve double the original load. It makes sense now, thanks everyone.

 

[my nuts]

I think there's a confusion between compression, halyard tension, and luff tension.

regardless of how many strings, blocks, locks, shackles, etc. there are at the top or bottom of the mast, the sail will still exhibit the same luff tension on the stick, call it P.

with a lock, your compression load is equal to your luff tension load, P.

with a n:1 lock, your compression load is equal to your luff tension, P.

with a 1:1 halyard, the mast head sees P from the sail, balanced by P from the halyard, for a total of 2P

with a 2:1 halyard, again, you have P from the luff of the sail, balanced by 0.5P from the halyard, for a total of 1.5P

hope this helps

 

[Flying Wasp]

Is mast compression the real benefit of the 2:1 setup or is it sail shape?

I thought the primary advantage behind the 2:1 being able to get suitable tension for square-headed mains and when used forward, for being able to get enough luff tension for a Code Zero.

 

[barnone]

Well when you talk to a mast designer they are concerned about compression. Look at the Volvo boats where they have a gennaker, staysail and mainsail all adding internal compression. Worse when the boat smacks into a wave at 30 kts, there is a dynamic component to all that compression as well and that is way more than static luff tension.

Mains are usually tensioned from the cunningham anyway so 2:1 has no advantage. Code zero, you always have a winch so what is the advantage of 2:1 for tensioning really. It takes longer to hoist and drop. Therefore generally you go 2:1 on the main first, then decide if you want it for anything else. Works well for a rollerfurler that rarely gets dropped.

There is advantage in that the line diameter can be smaller so less halyard weight in the mast, but this seems rarely to make a difference because most of the time you use the same or almost the same diameter halyard for handling and chafe resistance.

 

[beauvrolyk]

We use a 2:1 main halyard because with it a "normal" person can haul the main up without a winch. With a 1:1 halyard it takes a winch for the last 15' (or a really big person). Our mast is so freeekin' overbuilt the compression isn't an issue.

 

[my nuts]

as with practically every design choice, there are multiple advantages and disadvantages, compression, halyard loads seen by deck hardware, number of failure points, hardware weight, halyard line length & diameter, etc. it is up to the owner, rigger, engineers, etc. to determine the best choice based upon all of these factors.

 

[BalticBandit]

Mains are usually tensioned from the cunningham anyway so 2:1 has no advantage.

Just to clarify - since I had to read this twice for it to make sense - with squaretopped mains I can easily haul the main up the mast with 1:1 halyard by simply leaving off the vang, sheet and cunno tensions. IOW the primary vertical tension on the mainsail luff is created by the sail controls that pull on the bottom of the sail (including boomless mains here) - namely the cunno, vang and mainsheet. So "generating enough tension for squaretopped mains" is not a HALYARD issue. Which means it is either a mechanics issue (as per Beau) or a mast compression issue. Since high performance skiff masts (and volvo etc) are designed fairly close to tolerances both for shape control and for weight aloft, this becomes a significant factor

 

[hawaiiseadog]

I got super excited about doing this, and then I came across the price of the hardware and got super unexcited......

http://www.apsltd.com/c-768-antal-twin-halyard-block.aspx

I know that the cool sailing "jewelry" always cost an arm and a leg, but does anyone else feel that between $300 and $600 for this tiny piece of hardware is way to much??