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Old 24-01-2021, 10:48   #1
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Cunningham versus Main Halyard and other assorted wonderings

I get what it does, but is a Cunningham really necessary? Why not just tighten the luff on the main with the halyard? The halyard is right there on the cockpit winch while the Cunningham is forward on the mast requiring you to go up there to use it.


Boom vangs are another mystery. The main sheet attaches to the traveler so one could assume that it exerts downward force on the boom when tightened.

Now, purists will say that when you let the sheet out on a downwind, then there's no force holding the boom down, but wouldn't an arc shaped traveler track be a better option? The sheet would be tight, the traveler would be on that side and no accidental jib could occur since everything would be short and tight. You wouldn't even need a preventer.

Or do sailors just like lots and lots of ropes, I mean lines, all over the place to pick up, neaten up, coil up, hang up, stow all over the boat, trip over, and replace on a regular basis?
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Old 24-01-2021, 11:01   #2
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Re: Cunningham versus Main Halyard and other assorted wonderings

I can't speak for the cunningham, but the geometry of the boom vang is such that it exerts the same downward force, and limits the boom's vertical movement, on all tacks while the mainsheet does not. The boom vang is attached to the mast, so the triangle of mast/boom/vang is the same as the boom swings. The mainsheet, even on a traveler, only exerts downward force close hauled or nearly close hauled. With the boat running downwind, there is no downward force, and lots of mainsheet out to allow an up and over jibe. I still remember one of those on a 40' Rhodes in 1962. Awesome. Broken battens. Scary as hell. Damned dangerous. Don't go there. Never again.
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Old 24-01-2021, 11:27   #3
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Re: Cunningham versus Main Halyard and other assorted wonderings

You're right, the Cunningham is optional for cruisers, but to my mind the vang is not. It's when the boom is out over the rail, when the mainsheet has no downward pull, that the vang's benefits are obvious. The length of the curving traveller still wouldn't be practical especially for a cruiser, though there are old racing boats and multihulls that have those I've seen. Some folks run the main all the way up so the headboard is in contact at the top. Then the Cunningham, which could be rigged back to the cockpit is useful.
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Old 24-01-2021, 11:31   #4
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Re: Cunningham versus Main Halyard and other assorted wonderings

I think Cunninghams are an artifact of relatively stretchy halyards where applying more tension might just stretch the halyard rather than actually raise the sail a hair - the friction of the sail slides/bolt rope wouldn’t let things move. With modern, low/no stretch fibers and super slippery slides they may be less necessary.

For the Vang question, many catamarans don’t have a Vang because the traveler is wider, the rigging gets in the way of a main being way out, and the apparent wind gets moved forward in many cases. In that use the main sheet may only be adjusted +/- a meter or less to control twist/shape. This is harder to accomplish on a monohull, even with mid-boom sheeting. Whether or not a Vang is needed/desirable depends entirely on the geometry of the specific boat.

You can always rig a preventer instead of a Vang, but those come with their own set of issues/decisions.
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Old 24-01-2021, 12:04   #5
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Re: Cunningham versus Main Halyard and other assorted wonderings

It is much easy to harden a Cunningham than a main halyard. You should luff in order to harden a main halyard, that is not necessary with a Cunningham.
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Old 24-01-2021, 12:29   #6
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Re: Cunningham versus Main Halyard and other assorted wonderings

Quote:
Originally Posted by Dsanduril View Post
I think Cunninghams are an artifact of relatively stretchy halyards where applying more tension might just stretch the halyard rather than actually raise the sail a hair - the friction of the sail slides/bolt rope wouldn’t let things move. With modern, low/no stretch fibers and super slippery slides they may be less necessary.>>>>

There is great validity to this.


However, even with non-stretchy halyards, there are times when one wants to loosen the halyard for mainsail shape. Getting it tight again requires luffing, as jackdale points out. So, in this case, after you loosen the main halyard, it is much easier to use the cunningham.


To the OP, run your cunningham aft. That answers your non-functional system with the cunningham only at the mast. Who does that?
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Old 24-01-2021, 12:41   #7
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Re: Cunningham versus Main Halyard and other assorted wonderings

When racing, the height of the mainsail hoist is limited by the “black band” on the mast, and it’s against the rules to hoist the sail above that. So the sail is made to always reach that band, even if luff tension isn’t required. If luff tension is then required, the Cunningham is used instead of hoisting the sail further, which would be a rules infraction.
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Old 24-01-2021, 12:52   #8
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Re: Cunningham versus Main Halyard and other assorted wonderings

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When racing, the height of the mainsail hoist is limited by the “black band” on the mast, and it’s against the rules to hoist the sail above that. So the sail is made to always reach that band, even if luff tension isn’t required. If luff tension is then required, the Cunningham is used instead of hoisting the sail further, which would be a rules infraction.
And that too.
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Old 24-01-2021, 13:49   #9
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Re: Cunningham versus Main Halyard and other assorted wonderings

The Cunningham was invented by Briggs Cunningham. It is used to pull the draft of the sail forward after the wind picks up and pushes it too far towards the leech. It is designed so that when a sail is hoisted all the way up - the halyard can't go any further (and you do NOT want stretchy halyards, btw.) - and the downhaul is down as far as it can go,(there's a black band for the downhaul too) the sail is spread out as far as it can be - the Cunningham can still pull down on the luff of the sail and create a more efficient shape. ) If you don't like using it, have your sailmaker make the sail a bit shorter on the luff. You'll then have space to pull the halyard or downhaul tighter when the wind picks up. You'll have less sail area in light air though, since your sail will be smaller than it could be.
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Old 24-01-2021, 18:03   #10
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Re: Cunningham versus Main Halyard and other assorted wonderings

@ Rob P,

Our experience has been that it is not uncommon for us to want to gybe sailing off the wind, in fairly large seas. Therefore, we have a double vang system rigged all the time, ready to go. The control lines are led aft to the cockpit, to our secondary winches, so that we can ease the main across under control, and vang it down on the new side (where pulling it down also relieves chafe on the swept back shrouds), and not have it get away from us. These lines need to have some stretch, but not very much. For us that worked out to being nylon double braid on the 30 footer; and polyester 3 strand on the 36, and now, polyester double braid on the 46 footer. The present boom is ~ 19 ft, and it is not something you would want out of control, with a ~ 580 sq. ft. sail. Bigger boats generate bigger forces.

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Old 24-01-2021, 18:17   #11
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Re: Cunningham versus Main Halyard and other assorted wonderings

Back in the good old days the boom was on a track so it could be raised and lowered putting different tension on the luff to vary sail shape in differing wind conditions. Sails were cut short of full length restricted by the black bands. Unfortunately that meant the hoist of the sail had to be cut short until Cunningham invented the cunningham. Fortunately it works for both the racing crowd as well as the cruisers. The cunningham is run back to the cockpit on my Sabre so no different than any other of the mainsail control lines. BTW stretchy halyards were never the issue. Halyards were wire with very limited stretch on almost all boats and certainly on any boat that was raced.
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Old 24-01-2021, 18:52   #12
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Re: Cunningham versus Main Halyard and other assorted wonderings

The mainsail can already be at "full hoist", ie: the top of the mast - so it's just not physically possible to pull on any more main halyard tension.

That's so you can get maximum sail area and maximum sail depth from that size mast and sail.

When you want less than maximum, for sailing upwind, for heavier air, etc, you use the Outhaul and the Downhaul / Cunningham (and maybe other controls too, Vang, Backstay, etc) to flatten the sail.

As an example, Team Ineos UK had a problem with the Cunningham adjustment on their AC75 before the America's Cup Round Robin against Prada on Saturday.

They couldn't just use more main halyard tension either - because it doesn't work like that, or at least it's not meant to.

So they set and locked off the Cunningham at a 'guesstimate' position, which was 'about right' for upwind, but meant they couldn't get as much power out of the sail downwind, and couldn't even really 'mode' the boat properly upwind either.

In fact in puffy conditions the Cunningham would be in constant adjustment on an AC75 because it really has a big effect on the shape and power of the sail.

It's the same on a cruising boat too, but I suspect that many here don't bother to ease any tension and deepen the mainsail on a downwind leg, it's more set and forget.

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Old 25-01-2021, 08:24   #13
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Re: Cunningham versus Main Halyard and other assorted wonderings

I still don't get it.

If the Cunningham is used to pull the luff downward to change the shape of the sail, then wouldn't that mean the tack is too high to begin with? Otherwise, there wouldn't be any space on top of the boom to pull the main down.

And how does all of this affect or work with in-mast furling?





As to the vang, I can see that a curved track wouldn't work for every application. Not all boats would have enough room to mount enough track so the main could go all the way over to touch the shrouds before being trimmed in. Also, the mainsheet would always have to be mid-boom rather than at the rear which could be a problem for a center cockpit. So at least that question is answered after some thinking on my part.


BTW, I don't have a boat. I'm still taking my ASA classes and the only lines to the cockpit in the "learner boat" are the halyards and main/jib sheets. Everything else, vang, Cunningham, etc., requires that I go forward on deck.
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Old 25-01-2021, 09:38   #14
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Re: Cunningham versus Main Halyard and other assorted wonderings

As an ASA instructor, I taught the vang on a close reach.

Put the boat on a close reach about a 55-60 AWA. Now ease the traveler to the lee, and the boom over the traveler, the sail should be trimmed. If not use the AP to change the AWA so the sail is trimmed. If the main sheet is tensioned, it is exerting a downward force on the boom and closing the leech. Effectively replacing the need for a vang. Note the tension in the topping lift.

Note how far the boom is from the center of the boat. Release the vang.

Now move the traveler car to the middle of the boat and keep the boom in the same location relevant to the centerline. If the vang is not tensioned, you will see the topping lift is flopping. Why? Because the boom is higher. To see the effect on the sail, snug the topping lift. You will see how the leech is opened.

If the boat has a dodger, you can also see the boom rise vs the dodger.

WHEW!. Hope this makes sense.
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Old 25-01-2021, 09:44   #15
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Re: Cunningham versus Main Halyard and other assorted wonderings

The mainsail is built so that the tack and head do not touch when raised. You have to have room to stretch the luff as needed. Some boats, like mine, came with a gooseneck on a track and then you have a downhaul instead of a Cunningham to pull the luff down. I don't raise my main all the way to the top because the leech chafes and hangs up on the backstay. I set the tack position on the track and then I adjust the luff tension with the halyard so that even when I have increased tension, the leech still doesn't hang up (too much) on the backstay.

on edit... uh that first sentence didn't make sense did it? I guess you got the idea though.
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