Main downhaul vs. halyard tension (vs. Cunningham) - SailNet Community
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post #1 of 10 Old 06-02-2016 Thread Starter
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Main downhaul vs. halyard tension (vs. Cunningham)

I have a boom with a sliding gooseneck. I have the gooseneck tied to a cleat on the mast and I basically never touch that. I adjust the luff tension with the halyard.

I was talking with another sailor last night and he said no, no, no, never do that. He said you should always raise your main as high as it will go, then adjust luff tension with a downhaul.

I can't really see that there's a difference. I guess the halyard would have more friction since it goes through an extra block, but that's not much of an issue.

What's the standard practice?



On a semi-related issue, how does the effect on sail shape of a Cunningham differ from that of a main downhaul or halyard tension?

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post #2 of 10 Old 06-02-2016
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Re: Main downhaul vs. halyard tension (vs. Cunningham)

I tension the halyard just to where the luff horizontal lines are about to disappear. I have a cunningham with a 4:1 purchase so it is real easy to adjust. The thing about that kind of adjustment is what ever is easiest for you. Really no absolute right way. You just want the draft of the sail to be a little forward of center no matter how flat or deep the sail.
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Re: Main downhaul vs. halyard tension (vs. Cunningham)

The Cunningham exploits a race measurement rule. Racers want the sail as large as possible but are prohibited from hoisting above the black line or tacking below the lower black line. So the sail is made as large as possible for light conditions and trimmed flat by the Cunningham thru a second tack cringle as the wind comes up. Clever...

For non-racers one small advantage is that the Cunningham can be much easier to adjust than the halyard. I think that is about it.

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Re: Main downhaul vs. halyard tension (vs. Cunningham)

.. and the advantage, then, of a sliding gooseneck is you can go to the max hoist, then flatten the sail without the fold at the tack that a cunningham creates.

On our last little race boat, our Quantum main did not have a gooseneck 'tack' fitting. It only had a tack cringle that we hooked the cunningham to. We 'free-hoisted' to the 'black band' and then tensioned the luff with the 'sly pig'. Since the tack was not connected to the gooseneck it was a clean luff too.
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I've broken more then one halyard trying to get that last little bit of tension. Better to use a Cunningham.
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post #6 of 10 Old 06-03-2016
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Re: Main downhaul vs. halyard tension (vs. Cunningham)

I have the same setup with a sliding gooseneck, I hoist the sail, give it a bit of tension and then use the downhaul to control luff tension, this way I'm not jamming the headboard up at the masthead so it's free to rotate properly etc.
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Wink Re: Main downhaul vs. halyard tension (vs. Cunningham)

The functional difference between halyard tension and cunningham tension -

With a bolt-roped sail, halyard tension primarily controls the stretch-out of the bolt rope which allows for precise positioning of the sail's point of maximum draft in a fore/aft relationship. So therefore, halyard tension (beyond getting the sail up and raised) allows the luff to be stretched to its designed length AND correctly position the 'point of where maximum draft' occurs. This is because the bolt-rope is 'bound' to the bolt-rope sleeve/sail at both the head and tack of the sail.
Pull halyard tension ... the luff stretches in luff dimension, the tack stays in place, .... and the clew 'rises'.
'Perfect' halyard tension results when sufficient 'designed' stretch-out occurs .... so that the sail's designed 'tack angle' is met. The tack angle is usually derived from the boat designers requirements - typically most tack angles are in the range to 87-89 for boats with 'straight up' / non-raked masts, less with purposely designed raked masts.
Rx: halyard tension controls - 'weather helm'.

A cunningham's primary function is to aid shaping the (bolt-roped sail's) luff entry shape. The cunningham (cringle) is located well above the binding of the bolt-rope to the sail near the tack. This allows luff material to 'slide' somewhat along the bolt rope near the bottom and mid panels. Tensioning the cunningham will cause the luff to become 'more rounded' (for better aerodynamic effect in the higher wind ranges where the airflow 'can' stay 'attached' to the lee side at the luff for better energy transfer from the wind to the sail). The majority of the developed 'suction peak' (Bernoulli) occurs along and quite near the 'luff entry'!!!
When tensioned by a cunningham, the luff shape starts to become 'more rounded' and to a lesser extent the mid section of the sail becomes more 'flattened'. When over tensioned, the sail will develop a crease (girt) just behind or at the luff.
Rx- the cunningham is more of a 'speed control' due to its better sail 'flattening' of the mid section AND luff 'rounding' ability because the functional binding to the bolt rope is ONLY from the sail twine binding at the head of the sail.

Sliding goose necks.
Were an outgrowth from when wire halyards were popular when racing. The sail was raised, the wire was attached to the mast via a ball swaged on the wire and the swaged ball was inserted into a 'hook' or 'jaw cleat'. This allowed the sail to be raised 'precisely' to correct (racing legal) position of the 'black band' at the top of the mast - 'precisely'. Then, to obtain correct bolt rope tension the sliding gooseneck was pulled down and then locked into position according to 'helm pressure' when beating for each days wind strength and sea-state.
IF the sail's luff dimension with the halyard 'locked' in place exceeded the lower 'black band' then the cunningham was ALSO used to 'help' additionally tension the luff ... by stretching out the sail material along the luff; but, NOT the bolt rope, so that the sail's 'as raised' dimension was at or less than the (racing legal) dimensional space between BOTH black bands.

Racing 'cuts' vs. cruising 'cuts'.
The above discussion applies only/principally to dacron sails made with 'pre-loaded' (shortened) bolt-ropes. With plain vanilla woven dacron 'cruising' sails, since about the year ~2000, bolt rope preload has essentially been abandoned - and the shape you buy is the shape you get. You just raise such a sail and ignore any 'precision or high performance' shaping possibilities ----- but you still 'can' overstretch the bolt-rope to aid in lessening and control of 'weather helm'; but the sail will not develop its 'as designed' shape due to the now 'overstretched' luff bolt rope.
Racing dacron sails are usually 'cut' with 'preloaded' (shortened by 1" for each 10-11FT. of luff length) bolt ropes, and FLAT luff entry shapes ... a flat entry requires a very precise helmsman, as the range of the angle of attack is VERY narrow. The flatter entry shape also benefits from a cunningham, as increased c-ham tension increases luff entry 'roundness' - a much better shape for very FAST boats in HIGH winds, AND the 'more rounded' luff shape is 'more forgiving' vs. the range of attack angle at the higher wind ranges.

FWIW - here's a detailed article I did quite a few years ago on how to properly raise a woven dacron sail WITH PRELOADED BOLTROPE ... Plus, how to analyze the ever changing shape/dimensions and what to do about it, .... without breaking your savings account:
http://forums.sailboatowners.com/ind...insail.120970/

hope this helps.
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Last edited by RichH; 06-03-2016 at 09:58 AM.
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Re: Main downhaul vs. halyard tension (vs. Cunningham)

The person who told me I should always raise the sail to the top then use a downhaul to tension it sails a one-design racer, so the race stuff people here have posted makes sense.

I think I'll continue with my method of leaving the downhaul fixed and using the halyard to control luff tension/stretch the bolt rope.

Thanks all!

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post #9 of 10 Old 06-09-2016
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Re: Main downhaul vs. halyard tension (vs. Cunningham)

I have the same set-up. I raise the sail with the halyard, then finish tensioning with the boom downhaul. The only reason is that I do not have a winch for the halyard, and can take advantage of gravity, and have a 3:1 purchase on the boom downhaul. Neither go back to the cockpit on my boat, so, I don't adjust much.

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post #10 of 10 Old 06-09-2016
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Re: Main downhaul vs. halyard tension (vs. Cunningham)

Rich H
Great post very informative and useful
Thanks
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