Do I really need a cunningham?

[Javelin]

In truth I've not used it much on the yacht yet but I will once I start racing her.
In the FD, 505 and Javelin when racing it's a must.

Say you're cracking along upwind in 20 knots apparent and you're approaching a headland.
Chances are you'll get a shift and an increase in wind speed for a while until you're past it.
You could reef and then shake it later, time consuming and slow.
You could get someone to man the traveller and play that for a while though the jib will still be over powered.
You could wind on some main cunningham and also apply some extra tension on the Jib halyard which is equally if not more important.

As soon as the wind drops off make sure you release the cunningham and let of the Jib halyard again.

Foot tension is not so important.
The rule of thumb for both sails is that the top third of each sail does two thirds of the work.
In 20 to 25knots of wind coupled with the angle of heel when close hauled, the bottom third of the main is really not doing much anyway.
If there is a chop about and you need grunt to get you through it then easing a little can help but nowhere near as much as making sure the top third of each sail is set correctly.

Leech tension in the main is controlled upwind with the mainsheet and the fore and aft of the jib/genoa car. (Forward for more, aft for less)
Once you are out of the range of your traveller, usually a close to beam reach, the kicker takes over leech control from the traveller/mainsheet.

 

[bbg]

Okay, I'm still a little confused. When I raise the sail, the boom kicker (i don't have topping lift) raises the boom so that the luff is not constrained by the leech. Then when the halyard is tight, the leech is tensioned with the kicking strap. So - IMHO - the halyard is tight and the leech is tightened by the boom moving down.

Are you saying that when I'm sailing in a blow, I can flatten the sail still further by using the cunningham? Or that I can change the sail shape by pulling down which is a straight line down as opposed to trying to pull up against both the luff and the leech?

I'm quite willing to have a go next time I take the boat out and see what happens.

Not so much flatten the sail as move the draft forward. That is what the cunningham does: it changes the fore and aft position of the maximum draft. It changes the shape so the sail drives the boat forward instead of heeling her over. Again a simplification.

 

[Resolution]

Most of the above comments are assuming that the sail is a woven sail, ie dacron or similar material. If you have a modern "racing" sail of mylar laminate then you need very different techniques to change the sail shape. As the laminate is essentially un-stretchable, the best means of moving the draft fore or aft is by adjusting the boom outhaul and thus the foot curvature.
At least, this was the sailmaker's advice when we used to race Sigma 33s ten years ago.

 

[Javelin]

Most of the above comments are assuming that the sail is a woven sail, ie dacron or similar material. If you have a modern "racing" sail of mylar laminate then you need very different techniques to change the sail shape. As the laminate is essentially un-stretchable, the best means of moving the draft fore or aft is by adjusting the boom outhaul and thus the foot curvature.
At least, this was the sailmaker's advice when we used to race Sigma 33s ten years ago.

Not sure I agree with your sailmaker.
My sponsored sails over the years ranged from Kevlar, spectra, Mylar and even a suit of North 3dl and all responded to cunningham.
OK these were all big racing dinghies but I'd still expect the same rules would apply.

 

[Bosun Higgs]

What part is wrong? Try it yourself.

Going upwind, with the main sheet in hard and the halyard not quite at full hoist, try tensioning the cunningham and see how much you can pull it down. Quite a bit, partly because the main is not at full hoist, but also because you are not fighting the leech tension.

Then release it and without touching anything else tension the halyard to try to get the main to the top. Tell us what breaks first.[/QUOT

I said " Unless you have serious friction in the slides," and thats whats causing the situation you describe plus of course the weight of the sail itself. . It is basic simple physics, newtonian mechanics if you like, that means the forces involved are in balance or the sail would be moving up or down the mast until they were. The downward pull on the cunningham must equal the upward pull on the halyard plus the weight of the sail. So in your example, when you pull down on the cunningham with a certain force there will be a similar increase in the force in the halyard once the sail has stopped moving and ignioring sticky or jammed slides.

But all that is a bit irrelevant anyway. I always understood that the purpose of a cunningham in a race boat was to allow you to hoist the main to the height of the class mast band and still be able to adjust leach tension as required. Some say its also quicker than using the halyard though I dont see why this should be the case. It will be lighter than the halyard by the weight of the sail itself.

 

[dunedin]

http://www.northsails.com/uk/SailBetter/MainsailTrim/SetDraft/tabid/7035/Default.aspx

The definitive word from the experts

 

[bbg]

What part is wrong? Try it yourself.

Going upwind, with the main sheet in hard and the halyard not quite at full hoist, try tensioning the cunningham and see how much you can pull it down. Quite a bit, partly because the main is not at full hoist, but also because you are not fighting the leech tension.

Then release it and without touching anything else tension the halyard to try to get the main to the top. Tell us what breaks first.[/QUOT

I said " Unless you have serious friction in the slides," and thats whats causing the situation you describe plus of course the weight of the sail itself. . It is basic simple physics, newtonian mechanics if you like, that means the forces involved are in balance or the sail would be moving up or down the mast until they were. The downward pull on the cunningham must equal the upward pull on the halyard plus the weight of the sail. So in your example, when you pull down on the cunningham with a certain force there will be a similar increase in the force in the halyard once the sail has stopped moving and ignioring sticky or jammed slides.

But all that is a bit irrelevant anyway. I always understood that the purpose of a cunningham in a race boat was to allow you to hoist the main to the height of the class mast band and still be able to adjust leach tension as required. Some say its also quicker than using the halyard though I dont see why this should be the case. It will be lighter than the halyard by the weight of the sail itself.

I think you misunderstand. What I am saying will apply with no friction in the slides.

If you hoist the main 4" short of full hoist then sheet the main in hard (upwind setting) you ain't never gonna get the halyard up 4". Ain't gonna happen because the leech tension (due to the mainsheet) will prevent it. The luff can be as smooth and free-flowing as you like but the leech will prevent the head from being hoisted. Put the halyard on a winch, start grinding and something will break before you get those 4".

Compare that with tensioning the cunnungham. Easy peasy even with the mainsheet and kicker on hard. The difference has nothing to do with luff friction and everything to do with leech tension.

Go back and read my posts again. I never said anything about there being a difference in luff tension at different places along the luff. If you can find anyfactual statement that is wrong in any of my posts on this subject, by all means quote it verbtim and point out the error.