Do I really need a cunningham?

Burnham Bob

Burnham Bob

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I have a Trapper 500. The main halyard is at the mast, but led back to the cockpit is a cunningham. It attaches to an eye in the luff of the mainsail about eight inches above the tack. If I can tighten the halyard fully what use is the cunningham? Or am i missing something arcane due to the shape of the sail that pulling down with the cunningham (as oppposed to up with the halyard) makes for a flatter sail than halyard tension alone?

Advice (and explanation!) from forum experts please.
 
I have a cunningham on my sail. Never used it.

I take the view that it's one of things which, if you have to ask if you need it, you probably don't. But I'll be interested to see any helpful replies!
 
The halyard pulls the head of the sail up, so tensions both the luff and leech. It closes the top of of the leech while moving draft forward. To tension it you have to fight both luff and leech tension.

Cunningham pulls luff down without tensioning leech. This opens the leech while moving draft forward. It is easier to adjust because you are not fighting leech tension.

Simplified version.
 
I find mine useful to flatten the sail in a blow which reduces weatherhelm on my Leisure 27. I used to not bother but once i started using ut i found it saved me reefing as early.
 
A lot of people tend to over tension their main halyard and their jib halyard come to that.

You should be able to pinch a inch or two of luff once the sail is up.
If it's tighter than that you are already effectively applying a cunningham.
This is also true of the jib if it's a hank on or up a spar.

Think of the Halyard as a way of just pulling the sail up and no more.
The cunningham is there to apply the luff tension as the wind builds, to flatten and de-power the rig, opening the leech and giving you a little more time before you have to take in the first reef.
 
bbg said:
The halyard pulls the head of the sail up, so tensions both the luff and leech. It closes the top of of the leech while moving draft forward. To tension it you have to fight both luff and leech tension.

Cunningham pulls luff down without tensioning leech. This opens the leech while moving draft forward. It is easier to adjust because you are not fighting leech tension.

Simplified version.
Click to expand...

you failed to mention "Black Bands" & their function in relation the the main sail head board
 
Javelin said:
A lot of people tend to over tension their main halyard and their jib halyard come to that.

You should be able to pinch a inch or two of luff once the sail is up.
If it's tighter than that you are already effectively applying a cunningham.
This is also true of the jib if it's a hank on or up a spar.

Think of the Halyard as a way of just pulling the sail up and no more.
The cunningham is there to apply the luff tension as the wind builds, to flatten and de-power the rig, opening the leech and giving you a little more time before you have to take in the first reef.
Click to expand...


See #6
 
Twice now it has been said that applying the Cunningham without altering the halyard 'opens the leech'. Could anyone explain how that happens?
I would agree that employing the Cunningham to flatten the sail can make a marked reduction on heeling forces.
 
Black bands are really only relevant when racing and I sort of assumed this was a non racing associated question.

Basically the sail is a triangle.
Applying more tension on any of the three sides will effect the tension on the other two sides.
Not so much on the short side (the foot) as the length is so short in comparison.
Try it with a triangular piece of cloth.

It's more noticeable on a genoa where applying cunningham or halyard tension will often mean you need to side the car forward a hole or two on the track to retain the same leach tension and keep the leach tell-tail flying/stalling at 50%.
On the main by his time, you've probably let the traveller down to leeward a bit and you control the twist with the sheet tension, again flying the top batten tell tail 50% of the time.
 
I had a main made for my Foxcub which had quite a full foot. If you tensioned the halyard it reached a point at which the leech tension prevents the luff going any further up the mast (unless you loose off the kicker, but them the boom was not level).
So you had a full foot for light winds, but it was essential to use the cunningham to flatten the sail if the wind piped up.

I hadn't asked for this, but the sailmaker does mainly racing sails and I think he thought it was a good thing. I found it a bit tiresome. Setting the sail was always a bit of a chore.
 
bbg said:
The halyard pulls the head of the sail up, so tensions both the luff and leech. It closes the top of of the leech while moving draft forward. To tension it you have to fight both luff and leech tension.

Cunningham pulls luff down without tensioning leech. This opens the leech while moving draft forward. It is easier to adjust because you are not fighting leech tension.

Simplified version.
Click to expand...

Unless you have serious friction in the slides, you are wrong. The tension in the luff rope has to be the same all the way up the luff - if it wasnt then the luff would move until it was. Simple physics.

As I understand it the idea is to hoist the main using the halyard to get the head yp to the head band and then use the cunningham to adjust luff tension.
 
Lakesailor said:
I had a main made for my Foxcub which had quite a full foot. If you tensioned the halyard it reached a point at which the leech tension prevents the luff going any further up the mast (unless you loose off the kicker, but them the boom was not level).
So you had a full foot for light winds, but it was essential to use the cunningham to flatten the sail if the wind piped up.

I hadn't asked for this, but the sailmaker does mainly racing sails and I think he thought it was a good thing. I found it a bit tiresome. Setting the sail was always a bit of a chore.
Click to expand...
Does it matter whether the boom is level or not? Level compared with what? Do you really pull the mainsail up with the kicker tensioned? (Which is what you appear to imply you do.)
 
Bosun Higgs said:
Unless you have serious friction in the slides, you are wrong. The tension in the luff rope has to be the same all the way up the luff - if it wasnt then the luff would move until it was. Simple physics.

As I understand it the idea is to hoist the main using the halyard to get the head yp to the head band and then use the cunningham to adjust luff tension.
Click to expand...

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.
 
Remember, the halyard not only tensions the luff but also is holding the weight of the sail that reduces as you go higher up the mast, therefore the top of the sail is “carrying” more weight than the bottom of the sail.

Cunningham is usefull because it’s easy to adjust the position of max draft without playing with the halyard but also helps the sail be adjusted while keeping it within the back bands.
 
bbg said:
The halyard pulls the head of the sail up, so tensions both the luff and leech. It closes the top of of the leech while moving draft forward. To tension it you have to fight both luff and leech tension.

Cunningham pulls luff down without tensioning leech. This opens the leech while moving draft forward. It is easier to adjust because you are not fighting leech tension.

Simplified version.
Click to expand...

Great description. And the key thing is that this control adjusts the fore and aft position of the sail curve - the maximum point of which generally should be 1/3 to 1/2 way back from the mast.
One of the most important sail controls upwind - as if the maximum curvature moves too far back the boat will heel excessively and go very slowly. In that situation correcting with the Cunningham is a win win for comfort and speed.
 
Burnham Bob said:
I have a Trapper 500. The main halyard is at the mast, but led back to the cockpit is a cunningham. It attaches to an eye in the luff of the mainsail about eight inches above the tack. If I can tighten the halyard fully what use is the cunningham? Or am i missing something arcane due to the shape of the sail that pulling down with the cunningham (as oppposed to up with the halyard) makes for a flatter sail than halyard tension alone?

Advice (and explanation!) from forum experts please.
Click to expand...

For most it's a redundant item - really little use unless tou also use a flattening reef.
Effectively it pulls the draft forward and flattens the sail.

Of very little use on a fully battened main, but I do use my 1st, single-line reef as an alternative cunningham and play around with the vang to change the sail shape.
 
charles_reed said:
For most it's a redundant item - really little use unless tou also use a flattening reef.
Effectively it pulls the draft forward and flattens the sail.

Of very little use on a fully battened main, but I do use my 1st, single-line reef as an alternative cunningham and play around with the vang to change the sail shape.
Click to expand...

I have to disagree. For me it is adjusted regularly, usually look at outhaul at the same time.

Each control does something different to the sail. Learning how to use them all will help boatspeed and even comfort.
 
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.
 
Burnham Bob said:
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.
Click to expand...
any fore & aft sail needs the halliard tight enough for the luff to be "just standing" in light airs going up wind & increased tension as the wind spd gets stronger.
the sails luff should be cut to allow full hoist to the black band ( legal racing dims mark) at the upper wind range any further tension to get the sail draft / camber forward to reduce heeling is then done via the luff cunningham. after that its reefing time & the halliard is tensioned to suit the sail draft req as the luff is not constrained bu the black bands
 
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