Sail shape for Toppers and Lasers

I clearly have too much time on my hands at the moment, so I thought I'd put together this collection of photos to follow up the talks on sail shape on Sunday, which will hopefully help to make this incredibly confusing topic a bit clearer. Since I got my laser back in 1998 I have read countless articles and several books, watched closely the top sailors in the UK, had many discussions with my laser sailing peers, received some coaching and learned from my own experience. I still don't fully know how to achieve the perfect sail shape for every situation, but I think I can get fairly close most of the time. I'll try to give you the benefit of what I have discovered, but I recommend that if you're interested you also look at the articles that can be found at www.roostersailing.com and www.drlaser.org.uk

The controls

Lasers and toppers have just five bits of rope which affect the sail yet there are an infinite number of ways in which they can interact to get the perfect shape for the conditions. Here is a list of what they each do individually:

Mainsheet

Upwind: Controls leech tension
Downwind: Controls horizontal angle of the boom

Kicker

Bends the mast and thereby flattens the sail
Moves the centre of effort of the sail towards the leech
Upwind: Reduces leech tension by sharing the load of the bent mast with the mainsheet
Downwind: Increases power by stopping the boom from rising and allowing the leech to twist off too much.

Cunningham

Flattens the sail
Pulls the centre of effort of the sail towards the luff
Allows the top of the leech to open

Outhaul

Controls the fullness in the bottom third of the sail

Traveller

Affects the use of the mainsheet upwind

Traveller Tension

I know I have told you on many occasions that your travellers are often not tight enough. Above is a photo of a soling, which has a mainsheet rigged in a similar way to a laser, but the traveller is made of metal, not rope, and therefore it can be made to the ideal shape for a traveller. As you can see it curves gently upwards at the edges, so that even in light winds any tension in the mainsheet will cause the block to move towards the edge of the boat. This is an impossible shape to achieve in lasers and toppers, but we can try to get our traveller as close as possible to the shape of the soling's.

I am sure you have noticed that in light winds the block on the traveller has a tendency to move towards the middle of the boat. This is very slow as it means the boom is too close to the centreline and the effort of the sail will be almost entirely sideways rather than forwards. Keeping the middle of the traveller low by pulling it as tight as possible will help to keep the mainsheet block towards the outside corner. This is so vital to boatspeed in light-medium winds that laser sailors are willing to pay over £100 for flat carbon tillers which will make the traveller about 10mm lower in the middle than with the old fashioned gorilla tillers.

Rope choice is also more important for the traveller than for any other rope on the boat. It needs to be strong, low stretch, have decent abrasion resistance and be thin, as this will also affect how close to the corner the block will go. A dyneema or kevlar based rope I think is best, marlow excel V12 (spec 12) would be fantastic but it has the fatal flaw of a tendency to slip through the cleat! Last time I was there BLYM stocked some yellow 4mm kevlar which is ideal, and not too expensive.

Some of you have said to me that in light winds when the traveller is pulled as tight as you can the block has trouble crossing the tiller when you tack. This has always surprised me as it is not a problem I have ever had, and the reason has just struck me as I looked at this picture of J-Man going through a tack with no mainsheet tension. With the possible exception of extremely light and extremely strong winds, lasers should always begin a tack block to block, as this keeps the power in the sail for as long as possible and helps turn the boat into the wind, with it only being eased a foot or two depending on the conditions once it has gone head to wind and you have started to change sides. The tension should help to lift the block over the tiller as it changes sides.

The airflow

I was once told to think of the sail as a hump-back bridge at the bottom of a hill. A cyclist coming down the hill and over the bridge represents the wind. If the hill is shallow, the cyclist may not have enough speed to get over the hump without pedalling, in the same way that a very light wind will struggle to flow over a sail with too much fullness.

With a medium hill, the cyclist can get over the bridge without a problem, so in medium winds it is ok to search for power by increasing the fullness in the sail.

If the hill is steep, the cyclist will go so fast that he might fly off the top of the hump of the bridge, and a strong wind will behave in a similar way if it meets a sail that is too full.

So in light and strong winds the sail should be flat to help the wind flow over it smoothly, in medium winds you can give it more depth.

Upwind

Here are the basic facts for sail shape upwind:

Max Power

This photo shows a girl sailing upwind in marginal hiking conditions. This can be known as the 'max power zone', as in the object here is to extract the maximum power from the rig.

Her mainsheet is block to block, her traveller is tight and her clew tie-down has strapped the clew tightly to the boom, so that she has the maximum amount of leech tension possible. Her kicker is just tight enough to take up the slack, which means that all the spring in the bent mast is being held by the mainsheet, and therefore also by the leech of the sail. Any more kicker tension and the mast would also start to be bent by the boom being pushed into the mast, removing some of the load from the mainsheet and the leech. The cunningham is slack to keep some fullness in the sail, and the outhaul is loose enough to give the bottom of the sail plenty of power, although loosening it too far would create drag.

De-power

On a windy day you will have looked up at the sail and seen that the front of it is permanently luffing, as you are spilling power to keep the boat flat. While this is better than letting the boat heel, the luffing sail is a sail that isn't being used, and is therefore causing drag. Also the part of the sail that is doing the work is the back part, which will mean there's loads of weather helm. Therefore the moment when the sail begins to luff should be delayed as long as possible, which can be done by using the controls to effectively depower the sail. The objectives are:

This picture from the 2003 laser worlds shows boats beating in the 'depower' wind range. The outhaul has been pulled almost all the way on to reduce power and keep the wind flowing easily over the sail. There should be a little bit of depth, as power low down is usable power, but it is better to have it too tight than too loose. The mainsheet is still block to block, but the kicker has been pulled on harder, further bending the mast which will make the sail flatter and take away some leech tension, but moves the sail's centre of effort aft, increasing weather helm. This is countered by pulling the cunningham on hard, which by happy coincidence also flattens the sail still further, and allows more power to escape by opening the upper leech.

Here is a photo to give you some idea of how tight the cunningham needs to be. By the way you can tell that it's a masters' (oldies) event from the fact that he's depowered the boat rather than hiked out hard!

As the wind increases still further and the sail has been fully depowered, only then should the mainsheet start to be eased to decrease the leech tension still further. The tight kicker will mean that as the sheet is eased the sail will remain flat.

Drift

In light winds, in what is known as the 'drift zone', the key is to keep what wind there is flowing easily over the sail. As the wind gets lighter, typically at about the stage when you are sitting on the side rather than hiking out, a tight leech will stall the wind trying to leave the sail, so leech tension will have to be reduced. This is done by easing the mainsheet, not by easing the kicker.

The kicker should have the same tension as in the 'max power' zone, i.e. just taking up the slack when the sail is block to block (obviously toppers can't go block to block, but the same principle applies, the kicker should be taking up the slack when the sail is in tight). The effect is that when the mainsheet is eased, leech tension is reduced but the kicker prevents the mast from straightening, which would allow too much fullness in the front of the sail.

Here is Wee Man sailing upwind in the drift zone, and you can see that he has quite rightly eased the mainsheet considerably. However there is no kicker tension, and as a result there is a lot of depth in the front of the sail, which may be preventing the light air from being able to flow smoothly over it.

This picture shows top Swedish sailor Karl Sunesson sailing upwind in the drift zone, the mainsheet has been eased a few inches but the tight kicker is keeping the mast bent and the sail flat. The outhaul should be fairly loose, about a hand's length of depth in middle of the sail, to increase the power, drag is not such a problem in this wind strength, and as the curve is a long smooth one it should not inhibit the flow of wind.

Downwind

I will go quickly over downwind sail shape, as I think generally you are all pretty good at this. Basically a much fuller sail is required, so the kicker should be eased to straighten the mast, similarly the cunningham should be let right off, and the outhaul should be eased.

The kicker does do the job of tensioning the leech downwind, easing it too far will allow the top of the sail to twist off and loose power, however over-tightening it will reduce power by flattening the sail, and as the flow of wind over the sail is slower offwind than upwind, could stall the leech. Over-tightening it will also make the boat harder to sail in strong winds as it moves the centre of effort outboard, increasing the chance of a broach.

This picture of Gustavo Lima and Robert Scheidt, 1st and 2nd at the worlds this year, on the run in a good breeze shows how twisted the main should be. The loose leech makes the boat easy to steer down waves, and while it can make death rolling more likely, running by the lee should prevent this as effectively the luff becomes the leech, and as it is supported by the mast, it is a pretty firm leech! The most popular guideline is that the leech should be just opening, and flicking as the mainsheet is played or as the boat goes over waves, as these flicks act as pumps. Really it is just a case of experimenting with what looks and feels right.

On the reach, the stronger the wind and the tighter the reach, the flatter the sail should be so therefore the tighter the kicker and the outhaul should be. The bent masts in the photo above show that these boats have pulled some kicker on to flatten their sails. If you are really overpowered on a windy reach, you could even pull a bit of cunningham on.

Finally, just for a laugh, I couldn't go without showing you this picture from the 2002 Spa regatta. Learn from it what you will, I just love the fact that he's still apparently trying to steer!

By Joel Walker
09/12/2003