Sail Trim and Sail Settings
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Posted on Sunday, December 30, 2007 6:25 PM
Find out how to set your sails set correctly for the conditions you are sailing in.
Getting your sails trimmed (set) just right is important for any point of sailing, and they need to be trimmed differently depending what direction you’re sailing in, and also the conditions you are sailing in.
In our Article on Points of Sail, you can see the different settings your sails should be on according to the point you’re sailing on, but beyond that, there is fine tuning that can be done on the sails, using the sheet, kicking strap or boom vang, outhaul and downhaul.
Telltales are invaluable for determining if your sails are trimmed in enough, but the fine controls should be learnt, so you can just set them and get on with sailing!
The kicker, kicking strap or boom vang controls the twist in the main sail. In light or medium winds, the kicker should be loose and only taking up the slack; the kicking strap tightens the leech of the main sail (the back edge), which helps curve the sail by bending the lower half of the mast.
In medium winds, if you tighten the kicker, it reduces power in the sail. In strong winds, the kicker should be tightened to control twist in the sail. It should be tightened until there are no horizontal creases in the sail behind the luff, this will allow excess wind to spill out of the sail.
The outhaul controls the curve in the lower part of the main sail. In light and medium winds, you need a flatter sail, so the outhaul should be pulled tight, and only released a third to remove crinkles from the lower part of the sail. In stronger winds, if you find yourself becoming overpowered, you should loosen the outhaul, to curve the sail more, which depowers the sail.
However, sailing downwind on a run, you should loose the outhaul, as it curves the sail, and the sail performs better on a run with this shape.
Downhaul or Cunningham
The downhaul controls the curve in the lower parts of the main sail by tightening the luff (the front edge of the sail). In light or medium winds, no cunningham should be used.
In heavier winds when you become overpowered, you should pull on the Cunningham; this will smooth out the creases forming behind the mast, and curve the lower part of the sail; it also causes some mast bend, flattening the top of the sail. This change of shape disrupts the "slot" formed between the jib and mainsail, and reduces the efficiency and therefore the power of the mainsail.
These are used to control the amount of twist in the jib, and are usually the only sail controls for the jib, besides the sheets. In very light or very strong wind conditions move the jib tracks back, to give more foot than leech tension and allow the sail to twist. In medium winds, you should move the jib cars forward, to tighten leech, to help flatten sail, and allow the boat to point higher.
Sail twist is the amount by which the curve or shape of the top of the sail is different (at a different angle of attack to the wind) to the curve or shape of the sail at the bottom. Some twist is best, because the wind speed hitting a sail over it’s height varies, and is typically faster at the top than the bottom of the sail.
In light wind conditions, ideally less twist is better, and is achieved by slackening the luff (leading edge) of the sail; if you follow through the above points, the Cunningham should not be used in light winds; this means the luff isn’t tightened (i.e. it is slackened). Less twist gives the sail more power, which is what is usually wanted in light winds!
Again following through the points above, in heavy winds, more twist on the main sail is best; if the sail is twisted and curved well, it allows the sail to dump or spill excess wind out of it and slightly depowers it. While you might think “No, we need that power!”, think it through. If you slightly depower an overpowered sail, the boat will heel less, you will have to put less effort into hiking or trapezing to keep the boat flat, and you will actually get more straight line speed, with less effort on your part. Result!