The mainsail is the only sail on your boat that is used all the time. From winds of zero to thirty plus knots the main must be trimmed correctly to get maximum performance.

Let's first observe the many roles your main plays on the boat. Upwind, the main has two roles. First it acts as a strearing device and can be set to either increase or to reduce the helm. Secondly, the main has to be set up with the proper shape in order to have the wind flow over its surface efficiently. The ideal shape in a main is a sail that has a flat entry with the maximum draft forty percent aft, with a flat exit and a nice twist. The camber in the sail should be set at about thirteen to fourteen percent for light air and as flat as eight percent for heavy air. Aligning the top batten parallel to the boom can set up the initial twist.

To achieve the desired shape there are many items that can be adjusted. Each control line adjusts a different part of the sail and needs to be tweaked in order to get a well shaped main. Trimming controls available to most boats include the mainsheet, the halyard, outhaul tension and the position of the traveler on the track. The proper use of these controls will set your main to give you the maximum performance over a wide range of wind conditions.

The outhaul, which tightens the foot of the sail, will control the camber of the sail. A loose outhaul will produce a fuller sail for light upwind sailing or for reaching and running. As the wind increases, you can flatten the sail by tightening the outhaul. If your boat is equipped with a backstay adjuster this can also help control the camber in the main by bending the mast.

The halyard tension controls the position of the camber in the main fore and aft. By tightening the halyard the maximum draft point will move forward in the sail. Remember the optimum draft point should be maintained at about forty percent. A quick and easy way to set your halyard tension is to tighten it until the wrinkles come out of the luff. This typically will set the maximum draft in the correct position.

The main sheet controls the tension on the leech or the amount of twist in the sail. Remember that the starting point is to tension the leech until the top batten is parallel to the boom. This should produce the proper twist in the main. Observing the telltales on the leech of the main to see whether they are streaming can check the twist. If the telltales aren't streaming then ease the sheet until they stream.

The final control is the traveler position. In light air the traveler should be positioned to bring the boom to the centerline of the boat. As the wind increases the traveler will be eased to leeward. This will accomplish two things. It reduces the heal of the boat and will also reduce the weather helm. Don't be afraid to have the front of the sail luffing, this is normal when the wind increases.