How To Trim the Mainsail

How to trim the mainsail with twist.

Sail twist can be seen in the mainsail of this sloop by comparing the straight line of the luff along the mast to the curve of the leech. Photo:

We’ve put together some helpful tips for beginners about how to trim the mainsail. The mainsheet, kicker and traveller are used to control and trim the mainsail. To alter the sail angle you adjust these based on the wind and the amount of twist in the sail.


Twist is judged by watching the way the telltales stream out from the leech (outer edge of the sail) or by looking up the leech. This shows whether the head of the sail is falling to leeward more than the centre and foot sections of the sail. You need to trim the head of the sail to be looser than the foot to create twist and increase sail power. To control the twist going upwind, the mainsheet and the traveller are adjusted. If sailing off the wind, the kicker is used instead.


Mainsail Trimming Tips




The mainsheet adjusts both the angle of the mainsail and the amount of twist in the sail going upwind.

You need to adjust the mainsheet so the top batten becomes parallel with the boom. The telltales will be streaming straight out from the leech. Twist is reduced by increasing the sheet tension; you will see the telltales now stream to leeward.

After you have set the amount of twist, use the traveller to depower the mainsail when required.




The traveller can be used to power or depower the boat when going upwind. Initially, it should be set along the centreline.

If the boat starts to heel excessively in strong winds, move the traveller to leeward. This allows the luff to spill wind but keep the leech of the sail powered up. If you feel you are over-powered, start over by reefing the mainsail and re-centering the traveller. You should then re-adjust the traveller and mainsail accordingly. In the lulls, or if sailing in lighter winds, adjust the traveller to windward to increase power.

This action of using the traveller’s position to pull the boom down is similar to using a kicker (boom vang) to keep the boom from rising.




Adjusting the traveller works better when going upwind, whilst the kicker is more useful for downwind sailing. If the boom passes leeward of the traveller (or you have no traveller) you use the kicker to control leech tension and twist.

If you ease the kicker, the boom will rise which opens the leech and increases twist. Tightening the kicker causes a decrease in twist.


The best thing to do is to get out there and practice! Take a professional instructor or friend along who understands how to trim the mainsail correctly. Then play around and find out what suits your boat best in different conditions.