Correct sail trim is not just for racing sailors! Trimming your sails properly will make your boat easier to steer, you will go faster more efficiently and with less heel. Generally more fun on the water!

Alby Pratt from North Sails shares his expertise with us –

On any boat the headsail is important, not just because of the extra area it adds to the sail plan and thus more power to propel you forward but also in the role it has working in conjunction with the mainsail to balance the boat and to improve the efficiency of the mainsail.

Sail controls

The headsail has 4 primary controls which combine to control the depth and the twist of the sail. Like the mainsail, depth and twist are the keys to power in the sail and making you go.


The backstay tightens the forestay which makes the sail flatter.

A good way to visualize the effect of the backstay on the headsail is to imagine the leech of the sail always being in the same place. As you ease the backstay the forestay sags more bringing the luff closer to the leech making the sail deeper. As you tighten the backstay the opposite happens with the luff moving away from the leech to make the sail flatter.

A tighter headsail creates a flat, close winded and low drag sail shape best for heavier airs and flat water.

A looser backstay gives you a deeper, more powerful sail shape better in lighter airs and bumpier water.

As the wind increases the forestay will sag more thus more backstay is needed. As the wind lightens ease the backstay to deepen the sail and keep the power on.

Jib Car

Jib car position is determined by moving the jib car fore and aft on the jib track.

In the case of a self tacking headsail the car position is controlled by the position of the sheet onto the clew board. Moving the sheet up the clew board has the same effect as moving the jib car forward. Moving the sheet down the clew board is the same as moving the jib car aft.

As you move the car forward you make the sail deeper and decrease twist. Moving the car aft flattens the sail and increases twist.

Like the mainsail a deeper, less twisted shape is better in lighter winds and flatter water with a flatter more twisted sail better suited to rougher water and stronger winds.

To establish a good starting position for your jib car you can sight up the jib sheet to where it exits the car and through to where it attaches to the clew visualising where the sheet would intersect the luff. If you are between 30-40% up the luff you are in the ball park.

Here we see a nice all round jib car position with the red line representing the the jib sheet angle

Jib Sheet

Trimming the sheet affects the twist in the headsail and also the overall power. By trimming the sail on more you decrease the twist and power up the sail to allow you to point higher. Easing the sheet has the opposite effect – more speed and less pointing ability.

Here we see the effects of the sheet tension on twist. The differences in actual amount of sheet between these two illustrations is only 20-30mm on a typical 30-40’er


The jib halyard is probably the control most overlooked. Usually it is the hardest control to adjust so often gets put in the “too hard basket”. The Jib halyard helps to control the position of the draft in the sail (max depth) which we have been discussing with the other controls.

It is important because whilst overall depth is handled by the backstay the halyard keeps this depth in the correct place. The most common mistake people make is neglecting to tension the halyard as the breeze increases which allows the depth to move aft in the sail from its optimum position. If the draft moves aft in the sail the entry angle of the sail gets narrower making it much harder to steer.


The best thing about trimming the headsail is tell tales. These simple inexpensive little bits of wool tell you way more information than any electronic instruments can ever hope to.

Symptom                                              Cause                                          Remedy
Leeward (outside tell tales)          Sail is trimmed too hard     Ease jib sheet
not streaming (stalled)
Windward telltales lifting             Sail is too eased                     Trim jib sheet more
Windward upper telltale               Sail to open (twisted)          Move jib car forward
lifting                                                        in head
Leeward lower telltales                 Sail too deep in bottom.     Move jib car aft
All telltales flowing evenly           Perfect trim                             Enjoy your sail!

Good sailing,

Alby Pratt

North Sails Australia

All information / images courtesy of the North U trim book available from North Sails