A lot of racers are constantly tweaking their sails to get the best speed. Cruisers, on the other hand, often just set their sails and go. But even for cruisers, learning how to adjust your luff and leech tension can make a big difference.
Why bother? You’ll get to your destination (and that post-sail drink!) faster, sail straighter instead of slipping sideways, and enjoy a smoother, more comfortable ride.
What Does Luff Tension Do?
Luff tension controls where the deepest part (or “draft”) of your sail sits.
- More luff tension pulls the draft forward.
- Less tension lets the draft move back.
This matters depending on the wind:
- In strong winds, you want a flatter sail with less drag — so add tension.
- In light winds, you want more power — so ease off the tension a bit.
What Does Leech Tension Do?
Leech tension controls how much twist your sail has — that is, how open or closed the top of the sail is compared to the bottom.
- More leech tension pulls in the top of the sail (less twist).
- Less tension opens up the top, letting wind spill out (more twist).
So, What Is Twist?
Twist is when the top of the sail is angled differently from the bottom. This happens naturally because the wind at the top of the sail is stronger (less surface friction) and can come from a slightly different direction.
- More twist = top is open, letting air spill.
- Less twist = sail is more lined up from top to bottom.
Why Does Twist Matter?
- In light wind, twist helps you catch the stronger wind higher up and reduces drag below — making the boat go faster.
- In medium wind, you want less twist to keep the sail powered up.
- In heavy wind, you want more twist again, to allow the wind to spill out of the top of the sail and help you a avoid too much heeling.
Mainsail Controls?
Luff Tension: On the mainsail, the best way to control the Luff tension is with a Cunningham. The Cunnigham is typically 8-10 inches above the tack, and allows you to pull down on the sail luff increasing tension. Not all sails or boats have a Cunningham. If your boat does not have one, you will need to adjust thee luff tension with the Main Halyard.
Leech Tension: The leech tension is controlled by the mainsheet when going upwind and the boom vang when off the wind..