How-to

Lesson: 5

Twist & Shout: Understanding Mainsail Twist

Captain Paul Sullivan

First Reef Sailing

Today, our ASA class learned about twist in the mainsail. Don't worry, there wasn't actually any shouting involved. 😉

My goal was to help students understand what it is and how the boom vang acts as an important sail control when it comes to getting the right twist for the right conditions.

“More Twist = Less Power”


Understanding Twist

🔀 Twist is the difference in angle of attack between the bottom and top of the mainsail. In light wind, the top of the sail often opens up (twists off) to spill air, while the bottom stays powered.

🌬 More twist allows wind to “escape” from the top of the sail, reducing power and heel. Useful in gusty or overpowered conditions.

🔧 Less twist means a more uniform shape and power across the sail, creating more drive but increasing heel and weather helm.


Using the Vang

⬇️ Pulling on the vang (tightening) reduces twist by pulling the boom down, flattening and closing the leech (especially important downwind).

🔓 Easing the vang increases twist, letting the boom rise and the leech open—helpful in light air to prevent stalling at the top.

View the full trip on SeaPeople.