Will I Capsize?
Published on Sep 13, 2010
Keelboats have lots of ballast to keep them right-side-up in all but hurricane conditions, and maybe even then. Yes, all sailboats “heel” (lean over) in strong winds, sometimes so far that waves wash onto the deck. It’s just part of sailing, and one that many sailors enjoy the most. But when it comes to capsizing, keelboats have physics on their side.
First, as the boat heels, the wind pressure on the sails decreases because the sails present a smaller area to the wind. Imagine you’re standing in a windswept field holding a piece of plywood: If you try to hold the plywood straight up, the wind will blow it away, but if you lean it at a 45-degree angle, the pressure will be much less. The same thing happens with sails, and the farther the boat heels, the less pressure there is.
Second, the ballast is located in the keel, several feet below the waterline, so as the boat heels its leverage becomes greater. Imagine you’re holding a dumbbell in your hand, your arm hanging straight down from your shoulder. Now lift the dumbbell away from your body, keeping your arm straight— it gets heavier the closer your arm gets to horizontal, doesn’t it? That’s how ballast works when the boat heels.
Combine these two effects— sails producing less heeling moment, ballast producing more righting moment as the boat heels— and you’ll see that it’s very, very unlikely you’ll capsize in a keelboat. At first you won’t believe this, when you feel the boat heel farther and farther and water washes into the cockpit, but just give it a chance. It’s physics. It works. And it’s on your side.