When I was growing up, I had an inflatable plastic punching dummy. It was about as tall as I was and had a smiling face painted on it. My challenge was to hit it hard enough to make it stay down. But no matter how hard I tried, it always bounced right back up again. The secret? There was a lead weight in the bottom that always kept it upright. Sailboats operate by the same principle. The lead weights in their keels provide the ballast to keep them balanced and upright in strong winds.