When applying kicking strap or mainsheet tension to control the leech twist of a conventional mainsail, the question arises as to how hard you should be pulling. In the context of a cruising yacht, the answer is as simple as this: Heave down until the top batten of the sail lines up parallel with the boom when sighted from underneath it. The curve of the mainsail leech will then generally follow that of the genoa, giving rise to a good-looking rig that is working efficiently.