Even if you’re a cruising sailor who’s not concerned with performance, sail shape is critical to control heel. Full, stretchy sails rob power in light air, but – more critically – they create heel and weather helm when you want control. At some point, you have to sail upwind, usually at the least convenient times. One of the real luxuries and pleasures of a good cruising boat is the ability to sail effectively upwind when necessary. If your sails don’t have proper shape, the boat will not be able to go upwind effectively.