7. The faster your boat goes, the farther forward your apparent-wind angle becomes. For example, on a catamaran, even when the true-wind angle looks like a broad reach (the lower limit of a reacher-style sail), the actual apparent wind could have you sailing on a close reach, putting you back in the sweet spot for a code zero. Alternately, a heavy-displacement boat will have lower apparent-wind angles and may be a better candidate for a more traditional downwind spinnaker.
— Judy Blumhorst, Hyde Sails