It takes a ton more power to gain 1/2 knot. Our previous boat was a 31 footer medium-light displacement with a 16 hp Universal. It was fine in flat conditions but any headwind or seas on the nose slowed us down quite a bit. We could keep up with friends in a Catalina 30 with 30 hp (as I recall) when things were calm but once the waves came up it was a completely different story.