When most people hear the term surface drive, they think speed and high performance, but what these rather specialized propulsion units are really about is efficiency. Because the propeller blades break the water's surface — they are called surface-piercing propellers — the engines powering them run under less load than with fully submerged props. Half of the propeller spins in the water. The other half rotates above the surface. This lets the boat make better use of the power of its engines and go faster than one with submerged props.