Yes, the engine. Speaking of sailing, the angle and shape of the sails are both important to maintaining velocity. Racing boats adjust (trim) the shape of the

Yes, the engine. Speaking of sailing, the angle and shape of the sails are both important to maintaining velocity. Racing boats adjust (trim) the shape of the sails all the time. Merely deflecting the wind obeys conservation of momentum, but conservation of energy in an unpowered sailboat (overcoming losses due to friction) also means extracting energy from the airflow.