Abstract
DDWFTTW (Dead-DownWind Faster Than The Wind) refers to a wind powered car using rotary wings that runs faster than the wind in tailwind. It was found experimentally by Jack Goodman and was experimentally demonstrated in a nearly perfect form by Rick Cavallaro. A full scale model called Blackbird with weight 200kg and propeller diameter 5m has run at the 2.8 times faster speed than tailwind. On the other hand, the theoretical verification was given by Mark Drela. The absorbed energy through rotation of wheel or water turbine is transferred to air propeller, and the thrust is generated by the air propeller. If the running resistance of the car or ship is sufficiently smaller than the thrust, the car or the ship can advance faster than the tailwind speed. The present paper clarified the problem and direction when applied to a wave powered ship. A reasonable application would bring us a big energy saving effect.
