To the Editor of the New-York Times: In your issue of last Sunday I was much surprised to find a communication signed W, advocating the use of the double-propeller ... since a boat was built ...

Most famous of these is probably the toroidal propeller that made waves a while ago, mostly in the field of flying drones, but commercial toroidal boat props exist too. Test results of the ...

A double propeller/double rudder system gives them ... The bow propeller is used to stop the boat, as it can do so faster t h a n the stern propeller going in reverse. Maneuverability is another ...

A 3.3 m flat-bottomed aluminum boat has used a base, and an aluminum frame was bolted on for the motor and propeller. The motor is an 18 kW brushless motor, with a 160 cm/63-inch carbon fiber ...