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Contra-rotating propellers have benefits when providing thrust in marine applications. Contra-rotating propellers are used on torpedoes due to the natural torque compensation and are also used in some motor boats. The cost of boring out the outer shafts and problems of mounting the inner shaft bearings are not worth pursuing in case of normal ...
English inventor Francis Ronalds described what he called a propelling rudder in 1859 that combined the propulsion and steering mechanisms of a boat in a single apparatus. . The propeller was placed in a frame having an outer profile similar to a rudder and attached to a vertical shaft that allowed the device to rotate in plane while spin was transmitted to the propell
Other vessels may have twin, triple or quadruple screws. Power is transmitted from the engine to the screw by way of a propeller shaft, which may be connected to a gearbox. The propeller then moves the vessel by creating thrust. When the propeller rotates the pressure in front of the propeller is lower than the pressure behind the propeller.
Outboard motor shaft lengths are standardized to fit 15-, 20- and 25-inch (38-, 51- and 64-centimeter) transoms. If the shaft is too long it will extend farther into the water than necessary creating drag, which will impair performance and fuel economy. If the shaft is too short, the motor will be prone to ventilation.
In larger and more modern engines, a rubber bushing transmits the torque of the drive shaft to the propeller's hub. Under a damaging load the friction of the bushing in the hub is overcome and the rotating propeller slips on the shaft, preventing overloading of the engine's components. [44] After such an event the rubber bushing may be damaged.
In the conventional azimuth thrusters such as Z-drive and L-drive thrusters, the propeller is driven by an electric motor or a diesel engine inside the ship's hull. The propeller is coupled to the prime mover with shafts and bevel gears that allow rotating the propeller about a vertical axis. This type of propulsion system has a long tradition ...