| 摘要 |
<p>This marine propulsion unit has a main shaft for connection to a drive shaft, and at least one helical screw along the main shaft. A duct surrounds the main shaft and screw thereby creating a ducted area. The ducted area has a water inlet near its proximal end and a water outlet near its distal end, the ducted area being tapered from inlet to outlet, whereby water is accelerated through the ducted area to provide propulsion. A number of secondary inlet ports are disposed along and pass through the duct into the ducted area, for drawing in water to minimize cavitation along the ducted area. In an alternative embodiment, there is also a second duct coaxial with and surrounding the first duct, thereby creating a second ducted area. The second ducted area has a water inlet near its proximal end and a water outlet near its distal end, the ducted area being tapered from inlet to outlet. At least one helical screw is provided along the first duct in the second ducted area, and the first duct is connected to the main shaft so that the first duct rotates with the main shaft. Additional secondary inlet ports are provided.</p> |
