| 摘要 |
A propulsion and steering unit for a waterborne vessel. The propulsion and steering unit is in the form of an azimuth thruster 1 comprising a propeller 2 fixed to one end of a propeller shaft 4, which is rotatable about a longitudinal axis 6. Fixed to the other end of the propeller shaft 4 there is a beveled gear crown wheel 8. The crown wheel 8 is engaged with a driving pinion gear 10 and, in this particular embodiment, the crown wheel 8 is driven in a direction 7 by the driving pinion gear 10. The driving pinion gear 10 is mounted on a vertical drive shaft 12, which is connected to drive means (not shown) for the vessel. A longitudinal axis 18 of the drive shaft 12, about which the drive pinion 8 rotates, is substantially perpendicular to the longitudinal axis 6 of the propeller shaft 4 about which the propeller 2 rotates. On the top of the azimuth thruster 1 there is positioned a steering engine (not shown), which turns the thruster so that the pulling force vector can be orientated in a decided direction from 0-360 degrees, or a multiple of 360 degrees in both directions. Normally a steering engine consists of hydraulic or electric motors which are connected to a gear rim connected to a vertical stem on the thruster. If the thruster 1 is rotated in still water with the propeller disconnected, this will be easily rotated with a minimum of torque independent of direction. However, if the vessel is moving then due to the propeller forces and the dynamic characteristics of the slipstream there will be a variable torque resistance that varies with rotation rate and vessel speed. If the resistance is larger than the torque steering engine is able to give, the thruster will rotate against the pressure torque from the steering engine. The reason for this is the hydraulic (or flow induced) contribution and the torque archieved on the vertical shaft 12 due to the rotation of the shaft 12.
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