五、請將下列專業英文翻譯成中文。（20 分）Controllable pitch propellers are normally fitted to a flanged tail shaft as the operating mechanism is housed in the propeller boss. As its name implies, it is possible to alter the pitch of this type of propeller to change ship speed or to adjust to the prevailing resistance conditions. This change in pitch is effected by rotating the blades about their vertical axes, either by hydraulic or mechanical means. A shaft generator can be driven at constant speed while allowing at the same time a change of ship’s speed through the propeller. Since it is normally possible to reverse the pitch completely, this type of propeller is used with a unidirectional engine to give full ahead or astern thrust, when maneuvering.