Résumé | Vertical axis propellers have been widely accepted as a propulsion system for tugs because they provide several advantages over screw propellers. The principle attraction is their ability to vary thrust magnitude and direction, whilst maintaining a constant engine rotation rate. When applied to tug designs, the propellers are typically positioned so that they extend beyond the keel. This has the advantage of keeping the propellers in unobstructed flow, but has the disadvantage of placing them in a vulnerable position, which is normally compensated for by the addition of a protective cage. This type of propulsion system has been widely accepted for escort tugs, which use forces generated at high speeds and large yaw angles to control a tanker in an emergeny situation. |
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