Class 2 (2nd Engineer) MEKG 📅 Jul 2018

Exam Question

(a) Describe a transverse bow thrust unit using a controllable pitch propeller. Mention should be made of how it is supported and how the strength of thrust and reverse thrust are achieved.

(b) State with reasons. a suitable prime mover for the controllable pitch propeller.

(c) State whether the thrust unit delivers a relatively low-pressure head with high-volume output or high-pressure head with low-volume output.

Reference Answer

(a) A transverse bow thruster assists in docking, manoeuvring, or positioning a vessel, particularly at low speeds (typically below 4 knots). The most common arrangement is a tunnel thruster , consisting of a pipe tunnel running athwartship with protective guides at the ends and reinforcement bars along the top and bottom for added strength.
In a CPP-based system, the propeller blades’ pitch is controlled using a non-rotating servo motor housed within the gear housing. The servo motor operates based on input from the bridge:
Movement of the bridge lever moves the servo control valve piston , allowing hydraulic oil to flow into the appropriate side of the servo piston via the servo control block and check valve.
The force generated on the servo piston is transmitted via a push-pull piston rod inside the propeller shaft to the crosshead and crank mechanism in the gear housing.

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