Exam Question
(a) Why do you need an 'over-speed' trip despite a governor being fitted to a marine diesel engine? (8)
(b) With respect to an auxiliary engine governor, what is the significance of: (8)
(i) the Load limit knob
(ii) the compensation
Class 4 (4th Engineer)
MEKM
📅 Jul 2025
Reference Answer
### Part (a): Necessity of an Over-speed Trip
An over-speed trip is a mandatory, independent safety device fitted to marine diesel engines, in addition to the governor, to prevent catastrophic failure from excessive rotational speed. The governor is a primary *speed-regulating* device, whereas the over-speed trip is a secondary, purely *protective* device. The necessity arises from the potential failure modes of the governor and the severe consequences of an uncontrolled over-speed event.
**1. Governor Failure Modes:**
The governor, whether hydromechanical or electronic, is a complex system susceptible to failure. A failure could lead to the fuel racks moving to the maximum fuel position, causing the engine to accelerate uncontrollably.
An over-speed trip is a mandatory, independent safety device fitted to marine diesel engines, in addition to the governor, to prevent catastrophic failure from excessive rotational speed. The governor is a primary *speed-regulating* device, whereas the over-speed trip is a secondary, purely *protective* device. The necessity arises from the potential failure modes of the governor and the severe consequences of an uncontrolled over-speed event.
**1. Governor Failure Modes:**
The governor, whether hydromechanical or electronic, is a complex system susceptible to failure. A failure could lead to the fuel racks moving to the maximum fuel position, causing the engine to accelerate uncontrollably.
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