Marine Propulsion Systems and Auxiliary Machinery
What this domain tests
Here the examiner checks whether you understand the whole propulsion train and the auxiliary plant that supports it: shafting, stern tube, CPP and gearboxes, steering gear, thrusters, and the service systems - compressed air, fresh water, HVAC, sewage, oily water separator, incinerator, ballast pumps. Expect questions that link a propulsion symptom to an auxiliary root cause.
Core rules and concepts
- Shafting and stern tube. Know the difference between oil-lubricated and water-lubricated stern tubes, the purpose of the aft seal with its three chambers, header tank level alarms, and why a rising stern tube temperature with dropping header level means seal failure.
- CPP and gearbox. Hydraulic oil pressure, servo cylinder, feedback to the bridge, and blade pitch interlocks. Loss of hydraulic pressure normally drives the blades to a safe pitch or trips the system.
- Steering gear. SOLAS requires two independent power actuating systems; a single failure must be detectable and the gear must be able to put the rudder hard over to 35° on one side and 30° on the other, with a rudder angle indicator on the bridge. Drills and the emergency steering changeover are exam favourites.
- Compressed air. Main air receivers sized for a defined number of engine starts; air compressor interlocks, drains, relief valves; never open a receiver without draining and verifying pressure.
- Oily water separator. 15 ppm alarm and automatic stopping device; the 15 ppm bilge alarm must be operational and the overboard valve must close automatically on alarm. Recording in the Oil Record Book is mandatory.
- Sewage and incinerator. MARPOL Annex IV treatment standards and Annex VI incinerator rules; know which wastes may be incinerated and which are prohibited (e.g. PCBs, refined oils in certain cases, cargo residues).
Worked example
Stern tube header tank level falls slowly, the aft seal drain shows oil, and the stern tube bearing temperature is 8 °C above normal at full ahead. Reasoning: a sealing ring is passing oil to the sea side; the bearing is losing lubrication. Action: reduce rpm to lower heat input, monitor temperature continuously, check header tank level and top up with the correct grade, prepare for possible dry-docking decision, and record. The scoring answer links the physical evidence to the seal chamber affected and gives a bounded operational limit.
Traps that cost marks
- Quoting "35°" without saying which side and which SOLAS regulation context.
- Forgetting the 15 ppm alarm and automatic stop in OWS answers.
- Describing the incinerator as able to burn anything.
- Not mentioning pressure verification before opening any air or steam system.
- Mixing up CPP hydraulic failure response with a gearbox oil failure response.