Maritime and Marine Marine Engineering and Propulsion 2 — Questions and Answers
Question 1: What is the purpose of a raw water strainer on a marine engine?
- To filter debris from seawater before it enters the engine's cooling system (Correct answer)
- To remove fuel contaminants before fuel reaches the injectors
- To filter bilge water before it is pumped overboard
- To separate air from coolant in the freshwater cooling circuit
Correct answer: To filter debris from seawater before it enters the engine's cooling system
A raw water strainer catches marine growth, sediment, and debris from seawater before it enters the engine's raw water cooling circuit.
Question 2: What is the recommended action when a marine diesel engine shows a sudden drop in oil pressure?
- Stop the engine immediately to prevent catastrophic bearing failure (Correct answer)
- Reduce throttle to idle and monitor for 10 minutes
- Switch to the backup oil pump
- Add engine oil and continue at reduced speed
Correct answer: Stop the engine immediately to prevent catastrophic bearing failure
Low oil pressure means bearings are not being lubricated; continuing to run the engine will cause rapid and catastrophic internal damage.
Question 3: What is electrolysis (stray current corrosion) in marine context, and how is it prevented?
- Accelerated corrosion caused by stray DC current flowing through metal fittings; prevented by proper bonding and zinc anodes (Correct answer)
- Natural galvanic corrosion between dissimilar metals; prevented by using identical metals only
- Chemical corrosion caused by saltwater exposure; prevented by painting all underwater surfaces
- Vibration-induced metal fatigue in propellers; prevented by regular balancing
Correct answer: Accelerated corrosion caused by stray DC current flowing through metal fittings; prevented by proper bonding and zinc anodes
Stray current corrosion occurs when DC current from onboard systems flows through metal fittings into the water; bonding all metals and using zincs controls it.
Question 4: What is the purpose of the impeller in a marine raw water pump?
- To circulate seawater through the engine's cooling system using flexible rubber vanes (Correct answer)
- To pressurize fuel for injection into the engine cylinders
- To circulate engine oil through the lubrication system
- To drive seawater through the exhaust injection cooling system
Correct answer: To circulate seawater through the engine's cooling system using flexible rubber vanes
The raw water pump's rubber impeller creates suction to draw seawater in and push it through the engine's cooling heat exchanger.
Question 5: What does 'wet exhaust' mean on a marine engine installation?
- Exhaust gases are mixed with raw cooling water before exiting the vessel, cooling the exhaust and reducing noise (Correct answer)
- Exhaust gases exit through a dry stack above the waterline without water injection
- Exhaust gases pass through a water separator to recover condensate
- The exhaust manifold is water-jacketed to prevent heat damage
Correct answer: Exhaust gases are mixed with raw cooling water before exiting the vessel, cooling the exhaust and reducing noise
A wet exhaust system mixes raw cooling water with exhaust gases, lowering exhaust temperature enough for the mixture to pass through flexible hose below deck.
Question 6: What is the purpose of a marine transmission (gear box) on a powered vessel?
- To enable forward, neutral, and reverse operation and to reduce engine RPM to propeller shaft RPM (Correct answer)
- To convert engine torque to electrical power for onboard systems
- To regulate engine speed electronically for fuel efficiency
- To distribute engine power between multiple propeller shafts
Correct answer: To enable forward, neutral, and reverse operation and to reduce engine RPM to propeller shaft RPM
The marine transmission provides forward, neutral, and reverse gear selection and reduces high engine RPM to optimal propeller shaft speeds through a gear reduction ratio.
Maritime and Marine Marine Engineering and Propulsion 2
What is the purpose of a raw water strainer on a marine engine?