Maritime and Marine Marine Engineering and Propulsion 1 — Questions and Answers
Question 1: What does the term 'cavitation' mean in marine propulsion?
- Formation and collapse of vapor bubbles on the propeller blades causing erosion and loss of thrust (Correct answer)
- Vibration caused by propeller blade imbalance during high-speed operation
- Air entrainment in the fuel system causing engine performance loss
- Overheating of the propeller shaft bearing during extended operation
Correct answer: Formation and collapse of vapor bubbles on the propeller blades causing erosion and loss of thrust
Cavitation occurs when propeller blade pressure drops low enough to vaporize seawater, forming bubbles that collapse violently and erode the blade surface.
Question 2: What is the function of a heat exchanger on a marine engine?
- To cool the engine's freshwater coolant using raw seawater without mixing the two circuits (Correct answer)
- To heat fuel before injection for better combustion in cold weather
- To transfer heat from the exhaust to the air intake system
- To warm seawater before it enters the engine cooling jackets
Correct answer: To cool the engine's freshwater coolant using raw seawater without mixing the two circuits
A heat exchanger allows engine coolant (freshwater) to transfer heat to raw seawater in separate circuits, protecting internal passages from corrosion.
Question 3: What is the purpose of zinc anodes (sacrificial anodes) on a vessel's underwater hardware?
- To protect metal fittings from galvanic corrosion by being sacrificially corroded instead (Correct answer)
- To add weight for ballast and improve vessel stability
- To reduce drag by creating a smooth surface on the hull
- To conduct static electricity away from electronic equipment
Correct answer: To protect metal fittings from galvanic corrosion by being sacrificially corroded instead
Zinc anodes are more electrochemically active than bronze or steel; they corrode preferentially in galvanic cells, protecting propellers, shafts, and through-hulls.
Question 4: What does a two-stroke outboard engine require that a four-stroke engine does not?
- Oil premixed with the fuel or injected by a separate oil injection system (Correct answer)
- Regular valve adjustments for proper engine timing
- A separate crankcase oil reservoir and oil changes
- A carburetor heat system to prevent icing
Correct answer: Oil premixed with the fuel or injected by a separate oil injection system
Two-stroke engines lubricate internal components with oil mixed into or injected with fuel, since they lack a separate oil sump.
Question 5: What is the function of a seacock (sea valve) on a vessel?
- To shut off a through-hull fitting to prevent flooding if a hose or fitting fails (Correct answer)
- To control the flow of cooling water to the engine
- To regulate ballast water intake for stability adjustment
- To drain the bilge overboard when the vessel is at rest
Correct answer: To shut off a through-hull fitting to prevent flooding if a hose or fitting fails
A seacock is a valve at each through-hull that can be closed to stop seawater from flooding the vessel if a hose or fitting fails.
Question 6: What does 'shaft horsepower' (SHP) measure in marine engineering?
- Power actually delivered to the propeller shaft, after accounting for engine and gear losses (Correct answer)
- Gross engine output power before any mechanical losses
- Power required to push a vessel at its maximum hull speed
- The combined output of all engines on a multi-engine vessel
Correct answer: Power actually delivered to the propeller shaft, after accounting for engine and gear losses
Shaft horsepower is the useful power delivered at the propeller shaft, measured after accounting for gearbox and bearing losses from rated engine power.
Maritime and Marine Marine Engineering and Propulsion 1
What does the term 'cavitation' mean in marine propulsion?