Maritime and Marine Marine Engineering and Propulsion

Question 1

What does the term 'cavitation' mean in marine propulsion?

Accepted Answer

Formation and collapse of vapor bubbles on the propeller blades causing erosion and loss of thrust

Answer

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?

Accepted Answer

To cool the engine's freshwater coolant using raw seawater without mixing the two circuits

Answer

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?

Accepted Answer

To protect metal fittings from galvanic corrosion by being sacrificially corroded instead

Answer

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?

Accepted Answer

Oil premixed with the fuel or injected by a separate oil injection system

Answer

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?

Accepted Answer

To shut off a through-hull fitting to prevent flooding if a hose or fitting fails

Answer

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.

Maritime and Marine Practice Test

Maritime and Marine Practice Test

Maritime and Marine Marine Engineering and Propulsion