MST Marine Propulsion & Propeller Systems 2

Question 1

What causes propeller ventilation on an outboard motor?

Accepted Answer

Surface air or exhaust gases being drawn into the spinning propeller

Answer

Ventilation occurs when surface air or exhaust gases are drawn into the spinning propeller, causing it to over-rev as it loses its grip on water.

Question 2

What is the primary function of the splined connection on a propeller shaft?

Accepted Answer

To transmit rotational torque from the shaft to the propeller hub

Answer

The splined connection between the propeller shaft and hub transmits rotational torque from the engine to the propeller without slipping under load.

Question 3

When should a damaged propeller be replaced rather than repaired?

Accepted Answer

When a blade is missing or there is a crack extending through the hub

Answer

A missing blade or hub crack compromises structural integrity and dynamic balance to the point where repair is unsafe — replacement is required.

Question 4

What effect does increasing propeller diameter have on engine performance?

Accepted Answer

Increases thrust and torque load but typically reduces maximum RPM

Answer

A larger diameter propeller displaces more water per revolution, increasing thrust and the torque load on the engine, which typically prevents the engine from reaching maximum RPM.

Question 5

What alloy is a 'nibral' marine propeller made from?

Accepted Answer

Nickel, bronze, and aluminum

Answer

Nibral is an alloy of nickel, bronze (copper-tin alloy), and aluminum, prized for its high strength, excellent corrosion resistance, and use in demanding marine applications.

(MST) Marine Service Technician Practice Test

(MST) Marine Service Technician Practice Test

MST Marine Propulsion & Propeller Systems 2