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

Running in water that is too deep for the anti-ventilation plate

Answer

Using a propeller with too much pitch for the engine

Answer

Running at idle speed for extended periods in warm 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

To provide a watertight seal against water ingress into the shaft log

Answer

To allow the propeller to freewheel when the engine is in neutral

Answer

To automatically adjust propeller pitch based on engine 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

When it has minor pitch distortion from a light grounding strike

Answer

When blade erosion pitting from cavitation is superficial

Answer

When there is surface oxidation on the aluminum blades

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

Increases RPM while decreasing torque load on the engine

Answer

Decreases thrust while allowing higher top speed

Answer

Has no measurable effect if pitch remains constant

Question 5

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

Accepted Answer

Nickel, bronze, and aluminum

Answer

Nickel, iron, and brass

Answer

Nib rubber composite and aluminum

Answer

Non-corrosive iron-based alloy

Question 6

What causes a boat to 'prop walk' sideways when shifted into reverse?

Accepted Answer

The asymmetric thrust pattern created by the propeller's rotation in reverse

Answer

The pitch angle of the blades reversing to a negative angle

Answer

Ventilation drawing exhaust gases under the hull

Answer

Cavitation on the pressure face of the blades in reverse

Question 7

What is the purpose of the thrust bearing in a propeller shaft system?

Accepted Answer

To absorb and transfer the propeller's axial thrust force to the engine mounts and hull

Answer

To reduce friction between the rotating propeller and surrounding water

Answer

To prevent the propeller shaft from spinning when the engine is in neutral

Answer

To align the propeller shaft angle with the engine output flange