Marine Propulsion & Propeller Systems Flashcards
7 cards from real MST practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Marine Propulsion & Propeller Systems flashcards as text
What causes propeller ventilation on an outboard motor?
Answer: Surface air or exhaust gases being drawn into the spinning propeller
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.
What is the primary function of the splined connection on a propeller shaft?
Answer: To transmit rotational torque from the shaft to the propeller hub
The splined connection between the propeller shaft and hub transmits rotational torque from the engine to the propeller without slipping under load.
When should a damaged propeller be replaced rather than repaired?
Answer: When a blade is missing or there is a crack extending through the hub
A missing blade or hub crack compromises structural integrity and dynamic balance to the point where repair is unsafe — replacement is required.
What effect does increasing propeller diameter have on engine performance?
Answer: Increases thrust and torque load but typically reduces maximum RPM
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.
What alloy is a 'nibral' marine propeller made from?
Answer: Nickel, bronze, and aluminum
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.
What causes a boat to 'prop walk' sideways when shifted into reverse?
Answer: The asymmetric thrust pattern created by the propeller's rotation in reverse
In reverse, a single-rotation propeller creates an asymmetric thrust pattern (similar to P-factor) because blade loading differs between the top and bottom arcs of rotation, pushing the stern sideways.
What is the purpose of the thrust bearing in a propeller shaft system?
Answer: To absorb and transfer the propeller's axial thrust force to the engine mounts and hull
The thrust bearing transmits the propeller's forward or reverse axial thrust force from the rotating shaft to the engine mounts and ultimately to the hull, propelling the boat.