MTC MTC Steering & Propulsion Systems 2 — Questions and Answers
Question 1: What is the correct torque sequence when installing a propeller on a tapered shaft with a keyway?
- Install propeller, add key, install nut, torque to spec, install cotter pin or locking device (Correct answer)
- Install propeller without key, torque nut very tightly to prevent slipping
- Press propeller on with heat, install nut finger-tight only
- Install propeller, torque nut, then drive key in last
Correct answer: Install propeller, add key, install nut, torque to spec, install cotter pin or locking device
The woodruff key must be seated before the propeller, the nut torqued to the manufacturer's specification, and a cotter pin or locking tab installed to prevent the nut from backing off.
Question 2: When selecting a replacement propeller, which two specifications are MOST critical to match for correct engine loading?
- Color and material
- Diameter and pitch (Correct answer)
- Number of blades and material
- Hub diameter and blade thickness
Correct answer: Diameter and pitch
Diameter determines thrust and RPM band while pitch controls the theoretical advance per revolution; together they define the propeller's load on the engine and must match the power and application.
Question 3: A boat experiences constant pulling to one side at cruise speed with no steering input. What is the MOST likely cause?
- Low fuel level on one side
- Propeller torque effect or a bent/damaged propeller blade (Correct answer)
- Incorrect engine oil viscosity
- Fouled spark plugs on one cylinder bank
Correct answer: Propeller torque effect or a bent/damaged propeller blade
A bent or damaged propeller blade creates an asymmetric thrust that causes the vessel to veer, and propeller torque effect (prop walk) is inherent in single-engine vessels without compensation.
Question 4: What is the purpose of the 'anti-ventilation plate' (cavitation plate) located above a propeller on an outboard motor?
- To protect the propeller from impact with debris
- To prevent surface air from being drawn down to the propeller, which would cause loss of thrust (Correct answer)
- To direct exhaust gases away from the propeller
- To mount the trim tab and engine ID plate
Correct answer: To prevent surface air from being drawn down to the propeller, which would cause loss of thrust
The anti-ventilation plate creates a pressure barrier that separates the water surface from the propeller, preventing air ingestion that would cause the propeller to 'ventilate' and lose thrust.
Question 5: How is engine trim angle measured on an outboard or sterndrive application?
- In degrees of shaft rotation
- As the angle of the drive unit relative to vertical (or the transom) (Correct answer)
- By measuring the fuel flow difference at different speeds
- By the voltage differential between port and starboard trim sensors
Correct answer: As the angle of the drive unit relative to vertical (or the transom)
Trim angle describes how far the lower unit is tilted in or out relative to the transom; negative (in) trim digs the bow down while positive (out) trim raises the bow and reduces drag at speed.
Question 6: When inspecting a vessel's rudder post for wear, what is the technician checking for?
- Correct paint coverage on the rudder
- Excessive clearance (slop) between the rudder post and its bearings or gudgeons (Correct answer)
- The distance between rudder and propeller
- Rudder color consistency for inspection reports
Correct answer: Excessive clearance (slop) between the rudder post and its bearings or gudgeons
Worn rudder post bearings or gudgeons create excessive play that results in imprecise steering and can lead to complete rudder loss if left unaddressed.
MTC MTC Steering & Propulsion Systems 2
What is the correct torque sequence when installing a propeller on a tapered shaft with a keyway?