SAMS Propulsion and Machinery Systems 3 — Questions and Answers
Question 1: What does the term 'propeller slip' refer to in marine propulsion?
- Physical slippage of the propeller on the shaft taper
- The difference between theoretical and actual advance per revolution (Correct answer)
- Blade deflection under load
- Propeller hub corrosion causing pitch loss
Correct answer: The difference between theoretical and actual advance per revolution
Propeller slip is the difference between the theoretical pitch distance the propeller should advance per revolution and the actual distance traveled through the water.
Question 2: A surveyor notes that a vessel's inboard engine raw water cooling pump impeller is made of nitrile rubber. What inspection finding would indicate impeller failure is imminent?
- Impeller vanes are uniform in length and flexible
- Vanes show set (permanent curve), cracking, or missing pieces (Correct answer)
- The impeller housing shows minor staining
- The cam follower plate shows normal wear marks
Correct answer: Vanes show set (permanent curve), cracking, or missing pieces
A nitrile impeller with permanent vane set, cracks, or missing pieces is near failure and will rapidly cause engine overheating if not replaced.
Question 3: When evaluating a vessel with twin diesel engines and a common seawater intake manifold, what specific risk should a surveyor note?
- Fuel cross-contamination between engine fuel systems
- Cross-flooding or loss of cooling water to both engines if the shared intake seacock fails (Correct answer)
- Exhaust gas recirculation between the two engine spaces
- Excessive vibration from synchronization issues
Correct answer: Cross-flooding or loss of cooling water to both engines if the shared intake seacock fails
A shared seawater intake means a single seacock failure can simultaneously deprive both engines of cooling water, an important redundancy risk.
Question 4: What is the function of a cutless bearing in a propulsion system?
- To absorb axial thrust from the propeller shaft
- To support and center the propeller shaft at the strut or stern tube using water lubrication (Correct answer)
- To isolate engine vibration from the propeller shaft
- To prevent electrolytic corrosion on the propeller shaft
Correct answer: To support and center the propeller shaft at the strut or stern tube using water lubrication
A cutless bearing is a rubber-lined, water-lubricated bearing that supports the propeller shaft at the strut and maintains shaft alignment.
Question 5: A surveyor observes that a marine gas turbine vessel has an intake plenum with visible salt crystal deposits. What operational problem does this indicate?
- Inadequate fuel filtration causing combustor fouling
- Failure of the intake air filtration and washing system (Correct answer)
- Excessive turbine inlet temperature from overloading
- Oil seal failure allowing lube oil into the air path
Correct answer: Failure of the intake air filtration and washing system
Salt deposits in the intake plenum indicate the air filtration or anti-icing/wash system has failed, allowing corrosive salt-laden air to reach the compressor.
Question 6: When surveying an outboard motor on a fiberglass transom, what structural condition is most critical to evaluate?
- Color match between transom gelcoat and hull sides
- Transom core delamination or saturation that reduces motor mounting strength (Correct answer)
- Surface oxidation of the transom fiberglass
- Wiring conduit routing through the transom cap
Correct answer: Transom core delamination or saturation that reduces motor mounting strength
A delaminated or water-saturated transom core loses structural integrity, which can cause motor bracket failure and motor loss under load.
Question 7: What reading would alert a surveyor to excessive crankshaft main bearing wear on a running diesel engine?
- High coolant temperature on the thermostat gauge
- Abnormally low engine oil pressure at operating temperature and RPM (Correct answer)
- Elevated alternator output voltage
- High fuel consumption with normal exhaust temperature
Correct answer: Abnormally low engine oil pressure at operating temperature and RPM
Worn main bearings increase bearing clearances, allowing oil to escape faster and reducing oil pressure measured at the sender.
SAMS Propulsion and Machinery Systems 3
What does the term 'propeller slip' refer to in marine propulsion?