SAMS Propulsion and Machinery Systems 2 — Questions and Answers
Question 1: When inspecting a vessel's reduction gear, a marine surveyor notices pitting on gear teeth. What does this typically indicate?
- Normal wear from extended operation
- Lubrication failure or contaminated gear oil (Correct answer)
- Excessive shaft alignment error only
- Thermal expansion from overheating exhaust
Correct answer: Lubrication failure or contaminated gear oil
Pitting on gear teeth is a classic sign of lubrication failure or oil contamination, which prevents proper film formation between meshing surfaces.
Question 2: A diesel engine's turbocharger is producing an audible whine at elevated RPM. What should a surveyor check first?
- Intercooler efficiency
- Turbine and compressor blade condition and bearing wear (Correct answer)
- Fuel injector spray pattern
- Exhaust manifold backpressure
Correct answer: Turbine and compressor blade condition and bearing wear
An abnormal whine from a turbocharger typically indicates worn bearings or damaged blades in the turbine or compressor section.
Question 3: What is the primary purpose of a shaft seal (stuffing box or lip seal) in a propulsion system?
- To dampen vibration between shaft and hull
- To prevent seawater ingress into the vessel around the propeller shaft (Correct answer)
- To lubricate the propeller shaft bearings
- To maintain propeller pitch angle
Correct answer: To prevent seawater ingress into the vessel around the propeller shaft
A shaft seal prevents seawater from entering the vessel through the aperture where the propeller shaft penetrates the hull.
Question 4: During a sea trial, a surveyor observes that engine RPM drops when the vessel turns to starboard. This symptom most likely indicates:
- A starboard fuel injector is partially blocked
- Propeller cavitation or shaft misalignment exacerbated by hull loading in turns (Correct answer)
- The governor is malfunctioning under load
- Transmission fluid is overheating
Correct answer: Propeller cavitation or shaft misalignment exacerbated by hull loading in turns
RPM drop during turns often suggests propeller cavitation or shaft/strut misalignment that worsens when hull attitude changes in a turn.
Question 5: What does a high exhaust back pressure reading indicate in a marine diesel engine installation?
- The engine is running at optimal load
- A restriction in the exhaust system such as a blocked muffler or collapsed hose (Correct answer)
- Excessive fuel enrichment at idle
- The raw water pump is overperforming
Correct answer: A restriction in the exhaust system such as a blocked muffler or collapsed hose
Elevated exhaust back pressure points to a restriction downstream of the engine, commonly a blocked wet muffler, kinked hose, or collapsed exhaust riser.
Question 6: A surveyor finds bronze through-hull fittings adjacent to the aluminum stern drive. What corrosion concern should be documented?
- Crevice corrosion from the bronze fitting threads
- Galvanic corrosion due to dissimilar metals in an electrolyte (Correct answer)
- Stray current corrosion from the raw water pump
- Intergranular corrosion of the aluminum casting only
Correct answer: Galvanic corrosion due to dissimilar metals in an electrolyte
Bronze (copper alloy) and aluminum are far apart on the galvanic series; when coupled in seawater, the aluminum will sacrificially corrode rapidly.
Question 7: Which condition would a surveyor most expect to find associated with a cavitating propeller?
- Smooth leading edges with uniform pitch
- Erosion pitting on the suction face of the blades near the tips (Correct answer)
- Even thinning of blade trailing edges from abrasion
- Increased propeller diameter from metal deposition
Correct answer: Erosion pitting on the suction face of the blades near the tips
Cavitation causes vapor bubbles to implode violently against blade surfaces, leaving characteristic erosion pits primarily on the suction face near blade tips.
SAMS Propulsion and Machinery Systems 2
When inspecting a vessel's reduction gear, a marine surveyor notices pitting on gear teeth.
What does this typically indicate?