Propulsion and Machinery Systems Flashcards

A stern drive (I/O) unit shows heavy barnacle growth on the lower unit and cavitation plate. What propulsion concern should the surveyor investigate further?

Answer: Restriction of water flow to the engine cooling water intake on the lower unit

Heavy fouling on a stern drive lower unit can block the engine cooling water pickup, causing overheating and potential engine damage.

What does 'diesel knock' during a compression check indicate in a marine diesel engine?

Answer: Low compression in one or more cylinders suggesting worn rings, valves, or bore damage

Diesel knock during compression testing indicates low compression, which prevents proper fuel ignition and points to worn piston rings, valves, or cylinder bore damage.

A surveyor inspects a vessel with a hydraulic bow thruster and finds the hydraulic fluid reservoir level consistently low. The most important follow-up inspection is:

Answer: Tracing all hydraulic lines, cylinders, and connections for external leaks

Chronically low hydraulic fluid always indicates a leak somewhere in the system that must be located to prevent pump cavitation and system failure.

In evaluating a vessel's propeller shaft, a surveyor finds runout exceeding manufacturer limits when measured with a dial indicator. This finding indicates:

Answer: Shaft bend or distortion requiring replacement or straightening

Excessive shaft runout indicates the shaft is bent or distorted, which will cause vibration, accelerated bearing wear, and possible seal failure.

What does a 'wet stack' condition refer to in a marine diesel engine exhaust system?

Answer: Accumulation of unburned fuel and oil in the exhaust stack from chronic light-load operation

Wet stacking occurs when diesel engines are run at light loads for extended periods, causing incomplete combustion and accumulation of raw fuel and oil in the exhaust.

A surveyor finds that a vessel's fuel polishing system filter is black with contamination after only two weeks of operation. This most likely indicates:

Answer: Active microbial growth (diesel bug) or severe water contamination in the fuel tanks

Rapid black filter contamination typically indicates an active microbial infestation (Hormoconis resinae and similar organisms) thriving on water in the fuel.

What is the purpose of an engine alignment check during a marine survey, and what tool is typically used?

Answer: To confirm the engine and shaft are properly aligned to prevent vibration and bearing wear; performed with a feeler gauge at the coupling flanges

Engine alignment verifies the engine output shaft and propeller shaft are coaxial; feeler gauges measure the gap uniformity around the split coupling flanges to detect angular and parallel misalignment.