USCG General Engineering 5 — Questions and Answers
Question 1: What is the purpose of a 'coffin plate' in a marine boiler?
- A baffle that directs combustion gases across the tubes
- A reinforcing plate used at the junction of the furnace and boiler shell (Correct answer)
- A sacrificial plate protecting the boiler drum from corrosion
- A cover plate for the boiler inspection manhole
Correct answer: A reinforcing plate used at the junction of the furnace and boiler shell
A coffin plate (also called a gusset stay) reinforces the structural junction between the furnace and the boiler shell to resist pressure-induced stress.
Question 2: Which condition would cause a centrifugal pump to cavitate?
- Excessive discharge pressure
- Suction pressure falling below the vapor pressure of the liquid (Correct answer)
- Pump running at below-rated speed
- Discharge valve fully open
Correct answer: Suction pressure falling below the vapor pressure of the liquid
Cavitation occurs when suction pressure drops below the liquid's vapor pressure, causing vapor bubbles to form and then collapse violently, damaging the pump impeller.
Question 3: What is the correct action if the 15 ppm bilge alarm activates while overboard discharge is underway?
- Reduce pumping rate and continue discharge
- Immediately stop the overboard discharge and divert to a holding tank (Correct answer)
- Bypass the alarm and complete the discharge
- Increase separator flow rate to dilute the oil concentration
Correct answer: Immediately stop the overboard discharge and divert to a holding tank
MARPOL requires immediate cessation of discharge when oil content exceeds 15 ppm; the oily water must be diverted to a slop or holding tank.
Question 4: What is the purpose of a 'stuffing box' (packing gland) on a centrifugal pump?
- To lubricate the pump impeller
- To prevent leakage along the pump shaft where it exits the casing (Correct answer)
- To balance axial thrust on the pump shaft
- To cool the pump bearing
Correct answer: To prevent leakage along the pump shaft where it exits the casing
A stuffing box contains packing material compressed around the pump shaft to minimize fluid leakage where the rotating shaft passes through the stationary pump casing.
Question 5: In marine electrical systems, what does a 'dead front' switchboard mean?
- A switchboard that has lost all power
- A switchboard where all live parts are enclosed and inaccessible from the front (Correct answer)
- A switchboard with no circuit breakers installed
- A switchboard used only during emergency conditions
Correct answer: A switchboard where all live parts are enclosed and inaccessible from the front
A dead front switchboard has all energized conductors and bus bars enclosed behind the front panel, reducing the risk of accidental contact by personnel.
Question 6: What is the function of a governor on a marine diesel engine?
- To control cooling water temperature
- To automatically regulate engine speed under varying load conditions (Correct answer)
- To limit maximum cylinder pressure
- To control the turbocharger boost pressure
Correct answer: To automatically regulate engine speed under varying load conditions
A governor automatically adjusts fuel delivery to maintain a set engine speed regardless of changes in load, preventing overspeed or underspeed conditions.
Question 7: What is 'hydraulic lock' in a diesel engine, and why is it dangerous?
- A safety feature that locks the engine during maintenance
- Liquid in the cylinder that cannot be compressed, potentially bending the connecting rod (Correct answer)
- Excessive oil pressure that prevents the crankshaft from turning
- A condition where fuel injection pressure becomes too high to open injectors
Correct answer: Liquid in the cylinder that cannot be compressed, potentially bending the connecting rod
Hydraulic lock occurs when liquid (water or oil) accumulates in a cylinder; since liquids are incompressible, attempting to start the engine can bend or break the connecting rod.
USCG General Engineering 5
What is the purpose of a 'coffin plate' in a marine boiler?