Auxiliary Machinery and Shipboard Systems
What this domain tests
This domain tests command of the machinery that makes propulsion possible: pumps and their limitations, compressed air, boiler water and combustion, steering gear redundancy, and accommodation services such as ventilation and refrigeration.
Pumps and compressors
- Centrifugal pumps are not self-priming and lose head when air enters the suction; available NPSH must exceed required NPSH or cavitation erodes the impeller.
- Positive-displacement pumps must never run against a closed valve without a relief path; the discharge relief valve is that protection.
- A pump that has lost suction is primed before restart, and the suction line is checked for a closed valve, blocked strainer or empty tank.
- Compressor intercoolers reduce power and remove moisture; drains are blown down regularly and the unloader is proved so the motor starts against no load.
Boilers
- Water level is proved by gauge glass blowdown before any action; if the level cannot be confirmed, shut off fuel rather than feed water into a boiler of unknown level.
- Burner management, low-water alarm, flame failure protection and safety valves are tested to the maker's schedule and the results recorded.
Steering gear
- The main gear must turn the rudder from 35° one side to 35° the other at maximum ahead service speed and deepest draft, and from 35° to 30° in not more than 28 seconds; the auxiliary gear does 15° to 15° in 60 seconds at half speed or 7 knots, whichever is greater.
- Two independent power circuits and two pumps are arranged, with alarms for power failure, low oil level, hydraulic fluid loss and overload.
- Emergency steering drills are held at intervals not exceeding three months.
Worked example
During a steering test the rudder takes 40 seconds to swing from 35° port to 35° starboard. That fails the 28-second requirement. Reasoning: first check which pump is running, whether the second power unit is on line, oil level and temperature, and the hydraulic lock indicators before condemning the gear. Log the failure, inform the master, and raise it as a defect; the gear is not accepted for manoeuvring until the timing is met, and the bridge must be told before arrival so pilotage and tug arrangements can account for it.
Traps that cost marks
Running a positive-displacement pump against a closed valve; feeding a boiler whose level is unproven; testing steering only at slow speed or light draft; assuming an alarm means a faulty sensor; ignoring compressor intercooler drains until the air system carries water.
Key points
- Available NPSH must exceed required NPSH to avoid cavitation