Machinery, Electrical Systems, and Propulsion
Domain 4 covers the propulsion train and the electrical services that keep the ship controllable and safe - the systems an engineer is expected to specify, monitor and test.
Propulsion configurations
- Slow-speed two-stroke crosshead engines driving fixed-pitch propellers directly (around 100 rpm), the bulk-carrier and tanker norm.
- Medium-speed four-stroke engines through reduction gearing, common in ferries and offshore units.
- Diesel-electric and pod drives for redundancy and manoeuvrability.
- Dual-fuel and gas-fuelled installations under the IGF Code, with bunkering and emergency shutdown arrangements.
Steering and electrical essentials
SOLAS II-1 Reg 29 requires main and auxiliary steering gear, two independent power units, transfer within 45 s, and a change from 35° on one side to 30° on the other in 28 s; emergency steering drills every three months. The emergency generator must start and connect automatically within 45 s, with capacity for 18 h on cargo ships and 36 h on passenger ships.
Worked example
A main engine of 9,000 kW MCR runs at 90% of rated rpm. By the propeller law P ∝ n³, absorbed power ≈ 9,000 × 0.9³ ≈ 6,560 kW - a 27% reduction for a 10% rpm cut. Note that the continuous service rating is a separate, lower figure than MCR and must not be quoted as the same number.
Traps
- Confusing MCR with the continuous service rating.
- Forgetting that auxiliary steering gear needs periodic testing and that drills are recorded.
- Assuming a controllable-pitch propeller delivers full torque at any rpm.
- Overlooking hazardous-area classification (IEC 60092-502) around fuel and cargo systems.