Most naval ships are equipped with diesel-driven emergency generators. (Diesel engines are most suitable for this application because of their quick-starting ability.) Emergency generators furnish power directly to vital electrical auxiliaries, such as the steering gear and the ships gyro. In addition, emergency generators may serve as a source of power for the casualty power distribu-tion system. All engineering personnel should become familiar with the emergency and casualty power systems aboard their ship.

Emergency diesel generator sets must be ready at all times for immediate use. You should complete the following checks to ensure that the support systems and control system are aligned and that the emergency generator is ready for operation.

1. Fuel service tank filled, with all water drained.

2. Fuel system valves correctly aligned.

3. Air flask(s) charged

4. Air-starting system valves correctly aligned

5. Keep warm system(s) (if used) activated

6. Switchboard set to AUTOMATIC po-sition. (The green light should be on.)

A typical shipboard plant may consist of two emergency diesel generators, one forward (near the bow and above the waterline) and one aft (near the stern), in spaces outside the main machinery spaces. Each emergency generator has its individual switchboard and switching arrangement for control of the generator and for distribution of power to certain vital auxiliaries and to a minimum number of lighting fixtures in vital spaces.

The capacity of the emergency unit varies with the size of the ship in which it is installed. Regardless of the size of the installation, the principle of operation of the engine is basically the same as it is for any diesel engine. Emergency diesel engines are started either by compressed air or by a starting motor and develop full-rated load power within 10 seconds of starting. In a typical installation, the starting mechanism is actuated when the ships normal supply voltage on the bus falls to approximately 80 percent. (In a 440-volt system, this would be approximately 350 volts.) The generators are not designed for parallel operation. Therefore, when the ships supply voltage fails, a transfer switch automatically disconnects the emergency switchboard from the main distribution switch-board and connects the emergency generator to the emergency switchboard. With this arrange-ment, transfer from the emergency switchboard back to the main distribution switchboard is accomplished manually. Then, the emergency generator must be manually stopped and reset for automatic starting.

Since emergency diesel generators are of limited capacity, only certain circuits can be supplied from the emergency bus. These include such circuits as the steering gear and the interior communications switchboard. If some vital circuit is secured, another circuit may then be cut in, up to the capacity of the generator.