On the conning platform, an instrument called the engine order telegraph (fig. 2-8) communicates speed orders to the engineroom.
The engine order telegraph is circular, with duplicate dials divided into sectors for flank, full, standard, 2/3, and 1/3 speed ahead; 1/3, 2/3, and full speed back. A hand lever fitted with an indicator travels over the circumference of the circular face of the instrument.
When the handle is moved to the required speed sector, the engineroom complies with the order immediately and notifies the bridge by operating an answering pointer that follows into the same sector.
A ship with one engine has a telegraph with a single handle. Two-engine ships usually have a handle on the port side and another on the starboard side of the telegraph, controlling the engines on the corresponding sides. Be sure you have grasped the handle for the correct engine before you operate it.
If the answering pointer moves to the wrong sector, does not move at all, or moves to a line between two sectors so that you are in doubt about the speed set on the engine, repeat your operation on the lever. If the pointer does not move, report the situation immediately to the officer of the deck.
If a casualty occurs in the engineroom, the speed may be changed by the engineroom without orders from the officer of the deck. In such an event, the answering pointer moves to the speed set in the engineroom. Report any change in the engine order telegraph to the officer of the deck at once. Also report to the OOD immediately if you fail to receive an answer on the pointer when you indicate a speed. The safety of your own ship and others may depend on the immediate and correct transmission of orders to the engines.
Before getting underway, the telegraph is always tested by moving the handle to each sector, and checking the response on the answering pointer. In the event of casualty to the telegraph, the engineroom receives orders over the sound-powered phones.
Explanation From: Integrated Publishing Web Site - Courtesy of antiquesofthesea.com