A properly operating gear has a definite sound which the experienced engine operator can easily recognize. The operator should be familiar with the sounds of the gears aboard the ship during normal operation and at different speeds and under various operating conditions.

Often the readings of lube oil pressures and temperatures may help in determining the reason(s) for abnormal sounds. A burned-out pinion bearing or main thrust bearing may be indicated by a rapid rise in oil temperature for the individual bearing. A noise may indicate misalignment, improper meshing of the gear teeth, or gear tooth damage.

When there is either a burned-out bearing or trouble with the gear teeth, the main propeller shaft should immediately be stopped, locked, and inspected to determine the cause of the abnormal sound or noise. The trouble should be remedied before the reduction gear is placed back in operation.

In some cases, conditions of a minor nature may cause unusual noises in a reduction gear which is otherwise operating satisfactorily. When an investigation reveals the cause of the noise to be minor, the gear should be operated cautiously and under close observation by experienced per-sonnel. A more thorough investigation should be made, as soon as practicable, to determine the cause of the unusual noise. Upon discovery of the trouble, appropriate action should be taken to remedy the condition.

Vibration

If the main reduction gear begins to vibrate, a complete investigation should be made, preferably by a naval shipyard. Vibrations may be caused by bent shafts, damaged propellers, misalignment between prime mover and gear, a worn out bearing, or coupling, or an improper balance in the gear train. When these units are built, the gear wheels are carefully balanced (both statically and dynamically). Later any unbalance in the gears is manifested either by unusual vibra-tion and noise, or by unusual wear of the bearings. When a ship has been damaged, vibration of the main reduction gear may result from misalign-ment of the engine and the main shafting as well as from misalignment of the engine and the main gear foundation.

When the vibration occurs within the main reduction gear, trouble or damage to the propeller should be one of the first things to consider. The vulnerable position of propellers makes them more liable to damage than any other part of the main plant. Bent or broken propeller blading and propellers fouled with line and steel cable may transmit vibration to the main reduction gear.