The main (thrust) bearing transmits the axial thrust developed by the propeller to the ship's structure, and hence propels the ship. It transfers the propeller thrust (ahead and astern) from the propeller shaft to the thrust collar, then through the thrust pads to the bearing housing, which is anchored to the engine bedplate or ship's structure. It also locates the crankshaft/shafting axially, keeping the engine and shaft in correct axial position.

1. The axial (end) clearance between the thrust collar and the ahead and astern pads - the total end float of the shaft, measured with a dial gauge by levering the shaft axially (should be within maker's limits, typically tenths of a mm).
2. The radial clearance/sag of the shaft at the bearing, and the bearing clearances.
3. The pads' condition - measure the pad thickness/surface wear, check each pad's pivot/bearing for fretting and wear, the pad flatness, and that all pads are parallel beneath the collar.
4. The collar face condition (wear, grooving, out-of-flatness) and the bearing housing location/height so that the collar is centred on the pads.
5. The oil supply and clearances so the pads tilt freely; the pad support legs' pivot alignment.

The thrust bearing is cooled by having a continuous supply of lubricating oil circulated through the bearing housing, usually from the main engine lubricating oil system. The oil is directed through passages to each pad so a hydrodynamic oil film forms and the heat of friction generated by the thrust is carried away. The hot oil drains to the sump and passes through a cooler (heat exchanger) to reduce its temperature before re-circulation, so the pad and housing temperatures are kept within limits. Auxiliary, additional cooling may be via the adjacent main bearing cooling. Temperature sensors/pyrometers monitor the pad temperatures.

[Sketch notes: the thrust bearing is mounted on special chocks which transfer the thrust to the engine bedplate and ship's structure.] The thrust bearing, being subject to large axial loads, is placed on steel chocks/sof-fitting cast-iron or steel wedge chocks fitted directly below the bearing feet or bedplate, so that the axial load is transmitted positively to the bedplate and hull rather than through bolts which would stretch. On modern installations the main bearings, thrust bearing and engine are bedded on cast-iron/steel chocks and the whole engine is "chocked" using epoxy/cementitious (e.g. chocking compound) or metal chocks, so that the thrust load is taken with minimal settlement. The chocking is arranged under the bearing housing, spread over a sufficient area to keep bearing pressure low, and the holding-down bolts are tightened to hold the housing in place while the chocks carry the thrust. In some designs the thrust bearing is separate and bolted to a rigid foundation, with dowels/keys to locate it against the axial load; and epoxy chocks or metal liners are matched to give full face contact.