Glossary Term
Bearing Clearance
Bearing clearance is the designed or measured running gap between a shaft, journal, stock, or moving surface and the bearing that supports it. In yacht work, the term appears across main engines, gearboxes, rudder stocks, stern gear, pumps, and other rotating or oscillating machinery. The number itself only makes sense in relation to the specific component, its material, its lubricant, and the maker’s or class requirements.
Clearance is one of the simplest measurements with the biggest mechanical consequences. Too little and the bearing may overheat, wipe, seize, or lose its intended oil film. Too much and the component can start to move in ways it was never meant to, creating vibration, edge loading, leakage, unstable alignment, or poor steering and shaft behavior. Class rules also use bearing-clearance measurement directly in survey work. For rudders, ClassNK rules and related unified requirements set minimum or standard clearance logic and treat clearance measurement as an accepted basis for judging condition.
On a superyacht, bearing-clearance work usually sits inside a wider mechanical support decision rather than as a stand-alone number on a worksheet. The measurement only becomes useful when it is tied to load pattern, wear history, temperature, vibration, and the actual service expected from the component after the yacht returns to operation.