Marine shaft bearings: identify the part you need

Propeller-shaft bearings and seals

A water-lubricated cutlass bearing supports the rotating propeller shaft. It may sit in the stern tube or an external strut, P-bracket or skeg. A shaft seal or stern gland keeps water out where the shaft passes into the hull. Gearbox bearings are separate components inside the gearbox.

We stock Exalto cutlass bearings. For PSS dripless shaft seals, visit our sister store PSS Seals Australia. Consult the engine or gearbox supplier for internal drivetrain bearings.

Shaft bearings and rudder bearings

The bearing name often describes its location rather than its design. A rudder stock or pintle moves as part of the steering assembly, with its own load, clearance and mounting requirements. A propeller-shaft bearing cannot be selected for it by size alone. Our skeg bearing guide explains the distinction.

Choose the correct dimensions

Record the nominal shaft diameter, housing bore and specified length. Check metric, imperial and mixed-unit dimensions individually. Do not treat 25 mm as equivalent to 1 inch.

The nominal shaft size identifies the shaft the bearing is made to support. The finished bearing bore is larger to provide running clearance. Manufacturing tolerances describe the permitted range of bearing dimensions; they are not a range of compatible shaft sizes.

For a light interference fit, the bearing's outside diameter is slightly larger than the housing bore before fitting. Use the manufacturer's specified housing fit and clearance. A loose or oval housing needs assessment before you choose a replacement.

See the measuring guide for the measurement process.

Check shell compatibility

Exalto's standard brass, phenolic and GRP sleeve bearings all have a nitrile rubber lining. The names describe their outer shells. Choose a shell that suits the housing and the vessel's bearing specification.

• Phenolic: A phenolic outer shell with a grooved nitrile rubber lining. The non-metallic shell avoids galvanic corrosion between the bearing shell and a metal housing. Exalto allows for phenolic water absorption in its manufacturing tolerances.
• Brass: A brass outer shell with a grooved nitrile rubber lining. Exalto advises against fitting brass directly into steel or aluminium housings. A worn or oversized housing needs assessment; changing shell material does not correct its bore dimensions.
• GRP: A glass-reinforced composite outer shell with a grooved nitrile rubber lining. Exalto identifies GRP as suitable for steel and aluminium stern tubes as well as compatible non-metallic housings. Follow the specified fit and retention method.
• Rubber: An all-rubber bearing without a rigid outer shell. This design uses its own mounting arrangement. Choose it when the vessel specification calls for an all-rubber bearing, and confirm the dimensions and retention method before fitting.

See Exalto's shell and lining specifications for the manufacturer's guidance.

Inspect before replacing

Increasing shaft movement, damaged rubber or vibration warrants inspection. A water-lubricated bearing has running clearance when new, so movement alone does not prove it is worn out. Ask the yard to measure the clearance, inspect the shaft and compare the results with the manufacturer's guidance.

Follow the manufacturer's installation instructions and arrange the work with the yard. Check current availability before booking access or haul-out time.

Browse the size chart Ask for sizing help

Check the product page for its current price and availability before arranging the work. Prices include GST and shipping within Australia is free.