What is a cutlass bearing?

Where the bearing sits

A sleeve bearing may be fitted in a stern tube or an external shaft support such as a strut or P-bracket. Some installations incorporate the support into a skeg. The bearing carries shaft loads while the shaft seal performs a separate job: keeping seawater out of the boat.

Read our marine shaft bearing guide to distinguish these parts. A rudder skeg bearing supports the steering assembly and is not automatically interchangeable with a propeller-shaft bearing.

How water lubrication works

Water passes along the grooves and supplies the bearing surface. At suitable operating speeds, a water film supports the rotating shaft. Adequate clearance and water flow matter; simply being afloat does not prove the bearing has the water supply it needs.

Follow the bearing and vessel instructions for the installation. Exalto's standard rubber-lined bearings use water in service. Petroleum-based lubricants can obstruct that lubrication and should not be used during shaft installation.

Shell and liner materials

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.

How to identify the size

Start with nominal shaft diameter, housing bore and specified bearing length. Keep the units: a 25 mm shaft and a 1-inch shaft are different sizes.

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.

Use the measuring guide to record these dimensions and check the original specification.

How to check wear

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.

Life varies with operating conditions, alignment and water supply. The replacement guide covers planning the work and checking availability.

Cutlass or Cutless?

Cutless is the trademark used by Duramax Marine for its Johnson Cutless range. Cutlass is a common generic spelling. We sell Exalto bearings. When comparing brands, check dimensions, shell, clearance and application rather than assuming matching names or nominal sizes guarantee a replacement. See cutlass versus cutless.

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