Skeg bearings: identify the part and find the right size

Propeller-shaft bearing or rudder skeg bearing?

Follow the component the bearing supports. The propeller shaft runs from the engine or gearbox to the propeller. Its aft bearing may sit in a stern tube, skeg or separate shaft bracket. In a strut or P-bracket, a grooved sleeve bearing supports the rotating shaft and allows water to pass through for lubrication.

A rudder bearing supports the steering assembly. The term "skeg bush" can refer to a bush around a rudder stock or pintle, and some boats use a complete lower bearing fitting or rudder step. These arrangements can have different materials, clearances and fixing methods.

Check the boatbuilder's drawing or original part specification for a rudder application. Dimensions alone do not establish that a catalogue propeller-shaft bearing is a suitable replacement.

How to measure a skeg shaft bearing

For a sleeve-type cutlass bearing, record:

• The nominal propeller-shaft diameter. Measure an unworn section and check the result against the vessel's shaft specification.
• The bore of the housing that holds the bearing. If the bearing is still fitted and hides the bore, use a reliable drawing or have the yard confirm it when accessible.
• The specified bearing length. Check the existing installation and available support rather than calculating length from shaft diameter alone.

Keep the original units. A 1-inch shaft is 25.4 mm, so it needs a different nominal bearing size from a 25 mm shaft. Some Exalto bearings combine a metric shaft diameter with an imperial housing diameter; check every dimension, including length.

Nominal sizes and manufacturing tolerances describe different things. The bearing's finished bore includes running clearance around its designated shaft. Its outside diameter and the specified housing bore establish the fit. For an interference fit, the bearing's outside diameter is slightly larger than the housing bore before fitting.

Use Exalto's dimensions and fitting specification rather than adding an allowance yourself. Refer to the Exalto tolerances and clearances for the specified bearing.

Choosing the shell material

Exalto's standard brass, phenolic and GRP sleeve bearings all have a nitrile rubber lining. Water travels through grooves in that lining. The material names describe the outer shell, so comparing "phenolic versus rubber" as though they have different running surfaces can be misleading.

Phenolic bearings have a non-metallic shell that avoids galvanic corrosion between the shell and a metal housing. Phenolic absorbs some water, which Exalto allows for in its manufacturing tolerances.

GRP bearings are another non-metallic option. Exalto identifies GRP as suitable for steel and aluminium stern tubes; it is not restricted to fibreglass housings.

Brass bearings have a metal shell, but Exalto advises against fitting brass directly into steel or aluminium housings. A worn or oversized housing needs assessment before a replacement is selected. Changing shell material does not correct the bore dimensions.

All-rubber bearings have no rigid outer shell and use a different mounting arrangement. Choose them when the installation calls for that design.

Checking wear and planning replacement

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

For a rudder skeg bearing, investigate steering play or stiffness against the boatbuilder's instructions. The inspection and acceptable clearance depend on the bearing design.

Arrange access and removal with the yard before booking the work. Whether the shaft, propeller or rudder needs removal depends on the vessel. Record the existing bearing specification and check availability early, particularly if the boat will occupy a slipway while waiting for parts.

Exalto's standard sleeve-bearing instructions call for a light press fit, with suitable retention where specified. Support the shaft during installation and avoid damaging the rubber lining. The finished installation needs the specified running clearance and water flow. See the Exalto installation instructions.

Skeg bearing questions

Can a cutlass bearing replace a rudder skeg bearing?

Only when the vessel or bearing manufacturer specifies it for that application. Confirm the required design, material and clearance before ordering.

Will a bearing fit if all three dimensions match?

Matching dimensions narrows the choice. You must also check the shell material, housing condition, retention method and application.

What details should I send for sizing help?

Use our contact form to send the boat model, bearing location, shaft diameter, housing bore, length and any readable part code. Say whether it supports the propeller shaft or rudder. Product pages show current prices and availability; check those details before arranging the replacement.