How a cutless bearing works

Simple Boat Maintenance author Pat Manley walks us through the ins and outs of a yacht's cutless bearing

Most boats have a bearing at the outboard end of the propeller shaft that supports the propshaft. Generally this ‘cutless’ bearing will be made of rubber which will, over time, wear. Excessive wear will cause shaft vibration that can eventually damage the boat’s gearbox.

The cutless bearing is usually seawater-lubricated, designed with flutes that allow the passage of water through the bearing. Make sure the water supply is never obstructed (for instance, by a shaft anode mounted too close to it). Some play between the shaft and the bearing is normal but if you can feel movement then it’s time to replace the cutless bearing.

‘P’ or ‘A’ bracket?

Where there’s a length of propshaft protruding from the hull, the cutless bearing will be mounted in a bracket fixed to the underside of the hull. A ‘P’ bracket has one leg while the stronger ‘A’ bracket has two. The security of this bracket is important: if it comes loose the hull can be punctured. The best time to check this bracket is shortly after the boat has been lifted out and its surface has just dried.

Try to move the bracket sideways. Any movement will be indicated by water oozing from the joint. If you see water where the ‘P’ bracket enters the hull, but you feel no movement, check again next year.

If you can feel movement, ask a shipwright to check it. Refitting a ‘P’ bracket can be an awkward and dusty job, as its mounting will have to be ground away inside the boat. Secure refitting is essential and added strength may also be required.

Removing a cutless bearing

First of all, remove the propeller. Cutless bearings are often secured by ‘grub’ screws. Scrape paint from the bearing housing to reveal the grub screws. Remove the grub screws with a hexagonal wrench.

It’s never a good idea to drive the bearing out by hammering with a drift because the bracket itself could be loosened. You will need to devise some sort of puller which can be used without withdrawing the propshaft. A marine engineer will have one or you can hire one. If the propshaft has been removed, a threaded puller can be used.

Alternatively saw through the cutless bearing along its length from inside. Be careful not to cut into the bearing housing of the ‘P’ bracket or it will seriously weaken.

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