How do I replace the saildrive seal on a Rasmus 35?

Identify the installation first: a Rasmus 35 normally has a conventional propeller shaft, so the rubber component may be a shaft seal rather than a saildrive diaphragm. Both replacements normally require hauling out, but a shaft seal slides off the disconnected shaft, while replacing a saildrive diaphragm means supporting and dismantling the drive according to the instructions for that model.

Identify the drive and seal

Start behind the engine and follow the transmission towards the hull. Checking now avoids buying the wrong kit or dismantling parts unnecessarily, particularly if the boat has been re-engined.

• Conventional shaft: a gearbox coupling drives a metal shaft running aft through a stern tube. The seal surrounds that shaft inside the boat.
• Saildrive: the engine connects to a drive unit with a leg projecting down through the hull. A broad rubber diaphragm seals the opening around the drive.
• External saildrive skirt: the thin rubber fairing glued beneath the hull smooths water flow. It is separate from the watertight diaphragm.

Photograph the installation and record the details on the engine, gearbox and drive identification plates. For a shaft seal, measure the shaft diameter and the stern-tube connection diameter. A replacement engine does not necessarily mean the shaft was changed too.

Before disconnecting or moving the engine or drive, have the boat securely supported ashore, isolate the starting battery and use properly rated lifting equipment.

Replacing a propeller-shaft seal

Identify the seal: it may be a Volvo Penta moulded rubber seal, a bellows-mounted mechanical seal such as a PSS, or a traditional stuffing box. Each has its own installation and adjustment procedure.

1. Check that the shaft coupling can be removed before scheduling the work around a short lift-out. Corroded coupling bolts and a seized hub often cause the longest delay.
2. Disconnect the coupling and release its attachment to the shaft, following the coupling manufacturer's instructions. Support the shaft and arrange clearance outside the hull if it must move aft.
3. Remove the old seal and inspect the shaft's sealing surface for grooves, corrosion and burrs. Check the stern tube and accessible bearing for damage or excessive play.
4. Fit the correctly sized seal, using its protective installation sleeve where supplied. Protect the sealing lips from the shaft keyway and follow the specified lubrication or bellows-compression procedure.
5. Reassemble the coupling with the specified fasteners, tightening method and locking arrangements. Check alignment, particularly if any engine mounts were disturbed.