How do I replace the stern gland or shaft seal on a Najad 361?

Replace the shaft seal on your Najad 361 ashore by disconnecting the propeller shaft from the gearbox, removing the shaft coupling and sliding the old seal off the shaft's forward end. Identify the fitted seal and measure the shaft and stern-tube connection first, as previous replacements mean the boat model alone cannot reliably identify the correct kit.

Identify the seal and measure clearance

Look behind the gearbox with a torch, mirror and camera. A moulded black rubber body clamped to the stern tube is usually a Volvo Penta-style lip seal. A stainless rotor running against a carbon face identifies a mechanical face seal such as a PSS. A traditional stuffing box has a packing nut and locknut or a bolted follower.

The procedure below covers a rubber lip seal. Face seals have their own bellows-compression setting, rotor positioning and locking procedure. Packing glands need the correct packing section and adjustment.

• Measure the shaft on clean, unworn metal with a vernier calliper. Check whether it is metric or imperial: 25 mm and 1 inch are different sizes.
• Record the stern-tube outside diameter beneath the seal connection. If it is inaccessible, use drawings or measure it after removal.
• Measure the seal's installed length and the gap between its forward end and the coupling.
• Check propeller-to-rudder clearance outside before moving the shaft aft.

An unbolted coupling does not guarantee enough shaft travel. A rope cutter, propeller, shaft anode or rudder may limit movement. Removing the propeller may help, but some arrangements need more extensive dismantling.

Disconnect and support the shaft

Have the boat securely supported ashore and isolate the engine starting circuit before opening the gland or working around the coupling.

Remove access panels and clean the area before dismantling. Photograph the coupling, spacers, locking screws and any flexible coupling. Mark the shaft's insertion depth into its coupling. Support the shaft so its weight does not hang on the seal.

1. Unbolt the shaft coupling from the gearbox output flange, keeping any spacers in order.
2. Identify how the coupling grips the shaft: split clamp, taper bush or keyed solid hub. Remove its locking devices and follow the coupling's removal procedure.
3. Use a suitable coupling puller or the manufacturer's extraction arrangement. Do not hammer the shaft or use the gearbox flange as an improvised press.
4. Secure the shaft against uncontrolled movement, then move it aft only as far as the measured clearance permits.
5. Remove the coupling and key, loosen the seal's stern-tube clamp and slide the old seal forward off the shaft.