How do I replace the saildrive diaphragm on a Bavaria 37 Cruiser?

Replace the saildrive diaphragm with the Bavaria ashore, the engine and drive supported separately, and the saildrive removed and dismantled according to its model's instructions. Check the drive's identification plate and replacement history first: the boat's name alone cannot identify the correct seal kit, dismantling procedure or tightening torques.

Identify the drive and seal

Bavaria fitted different engines and saildrives during the 37 Cruiser's production, and some boats have replacement machinery. Volvo Penta installations are common, including 120S or 130S family drives depending on the year and engine. Order parts against the complete drive designation and serial number.

The large rubber diaphragm clamped inside the hull forms the watertight seal. The thin rubber fairing glued around the leg outside the hull reduces drag. Replacing the fairing does not renew the diaphragm.

Volvo Penta normally specifies diaphragm replacement every seven years. Look for an installation invoice and any date marking, but remember that a manufacturing date does not establish when the seal was fitted. For a Yanmar installation, follow its own maintenance schedule and procedure. Its twin-diaphragm arrangement and water sensor require different treatment.

Obtain the correct workshop instructions before starting. There is no safe universal torque figure for the diaphragm clamp, drive casing or engine connections.

Prepare the boat and access

This is a substantial mechanical job because of the restricted access, the weight involved and the consequences of trapping the new seal incorrectly. An experienced owner can tackle a suitable Volvo installation, but a marine engineer should handle or inspect the assembly.

Have the yard cradle the boat securely, isolate the batteries and use rated lifting equipment before releasing any engine or saildrive mount.

1. Remove the companionway steps and engine enclosure panels needed for access. Check the route for lifting the drive into the boat.
2. Photograph the installation and label the gear cable, cooling-water connections, electrical connections and anything else that must be disconnected.
3. Remove the propeller and any fittings specified in the drive's removal procedure, keeping spacers and washers in order.
4. Drain the saildrive oil into a clean container and check for milkiness, water or metallic debris.
5. Support the engine and saildrive separately before releasing mounts or separating the transmission from the engine.

On many installations, the engine must move forwards to disengage the drive. Measure the clearance first. Hoses, exhaust connections and wiring must neither carry the engine's weight nor restrict its movement.

Remove the drive and diaphragm

The removal sequence depends on the drive. On common Volvo units, diaphragm renewal involves separating the engine connection, releasing the hull clamps, lifting out the drive and separating the relevant drive sections to release the diaphragm.