H21C

Common issues

• Hydraulic oil leakage at rotor/vane seals
• Low hydraulic oil level triggering low-level alarms
• Undetected failure of one power unit where the duplicated unit masks the fault until the changeover test
• Rudder angle transmitter or feedback linkage misalignment causing bridge/local indication errors
• Relief valve set-point drift over time
• Air entrainment in the hydraulic system causing sluggish or erratic rudder movement
• Bearing wear in the rotor housing causing excess backlash or abnormal noise
• Corrosion of the tiller/rotor housing where seawater or condensation ingress occurs

Inspection checklist

• Check hydraulic oil level and condition (water content, particulate contamination)
• Function-test both power units independently, including automatic and manual changeover
• Test emergency/local steering operation from the steering gear compartment
• Check rudder angle indication agreement between bridge, local, and actual rudder position
• Check relief valve settings against the approved maximum working pressure
• Test low oil level, power failure, and phase failure alarms
• Inspect for oil leakage at seals, pipework, and valve blocks
• Check follow-up and non-follow-up steering modes function correctly
• Verify communication between bridge and steering gear compartment during drills

Service intervals

Typical wear limits

Ranges are typical for this design class. Always confirm against the manufacturer documentation for your serial number.

Critical spares

• Rotor/vane seal kit
• Relief valve
• Hydraulic pump/motor unit components
• Rudder angle transmitter
• O-ring and gasket set
• Non-return and changeover valves

Safety

• High-pressure hydraulic fluid injection injury risk when working on pressurized lines - depressurize and isolate before opening any joint
• Heavy rotating/moving parts within the steering gear compartment - fully isolate power before entering the rotor housing envelope
• Entrapment risk if the rudder moves during testing - maintain positive communication and a lookout during trials
• Confined-space and access considerations for the steering gear compartment

Class survey

SOLAS requires main steering gear to move the rudder from 35 degrees on one side to 30 degrees on the other within 28 seconds; class surveys check this performance, the emergency changeover time, alarm functionality, and general condition of the compartment (bilge alarms, communication with the bridge) against the ship's approved steering gear trial records.