Steering Gear
Steering gear is the one system SOLAS insists every ship duplicates for redundancy, and the choice between a rotary vane unit and a two-ram or four-ram cylinder design decides both the torque available and how the gear fails when something goes wrong.
What to check on a Steering Gear.
14 models from SEIMI in Steering Gear. Below: the full model list.
What distinguishes the main steering gear types
Two hydraulic architectures dominate. Ram-type gear uses one or more hydraulic cylinders acting on a tiller arm keyed to the rudder stock, giving high torque and a design that is mechanically simple to understand and repair; four-ram arrangements add redundancy since losing one ram pair still leaves steering available at reduced torque. Rotary vane gear uses a vane rotor fixed to the rudder stock inside a stator housing, with hydraulic pressure applied to one side of the vanes to rotate it; it is more compact for a given torque and gives a larger rudder angle range without the geometry constraints of a ram's stroke, at the cost of tighter seal tolerances between vane chambers.
Legend
- ram (hydraulic cylinder) x2
- tiller (crosshead)
- RUDDER STOCK
- foundation (ship structure)
- hydraulic supply lines
- HYDRAULIC POWER UNIT
- local control position
Main components
Rudder actuator (ram or rotary vane)
Converts hydraulic pressure into the torque that turns the rudder stock.
Hydraulic power unit
Pumps, usually two independent units for redundancy, plus the hydraulic reservoir, filters and relief valves that supply and protect the actuator circuit.
Read the full guide
Control system
Follow-up and non-follow-up control linking the helm or autopilot demand to the pump's variable displacement or to directional valves, plus the rudder angle indicator feedback loop.
Rudder stock and tiller
The mechanical link between actuator and rudder itself, including the locking arrangement that lets the rudder be secured mechanically for emergency steering or maintenance.
Selection and sizing
- Required torque at the design rudder angle and ship speed, calculated from rudder area and the vessel's manoeuvring requirements, not scaled by displacement alone.
- Redundancy configuration - two independent power units as a minimum, four-ram or twin rotary vane arrangements for vessels needing to retain steering after losing one circuit.
- Hardover-to-hardover time, which SOLAS constrains directly and which sizing must meet at the vessel's deepest service draught and speed.
- Available space and rudder trunk geometry, since rotary vane units generally need less headroom for the same torque than an equivalent ram system.
Regulations and class
SOLAS Chapter II-1 requires a main steering gear and an auxiliary steering gear, sets the maximum time allowed to move the rudder from 35 degrees on one side to 30 degrees on the other, and requires that a single failure in the piping or in one power unit does not disable steering entirely on ships above the thresholds set in the regulation. Class rules require periodic testing of both main and auxiliary steering gear, including a full changeover test, and require the steering gear compartment to be clearly identified with instructions for emergency operation.
Typical faults
| Fault | Cause | Consequence |
|---|---|---|
| Sluggish or reduced rudder angle response | Air in the hydraulic system, worn pump, internal leakage past actuator seals | Hardover time increases, may exceed the regulatory limit |
| Rudder hunting or oscillating | Worn control valve, incorrect follow-up feedback calibration | Increased wear on the whole system and unnecessary fuel burn from constant correction |
| Loss of one hydraulic circuit | Pipe fracture, pump failure, contaminated oil damaging a pump | Should fail safe to the remaining circuit if redundancy is properly isolated; tests this isolation |
| Oil contamination | Water ingress through a damaged seal or breather, wrong oil topped up | Accelerated wear of pump and actuator seals, potential for sudden failure |
What to look for in a supplier
- Type approval and torque rating matched to the actual rudder stock and rudder area on the vessel, confirmed by the original design data, not estimated.
- Compatibility of the control system with the existing bridge autopilot and steering control interface.
- Spare parts availability for seals and valve components specific to that actuator type, since ram and rotary vane seals are not interchangeable.
- Documented sea trial or works test data for the specific unit or unit type being supplied.
Run the full changeover test to auxiliary steering at the actual required frequency, not just before survey - a hydraulic isolation valve that has not been cycled in months is the most common reason redundancy fails when it is actually needed.
Models in this type.
The best-documented model of each manufacturer first, then the next — 14 of 14 models in Steering Gear. Every row links to full specifications, documents and service notes.
Manufacturers.
All 36 manufacturers with models of Steering Gear. Names with a manufacturer page open it; the others open a search across the full library.
All manufacturersAlso in Steering Gear.
The other equipment types in this category.
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Is Steering Gear data free?
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My model is missing — what now?
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