Marine Steering Gear: Types, SOLAS Rules, Operation

Marine steering gear is the machinery that converts helm orders from the bridge into mechanical rotation of the rudder stock. The system spans three connected subsystems: the actuator that physically moves the rudder, the hydraulic power units that supply pressurized fluid to the actuator, and the control chain from wheel or joystick on the bridge down to the servo valves in the steering gear room. SOLAS Chapter II-1 Regulations 29 and 30 set binding performance floors for every ship over 100 GT on international voyages, and class society rules (DNV, Lloyd’s Register, ABS, and others) add detailed construction and survey requirements on top.

The steering gear machinery is covered here. The rudder itself, its geometry, hydrodynamic lift, area sizing, and stock-diameter calculation are covered in the companion article on rudder and steering systems. For hydraulic system design outside the steering context, see marine hydraulic systems.

Related calculators: steering gear hydraulic torque, SOLAS V/26 steering gear tests and drills, rudder rate calculator, and hydraulic pump power.

Why the steering gear is safety-critical

A steering failure at sea is a serious casualty. The vessel loses the ability to take avoiding action under COLREGS Rule 8, cannot maintain position in a traffic separation scheme, and in confined waters will ground or collide within minutes. The Amoco Cadiz (1978) grounding off Brittany, which released 223,000 tonnes of crude oil, began with a steering gear hydraulic failure in heavy weather. The subsequent SOLAS amendments tightened requirements for tanker redundancy specifically because of that event.

SOLAS provisions are built on one principle: no single component failure should produce complete loss of steering. That principle drives the requirement for an auxiliary steering gear, the duplicated-power-unit rule for tankers, the automatic isolation valve requirement, and the mandatory pre-departure test.

Actuator types

Rotary vane steering gear

The rotary vane design mounts a rotor directly on the rudder stock. The rotor carries two or four radial vanes that slot into matching recesses in the surrounding stator housing. Hydraulic oil delivered to one set of chambers pushes the vanes and rotates the stock; oil on the other side is displaced back to the reservoir. The rudder angle is proportional to the volume of oil moved into the active chambers.

The design is compact: the housing sits tightly around the stock and takes up a fraction of the deck footprint compared with a ram arrangement. That compactness suits container ships, car carriers, and passenger vessels where steering gear room space is limited. The practical upper limit on rotary vane systems is roughly 1,500 to 2,000 kNm of rudder torque, which rules them out for the largest VLCCs and ultra-large bulk carriers whose rudder stocks may be 700 to 900 mm in diameter and whose required torque can exceed 3,000 kNm.

Rotary vane units typically have two or four vane-sets, giving either two-compartment or four-compartment symmetry. The four-compartment version is hydraulically stiffer (less compressibility-related lag) and is preferred on fast ships where helm response time matters.

Ram-type steering gear (Rapson-slide)

The ram arrangement uses two or four hydraulic cylinders whose pistons act on a tiller arm or a crosshead yoke attached to the rudder stock. In the Rapson-slide variant, the rams connect to a crosshead that slides on a fixed transverse guide bolted to the ship structure; as the crosshead moves, a pin running in a slot in the tiller converts the linear ram motion into rotary stock motion.

The Rapson-slide geometry gives a valuable mechanical property. When the rudder is amidships, the ram-to-stock moment arm is at its shortest; as the rudder moves toward 35 degrees, the effective moment arm grows, so the same ram force produces a larger torque. This matches the hydrodynamic reality that rudder torque is highest at large deflection angles, partially self-compensating for the rising load.

Two-ram systems use one pair of double-acting cylinders; the active cylinder extends while the opposing cylinder retracts, both connected to the same crosshead. Four-ram systems add a second pair of cylinders 90 degrees away, giving two independent hydraulic circuits each capable of operating the rudder alone. Four-ram systems are standard on tankers above 10,000 GT to meet the SOLAS duplicated-system requirement.

Ram-type gear handles torques well above 3,000 kNm and is the dominant choice for VLCCs, ULCVs, and large bulk carriers. The trade-off is a larger steering gear room: a four-ram system for a 320,000 DWT VLCC may occupy a footprint of 8 by 6 metres and require a deck head of at least 3 metres.

Electric-direct steering gear

A small minority of ships, typically vessels below 500 GT or ferries with modest rudder torque requirements, use an electric motor driving a gearbox or worm gear that acts directly on the rudder stock, with no hydraulic circuit. Electric-direct steering eliminates hydraulic oil fire risk and simplifies maintenance. The practical ceiling is roughly 50 to 100 kNm, limiting the design to smaller vessels.

Performance comparison

Hydraulic power units

Variable-displacement axial-piston pump

The standard prime mover in a modern electro-hydraulic steering gear power unit is a variable-displacement axial-piston pump driven by a fixed-speed electric motor. The pump’s swashplate angle sets the stroke of each piston and therefore the volume of oil delivered per revolution. When the rudder is at its ordered angle and no further movement is commanded, the swashplate angles back toward zero; the pump idles against the load rather than sending fluid through a bypass or relief valve. This “pressure-compensated” operation cuts standby power consumption to 5 to 15% of peak demand.

In older “constant-pressure” designs the pump ran at full output continuously and a relief valve recirculated excess flow, wasting energy as heat. Variable-displacement pumps from manufacturers including Rexroth, Parker, and Eaton Vickers have replaced the constant-pressure approach on most ships built after about 1990.

Pump motor ratings on ocean-going ships range from roughly 15 kW for a small general cargo vessel to over 300 kW per unit on a VLCC with four-ram gear. Motor supply is three-phase, 440 V or 690 V AC from the main switchboard, with emergency supply from the emergency switchboard for at least one power unit.

Hydraulic reservoir and conditioning

Each power unit has a dedicated reservoir holding typically 1.5 to 3 times the swept volume of its connected hydraulic circuit. The reservoir carries a return-line filter (usually 10-micron absolute), a breather filter, a level sight glass, a low-level float switch, and an oil temperature sensor with alarm. System oil cleanliness is maintained at ISO 4406 Class 16/14/11 or better; degraded cleanliness causes valve spool wear, increases internal leakage, and reduces servo response accuracy.

Hydraulic oil temperature is held in the range 30 to 70°C. A plate heat exchanger using seawater cooling limits the upper end; an immersion heater on the reservoir maintains the lower end in cold climates. Both extremes matter: oil below 20°C has viscosity too high for fast servo response; oil above 70°C degrades additive packages and accelerates seal wear.

Isolation and transfer valves

Between the power units and the actuator sits a bank of motorized isolation valves. These allow any single power unit or actuator hydraulic circuit to be isolated while the others remain operational. On a four-ram system the typical arrangement lets each ram pair run from its own power unit, with cross-connect valves that allow one unit to supply both ram pairs if the other unit fails. SOLAS Regulation 29.11 requires that any single hydraulic pipe failure can be isolated and steering maintained; the isolation valve layout is the hardware implementation of that requirement.

Control system

Signal path from bridge to actuator

The bridge wheel, joystick, or autopilot computer sends an ordered rudder angle to the steering gear control system. On ships built since roughly 1990, this signal is electrical: a potentiometer or resolver on the wheel shaft produces a voltage proportional to wheel position. Older ships used a telemotor, a small hydraulic transmitter on the bridge connected by copper pipe to a receiver unit in the steering gear room; telemotors are now rare on newbuildings but remain in service on older tonnage.

The control signal arrives at the power unit servo amplifier, which compares the ordered angle to the actual angle signal from the rudder feedback unit (a potentiometer or rotary encoder on the rudder stock) and drives the pump swashplate solenoids to move oil in the direction that reduces the error. When the error reaches zero, the swashplate backs off and the rudder holds position.

Follow-up and non-follow-up modes

In follow-up (FU) mode the rudder tracks the wheel angle continuously. Rotating the wheel to 20 degrees starboard commands 20 degrees rudder; releasing the wheel holds the rudder at 20 degrees. This is the normal at-sea mode.

In non-follow-up (NFU) mode the rudder moves only while the operator holds the command lever to port or starboard, and stays at whatever angle it has reached when the lever is released. NFU is the backup mode for hand steering from the bridge wings, and is the mode used from the local (steering gear room) control panel in an emergency. The distinction is operationally important: a helmsman accustomed to FU who accidentally operates in NFU can easily drive the rudder to the stops.

Autopilot and track control interface

The autopilot replaces the helmsman as the command source. It measures heading error from the gyrocompass, applies a PD or PID control algorithm, and sends a corrective rudder-angle demand to the same follow-up control loop that the wheel uses. The track control system does the same but derives the commanded heading from the planned route and the vessel’s position from GPS or ECDIS, adding a cross-track-error correction term on top of the heading error. Both are covered in the article on marine bridge equipment and integrated bridge systems.

Rudder angle indicators and alarms

SOLAS Regulation 29.10 requires a rudder angle indicator on the bridge readable in the normal steering position, a second indicator at any other steering position, and a repeater in the steering gear room. The indicators are driven by the same feedback transducer that closes the control loop. A separate alarm system monitors power unit status, hydraulic oil level, oil temperature, and (on tankers) the operational state of each independent power unit. Under Regulation 29.13, alarms must be given on the navigation bridge and in the engine room for power unit failure and for any hydraulic fluid low-level condition.

SOLAS Chapter II-1 Regulations 29 and 30

Regulation 29: main and auxiliary steering gear

The 28-second criterion. SOLAS Chapter II-1 Regulation 29.3.1 requires the main steering gear to be capable of putting the rudder over from 35 degrees on one side to 35 degrees on the other side with the ship at its deepest service draft and proceeding at maximum ahead service speed, and specifically from 35 degrees on either side to 30 degrees on the other side in not more than 28 seconds at that same speed and draft.

The 28 seconds is the safety margin for collision avoidance. At a typical service speed of 14 to 16 knots and a length of 200 to 300 metres, a ship takes 1 to 3 minutes to complete a 90-degree turn after the rudder reaches its ordered angle; 28 seconds of rudder transit time is tolerable within that envelope. For context, a 35-to-30-degree transit at 28 seconds implies a minimum rudder angular rate of roughly 2.5 degrees per second.

The 60-second auxiliary criterion. Regulation 29.4 requires an auxiliary steering gear capable of putting the rudder from 15 degrees on one side to 15 degrees on the other side in not more than 60 seconds at half maximum service speed or 7 knots, whichever is greater. The auxiliary gear must be independent of the main gear: its own power source (or operable by hand), its own hydraulic circuit, and its own control connection from the navigation bridge.

The 15-degree limit in the auxiliary criterion reflects the reality that at low speed and under auxiliary power, a moderate rudder angle is sufficient to control the ship; full 35-degree deflection is not required for safe navigation to port.

Where auxiliary gear is not separately required. Regulation 29.5 provides that ships fitted with two or more identical main steering gear power units, each individually meeting the 28-second criterion, do not need a separate auxiliary steering gear. The second (or third) power unit IS the auxiliary. This is the normal situation for tankers above 10,000 GT and is the practical approach for most ships above about 5,000 GT where fitting a separate dedicated auxiliary system would be wasteful.

The tanker duplicated-system rule

SOLAS Regulation 29.15 (applicable to tankers, chemical tankers, and gas carriers of 10,000 GT and above) goes further than the basic main-plus-auxiliary structure. These ships must have:

• Two or more identical power units, each capable of independently meeting the 28-second criterion.
• The second power unit capable of being brought into operation from the navigation bridge within 45 seconds of the failure of the first.
• Two independent hydraulic systems: after any single failure in one hydraulic system (pipe, pump, valve, seal), the other system must remain able to steer the ship.
• Two independent control systems, each associated with its own power unit.

The 45-second switchover time is the operational link: an officer at the bridge must be able to activate the standby unit within that window, whether by remote control from the bridge or by telephone instruction to the steering gear room. Regular drills on this switchover are not optional; they form part of the quarterly emergency steering drill record.

The Regulation 29.15 requirement was strengthened after the Amoco Cadiz casualty. The March 1978 grounding killed its rudder hydraulics in 7-metre seas while in ballast 4 miles off Portsall; the vessel couldn’t anchor or steer, the tug’s tow parted, and the ship drove aground over the next several hours. The IMO response was to require that no single hydraulic failure on a laden tanker could eliminate all steering.

Regulation 30: additional requirements for passenger ships and large cargo ships

SOLAS Regulation 30 applies the tanker-level duplicated-power-unit requirement to all passenger ships of 10,000 GT and above and to cargo ships of 70,000 GT and above. For cargo ships between 10,000 GT and 70,000 GT, Regulation 30.2 requires that the main steering gear can be restored to operation within 45 seconds of power failure by use of the emergency power supply or the auxiliary steering gear.

The boundary at 70,000 GT for cargo ships reflects a deliberate risk-weighting: the potential consequences (grounding, collision in a traffic separation scheme) grow with ship size and cargo volume.

Emergency steering

Local control from the steering gear room

Every ship must be able to steer from the steering gear room using local controls if the bridge-to-steering-gear-room control link fails. The local arrangement typically consists of:

• A local hydraulic control panel adjacent to each power unit, with start/stop buttons and a handwheel or push-button for the swashplate servo.
• A local rudder angle indicator.
• A sound-powered telephone or fixed communication from the steering gear room to the navigation bridge.
• A local control position visible from the access door so that a single operator can both observe the controls and communicate.

SOLAS Regulation 29.7 requires that the transfer from bridge control to steering gear room control can be completed within 2 minutes. In practice this means clear labelling, simple valve arrangements, and drilled procedures.

Hand pump operation

Many ships carry a hand-operated hydraulic pump in the steering gear room that can maintain rudder position or move the rudder slowly in a complete power failure. On ships below roughly 5,000 GT, hand pump operation may be the designated auxiliary steering system. For large vessels, hand pump serves as a last resort: the flow rate achievable by two operators is typically 5 to 20 litres per minute, enough to move a small rudder at 0.5 to 1 degree per minute, which is marginal for open-sea emergency navigation but sufficient to confirm that the actuator is functional.

Emergency power supply

SOLAS requires that the emergency switchboard, whose power source is independent of the main switchboard (a separate battery or emergency generator), can supply at least one steering gear power unit motor. The emergency supply must be sized to start the motor under full load. This means that in a main power failure, the officer of the watch can maintain steering on emergency power alone while the main generator is restarted.

Pre-departure testing and drills

Pre-departure test (SOLAS V/26)

SOLAS Chapter V Regulation 26.1 requires the following checks to be completed within 12 hours before departure. The SOLAS V/26 steering gear test calculator covers the interval and documentation requirements:

• Operate all steering gear power units, individually and simultaneously.
• Test all remote steering gear control systems.
• Test the emergency steering gear control system.
• Verify communication between the bridge and the steering gear room.
• Move the rudder through its full range of travel in both directions.
• Check the rudder angle indicator against the actual rudder position.
• Record the test and any defects in the official logbook.

The 12-hour window means the test can be carried out during the port stay but must be recent enough to confirm the system is functional after maintenance that may have been done in port.

Emergency steering drill (SOLAS V/26.4)

SOLAS V/26.4 requires a drill at least every three months. The drill must include:

• Direct control of steering from the steering gear room.
• Communication procedures between bridge and steering gear room during the drill.
• Operation of any alternative power supply.

These drills form part of the Safety Management System (ISM Code) records and are inspected at port-state control. A ship that cannot produce drill records for the past three months will receive a deficiency notation. The quarterly interval is not a maximum; operators with high-traffic coastal routes often drill monthly.

Class society surveys

DNV, Lloyd’s Register, ABS, Bureau Veritas, and the other IACS member societies carry out annual surveys of steering gear as part of the Machinery Survey. A typical annual survey covers:

• Operational test of all power units including performance timing (rudder rate check against the 28-second criterion).
• Inspection of rams, seals, and cylinder bores for wear, scoring, or leakage.
• Hydraulic oil sample analysis (cleanliness, water content, acidity, viscosity).
• Relief valve function and set-point check.
• Control system sensor calibration: rudder angle feedback, swashplate position.
• Check of all alarm functions.

A four-year Special Survey (or Continuous Survey cycle) includes a more detailed strip-down: tiller pin and bearing inspection, rudder stock upper bearing clearance measurement, and hydraulic reservoir internal inspection.

Steering modes in service

Manual (follow-up) steering

Manual FU steering is the default mode on ocean passages when the autopilot is switched off for practice or when conditions require close attention. The helmsman keeps a heading by small wheel inputs, typically 1 to 5 degrees of rudder, corrected as the vessel yaws under wind or sea. The performance of the control system in manual FU mode is limited by the helmsman’s reaction time and the steering gear’s response lag, which is typically 0.5 to 1.5 seconds from wheel movement to measurable rudder motion.

Autopilot

The autopilot’s heading-hold function uses the heading error from the gyrocompass as its primary input. A well-tuned autopilot on a stable, deep-loaded vessel will apply rudder commands of 0.5 to 3 degrees amplitude, giving a rudder-induced yaw of less than 0.5 degrees peak-to-peak from the planned heading. A poorly tuned autopilot, or one set up for weather conditions different from those encountered, will swing the rudder repeatedly to larger angles, increasing wear on the feedback unit bearings and the swashplate servo.

Modern autopilots include an adaptive gain-scheduling algorithm that adjusts the heading-gain, cross-track-gain, and derivative-gain parameters in response to measured speed over ground and sea state, reducing rudder activity on stable headings and increasing responsiveness on cross-current legs.

Non-follow-up and bridge wing control

NFU mode from the bridge wing is used during berthing when the pilot or master wants to stand at the bridge wing and control the rudder directly. The wing panel carries a toggle or push-button: push left and the rudder moves left; release and it stops. The bridge wing NFU signal overrides the wheel and autopilot. Most bridge alarm systems signal which control location is active (bridge, bridge wing port, bridge wing starboard, steering gear room) so there is no ambiguity about where commands originate.

Alarms, monitoring, and redundancy architecture

Required alarms

SOLAS Regulation 29.13 lists the minimum alarms that must be audible and visible on the navigation bridge and in the engine control room:

• Power unit motor failure (overcurrent trip, phase loss, thermal trip).
• Hydraulic oil low level (each power unit reservoir independently).
• Rudder angle deviation alarm (optional on some class rules but standard practice): triggered if the actual rudder angle deviates from the commanded angle by more than a set threshold (typically 5 degrees) for more than a set time.

In practice, modern steering gear control systems add further monitoring: pump output pressure, oil temperature high, filter differential pressure, control power supply voltage, and feedback unit signal loss. Each alarm has a dedicated logic path to the bridge alarm management system (BAS), which is in turn connected to the integrated alarm system under SOLAS Chapter II-1 Regulation 51.

Automatic isolation after hydraulic failure

The SOLAS requirement that any single hydraulic pipe failure be isolated without losing all steering is implemented through automatic (motor-operated) or solenoid isolation valves on each hydraulic circuit. If a pressure sensor detects a rapid pressure drop consistent with a burst pipe rather than a normal stop command, the valve closes within 2 to 5 seconds, isolating the failed circuit. The design and response time of these valves is verified during the class Special Survey. On a four-ram system where each pair of rams has its own circuit, isolating one pair halves the available torque but maintains directional control.

Segregation of electrical supplies

The two power units on a tanker must draw from different sections of the main switchboard, or at minimum be protected by separate feeders that can be isolated independently. If a busbar fault trips one section of the switchboard, the second power unit on a separate section stays live. Emergency power from the emergency switchboard covers at least one unit. These segregation rules come from SOLAS Regulation 29.14 and are verified by the electrical installation survey.

Hydraulic circuit design parameters

System pressure and flow rate

The working pressure in a modern steering gear hydraulic circuit is typically 160 to 250 bar. Higher pressure allows smaller bore actuator cylinders, reducing overall system weight, but increases the mechanical stress on pipe connections and seal faces. The design pressure is chosen by the actuator manufacturer based on the rudder torque requirement and the physical space available in the steering gear room.

The required flow rate determines how fast the rudder can move. To meet the 28-second criterion a four-ram system for a VLCC with a rudder torque of 3,500 kNm and a system pressure of 200 bar needs each double-acting cylinder to move roughly 400 litres of oil in 28 seconds, requiring a pump output of approximately 900 litres per minute at peak demand. At 200 bar working pressure that corresponds to a pump shaft power of about 300 kW per unit, which is why VLCC steering gear power units carry motors in the 250 to 350 kW range.

For the steering gear hydraulic torque calculator, the input parameters are rudder torque (in kNm), system pressure (in bar), and actuator geometry; the output is the required piston area and, from that, the pump flow rate needed to achieve a target rudder rate in degrees per second.

Relief valve settings

Each hydraulic circuit carries a pair of pressure relief valves, one on each side of the actuator. Their set point is typically 10 to 15% above the maximum working pressure, capping at 275 to 300 bar for a 250-bar system. The relief valves protect the circuit from two hazard modes: a blocked port with the pump still running (producing a pressure spike that could burst a pipe), and a wave-induced rudder impact force that tries to push the actuator back against its locked pump. Without relief valves, wave slam loads on the rudder at full deflection in severe sea states could fracture the tiller arm or the rudder stock.

Relief valve set point is verified during every annual survey and after any hydraulic circuit repair. A valve set too low will “crack” during normal hard-over maneuvers, bypassing oil back to the reservoir and preventing the gear from reaching the commanded angle. A valve set too high provides inadequate protection against circuit overpressure.

Maintenance and common failure modes

Hydraulic seal wear

The most frequent source of unplanned steering gear downtime is seal leakage in the actuator. Ram seals in a rotary vane unit or a ram cylinder operate under pressures of 100 to 250 bar and must contain oil against a moving surface. On high-cycle routes (ferries, short-sea ships) the seal lifecycle is 12,000 to 20,000 hours; on deepwater tankers with slow, infrequent rudder movements, seals routinely last 40,000 hours or more. Leakage shows first as an oil level drop in the reservoir, triggering the low-level alarm before performance is affected.

Pump swashplate and servo valve

Variable-displacement pump servo valves are precision components with clearances of 5 to 10 microns. Contaminated oil above ISO 4406 Class 18/16/13 (a common finding on vessels that skip oil analysis) causes servo valve spool stiction, resulting in sluggish swashplate response and a rudder that lags its commanded position. The symptom is a heading-hold hunt: the autopilot keeps commanding corrections that the gear is slow to execute, producing a continuous yawing oscillation. Oil analysis every 3,000 hours and filter replacement every 1,000 hours (or on differential pressure indicator) prevent this failure mode.

Feedback unit failure

The rudder angle feedback transducer connects the rudder stock to the control system. If the transducer fails open-circuit, the control system reads zero angle regardless of actual rudder position and drives the rudder to full deflection trying to null the apparent error. If it fails short-circuit, it may read a constant non-zero angle, producing a steady offset. The symptom of a feedback unit failure is a sudden helm bias that doesn’t respond normally to wheel input, followed by a limit alarm. Dual redundant transducers, now common on vessels built since 2010, prevent a single transducer failure from causing a runaway condition.

Telemotor pipe failure (older ships)

On vessels with telemotor-type transmission (hydraulic signal pipe from bridge to steering gear room), a pipe crack or union failure empties the telemotor fluid and removes helm control from the bridge. The remedy is to switch to local steering gear room control, which is why communication readiness and crew familiarity with that transfer are drilled. Class society surveys on older vessels include a detailed inspection of all telemotor pipework for corrosion and joint condition.

Cybersecurity considerations

Steering gear control systems have moved from dedicated hard-wired circuits to software-driven PLCs and networked control units. A typical 2020s-era steering gear control cabinet runs a proprietary PLC communicating over a CAN bus or Modbus RTU backbone to the pump servo amplifier, with an Ethernet interface to the bridge alarm management system. IMO Resolution MSC.428(98) (Maritime Cyber Risk Management in Safety Management Systems) entered force in January 2021 and requires flag-state administrations to ensure that cyber risk is addressed in the vessel’s ISM Code Safety Management System.

For steering gear this means identifying the control network as critical infrastructure, restricting USB and network access to the PLC cabinets, maintaining firmware update records, and including a cyber-incident scenario in the emergency steering drill. The ISM implications are audited by class societies as part of the Document of Compliance (DOC) and Safety Management Certificate (SMC) verification cycle. A vessel whose steering gear PLC has a remote maintenance port open to the ship’s crew Wi-Fi network would be flagged as a deficiency.

Major manufacturers and product families

The market has consolidated substantially. The main suppliers as of 2026 are:

Kongsberg Maritime (incorporating legacy Rolls-Royce Marine, Tenfjord, and Frydenbo brands after the 2019 acquisition): rotary vane and ram-type units across the full torque range, digital control systems with IBS integration.

MacGregor (Cargotec), through the Hatlapa brand: ram-type systems for large tankers and bulk carriers, with electro-hydraulic power units.

Wartsila: steering gear as part of its broader propulsion and maneuvering portfolio, primarily for smaller and medium-sized vessels.

Kawasaki Heavy Industries and Mitsubishi Shipbuilding: Japanese-built systems for vessels constructed at Japanese yards, predominantly ram-type for large bulk carriers and VLCCs.

Hyundai Heavy Industries: Korean-built systems integrated into ships built at HHI yards.

Product families are generally not interchangeable between manufacturers: the hydraulic circuit geometry, the tiller and crosshead dimensions, and the control system bus protocols are proprietary. A like-for-like spare pump from a different manufacturer requires verification that the pressure and flow ratings match the actuator’s design envelope.

Limitations of this article

The performance numbers cited for the 28-second and 60-second criteria are from SOLAS Chapter II-1 as consolidated through 2024. The IMO MSC continues to adopt amendments to Chapter II-1; readers should verify against the edition in force under their flag state’s implementing legislation before using these figures for compliance purposes.

Rudder torque sizing, stock-diameter calculation, and hydraulic circuit flow-rate design are covered in the companion articles and calculators: rudder and steering systems for the hydrodynamic torque calculation, the steering gear hydraulic torque calculator for power unit sizing, and the rudder rate calculator for verifying the 28-second compliance margin.

Class rule requirements from DNV, LR, ABS, BV, NK, KR, RINA, and CCS each carry additional detail beyond the SOLAS minimum: specific material specifications, weld inspection requirements for tiller-to-stock connections, and mandatory type-approval testing of relief valves and servo valves. These are not reproduced here; consult the relevant class society rule set edition for the vessel’s assigned class.

SOLAS Regulation 29.15 tanker figures in particular are subject to interpretation in unified IACS requirements (UR S17 and related) and in MSC circulars. Flag state administrations have issued national interpretations that differ slightly on the 45-second switchover timing. A P&I Club or class surveyor should be consulted before a non-standard arrangement is proposed.

See also

• Rudder and Steering Systems
• Marine Hydraulic Systems
• SOLAS Chapter II-1: Construction, Subdivision, Stability, Machinery and Electrical Installations
• SOLAS Chapter V: Safety of Navigation
• Marine Bridge Equipment and Integrated Bridge Systems
• COLREGs Steering and Sailing Rules
• SOLAS Convention

Related calculators

• Steering Gear Hydraulic Torque
• SOLAS V/26 Steering Gear Tests and Drills
• Rudder Rate Calculator
• Rudder Force and Torque Calculator
• Hydraulic Pump Power
• Steering Gear System: Rotary Vane / Ram