Ship Steering Gear: Parts, Types, Modes and SOLAS Rules

Steering gear is the machinery that turns a ship’s rudder to the angle ordered from the bridge and holds it there. On merchant ships it is almost always electro-hydraulic and sits in the steering gear room at the stern.

This guide is written for deck and engineering cadets and junior officers. It covers where the steering gear is, how it works, its modes, parts and types, and the SOLAS rules for performance, testing and drills.

What Is Steering Gear on a Ship?

Steering gear is the system of controls, pumps and actuators that moves the rudder to port or starboard on the bridge’s order. It also holds the rudder amidships, so the ship can alter course or keep a steady heading.

Every SOLAS ship has a main steering gear and a means of steering if it fails. That is either a separate auxiliary steering gear or a main gear with two or more identical power units.

Where Is the Steering Gear Located on a Ship?

The steering gear is in the steering gear room, also called the steering gear compartment or steering flat. This is the aftermost compartment, directly above the rudder stock and abaft the aft peak bulkhead.

It usually lies below the poop deck at the stern of the ship, reached from the engine room or from the deck. SOLAS Chapter II-1, Regulation 29 sets out what the compartment must have.

• Ready access, and separation from machinery spaces as far as practicable.
• Working access to the machinery and controls, with handrails and gratings or other non-slip surfaces for oil leaks.
• A means of communication with the bridge.
• A rudder angle indicator, so the person steering locally can see the rudder position.
• Simple operating instructions and a block diagram of the changeover procedures, permanently displayed.

The steering gear room is also the local control station. If remote control from the bridge fails, the rudder is steered from here by direct control.

How Does Ship Steering Gear Work?

The bridge orders a rudder angle and the telemotor carries it aft. The control unit puts a pump on stroke, and the power unit moves the rudder. Feedback from the rudder stops the pump when the ordered angle is reached.

1. The helmsman sets the ordered angle with the wheel, tiller or autopilot at a bridge steering stand.
2. The telemotor transmits the order to the steering gear room by hydraulic pipes or electrical cables.
3. The control unit moves the hunting gear, which puts the variable delivery pump on stroke in the required direction.
4. The power unit pumps oil to the rudder actuator, and the rams or vanes turn the tiller and rudder stock.
5. As the rudder turns, the hunting gear takes the pump off stroke. The rudder stops and holds at the ordered angle.
6. A rudder angle transmitter on the stock drives rudder angle indicators on the bridge and in the steering gear room.

The order the helmsman acts on comes from the mmaster, pilot or officer of the watch as a helm order or a course to steer. The helmsman repeats it and confirms the rudder position on the indicator.

What Are the Modes of Steering on a Ship?

Ships have four steering modes: autopilot, follow-up, non-follow-up and local (emergency) control. Follow-up holds the rudder at the ordered angle, while non-follow-up moves it only while the control is held.

Mode	Controlled from	How the rudder responds	Typical use
Autopilot	Bridge (heading or track control)	Rudder moved automatically to hold a set heading or track	Open sea passages
Follow-up (FU)	Bridge wheel or FU tiller	Rudder goes to the angle set and stays there	Hand steering in pilotage, traffic and harbour
Non-follow-up (NFU)	Bridge lever or push buttons	Rudder moves while the control is held and stops where it is when released	Backup if follow-up fails
Local / emergency	Steering gear room	Rudder moved by direct control of the pump or solenoid valves	Failure of bridge control

In NFU mode there is no feedback, so the helmsman watches the rudder angle indicator and releases the control at the wanted angle. The rudder does not return amidships on its own.

SOLAS Chapter V, Regulation 24 requires that manual steering can be engaged immediately in heavy traffic, restricted visibility and other hazardous situations. Manual steering must also be tested after prolonged autopilot use.

In local mode the crew steers by a handwheel, a trick wheel or the manual push buttons on the solenoid valves. Orders reach the steering gear room by sound-powered telephone.

What Are the Main Parts of Steering Gear?

The three main parts of steering gear are the telemotor, the control unit and the power unit. The power unit drives the rudder actuator, which turns the rudder stock through the tiller.

Telemotor

The telemotor carries the ordered angle from the bridge to the steering gear room. It has a transmitter at the wheel and a receiver at the steering gear.

Its parts, the hydraulic and electric types, and maintenance are covered in detail in the guide to the telemotor in steering gear.

Control Unit and Hunting Gear

The control unit takes the telemotor signal and sets the output of the main pump. On many gears this is done by the hunting gear, or floating lever.

One end of the floating lever is moved by the telemotor receiver and the other by the rudder stock. When the order changes, the lever puts the pump on stroke, and as the rudder follows, the feedback end takes it off stroke again.

On electrically controlled gears, a small servo pump, solenoid valves and a cylinder do the same job. The servo cylinder moves the stroke control of the main pump.

Power Unit

The power unit is a variable delivery pump driven by a constant-speed electric motor. It supplies the oil flow and pressure needed to move the rudder and hold it against water forces.

The pump is usually an axial-piston type with a tilting swash plate, or a radial-piston type with a floating ring. Changing the stroke changes the direction and rate of oil flow without stopping the motor.

Rudder Actuator, Tiller and Rudder Stock

The actuator turns pump pressure into torque on the rudder stock. On a ram-type gear the rams push a tiller keyed to the stock, while a rotary vane gear turns the stock directly.

• Tiller: the arm keyed to the top of the rudder stock.
• Rudder stock: the shaft that carries the rudder and passes up through the hull to the steering gear.
• Rudder angle transmitter: sends the actual rudder angle to the indicators and the control system.
• Mechanical rudder stops: fixed stops just beyond the maximum rudder angle, with limit switches that stop the gear first.

What Are the Types of Steering Gear?

Steering gear is classed by its actuator as ram-type or rotary vane, and by its power source. Almost all merchant ships use electro-hydraulic steering gear; manual hydraulic steering is found on small craft.

Ram-Type Steering Gear

Hydraulic rams in cylinders push on the tiller, usually through a Rapson slide that converts the straight ram motion into rotation. The Rapson slide gives more torque as the rudder angle increases, when rudder forces are highest.

• Two-ram gear: one pair of opposed rams on a single tiller arm, common on smaller ships.
• Four-ram gear: two pairs of rams on a cross-head tiller, used on large ships. If one pair fails it can be isolated and the ship steered on the other pair at reduced torque.

Rotary Vane Steering Gear

A rotor with vanes is keyed to the rudder stock and turns inside a fixed housing, or stator. Oil pressure on the vanes turns the rotor and stock directly.

Rotary vane gear is compact and lighter than ram gear and gives constant torque at all rudder angles. It needs good sealing between vanes and housing to hold pressure.

Electro-Hydraulic Steering Gear

An electric motor drives the hydraulic pump, and the oil drives rams or vanes. This is the standard arrangement on merchant ships, controlled from a wheel, tiller or joystick on the bridge.

The power units of large ships are fed from the main switchboard, with an alternative supply for steering during a blackout. Two or more pump units allow one to be stopped for maintenance or used as the standby.

Manual Hydraulic Steering Gear

On small boats, turning the wheel drives a helm pump that sends oil straight to a steering cylinder at the tiller. No electricity is needed, so this type is also used as a simple backup system on small craft.

Older ships used steam steering engines and all-electric gears, but these have been replaced by electro-hydraulic gear in modern merchant ships.

What Are the SOLAS Requirements for Steering Gear?

SOLAS Chapter II-1, Regulation 29 requires a main and an auxiliary means of steering. The main gear must swing the rudder from 35° on one side to 30° on the other within 28 seconds.

Requirement	Main steering gear	Auxiliary steering gear
Rudder movement	35° one side to 35° the other; and 35° either side to 30° the other in 28 s or less	15° one side to 15° the other in 60 s or less
Test condition	Deepest seagoing draught, maximum ahead service speed	Deepest seagoing draught, half maximum ahead service speed or 7 knots, whichever is greater
Power-operated when	Rudder stock over 120 mm diameter at the tiller	Rudder stock over 230 mm diameter at the tiller
Astern	Must not be damaged at maximum astern speed	n/a

The 35°-to-30° figure allows for the hunting gear slowing the pump as the rudder nears its ordered angle. That makes the final few degrees hard to time.

Where trials at deepest draught are not practicable, SOLAS allows trials at even keel with the rudder fully submerged. The results are then corrected to full-load conditions.

• Main and auxiliary gear must be arranged so that failure of one does not disable the other.
• No auxiliary gear is needed if the main gear has two or more identical power units. It must still steer after a single failure in its piping or one power unit.
• Main and auxiliary power units must be startable from the bridge and restart automatically when power returns.
• Power failure to any power unit or its control system triggers an audible and visual alarm on the bridge.
• Steering control is provided on the bridge and in the steering gear room. Gears with two or more identical power units need two independent control systems, both operable from the bridge.
• Each hydraulic reservoir has a low-level alarm on the bridge and in the machinery space. A fixed storage tank holds enough oil to recharge at least one power system.
• Where the rudder stock exceeds 230 mm, an alternative power supply must start within 45 seconds. It must last 30 minutes on ships of 10,000 GT and above, and 10 minutes on others.
• Tankers, chemical tankers and gas carriers of 10,000 GT and above must regain steering within 45 seconds after a single power system failure.

Regulation 30 adds the electrical requirements for electric and electro-hydraulic gear. Classification societies apply these rules at plan approval and survey.

How Is Steering Gear Tested Before Departure?

SOLAS Chapter V, Regulation 26 requires the steering gear to be checked and tested within 12 hours before departure. Ships on regular short voyages may test weekly instead, if the flag state allows.

• The main and auxiliary steering gear.
• Remote steering control systems and the steering positions on the bridge.
• The emergency power supply.
• Rudder angle indicators against the actual rudder position.
• Remote control system and steering gear power unit failure alarms.
• Automatic isolating arrangements and other automatic equipment.

The checks also cover full rudder movement and a visual inspection of the gear and its linkage. Communications between the bridge and steering gear room are tested too.

Many companies add a functional test about an hour before sailing. The steering gear is powered up and the rudder put to different angles from each control position.

How Often Are Emergency Steering Drills Held?

Emergency steering drills are held at least once every three months under SOLAS Chapter V, Regulation 26. The drill includes direct control from the steering gear room and the communication procedure with the bridge.

Where fitted, the drill also covers changing over to the alternative power supply. It is one of the regular shipboard safety drills, and the date and details are entered in the logbook.

Officers concerned must know how to operate the steering systems and change from one to another. SOLAS Chapter V, Regulation 25 also requires more than one power unit running in areas that call for special caution.

How Is Steering Gear Maintained?

Steering gear maintenance centres on clean hydraulic oil, no leaks and well-greased linkage. Most work is done in port, when the gear is not needed.

• Check the hydraulic oil level in each reservoir and look for leaks at every watch round.
• Grease the rudder carrier, tiller, Rapson slide and linkage points on schedule.
• Keep the storage tank full, with enough oil to refill at least one power system.
• Change filters and send oil samples for analysis to keep the hydraulic fluid clean.
• Check the alignment and clearances of the rudder stock and carrier bearing.
• Keep the emergency steering instructions and changeover diagram posted and legible.

Related Topics

• Guide to steering a ship
• How a ship’s rudder works
• Berthing and unberthing of a ship

Frequently Asked Questions