Steering Gear System

Question 1

what does the ships stabiliser consist of?

Answer 1

This system consists of three parts, electronic control, hydraulic operation and gear and the fin detail.

Question 2

how does the electronic control work for a ship stabiliser?

Answer 2

A selection switch on the bridge gives settings related to hand control, normal stabilising or automatically controlled rolling, together with an output control switch for beam sea, following sea conditions. The electrical control is identical with the hydraulic telemotor principle but functions with electrical relays. This means that a transmitted signal produces a corresponding movement at the the stabiliser station, through a hunting gear, which is converted to a mechanical movement with hydraulic amplification to operate the fin operating gear. There are two gyroscopes. One is vertical keeping gyroscope whose signal goes through two selective transmitter magslips to a follow through magslip that is similarly operated by a rolling velocity gyroscope. The combined selected signal is transmitted tom the hunter magslip of the oil motor and pump. The mechanical movement of a gyroscope alters the rotor position of the transmitter magslip and the current flow moves the rotor of the hunter magslip to a corresponding position. The rotor movement of the hunting magslip operates to allow oil to be pumped from the pump to the oil motor, which rotates. The pump is driven at constant speed and direction by small motor. The oil motor can rotate in either direction from neutral depending on the direction of movement of the hunter magslip rotor. As the motor rotates, a mechanically driven resetting transmitter magslip serves as a hunting gear and tends to fetch the hunter magslip back to neutral position and stop rotation of the oil motor.

Question 3

what is the purpose of the hydraulic operation?

Answer 3

This has two functions. One to extend or house the fins and the second, which controlled by gyroscope is to tilt the fins. Oil is supplied from storage tank to servo pump, which is driven at constant speed and direction by a motor. The pump type is a variable delivery tilting box and has no reversal of suction and discharge lines.

The pump supplies oil in two pressure settings, low pressure (29bar max) for tilting control and high pressure (77 bar max) for fin housing. Selection is done by change over valve and control by control cylinder.

Question 4

what is the purpose of the fin detail and how does the fin detail work?

Answer 4

The principle operation is to impose on the hull rolling motion equal and opposite to that caused by the wave motion. This is achieved by using the forward velocity of the ship through the water. On the ship rolling to starboard the starboard fin is set by gyroscope signal so that its leading edge is above the axis of tilt, causing an upward thrust. The port fin is set to the opposite tilt so with its leading edge below the axis of tilt giving a downward thrust.

Two rectangular fins one at each side of the ship located directly opposite and are of aerofoil section. To the trailing edge of each is a hinged tail flap that is moved automatically by a simple linkage when the main fin shaft is rotated. This flap gives a very much more pronounced restoring torque action of the fin than would a plain large fin. The fins are mounted on stainless steel shafts, the fin being fitted on to a taper and is bolted up internally, the fin plating being welded over the built up internal structure. The main fin can be tilted 20° each side of the neutral horizontal position. The tail flap is inclined at 30° to the main flap when this flap is at its maximum 20° position and in neutral position.

Question 5

describe the following

a.) Fin housing
b.) Fin tilting operation

Answer 5

a.) fin housing

When extending the fins the oil is supplied to the housing piston rod and flows through an inner tube into the fin shaft, which is the pushed out to the extreme position. Oil behind the piston flows through a port and along the outside of the central tube back to the pump suction. Surplus oil due to the volume of piston rod is stored in storage tank during the housing operation when the flow of oil is reserved. Control valves for this operation are located in central control box.

b.) Fin tilting operation

With the fins extended the tilting operation is controlled by the gyroscope signal, which is transmitted to the hunter magslip which then controls the amount and direction of movement of the oil motor. The output shaft of the oil motor is connected by gearing to the reset magslip rotor, which serves to hunt the gear back to neutral position and stop motor rotation at the required position.

Question 6

Describe some rules relating to electro hydraulic steering gear systems

Answer 6

With electro hydraulic systems

There should be two hydraulic pumps driven by different electric motors and any hydraulic circuit should be arranged so that two separate hydraulic systems are available for redundancy.

On very small craft a mechanical tiller can be used as the emergency back up steering mechanism.

All vessels have to carry a fresh charge of oil in case the original oil is lost for whatever reason

one regulation states that the steering gear has to be capable of driving the rudder from 35° port to 30° starboard and vice versa within 28secs.

Question 7

where can the rules and requirements for vessels steering gear be found

Answer 7

The IMO developed the rules for the construction and use of steering gear on ship, these must be followed and are set out in chapter 2 of the SOLAS convention.

Question 8

when where the rules and requirements for steering gear developed

Answer 8

The regulations were set out when the conventional system for steering a ship was one or two rudders being turned by an electro-hydraulic steering engine like the four ram type or rotary vane type equipment. With the development of azimuthing propulsors and water jets for propulsion and steering of large ships the rules had to be updated.

Question 9

do all modern vessels use rudders?

Answer 9

Some modern vessels do not have a rudder and instead have a podded drive. Testing the steering on ship with a podded drive consists of turning each pod through 360° in each direction. Redundancy is important so a set up of electrical cables or and data signals should be duplicated and follow different routes.

Question 10

1. Describe the procedure for testing the ship’s steering gear and associated
   equipment prior to departure from port. / 4 Describe the procedure for testing a steering gear within 12 hours of sailing.

Answer 10

Obtain permission from the bridge to conduct local steering gear test because they’re going to check whether the stern of ship is clear for rudder movement.

Proceeded to steering gear compartment and check all levels including grease, oil level in each steering tank ,emergency oil and submerged oil level for pumps.

check compartment is well enough lit, equipment stored correctly, nothing obvious been removed/isolated/tagged out from steering gear or in position to
impede rudder movement.

Contact bridge and confirm that local communication for both systems, main and emergency steering gear is working.

First conduct a test where u have the telemotor switched to on position to isolate the controls from bridge. This is to check that steering gear can be controlled from local position.

Read out Gyro repeater (compass) to ensure both the bridge and steering flat are reading the same, confirm once again stern is clear and it’s ok to conduct local steering gear checks.

Start main steering gear pump no.1 in local control and allow to settle, noting amps on control panel, pressures, look around for any leaks and listen for any obvious noises etc. Then stop this pump and start other pump to ensure that can run normally as well. Then check that both pumps can run simultaneously. Ensure any alarms and standby cut in on pumps operate correctly as per manufacturers’ recommendation

Using local control swing steering gear and rudder from 35 degrees port to STBD 30 degrees stopping periodically to confirm gyro repeater reading for ruder matches with bridge, swing steering gear to limits and stop at hard to port/stbd to ensure steering gear can preform these movements.

Always look at rudder
movement to be smooth, the load being drawn on motors and pressures for system. As well as linkages hunting gear and any leakages.

Repeat the same test for auxiliary (emergency) steering gear.

Return steering gear to bridge control by flipping the telemotor isolation switch to off that way your giving control back to bridge and then test again in this mode

Return to ECR and fill in log book with data acquired and response timings of steering rudder movement systems as required

Question 11

2. With reference to the testing of a ship’s steering gear prior to departure, list eight items of machinery or control systems whose operation must be tested.

Answer 11

1 Check the oil level of hydraulic header tanks, top up as required and check Check the temperature of the hydraulic oil level

2 Check the pumps and motors for excess noise, vibration, and heat. Check the electrical load of the steering gear motors. Test one pump then the other and then both and check parameters

3 Check the grease pump for operation, and that sufficient reserve of grease is available.

4 Check all bilge wells for oil/water accumulation and check all filters and steering gear compartment is clean.

5 Check the carrier bearing (rudder stock) for excess leakage making sure its sufficiently lubricated to not cause wear and tear and then check the condition of all linkages, pipe brackets for security and damage.

6 Check alarm system to ensure its working and Check communication system between steering gear compartment and bridge.

7 Check hunting gear and telemotor is in good condition so the transmission to the rudder is good.

8 check and test the steering gear rudder movement from 35degrees port to 30degrees starboard

Question 12

3. Describe the routine watch-keeping duties carried out in the steering flat.

Answer 12

Routine watch keeping duties include inspecting the steering gear
compartment every watch. and preforming the following checks

• listen for any abnormal noise or vibration.
• Check hydraulic oil level in tank. check hydraulic oil level and temperature in steering gear header tank and top up if required
• Check the grease pot levels and top up as required. also check grease for pumps use reserve grease when required
• Check the steering gear linkage points are greased and moving freely, such
  as Rapson slide.
• Observe oil temperatures before and after cooling system using
  thermometers.
• Observe the running amps or motor electrical load of the steering gear motors to ensure there no sign of overheating and sufficient power is being supplied
• Check the steering flat bilges are empty.

Question 13

What are the types of telemotor systems for steering gear on ships ?

Answer 13

1.Hydraulic system
2.Electric system

Question 14

What are the types of steering gear systems used on ships?

Answer 14

Electro hydraulic system

Ram type system (2 ram or 4 ram)

rotor Vane type system

All electric systems

a.) Ward Leonard system

b) Single motor system

Question 15

What is meant by non follow up system in steering gear ?

Answer 15

When the steering gear is set to required position, rudder is moved & when rudder reach the requiredposition, steering gear must be set to off position. This system uses the three solenoid valve.

Question 16

What is meant be follow up system in steering gear ?

Answer 16

When steering gear is set to required position, rudder is moved & when rudder reaches the setposition, steering gear still remains at that position. This system uses the hunting gear arrangement.

Question 17

What is hunting gear ?

Answer 17

It is a feed back mechanism for steering gear which repositions the floating lever of hydraulicpump as the tiller moves to the desired position.

Question 18

What are the safety devices for steering system ?

Answer 18

1.Hunting gear
2.Buffer spring
3.Angle adjusting stop (Hand over position limit switch)
4.Double shock valve
5.Relief valve
6.Tank level alarm (oil)
7.Over load alarm

Question 19

What is the indication of air in the steering system ?

Answer 19

Jumping pressure gauges
Jerky operation
Defective steering

Question 20

What is the effect of air in the steering system ?

Answer 20

Air being compressible gives incorrect balance between units, time lags and irregularoperation. ( which can be dangerous )

Question 21

How is Emergency steering gear operation carried out?

Answer 21

In the case of Telemotor failure, by switching the change over pin, emergency steering canbe carried out by isolating the receiver cylinder and directly controlling the connecting rod of the main steering power unit’s pump lever. The emergency rudder angel indicator and communication system to bridge being providedat the emergency station.

Question 22

Action in case of electrical telemotor failure ?

Answer 22

Put bridge control to manual

Emergency steering gear system is operated by (solenoid button) whether port or starboard.

Rudder angle indicator and communication system between steering room and bridge must beprovided.

Question 23

How to operate emergency steering gear ?

Answer 23

1.Disconnect auto pilot system.
2.Take out change over pin from attachment with telemotor receiver & fit to the hand gear.
3.Use communication system with telephone from steering gear room to bridge.

Question 24

What are steering gear tests & maintenance ?

Answer 24

Control test

Just prior to 1 hour before departure of vessel.

12 hour before departure

Operation of main & auxiliary steering gear.
Operation of remote control system.
Operation of emergency power supply.
Alarm test.
Actual rudder angle & indicator.
Communication system.(Bridge, Engine room & Steering gear room)

Every 3 months interval

Emergency steering gear drill at steering gear room to bridge with sound communication system.

Question 25

Types of pump used in hydraulic steering system ?

Answer 25

Motor driven constant speed variable stroke delivery pumps.

There are two types.

1.Radial piston type ( hele- Shaw pump )

2. Axial piston type ( swash plate pump )

Question 26

What are the advantages of rotary vane type over ram type ?

Answer 26

Smaller space required
Low installation cost
Less weight
Smaller power required, for the same load, because it can transmit pure torque to therudder stock.

Question 27

What are the disadvantages of rotary vane type over ram type ?

Answer 27

Synthetic rubber backed steel sealing strips at vane tops are not strong enough for largeship gear.

Can be used for rudder stock ratings of about 1700 KNm and less torque generated by tworam is 120 to 160 KNm and for four ram 250 to 10,000KNm.

Question 28

Steering tests required before departure ?

Answer 28

1.Steering gear should be checked at least one hour prior to departure.

2.Telemotor transmitter oil level to be checked

3.Oil level of actuating system tank should be checked and replenished if necessary.

4.Rudder carrier bearing and bottom sea gland checked and greased.

5.Start pump and check response of the gear

6.Check abnormal noise and heat

7.Check load carrying and running of the gear ( swing from port 35° to stbd 30° within 28 sec )

Question 29

What are the properties of telemotor hydraulic fluid ?

Answer 29

Good quality mineral lubricating oil is used.

Its properties are-
1.Low pour point (-50°C)
2.Low viscosity ( to reduced fractional drag, but not too thin to mate gland sealing, 30Redwood Secs at 60°C)
3.High viscosity index (110)
4.High flash point (150° C closed)
5.Non sludge forming
6.Non corrosive
7.Good lubricating properties
8.Specific gravity 0.88 at 15.5° C

Question 30

What is the purpose of buffer spring ?

Answer 30

To prevent the damages of the control system.

Question 31

What are therequirements for steering gear ?

Answer 31

To move the rudder in either direction instantly when required

Should come to reset immediately in the position corresponding to that shown on indicatoron the bridge.

Provision must be made to protect the steering gear from damage should a heavy seastrike the rudder.

The design should be sample, the construction robust and its performance reliable at alltimes.

Question 32

Purpose of swivel block in steering gear ?

Answer 32

To control linear movement of the rams to the rotary movement to the tiller arms and rudderstocks.

Question 33

Explain Ward Leonard system?

Answer 33

It is the one type of electrical steering gear system. Which controls the speed of DC motorfrom zero to maximum in either directions.

Question 34

In four rams type steering gear system, what unit you put in servicewhen one cylinder damaged ?

Answer 34

If one cylinder damage, four rams steering gear can be used as two rams type steeringgear.
First place the rudder at mid position.
Isolate the circuit valves of two cylinder inlet.
One cylinder is defective and another one, but they are not in diagonal position. Open the vent atthat cylinder.

Question 35

Purpose of buffer spring ?

Answer 35

Absorb the difference between the steering order speeds and follow up speed.

Absorb the movement of steering wheel if it is mishandled when the hydraulic pumpstop in.

Absorb the movement of the control lever when rudder drift

Absorb the vibration and shocks from the rudder.

Question 36

When carry out emergency steering system ?

Answer 36

Every voyage (UHA)

Once at least within 3 Months (SOLAS)

During Survey

Question 37

What are daily check in steering gear room ?

Answer 37

Pressure gauge of steering pump.
Motor ampere on the steering switch board & motor hand touch feeling
Noise and vibration.
Oil level in tank
Oil leakage in system
Grease in rudder carrier bearing
Check the bottom seal gland whether good or not.

Question 38

What aresteering system regulations?

Answer 38

1.Every ship shall be provided with a main steering gear and an auxiliary steering gear.

2.The failure ofone of them will not render the other one inoperative.

3.Relief valves shall be fitted to any part of the hydraulic system.

4.The main steering gear and rudder stock shall be:

5.(a)of adequate strength and capable of steering the ship at maximum ahead service speed. (b)capable of putting the rudder over from 35′ on one side to 35′ on the other side with the ship at itsdeepest sea going draught and running ahead at maximum ahead service speed and, under thesame conditions, from 35′ on either side to 30′ on the other side in not more than 28 seconds. (c)So that they will not be damaged at maximum astern speed.

6.The auxiliary steering gear shall be: (a)of adequate strength and capable of steering the ship at navigable speed and of being broughtspeedily into action in an emergency. (b)capable of putting the redder over from 15′ on one side to 15′ on the other side in not more than 60seconds with the ship at its deepest seagoing draught and running ahead at one half of the maximumahead service speed or 7 knots, whichever is the greater.

7.In every tanker, chemical tanker or gas carrier of 10,000 gross ton and upwards and in every ships of70,000 gross ton and upwards, the main steering gear shall comprise two or more identical powerunits.

Question 39

what is the purpose of the steering gear

Answer 39

steering gear is the machinery used on-board to control the movement of the ship from port side (left side) to the starboard (right side) while the vessel is moving. The steering gear doesn’t produce any effect while the vessel is stationary. The steering gear provides a movement of the rudder in response to a signal from the bridge through the control equipment, which conveys the rudder ordered signal from the bridge and activates the steering gear to move the rudder to the desired angle. The system can be of different types (hydraulic, electro-hydraulic, electric), but mostly on vessel you will find electro-hydraulic type. The most common steering gear type met on vessels are 2 rams, four cylinder Rapson slide type and electro-hydraulic rotary vane type.

Question 40

describe the 2 ram steering gear system type

Answer 40

2-ram steering gear

The steering gear type is composed of two rams with four hydraulic cylinders that are powered by oil supplied by two electrically-driven pumps, one of which is a back-up pump. The pumps have axial pistons with variable displacement and separate hydraulic oil tanks. Each primary pump is linked directly to an auxiliary gear-type pump that supplies control oil to the servo system and also circulates the oil and cools the pump casing. Both pumps are capable of putting the rudder through the working angle in the specified time. In normal operation at sea, one pump is enough to run, but the second pump unit can be connected at any time by starting the motor. When manoeuvring or operating in confined waters, both pumps should be in service.

Question 41

describe the 4 ram steering gear system type

Answer 41

Four ram steering gear

the steering gear system type consists of an actuator, power units, electro/hydraulic control system and associated electric components. The actuator has a vane rotor and the hydraulic force is transferred to the rudder stock/rudder by means of a frictional connection between the rotor hub and rudder stock taper. There are two sets of pressure and return chambers in the actuator/rotor housing. Internal oil distribution is accomplished through the use of channels in the cover that direct oil to the pressure chambers and away from the return chambers. Control valves open and close oil flow channels; there are four cross-connection valve blocks mounted on the cover, and all valves are open during normal full operation, but two are closed if the steering gear is divided into two units. The dividing walls of the oil pressure chamber act as mechanical stoppers for rotor movement and rudder angle limitations.
The rotor has two upper and lower radial bronze bearings, as well as one vertical bronze bearing rudder carrier which are lubricated by the hydraulic oil from the pressure chambers. The rotor has two vanes, and the housing is divided into two cylinders by two mechanical stoppers that are bolted into the housing. Spring-loaded cast iron sealing bars are used to seal the pressure chambers and the gland seals are used to connect the actuator and the rudder stock. On top of the actuator is a header/expansion tank that serves as an oil reservoir tank for the system oil. The system includes two motor and pump units which consist of an electric motor, a hydraulic pump, an oil reservoir, and filters. Electric solenoid valves and hydraulic spool valves directly mounted on the actuator housing control the rudder.

The hydraulic systems are linked by solenoid-operated isolating valves, which allow both systems to work together to produce the torque required to move the rudder under normal conditions. When one of the systems fails and there is a loss of hydraulic fluid, the float switches in the affected hydraulic tank are activated and sends a signal to the isolation system, which divides the steering gear into two distinct systems.
The faulty system is isolated and the pump is turned off, while the intact system continues to function normally and steering capability is maintained, but only half of the rudder torque is available. When the oil-hydraulic piping failure causes the ‘Low’ level switch to be actuated, the isolation valve goes into operation to separate the hydraulic oil circuit into No.1 system and No.2 system, thereby reducing the steering capability to 50%. Therefore, upon sounding of the ‘Low’ level alarm, either promptly reduces the ship speed or, if the ship continues going full ahead, limit the steering angle to within 15°. It is important to know that the oil tank ‘Low’ level switch for visible and audible alarms is provided in accordance with ship classification society rules and regulations, and the one for auto-isolation of the system are separately installed and are independent of each other. Both, nevertheless, are actuated upon reaching the same oil level.

Question 42

describe the rotary vane type steering gear system

Answer 42

In case of rotary vane type the electrical signals activate solenoid valves to direct pressure and vent oil to and from the hydraulic cylinders formed by the vanes, casing and stoppers. Steering gear feedback transmitters supply the actual position signal for the systems, allowing the bridge actuator to know the actual position of the rudder at all times. Under normal circumstances both vanes will be in use, with oil supplied by any one or two of the pump units.

In case of rotary vane steering gear type, the steering gear is designed to meet a requirement of double separation when in operation as well. It is possible to separate (set in bypass) one rotor vane and operate the steering gear with the other vane. It is also possible to separate (set in bypass) one stopper and operate the steering gear by means of the other stopper. These separation arrangements effectively give a single cylinder operation with pressure oil on one side of a vane, or stopper, and vent oil on the other side of the vane, or stopper. The separation of one vane is a fully automatic function, with activation being brought about by failure of the oil distribution system, but vane separation may also be done manually from controls located on the bridge. The steering gear can work as two single actuators, or as two actuators operating on different sides of the same stopper. In the wheelhouse panel there are MAN SEP1 and MAN SEP2 push-buttons to allow for these forms of separation.

Question 43

what is located at the main panel in the steering gear room?

Answer 43

At the main panel in the steering gear room there is a Test/Function switch, which enables all the different arrangements to be tested. Each pump may be operated with separated vanes and separated stoppers. Normally the switch should be in position NORMAL operation. There are also other switch positions available but these are for testing and simulating separation conditions only and should not be used for normal operation of the steering gear.

Question 44

briefly describe how variable steering flow pumps are controlled

Answer 44

The variable-flow pumps are controlled by an electric torque motor, which is linked to the servo valve via the control lever, which activates the servo piston of the tilting lever for the piston thrust (swash) plate. This moves the pistons out of neutral and causes oil to be discharged to one pair of hydraulic rams while suction is taken from the other. The feedback linkage causes the pump’s tilting lever to move as the rudder turns, reducing the pump’s stroke. When the rudder has reached the desired angle, the tilting lever is returned to neutral, and oil delivery from the pump is stopped.

Question 45

a.) list 8 daily checks that should be carried out on the steering gear

b.) list 6 monthly checks that should be carried out on the steering gear

Answer 45

a.) Daily checks:

Check the oil level in the pump tanks and refill as necessary. The level should not exceed ¾ of the glass at the normal working temperature.

Check the system pipework and valves for leakage.

Check the lubrication system and replenish the grease injection pump tank as required.

Note the temperature of the oil in the hydraulic system.

Visually check the components such as the indicators and linkage arms.

Check the gauges for any abnormal readings.

Check for abnormal noise when the rudder is moving.

Ensure that the rudder carrier bearing grease system is functioning correctly and that there is sufficient grease in the container.

b.) Monthly checks:

Check the tightness of all coupling bolts and pipe connections.

Check the settings of limit switches.

Carry out a function test on the entire alarm system (see the manufacturer’s operating manual for full details).

Check that the rudder indicator is functioning correctly.

Check the ram V-packing and pump control unit oil seals.

Check the stop valves and isolating valves.

Question 46

what is a rule that must be followed with regard to steering gear when manoeuvring through restricted waters?

Answer 46

When manoeuvring in restricted waters, it is compulsory that two pump units are running, in order to achieve the IMO required rudder movement of 35° one side to 30° the other side in 28 seconds (with one pump in 56 seconds), but usually the systems are designed to perform these movements in shorter time (e.g. in 24 seconds and 48)

Question 47

what are limit switches used for in steering gear

Answer 47

Limit Switches are installed so that when the rudder reaches the max.stbd or port angle (37.5degrees), the rudder should not go beyond this point. The limit switch if activated in either of the direction it’ll cut-off the hydraulic oil and prevent the rudder from going in that direction. Limit switches limit the rudder’s operational angle of movement to 35° port and 35° starboard, but mechanical stops are also installed to physically limit any movement greater than 37.5 degrees port or starboard.

Question 48

briefly describe what action to take when the steering control system has failed and the NFU tiller system is inoperative

Answer 48

The hydraulic system must be operated manually and this involves the local control of the pump directional pilot valves. The push-buttons at the ends of the solenoid valves must be pressed or the lever for control oil pumps, one for port and one for starboard turning of the rudder. Instructions must be transmitted to the steering gear room from the bridge by telephone. As the pump directional pilot valves are controlled individually by hand, it is not possible to ensure that control of two pumps would take place at exactly the same time. Only one pump unit must be operating when in emergency control from the steering gear room.

Question 49

how is steering gear controlled?

Answer 49

The autopilot control or hand steering from the wheelhouse are used to control the steering gear, from where all commands are transmitted electrically to the steering compartment and the actual position signal for the systems is supplied by steering gear feedback transmitters.

Question 50

In addition to the central steering console, the wheelhouse control panel is provided with an FU ((Follow up) Tiller unit and a NFU (Non Follow Up) Tiller unit. what is the purpose of these and where are they located

Answer 50

The bridge wings are provided with FU Tiller and NFU Tiller units, allowing for control of the steering from the bridge wings. The FU Tiller units allow for normal (follow-up) steering from the wheelhouse console or the bridge wings. The NFU Tiller units are emergency controls and allow for emergency (or non-follow-up) control of the steering gear. The emergency procedure used depends upon the nature of the failure. If the bridge steering unit or transmission system has failed but the steering gear is still fully functional, steering may take place by means of the NFU Tiller unit in the wheelhouse or bridge wing panels. An alternative is to use the NFU tiller in the steering gear room.

Question 51

what are some rules set out by IMO/ SOLAS regulations pertaining to steering gear systems

Answer 51

In accordance with IMO regulations the pumps, hydraulic power circuits can and must operate as isolated systems, to allow for operation of the steering gear in the event of a vane or cylinder failure.

System is also arranged that any one of the pumps can operate the system under failure of a cylinder or a vane. This reduces the capacity of the steering gear by 50% and so the speed at which the rudder can turn is also reduced. Under such conditions the speed of the ship must be reduced in order to maintain manoeuvrability.

hydraulic pumps used in the steering gear must be supplied with power from two independent sources. that way In the event of power failure from the main switchboard, one pump can be supplied from the emergency switchboard.

The control system operates automatically in the event of a hydraulic system failure and will operate the valves to isolate that part of the system which has failed, thus allowing one vane or one pump, depending of the steering gear type, to remain operational.

Failure of a running pump will produce auto start of the power unit selected for standby operation, that is why the second pump must be always on Stand-by mode while is not in operation.

In the event of oil leakage, the control system senses in which part of the system the leakage has occurred and will isolate that section of the hydraulic system, stopping the pump linked to that section if it is running and an alarms will trigger to warn the engineers that a failure has occurred. Under such circumstances only half of the steering gear capacity is available. Normally, the system is designed on the basis of “single failure”, but if all of the oil alarms are activated one power unit will still be running.

Another requirement of SOLAS is there must be arrangement for contact between the steering flat and the bridge and in the event of the telemotor not working the engineer can operate the controls directly on telemotor receiver after reacting to command given from bridge. Both the receiver unit and hand gear unit linkage operate the receiver control unit through a sliding rod. When the telemotor pin is fitted to the receiver linkage hole the receiver motion is given to control unit, the hand gear is merely sliding in the sleeve. If the pin is removed and put into hand gear sliding linkage hole this operates the control unit and the telemotor connection slides in the sleeve. Only one telemotor pin is provided to be used in the required position, in port on emergency steering the pin should be in the hand position.

Question 52

what alarms are typically activated in the event of electrical failure?

Answer 52

Usually, in the event of electrical failure the following alarms are activated:

Overload alarm
Phase alarm
Steering control alarm

Question 53

which chapter in SOLAS provides the statutory requirements for steering gear.

Answer 53

> > SOLAS, Chapter II-1 Construction – Structure, subdivision and stability, machinery and electrical installations, in Part C – which is Machinery installations- Regulation 29 – Steering gear provides the statutory requirements for the steering gears. Regulations 3 and 29 of SOLAS give definitions and descriptions of the constructional arrangement of both the main and auxiliary ships steering systems.

Question 54

Which ships are required to have a steering gear?

Answer 54

Unless expressly provided otherwise, every ship shall be provided with a main steering gear and an auxiliary steering gear to the satisfaction of the Administration. The main steering gear and the auxiliary steering gear shall be so arranged that the failure of one of them will not render the other one inoperative.

In everytanker, chemical tanker or gas carrierof10,000gross tonnage and upwards-AND-
Every other shipof70,000gross tonnage and upwards, the main steering gear shall comprise of two or more identical power units. Where the main steering gear comprisesof TWO OR MORE IDENTICAL POWER UNITS, an auxiliary steering gear doesn’t need to be fitted.

The following conditions to be satisfied with as well.

In a passenger ship, the main steering gear is capable of operating the rudder as required by operating conditions while any one of the power units is out of operation. Meaning in passenger ship each steering unit shall have 100% redundancy.

In a cargo ship, the main steering gear is capable of operating the rudder as required by operating conditions while operating with all power units. Meaning in cargo ship each steering unit shall have 50% redundancy.

Third requirement is the main steering gear is so arranged that after a single failure in its piping system or in one of the power units the defect can be isolated so that steering capability can be maintained or speedily regained.

Question 55

list one SOLAS operational requirement for the following

• main steering gear
• auxiliary steering gear
• power (amplifier) units
• communication system

Answer 55

main steering gear

Shall be capable of putting the rudder over from 35° on one side to 35° on the other side with the ship at its deepest seagoing draught and running ahead at maximum ahead service speed and, under the same conditions, from 35° on either side to 30° on the other side in not more than 28 s;

auxiliary steering gear

Shall be capable of putting the rudder over from 15° on one side to 15° on the other side in not more than 60 s with the ship at its deepest seagoing draught and running ahead at one half of the maximum ahead service speed or 7 knots, whichever is the greater

power (amplifier) units

The design pressure for calculations to determine the scantlings of piping and other steering gear components subjected to internal hydraulic pressure shall be at least 1.25 times the maximum working pressure to be expected under the operational conditions specified.

communication system

 A means of communication must be provided between the navigation bridge and the steering gear compartment.

steering gear angular position indicator

The rudder angle indication shall be independent of the steering gear control system.

Question 56

What are the requirements on steering gearcontrol system?

Answer 56

1.Control shall be provided for the main steering gear, both on the navigation bridge and in the steering gear compartment.

2.Similarly, for the auxiliary steering gear as well there shall be control from both locations independent of each other.

3.Irrespective of either main or auxiliary steering gear, the control system operable from the navigation bridge shall comply with the following requirements.

4.If electric, should be fed from own separate circuit supplied from a steering gear power circuit from a point within the steering gear compartment, or directly from switchboard busbars supplying that steering gear power circuit….That also, at a point on the switchboard adjacent to the supply to the steering gear power circuit;

5.Means shall be provided in the steering gear compartment for disconnecting bridge control.

6.The system should be able to be started from bridge.

7.Alarm both visual & audible in case of a power failure in bridge.

8.Short circuit protection is allowed only for control system.

9.The electrical power circuits and the steering gear control systems, cables and pipes shall be separated as far as is practicable throughout their length.

Question 57

list 3 requirements for Hydraulic power-operated steering gear system

Answer 57

1. Arrangements to maintain the cleanliness of the hydraulic fluid shall be provided.
2. Low-level alarm for each reservoir for early indication of hydraulic fluid leakage. Audible and visual alarms shall be given on the navigation bridge and ECR.
3. A fixed storage tank with level indicator having sufficient capacity to recharge at least one power actuating system including the reservoir. The storage tank shall be permanently connected by piping so that the hydraulic systems can be readily recharged.

Question 58

what are 3 statutory requirements for the steering gear compartment?

Answer 58

1.Readily accessible and, as far as practicable, separated from machinery spaces

2.Provided with suitable arrangements to ensure working access to steering gear machinery and controls.

3.These arrangements shall include handrails and gratings or other nonslip surfaces to ensure suitable working conditions in the event of hydraulic fluid leakage.

Question 59

Does the steering gear require to be supplied by Emergency Generator? (Emergency power supply)

Answer 59

Where the rudder stock is required to be over 230 mm diameter in way of the tiller,excluding strengthening for navigation in ice, an alternative power supply should be available.

This power shall be able to supply at least the Auxiliary steering gear and its requirements as mentioned above. If your ship doesn’t have an Auxiliary steering gear, then one of the 2 steering gears should be supplied by the emergency supply.

Not only the steering power but also provide power to its associated control system and the rudder angle indicator.

All of the above mentioned item should be suppliedwithin 45 seconds, either from the emergency source of electrical power or from an independent source of power located in the steering gear compartment. This independent source of power shall be used only for this purpose.

In every ship of 10,000 gross tonnage and upwards, the alternative power supply shall have a capacity forat least 30 minutesof continuous operation and in any other ship forat least 10 minutes.

Question 60

what are some special requirements for every tanker, chemical tanker or gas carrier of 10,000 gross tonnage and upwards in reference to steering gear?

Answer 60

1.The main steering gear shall be so arranged that in the event of loss of steering capability due to a single failure in any part of one of the power actuating systems of the main steering gear, excluding the tiller, quadrant or components serving the same purpose, or seizure of the rudder actuating system shall not put the other non-defective unit also out of operation.

2.The main steering gear shall comprise either:

3.Two independent and separate power actuating systems, each capable of operating conditions of main steering gear as we have seen above.

-OR-

1.At least two identical power actuating systems which can act simultaneously during normal operation capable of operating conditions of main steering gear. If necessary, interconnection of hydraulic power actuating systems shall be provided, But Loss of hydraulic fluid from one system shall be capable of being detected and the defective system automatically isolated so that the other actuating system shall remain fully operational.

Question 61

a.) provide 2 Additional requirements for electric and electro hydraulic steering gear in reference to regulation 30

b.) provide 3 requirements for Short circuit and overload protection

Answer 61

a.) 1.ECR & Bridge should have motor running indication.

2.Each electric or electro-hydraulic steering gear comprising one or more power units shall be served by at least two exclusive circuits fed directly from the main switchboard; however, one of the circuits may be supplied through the emergency switchboard.

b.) Short circuit protection and an overload alarm shall be provided for circuits and motors. Protection against excess current, including starting current, if provided, shall befor not less than twice the full loadcurrent of the motor or circuit so protected, and shall be arranged to permit the passage of the appropriate starting currents.

Where a three-phase supply is used an alarm shall be provided that will indicate failure of any one of the supply phases.

The alarms shall be both audible and visual and shall be situated in a conspicuous position in the main machinery space or control room from which the main machinery is normally controlled.

Question 62

explain how to control the emergency steering gear

Answer 62

The method of control used for emergency steering depends upon the system or part of system which has failed. If it is only the bridge main steering unit that has failed the steering gear can be controlled from the steering gear room using the NFU-Tiller unit. This provides control of the steering gear, but there will be no backup or automatic change over of the pumps in the event of failure. For operation of the steering gear from the steering gear room the Location switch must be turned from the BRIDGE position to the STEERING GEAR local position. When normal steering is resumed the switch must be returned to the BRIDGE position. When using the NFU-Tiller control (if available) only one pump must be operated, as it is not possible to control two pumps simultaneously. The operator turns the tiller wheel or handle in order to turn the rudder according to instructions telephoned from the wheelhouse. The operator must watch the rudder angle on the steering indicator and take care not to over-steer. An alternative to using the NFU-Tiller control is manual operation of the pump directional pilot valves, which are controlled by means of the directional push rods at the ends of the valves or the push rod at the control pumps. On some steering gear systems the operating push rod must be pressed at the same time as the direction push-rod and both must be held in the “in” position whilst the rudder is turning. Both must be released together when turning of the rudder is to stop. Pressing the directional push rod and operating push rod causes the directional pilot valve to send pressurized oil to the steering gear actuator, so that the rudder turns; pressing the push rod at the other end of the directional valve changes the direction of oil flow and the direction of rudder rotation. Release of the push rods at any point stops the oil flow and the rudder stops rotating. When operating under emergency steering only one of the two or three pumps, depending of the steering gear system, may be operated and the associated directional pilot valve is used to control the steering gear movement. Instructions must be transmitted to the steering gear compartment from the bridge by telephone. It is essential that effective communication is maintained between the bridge and steering compartment at all times when operating under emergency steering. All personnel involved must be made fully aware of the need for communication in both directions between the bridge and steering gear compartment.

Question 63

Provide the procedure for operating emergency steering gear

Answer 63

Proceed to the steering gear room and establish communications with the bridge either by radio or sound-powered telephone.

On the bridge, turn the non-follow-up switch unit on the
manoeuvring console to OFF.

In the steering gear room, turn the MANUAL-AUTO switch on No.1 and No.2 steering gear starter cabinets to MANUAL.

In the steering gear room, turn the POWER switch, for the auto-pilot to OFF position.

Go to either No.1 or No.2 emergency steering position.

Operate the emergency steering lever in accordance with instructions from the bridge. Direction arrows for PORT and STBD are usually located at the emergency steering position.

Observe the rudder angle on the rudder angle indicator. The figures on the rudder angle indicator are colour-coded for port (red) and starboard (green).

On some systems, in the event of serious damage the rudder can be locked by means of a device fitted below the steering gear actuator. The device is hydraulically actuated by means of a separate pump unit, which is located in the steering gear compartment. The locking device exerts a torque of 20% of the steering gear torque. The main steering gear pumps cannot be operated when the locking device is activated and the locking device must be deactivated before the steering gear pumps can be started. it is important to remember that when operating under emergency condition with only one pump in use the steering operation is limited. For example, the rudder will move from 35° on one side to 30° on the other side in 46 seconds, which is slower than with two pumps operating, when a similar rudder movement is made in 23 seconds. It must be notices that with slower operation of the rudder the steering of the ship is less effective than when operating with two pumps. The navigating officer must be aware that the vessel will not be as responsive to commands as when two pumps are operating. When operating with one half of the steering gear, steering capability is maintained at a reduced ship operating speed of two thirds maximum, with 50% of the rudder torque available.

Question 64

what does SOLAS chapter 2 regulation 29 and 30 include?

Answer 64

Chapter 2 regulation 29 and 30 of SOLAS includes the requirements for the steering to be operated from the bridge and due to distance between the bridge and the steering engine requires a control system.

Question 65

what does Electro-hydraulic steering gear system contain?

Answer 65

This system is made up of two rotary electro-mechanical position sensing devices, which look like small three phase electric motors. Each device has a stator, with the field coils arranged in star or delta and a rotor. The stator windings are connected together and the two rotors are interconnected to the same voltage. Sometimes refereed to as interconnected variable transformers. The arrangement of the system means that the two rotors will align themselves. When the master unit, situated behind the wheel on the bridge, is moved the two will be out of alignment. This produces an offset signal that can be used to activate the solenoid valves controlling the direction of flow from a small oil pump to one side or the other of the telemotor ram, which in turn is connected to the actuator control rod for the main steering pump. When rudder come into line with the helm order the second rotor is turned into line with the first and the offset signal is removed and the main steering pump will stop.

Question 66

what fluid is used for the telemotor and what properties must the fluid posses?

Answer 66

good quality LO is used with following properties

Low pour point
Non sludge forming
Non corrosive
Good lubricating properties
High flash point
Low viscosity to reduce frictional drag but not too thin to make gland sealing difficult. Typical properties would be density 880kg/m3 at 15.5℃, viscosity 12 cSt at 50℃, closed flash point 150℃, pour point 30℃.

Question 67

with reference to steering gear list the equipment which must be checked prior to departure:

Answer 67

Main and auxiliary steering gear
All remote steering control systems (and from different bridge positions)
Emergency power supply
The rudder indicators ( ensure they match actual position of rudder)
All power failure alarms
All automatic equipment and isolating arrangements

Question 68

is it possible to lose electrical signal or data due to a fault in the system

Answer 68

A regulation in chapter 2 of SOLAS gives details of the need for at least two independent electrical supplies so that n the event of partial or totals of steering system there is a backup system (redundancy). Modern vessels have the telemotor or control circuit arranged so that two independent sets of wiring follow different routes from bridge to steering flat (steering gear room/compartment) Therefore its highly unlikely signal is lost, especially since there is Can-BUS technology where data signals are routed through wiring that has several pathways.

Question 69

describe what is meant by CAN BUS technology

Answer 69

Steering systems now use Can-BUS technology. This system is configured in different ways depending on the application. Ships have twin rudders or podded drive system. They can also have multiple steering positions where the input control can be changed from a central position on bridge to one of the bridge wings. This is common on RORO ships and cruise ships where control is changed to the bridge wing for berthing or leaving port. The design of this arrangement is important as controls must be synchronised to give a smooth transition of control from one station to another. The Can-BUS technology will easily integrate the rudder or pod angle into the system, which allows either manual or automatic steering to be adopted . These are follow up or non follow up. Non follow up systems are designed to directly move the rudder after an input action from the helm. The follow up systems allow the helm to request a specific rudder angle and the system will keep turning the rudder until requested angle is reached. The Can-BUS technology will also have outputs to the voyage data recorder, central alarm system, compass repeaters as well as interface with the engine control system. The control system can also be connected to the gyro compass and or magnetic compass in auto pilot mode. This allows the vessel to sail in a selected route without having the constant input from the helm. There will also be a link to the GPS system which allows for dynamic positioning control.

Question 70

what SOLAS chapter set out the requirements for test a ships steering gear

Answer 70

SOLAS chapter 5 sets out the requirements to test the ships steering machinery within 12hours prior to departure from any port. This has been put into standard practice for ships officers and incorporated into a procedure in the ships management system (SMS). for efficient operation and meeting statutory requirements the steering gear is tested in accordance with the pre-sailing checks carried out by the bridge officer of the watch and EOOW. The officers work together with one operating the controls and the other checking operation this ensures a visual verification of correct operation is carried out prior to sailing.

Question 71

what’s the function of a power unit?

Answer 71

The function of the power unit is to amplify ( and possibly transduce) the receiver output signal in the correct direction for transmission to the final controlling actuator operating the rudder.

Question 72

explain what telemotor is used for

Answer 72

The hydraulic pump is mechanically operated by afloating lever gaugewhich, in turn, runs on electric power and works based on the instructions from a telemotor that receives transmitted electrical signals from the control units and is connected to one end of this lever.The telemotor is an important component that acts as an intermediate member in this sequence of operations. The function of the telemotor is firstly, it receives electrical signals from the bridge deck through itstransmitter. Then it further connects this signal to thereceiverlocated in the main steering gear compartment. The receiver further transmits these signals to the control and powering units that have the main task of driving the steering gear system. So, the telemotor is a part of the transmission unit of the steering gear system.A telemotor is a hydraulic control system with an extensive network and runs from the bridge deck to the steering gear system through cables and supporting pipelines along with suitable charging units. All modern telemotors are of electrical type, while the older vessels used mechanically linked systems that comprised the telemotor unit.One of the main tasks of the telemotor is conveying the electrical signals to the control units responsible for turning the rudder unit to the desired rotation angles under the application of a desired torque or turning moment.This control unit is a crucial link between the telemotor and the powering unit, supplying the torque to the tiller and, finally, the rudder. Thus, under the interplay of the powering and the control units, the rudder receives the necessary power in the desired direction to turn the vessel.

Question 73

explain what the hunting gear is used for

Answer 73

The Hunting gear mechanism is designed to operate in the reverse direction and transfer the resultant action of the rudder. After the powering to the rudder unit ceases, all other interconnecting components of the steering gear receive these feedback signals. Moreover, as a result, the hunting gear also repositions the position of the floating lever or control rod (to a neutral position) mounted on the hydraulic variable displacement pump, changing the latter’s pressuring conditions, strokes, and delivery. The hunting lever is connected to one end of this lever (the other end being the telemotor system). Hence, a hunting gear is essentially a feedback control mechanism for the steering gear.Hunting gear can be more simply visualised with the example of a car’s power steering. When you turn the car in the desired direction and release the wheel, the steering automatically disengages, and the turning is stopped in the desired direction.But for older cars with manual steering, the driver had to put more effort into repositioning the vehicle in the new direction and stopping the turning by moving the wheel in the reverse direction. This is a viable option for cars as you have a decent amount of control over your vehicle and a fairly accurate sense of understanding the motions on the road.Impossible for ships. An exact angle of turn-in values always needs to be specified from the bridge deck or navigation deck. after the rudder is instructed to make that angle, there needs to be a way to ensure that after the accurate turn is achieved, there has to be a mechanism to ascertain that and, at the same time, cut off the powering to the systems such that the entire process of turning comes to an immediate halt. Another important related usage of hunting gear is that it acts as a constant reciprocator that repositions the rudder angle when the set deflection is disturbed by waves and other sea conditions, which is quite normal. The principle remains the same: any deflection of the rudder is captured by this hunting gear, and it initiates the other connected equipment, and these, in unison, once again re-enters the rudder back to its original angle.

Question 74

List 9 principal rules relating to the construction and use of steering gears found in chapter 2 reg 29 and 30 of SOLAS.

Answer 74

1.All vessels must be provided with efficient main and auxiliary steering gear of power operated type. An auxiliary gear is not required if main gear is provided with duplicate power units and duplicate connections up to the rudder stock

2. The vessel must have means provided to allow steering from aft position

3.Two tillers or equivalent are required unless working tiller is of special design and strength

4.Power operated gears must be fitted with a device to relieve shock on the rudder from outside forces such as a heavy sea

5.Power supplies:

Must be arranged so that at least two separate cables are provided for each electric electro hydraulic arrangement

Steering gears should only fail if a short circuit occurs and therefore the electrical cables and fuses must allow for 200% over current for a minimum of 60secs

Electrical cables should protected from fire damage and conform to the regulations within part D of SOLAS, which relates to electrical installations including the regulations for electrical supplies

Each of the electrical supplies can be from the main switchboard or alternatively one supply can be from the emergency switchboard

 The electric motors for steering gears should, be rated according to the (international electro technical commission) IEC60034 standard for rotation electrical machines. The S6-25% rating is required for electro-hydraulic systems and S3-40% for electro mechanical systems

6.Moving parts of steering gears should be guarded to avoid injury to personnel

7.Hydraulic systems should employ non freezing fluid

8.A clear view from the steering position is required and the wheel, tell- tale indicators and rudder movement must correspond in the correct amount and the correct direction for the ships head

9. During the ships operating trials the steering gear systems will be tested to ensure that the limits of movements, time of operation and angle of heel at speeds all meet regulatory requirements

Question 75

list 3 requirements for conventional rudder system and power system

Answer 75

Should be capable operating the rudder from 35°of helm in one direction to 30° helm in the other within 28secs

Moving the rudder to 35° in either direction port or starboard

Operating the rudder from 35° of helm in one direction to 30° of helm in the other within 20 secs for ice class vessels, tugs and supply vessels. Should be completed whilst ship is at max draught and speed

Question 76

what rules must be followed by Oil tankers, chemical tankers or gas carriers of 10,000 gross tonnage and upwards and ships of 70,000 gross tonnage and upward

Answer 76

Oil tankers, chemical tankers or gas carriers of 10,000 gross tonnage and upwards and ships of 70,000 gross tonnage and upward should comply with following

1.The main steering gear shall arranged so that in event of loss of steering due to a single failure in any part of the power actuating systems of the main steering gear, excluding the the tiller, quadrant or components serving the same purpose, or seizure of the rudder actuators, steering should be able to be regained in no more than 45secs after the loss of one power actuating system

2.The main steering gear should have either;

Two independent and separate power actuating systems capable of meeting requirements or;

At least two identical power actuating systems which acting simultaneously in normal operation shall be capable of meeting requirements. If required to comply with this requirement , inter connection of hydraulic power actuating systems should be provided. Loss of hydraulic fluid from one system should be able to be detected and then defective system should automatically be isolated so that other actuating system can remain operational

3.Steering gears other than of the hydraulic type shall achieve equivalent standards.

4.Ships should carry a fixed storage tank with a fresh charge of oil for at least one power actuating system.

Question 77

Explain with the aid of sketches operating principle of the hele-shaw pump (variable delivery pump) ?

Answer 77

A number of different designs of variable delivery pump exist. Each has a means of altering the pump stroke so that the amount of oil displaced will vary from zero to some designed maximum value. This is achieved by use of a floating ring, a swash plate or a slipper pad. Variable delivery pumpscan run continuously in one direction but have the capability of an infinitely variable discharge from zero to maximum either way. Hele shaw pump is a variable delivery pump The operating principle will now be described by reference to Figure 12.2. When the circular floating ring is concentric with the central valve arrangement the pistons have no relative reciprocating motion in their cylinders (Figure 12.2(a)). As a result no oil is pumped and the pump, although rotating, is not delivering any fluid. If however the circular floating ring is pulled to the right then a relative reciprocating motion of the pistons in their cylinders does occur (Figure 12.2(b)). The lower piston, for instance, as it moves inwards will discharge fluid out through the lower port in the central valve arrangement. As it continues past the horizontal position the piston moves outwards, drawing in fluid from the upper port. Once past the horizontal position on the opposite side, it begins to discharge the fluid. If the circular floating ring were pushed to the left then the suction and discharge ports would be reversed (Figure 12.2(c)). This pump arrangement therefore provides, for a constantly rotating unit, a no-flow condition and infinitely variable delivery in either direction. The pump is also a positive displacement unit. Where two pumps are fitted in a system and only one is operating, reverse operation might occur. Non-reversing locking gear is provided as part of the flexible coupling and is automatic in operation. When a pump is stopped the locking gear comes into action; as the pump is started the locking gear releases. The swash plate and slipper pad designs are both axial cylinder pumps. The slipper pad is an improvement on the swash plate which provides higher pressure.

Question 78

Explain the function and what Steering gear is?

Answer 78

The steering gear provides a movement of the rudder in response to a signal from the bridge. The total system may be considered made up of three parts, control equipment, a power unit and a transmission to the rudder stock. The control equipment conveys a signal of desired rudder angle from the bridge and activates the power unit and transmission system until the desired angle is reached. The power unit provides the force, when required and with immediate effect, to move the rudder to the desired angle. The transmission system, the steering gear, is the means by which the movement of the rudder is accomplished. Certain requirements must currently be met by a ship’s steering system. There must be two independent means of steering, although where two identical power units are provided an auxiliary unit is not required. The power and torque capability must be such that the rudder can be swung from 35° one side to 35* the other side with the ship at maximum speed, and also the time to swing from 35° one side to 30° the other side must not exceed 28 seconds. The system must be protected from shock loading and have pipework which is exclusive to it as well as be constructed from approved materials. Control of the steering gear must be provided in the steering gear compartment. Tankers of 10000 ton gross tonnage and upwards must have two independent steering gear control systems which are operated from the bridge. Where one fails, changeover to the other must be immediate and achieved from the bridge position. The steering gear itself must comprise two independent systems where a failure of one results in an automatic changeover to the other within 45 seconds. Any of these failures should result in audible and visual alarms on the bridge. Steering gears can be arranged with hydraulic control equipment known as a ‘telemeter’, or with electrical control equipment. The power unit may in turn be hydraulic or electrically operated. Each of these units will be considered in turn, with the hydraulic unit pump being considered first. A pump is required in the hydraulic system which can immediately pump fluid in order to provide a hydraulic force that will move the rudder. Instant response does not allow time for the pump to be switched on and therefore a constantly running pump is required which pumps fluid only when required. A variable delivery pump provides this facility.

Question 79

explain the telemotor?

Answer 79

Telemotor control Telemotor control is a hydraulic control system employing a transmitter, a receiver, pipes and a charging unit. The transmitter, which is built into the steering wheel console, is located on the bridge and the receiver is mounted on the steering gear. The charging unit is located near to the receiver and the system is charged with a non-freezing fluid. Two rams are present in the transmitter which move in opposite directions as the steering wheel is turned. The fluid is therefore pumped down one pipe line and drawn in from the other. The pumped fluid passes through piping to the receiver and forces the telemotor cylinder unit to move. The suction of fluid from the opposite cylinder enables this movement to take place. The cylinder unit has a control spindle connected to it by a pin. This control spindle operates the slipper ring or swash plate of the variable delivery pump. If the changeover pin is removed from the cylinder unit and inserted in the local handwheel drive then manual control of the steering gear is possible. Stops are fitted on the receiver to limit movement to the maximum rudder angle required. The charging unit consists of a tank, a pump, and shut-off cocks for each and is fitted in the main piping between the transmitter and receiver. In the transmitter a replenishing tank surrounds the rams, ensuring that air cannot enter the system. A bypass between the two cylinders opens as the wheel passes midships. Also at mid position the supercharging unit provides a pressure in the system which ensures rapid response of the system to a movement of the wheel. This supercharging unit also draws in replenishing fluid if required in the system, and provides a relief valve arrangement if the pressure is too high. Pressure gauges are connected to each main pipeline and air vent cocks are also provided. In normal operation the working pressure of about 20 to 30 bar, or the manufacturer’s given figure, should not be exceeded. The wheel should not be forced beyond the ‘hard over’ position as this will strain the gear. The replenishing tank should be checked regularly and any lubrication points should receive attention. Any leaking or damaged equipment must be repaired or replaced as soon as possible. The system should be regularly checked for pressure tightness. The rudder response to wheel movement should be checked and if sluggish or slow then air venting undertaken. If, after long service, air venting does not remove sluggishness, it may be necessary to recharge the system with new fluid.

Question 80

Two types of hydraulically powered transmission units for steering gear are in common use (power units), the ram and the rotary vane. explain both of them?

Answer 80

Rotary vane type

With this type of steering gear a vaned rotor is securely fastened onto the rudder stock (Figure 12.9). The rotor is able to move in a housing which is solidly attached to the ship’s structure. Chambers are formed between the vanes on the rotor and the vanes in the housing. These chambers will vary in size as the rotor moves and can be pressurised since sealing strips are fitted on the moving faces. The chambers either side of the moving vane are connected to separate pipe systems or manifolds. Thus by supplying hydraulic fluid to all the chambers to the left of the moving vane and drawing fluid from all the chambers on the right, the rudder stock can be made to turn anti-clockwise. Clockwise movement will occur if pressure and suction supplies are reversed. Three vanes are usual and permit an angular movement of 70°: the vanes also act as stops limiting rudder movement. The hydraulic fluid is supplied by a variable delivery pump and control will be electrical, as described earlier. A relief valve is fitted in the system to prevent overpressure and allow for shock loading of the rudder.

Ram type

Two particular variations, depending upon torque requirements, are possible the two-ram and the four-ram. A two-ram steering gear is shown in Figure 12.6. The rams acting in hydraulic cylinders operate the tiller by means of a swivel crosshead carried in a fork of the rams. A variable delivery pump is mounted on each cylinder and the slipper ring is linked by rods to the control spindle of the telemotor receiver. The variable delivery pump is piped to each cylinder to enable suction or discharge from either. A replenishing tank is mounted nearby and arranged with non-return suction valves which automatically provide make-up fluid to the pumps. A bypass valve is combined with spring-loaded shock valves which open in the event of a very heavy sea forcing the rudder over. In moving over, the pump is actuated and the steering gear will return the rudder to its original position once the heavy sea has passed. A spring-loaded return linkage on the tiller will prevent damage to the control gear during a shock movement. During normal operation one pump will be running. If a faster response is required, for instance in confined waters, both pumps may be in use. The pumps will be in the no-delivery state until a rudder movement is required by a signal from the bridge telemotor transmitter. The telemotor receiver cylinder will then move: this will result in a movement of the floating lever which will move the floating ring or slipper pad of the pump, causing a pumping action. Fluid will be drawn from one cylinder and pumped to the other, thus turning the tiller and the rudder. A return linkage or hunting gear mounted on the tiller will reposition the floating lever so that no pumping occurs when the required rudder angle is reached. A four-ram steering gear is shown in Figure 12.7. The bask principles of operation are similar to the two-ram gear except that the pump will draw from two diagonally opposite cylinders and discharge to the other two. The four-ram arrangement provides greater torque and the flexibility of different arrangements in the event of component failure. Either pump can be used with all cylinders or with either the two port or two starboard cylinders. Various valves must be open or closed to provide these arrangements. The use of a control valve block incorporating rudder shock relief valves, pump isolating valves, ram isolating and bypass valves, offers greater flexibility with a four-ram steering gear. In normal operation one pump can operate all cylinders. In an emergency situation the motor or a pair of hand pumps could be used to operate two port rams, two starboard rams, two forward rams or two after rams. The crosshead arrangement on the four-ram type steering gear described incorporates what is known as the ‘Rapson Slide’. This provides a mechanical advantage which increases with the angle turned through. The crosshead arrangement may use either a forked tiller or a round arm tiller (Figure 12.8). The round arm tiller has a centre crosshead which is free to slide along the tiller. Each pair of rams is joined so as to form a double bearing in which the trunnion arms of the crosshead are mounted. The straight line movement of the rams is thus converted into an angular tiller movement. In the forked tiller arrangement the ram movement is transferred to the tiller through swivel blocks. To charge the system with fluid it is first necessary to fill each cylinder then replace the filling plugs and close the air cocks. The cylinder bypass valves should be opened and the replenishing tanks filled. The air vents on the pumps should be opened until oil discharges free of air, the pumps set to pump and then turned by hand, releasing air at the appropriate pair of cylinders and pumping into each pair of cylinders in turn using the hand control mechanism. The motor should then be started up and, using the local hand control, operation of the steering gear checked. Air should again be released from the pressurised cylinders and the pumps through the appropriate vents. During normal operation the steering gear should be made to move at least once every two hours to ensure self lubrication of the moving parts. No valves in the system, except bypass and air vent, should be closed. The replenishing tank level should be regularly checked and, if low, refilled and the source of leakage found. When not in use, that is, in port, the steering motors should be switched off. Also the couplings of the motors should be turned by hand to check that the pump is moving freely. If there is any stiffness the pump should be overhauled. As with any hydraulic system cleanliness is essential when overhauling equipment and only linen cleaning cloths should be used.

Question 81

how is electric steering achieved?

Answer 81

Steering gears which comprise electric control, electric power unit and electrical transmission, are of two types, the Ward—Leonard system and the Direct Single Motor system. Both types have a geared-down motor drive via a pinion to a toothed quadrant. A Ward—Leonard arrangement has a continuously running motor-generator set this has a directly coupled exciter to provide the field current of the generator. The exciter field is part of a control circuit, although in some circuits control is directly to the field current of the generator with the exciter omitted, When the control system is balanced there is no exciter field, no exciter output and no generator output, although it is continuously running. The main motor which drives the rudder has no input and thus is stationary. When the wheel on the bridge is turned, and the rheostat contact moved, the control system is unbalanced and a voltage occurs in the exciter field, the exciter, and the generator field. The generator then produces power which turns the rudder motor and hence the rudder, As the rudder moves it returns the rudder rheostat contact to the same position as the bridge rheostat, bringing the system into balance and stopping all current flow. In the single motor system the motor which drives the rudder is supplied directly from the ship’s mains through a contactor type starter. Reversing contacts are also fitted to enable port or starboard movements. The motor runs at full speed until stopped by the control system, so a braking system is necessary to bring the rudder to a stop quickly and at the desired position. The usual electrical maintenance work will be necessary on this equipment in order to ensure satisfactory operation