steering gear ff

DME/MECC/ Marine Engineering Knowledge/ Jan 2007 /Steering Gear 1 1

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Application




Steering gear

• Ship steering system is mechanism that transmits power from the steering engine to the rudder.

• Hydraulic system is made of Steering gear rudder, stern planes, and tiller




Principle of operations

• Hydraulic system operate on Pascal law, that states that – “Pressure in a fluid acts equally in all directions”

• and using the (Shapelessness, Incompressibility, Transmission of force) Properties of liquid

PRESSURE = FORCE/AREA

Find PressureFind F2

F2 =

F1 = 20 lbf

A1 = 2 in2

A1 = 20 in2

Pressure = 10 psi

200 lbf




• Reservoir - Storage Tank• Pressure source - Hydraulic pump (A-end)• Pressure user - (B-end)

– Hydraulic motor - rotary motion– Hydraulic cylinder - linear motion

• Piping systems– valves, filters, heat exchangers

• Accumulator - stores pressurized oil• Hydraulic fluid (normally oil)




Method of operations

• Different method is use to connect the ram to the tiller, however the same principle apply. An electro hydraulic steering system has system that has the following components that work in a similar way and principle.

• Electro-hydraulic Steering Gear • Ram unit

– Tiller– Cylinder– Hand pump– Follow-up Shaft

• Electro-hydraulic Steering Gear• Power unit

– Electric motor– Waterbury pump (A end)– Transfer valves– Remote steering unit– Trick wheel




Description and specification of

components• A simple The steering system of the ship has an arrangement where the pumps are connected by piping to the cylinder,

• two pipes are connected to by multiported valves

• and other pipe s from other pumps are connected for bypassing

• and the ram is also connected to the tiller.




Method of control

• Normal control from ship's bridge– Utilizes remote electrical signal to control tilt-box position of

hydraulic pump• Alternate control from after steering

– "Trick wheel” manually operated to control tilt-box angle• Emergency control

– Hand pump - Manually pressurizes hydraulic fluid to take local control of rudder

• The steering gear use oil as fluid and advantage non-corrosive and superb lubrication give steering gear good performance.

• Moreso it is convenient, flexible, variable speed control, safety and reliability method of power transmission over long distances, however backdrop lies leaks in high pressure systems that pose a safety hazard

• and adequate oil filtration must be maintained




Ships autopilot systemBackground

• Control of ship movement started with use of celestial observation - earlier ship fearer stared with us of almanac, map, and sextant, to invention of electrically driven gyroscope and magnetic compass until 1911 when gyrocompass- autopilot system which uses a control feedback was invented.




Principle of operations

• The auto plot system work on control three term control law –proportional-integral-derivative (PID).

• Simple autopilot system use a single input single output control system where the heading of the ship is measured by gyrocompass.

• With introduction of control feedback system the signal is fed back to the computer PID (autopilot), which follow commands of the software.




Description and specification of

components




• Feedback system in auto plot system maintain the following:

• Position data• Rate of data • Accumulation of error data

Heading anglePilot inputAutopilot

Ruder servo Compass




The autopilot system is complex system divided into following components

The input –Connected from different sensor to the controller • Gyrocompass• GPS• Wind sensor• Human inputOutputs- To move vessel around to desired position• Main propulsion • Tunnel thrusters• AzimuthController- It is recommended for efficient control system

that autopilot system to have • Good output feedback• Good wave notch filtering • And good integral action for compensation of wave drifts.




Methods of control Course changing – Here the input come from the pilot as a step command,• the rudder is then rotated in the direction of the desired

course. • The amount of heading change is determined by the

amplitude of the step command and heading• and position of the pilot are determined by the

judgement of the helmsman.

Desired response Controller response Vessel

response

StateInput comman

Controller response




TRACKEEPING:

• Here the control of the heading and the position is done by the autopilot.

• It takes position information and calculates the heading and correction in real-time to make the vessel follow the prêdermined course.

Desired response Controller response Vessel

response

stateInput command

Controller response

Vessel position dataresponse




Conclusion

• A good auto pilot can improve vessel profit margin by reducing number of ship personnel and fuel consumption. the drawback remain with leak associated the hydraulic system

steering gear ff

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