SINGLE ELEMENT WATER LEVEL CONTROL

• Boiler water level is compared with a constant head (condensing pot) applied to a differential transmitter which
converts the measurement to a proportional pneumatic signal.

• This signal is passed to controller as measured variable signal (MV) & compared with desired value (DV)

• Deviation between the two causes controller output to feedwater control valve to change.

• This single Element Water level control can be used on boilers where the load variations on boiler are of limited
magnitude & ratio of steam off take to water in boiler is low

• Since drum water level is compared with the desired level for operation of the feedwater control valve, water level
must fall for the feedwater control valve to open.

• However, where there are sudden load changes, on marine water-tube boilers, single element control has its
limitations

• For a boiler with large amount of water and relatively low steam production, a single water level transmitter on the
steam drum is sufficient for the level controller to maintain a level with acceptable variation.

• A more sophisticated method is required for boilers with high steam production and relatively small water volume.

• The method used is as follows:

• The outlet steam-mass is measured and the inlet feed-water-mass is adjusted to the very same amount.

• The level transmitter is merely used to tune up the system so the water level lies within the limits.

TWO ELEMENT WATER LEVEL CONTROL

• The two elements of the signal are:

 First element - Level signal from the water within the boiler.

 Second element - Flow signal from the steam flowmeter in the boiler steam off-take.

Two element control (level & steam flow) ensures that water quantity in boiler stays constant at all loads.

• Feedwater control valve opens during periods of increased, sudden steam demand.

• Operation: signal from steam flowmeter in steam outlet pipe increases level controller set point at high steam loads
THREE ELEMENT WATER LEVEL CONTROL

• In a balanced condition, the steam flow must be equal to the feed-water flow.

• These two signals are compared by a differential relay

• The relay output is fed to a two-term (P & I) controller and comparator into which the measured drum level signal is
also fed.

• Any deviation between the desired value and the actual drum level and any deviation between the feed-water flow and
steam flow will result in adequate controller action to adjust the feed water flow by controlling the feed water control
valve.

• A change in steam demand results in a deviation signal from the differential relay that will initiate an output signal to
open the feed water control valve.

• The swell effect will not influence the operation of the water level control system.

Similarly, for reduction in steam demand, an output signal will cause the feed valve to close, thus avoiding the effect of
shrinkage

• Any change in the feed water pressure would result in the feed-water control valve operating to correct the change and
maintain the correct drum level.
LEVEL MEASURING DEVICES

• 1. DIP STICK Method

• 2. SIGHT GAUGE GLASSES.

• 3. Magnetic FLOAT SWITCHES

• 4. AIR BUBBLER TUBE OR AIR PURGE TUBE

• 5. CAPACITANCE TYPE LEVEL SENSORS

• 6. CONDUCTIVITY TYPE LEVEL SENSORS

• 7. BILGE LEVEL FLOATS

• 8. LEVEL TRANSMITTERS/TRANSDUCERS

• 9. Igema Level Gauge for remote level indicator

• 10. SAAB TANK RADAR.

FLOAT TYPE LEVEL SENSOR

• Most tanks have high and low level float indicators provided on the tank walls. When the liquid level in the tank reaches
maximum, the float is lifted up by the rising liquid surface. The opposite end of the float device has a magnet which flips
another magnet in the fixed body. The magnet's flipping action makes or breaks the circuit which causes an alarm. They
also have a provision for testing the alarm manually.

• Float type level sensors may be of different types. They may indicate continuous variation in liquid level ,called Level
Transmitter or just alarm high or low level. Floats are also used for filling a tank when the level drops and stopping
filling when the level reaches optimum. These are similar to toilet flush mechanisms.

PRINCIPALE OF CONDUCTIVITY PROBE METHOD Used On Boiler

• Conductivity probe level detector system has one or more level detectors, an operating relay, and a controller. When
the liquid makes contact with any of the electrodes, a electric current will flow between the electrode and ground. This
current energises the relay ( floatless). Contacts to open or close depending upon the state of the process involved. The
relay in turn will actuate an alarm, a pump, a control valve, or all the three. A typical system has probes :

• - low level probe.

• - low low level probe

• - high level probe

• - high level alarm probe

Application OF CONDUCTIVITY PROBE METHOD

 The principle of conductivity is used to give a point measurement. When the water level touches the probe tip, it
triggers an action through an associated controller.
This action may be to:

– Start or stop a pump

 – Open or close a valve

– Sound an alarm

– Open or close a relay

• But a single tip can only provide a single or point action. Thus, two tips are required with a conductivity probe in order
to switch a pump on and off at predetermined levels. When the water level falls and exposes the tip at point A, the
pump will begin to run. The water level rises until it touches the second tip at point B, and the pump will be switched
off.

SAAB MODEL TANK RADAR

A SAAB model Tank Radar - liquid level measuring device for measuring the liquid level in fixed tanks up to 40 metres high.

• Measuring Principle

• The level gauging system is based on Frequency Modulated Continuous Wave(FMCW) radar. Radar microwave Signal is
emitted via an antenna (a parabolic reflector type or cone type antenna), reflected on the product and reception is
achieved after time ‘t’ by means of a waveguide projecting into the tank.The FMCW radar transmits a high frequency
signal whose frequency increases linearly during the measurement phase ( called frequency sweep). The signal is
received with a time delay ‘t’ Delay time t = 2 d/c where d is the distance to the product surface and ‘c’ is the speed of
light in the gas above the product. Forfurther signal processing the difference f is calculated from theactual
transmitted frequency and the received frequency. The difference is directly proportional to the distance . A large
frequency difference correspondto a large distance and vice versa.

• The level is determined periodically (≤ 0.5 seconds) and the value output is displayed in millimetres

ULTRA SONIC METHOD

Level by Ultrasonic METHOD because they are non contact type measurment technique, no physical contact with the liquid.

• Such devices use the technique of acoustic energy transmission.

The measurement depends on the length of time taken for reflections of an ultrasonic pulse from the surface of the
material. Pulses of high frequency sound waves are applied by using a piezo electrical crystal.

• The electrical pulses produced by the transducer converts it into the mechanical viberation or sound waves. The sound
wave is in the ultrasonic frequency range of 35 to 40 KHz.The energy is reflected back

• The signals received are shown on the CRT, which shows the distance between the crystal generator and the surface
from which it originates.

• The ultra sonic transmitter and receiver are located above the tank, Two echoes are received, one from the liquid level
and other from the tank bottom.

• The time separation between the two echoes is proportional to the level of the liquid.
 • Ultra-Sonic/Microwave Level Sensor:

• These devices use ultrasonic or microwaves to determine the ullage level of the liquid in the tank. The device emits
microwaves or ultrasonic sound waves, which hit the surface of the liquid inside the tank and bounces back to the
transmitter itself. The time taken to receive the signal back is calculated and thus ullage of the tank is determined. Main
advantage of this type is there are no moving parts and mainly used for LNG/LPG tankers where manual sounding is not
possible.

DC TYPE TACHMETER GENERATOR

• Tachometer generators ( tacho generators) are electromechanical devices which generates a voltage proportional to
their shaft speed. They are used to power tachometers and to measure the speed of motors, Engines, and other
rotational devices.

• Design

• The majority of modern tacho generators are permanent magnet types. These devices use a rotating armature, one end
of which is attached to a machine shaft, to measure rotational speed. The armature rotates within a fixed magnetic
field, so that its rotation induces electromotive force (voltage) proportional to the shaft's speed. The armature
contacts are connected to a voltmeter circuit, which converts the voltage into a speed value. The output of this device
is 2 to 10 volts per 1,000 revolutions/minute.

• Use and Applications

• Tacho generator use has numerous advantages. For example, when a corresponding shaft reverses direction, a
permanent magnet DC tacho generator's voltage polarity will also reverse. Tachometer generators are therefore ideal
in control or measurement applications which require directional indication.

• The input to the tachometer is the shaft angular motion , the output voltage is proportional to the rotating speed.

• Generated output ( eT ) = kT wt

• Whereas , kT is the tachometer sensitivity.

• wt is the angular motion of the shaft.

• eT is the generated output

AC TACHOMETER-GENERATOR: Cup type

• In order to overcome some of the diffculties of DC tachometer, AC.Tachometer Generators are used.The Tachometer
has Rotating Magnet which may be either Permanent Magnet or an Electromagnet.The Coil is wound on the Stator and
therefore the problems associated with Commutator (as in D.C.Tachometer) are absent.

• The rotation of the Magnet causes an E.M.F to be induced in the Stator Coil. The Amplitude and the Frequency of this
E.M.F. are both proportional to the speed of Rotation. Thus either Amplitude or Frequency of induced voltage may be
used as a measured of Rotational Speed.

• The Output Voltage of A.C.Tachometer Generators is rectified and is measured with a Permanent Magnet Moving Coil
Instument type Galvanometer.

DIFFERENCES BETWEEN INDUCTIVE & CAPACITIVE PROXIMITY SWITCHES

• Inductive and Capacitive Proximity Sensors are devices that will make an electrical change in a circuit as a result of
material approaching the sensor head.

• The main difference between the two types is that capacitive proximity sensors produce an electrostatic field instead of
electromagnetic field.

• The primary difference is sensing material. Inductive sensors only detect metallic objects while capacitive sensors will
detect other materials such as wood, paper, liquids, cardboard, etc.

• Switching frequency is the speed in which a sensor detects an object, resets, and senses another object. For example, if
a sensor has a switching frequency of 100 Hz (100 cycles per second) it can detect a maximum of 100 objects per
second. This is very critical in many applications such as gear rotation measurement.

AIR COMPRESSOR

STARTING INTERLOCKS :

 1. Motor overload.

 2. Lub Oil Pressure Low. Trip at 1 Kg/Cm, Cut In > 1.4 Kg /Cm

 3. Air Temperature High

 4. Cooling water pressure Low alarm & trip.

 4. In addition mechanical safeties such as relief valves, bursting discs, non return valves etc are provided.

WHY COMPRESSOR BE UNLOADED DURING START

 All compressors need to be unloaded during starting, stopping, and at regular intervals. It is for the following reasons:

 1. During the starting of a motor the starting current is very high, so to avoid further overloading of the motor the
compressor is started unloaded. When the current comes down to the running value, the unloader is closed and the
compressor comes on load.

 2. The air is compressed in volume it releases a large amount of moisture. This oily water mixture is incompressible and
if it is present inside the compression chamber it can damage the piston and the valves. For this reason also the
compressor is started unloaded so that all the moisture present inside is drained.

 3. At stopping the same is done so as to drain all the moisture inside and in preparation for the next starting.

 4. Intermittently the compressor is unloaded to remove the condensed water inside which could go outside with the
air.
  For the purpose of unloading there are different types of unloaders some of them are solenoid operated. They all have
a timer in the circuit which energizes the solenoid at the starting, stopping, and intermittently.

SAFETY TRIPS AND ALARMS

• 1.Lube Oil low-pressure alarm and trip: If the lube oil pressure goes lower than the normal, the alarm is sounded
followed by a cut out trip signal to avoid damage to bearings and crank shaft.

• REASON: DUE TO LEAKAGE IN PIPES, SUCTION STAINER CHOKED, WRONG OIL GRADE, GEAR PUMP FAULTY, FAULTY
PRESSURE GAUGE, INCREASED CLEARANCES OF BEARINGS, OIL LEVEL LOW IN CRANK CASE.

• 2.Water high temperature trip If the intercoolers are choked or the flow of water is less, then the air compressor will
get over heated. To avoid this situation high water temperature trip is activated which cut offs the compressor.

• REASONS : cw VALVE CLOSED, CW PIPE CHOKED,, CW PUMP FAULTY,, NO FLOW OF CW,, LOW WATER LEVEL IN
EXPANSION TANK.

• 3.Water no-flow trip: If the attached pump is not working or the flow of water inside the intercooler is not enough to
cool the compressor then moving part inside the compressor will get seized due to overheating. A no flow trip is
provided which continuously monitor the flow of water and trips the compressor when there is none.

• 4.Motor Overload trip: If the current taken by motor during running or starting is very high then there is a possibility of
damage to the motor. An overload trip is thus fitted to avoid such situation.

• 5.High Air Temperature Trip

ISOLATED NEUTRAL SYSTEM:

• The priority requirement on board ships is to maintain continuity of the Electrical supply to equipment in the event of
single earth fault.

• Majority of the marine vessels use ISOLATED Neutral System,except dredgers.

• An ISOLATED Neutral System is one that has its neutral electrically isolated from the earth.

• Very little current will flow due to an earthed fault on one phase, because there is no easy path for it through the hull
and back to the electrical system.

ADVANTAGES

• 1.This system avoids the risk of loss of essential services such as Steering gear equipment.

• 2.In an isolated Neutral system, one earth fault

does not interrupt the supply, but earth leakage detection system would give an alarm.

• 3.A much lower fire risk because leakage current is very low.

Disadvantantages:

1. Difficult to trace the fault of earth leakage.

Earthed Neutral System

 • In Earthed neutral system , the faulty equipment would immediately isolate from the supply , however the loss of
supply , could create a hazardous situation , specially if the equipment is classed as essential equipment. Eg. steering
gear.

• Large fault current would also cause arcing and cause fire risk .

INSULATED NEUTRAL SYSTEM

• Insulated Neutral System--The Reason for Using it Onboard for Ship grounding

• The requirement ashore is the safety of human beings. So, in order to prevent human-electrical accidents, the neutral is
earthed. The priority is neither the safety of the machinery nor the continuous necessary operation of the machinery.

• But the scenario onboard ship is totally different. The priority is the continuous operation of the machineries which are
classed "essential".

• The distribution system followed onboard is "insulated neutral" system. The main priority onboard is the safety of ship
which includes navigation & fire safety..etc. If due to earth fault, the machinery classed as"essential" gets isolated, say
for eg: steering gear, then the safety of ship is at question, which may lead to collison, grounding, fire & pollution
etc..So the priority onboard ship is to maintain the continuity of the supply to the machinery in the event of "single
earth fault occurring".

Advantages Of Insulated Neutral System

• If a single earth fault occurs in "insulated neutral distribution system", will not cause any equipment to go out of
operation and thus maintains the continuity of operation of the equipment and the machinery still continues to
operate".

 Thus a single earth fault will not provide fault current to flow in the circuit. Small current of few milliamps flow due to
earth fault and does not creat any SHOCK or fire risk. There is no damage to the equipment.

 If a second earth fault occurs, then the two earth faults together would be equivalent to a short circuit fault ( via ships
hull) thus resulting large current would operate the protection devices, cause disconnection of, perhaps, essential
services creating a risk to the safety of the ship.

 An insulated neutral distribution system requires two earth faults on two different lines to cause an earth fault current
to flow. Thus an insulated neutral system, is ,therefore, more effective than an earthed system in maintaining
continuity of supply to equipments.

 Hence it is adopted for most Marine electrical distribution systems

Disadvantages Of Insulated Neutral System

• Difficulty in identifying the earth fault on engine room machinery.

• Arcing due to earth fault causes break down of the insulation.

WHAT IS AN EARTH FAULT

• An earth fault occurs when the insulation resistance between live part of conductor touch the metal part of the M/C &
falls below a value as set by relevant regulation.
• Majority of the earth faults occur within the electrical equipment itself. This is due to the insulation failure.

• Therefore , the body of the electrical equipment is grounded to the ships hull.

• For exemple the earth fault should be at least 1 Meg Ohm when carrying 500 volts .

• How ever , 5 megohms is considered to be normal.

DETECTION & CLEARANCE OF AN EARTH FAULT

EARTH FAULT INDICATOR

AC EARTH FAULT LAMPS ON MSB

SAFETY FEATURES OF ENG- ROOM CRANE

 The most important safety feature of the crane is the electromagnetic fail safe brakes which do not allow the crane to
fall with the load even when there is failure of power. For this:

• - Normally centrifugal brakes are used which are fitted inside the rotating drum.

• - The brake pads are always in applied state and pushed by magnetic springs when not in operation or when there is a
power failure.

• Start/(emergency) stop button

• Overload slip clutch, also for stop of hook in top and bottom position

• Limit switches for trolley- and bridge travelling

• 1 .As the crane is operated or the power is supplied, the spring gets pulled inward or compressed due to the
electromagnetic effect of the current. This allows the crane to be operated normally.

• 2. Emergency stop is provided in the remote so that the operator can stop the crane at any time.

• 3) The motor is fitted with distance limit switch in both transverse and longitudinal direction so that the travel of the
trolley and hence crane should not overshoot the rack’s end.

• 4) Mechanical stoppers are provided for both directions in case the electrical distance limit trips fail.

• 5) The up and down travel of the hook is also attaches with automatic stopper to avoid overloading of the motor.

• 6) The motor is fitted with thermal protection trip. When the motor windings get overheated, trip will activate saving
the motor winding from burning.

• 7) Load limit switch is also fitted which will trip the motor if the load to be lifted is above the crane capacity.
• 8) It’s the responsibility of senior officers to operate the crane and to make sure all the personnel involve in any
lifting operation are at a safe distance during operation of the crane.

• 9) Additional tools like i-bolts, shackle, wire sling, belts etc. used for lifting must be checked before use.

• 10) It should be noted that no one walks or stand below the crane when it is in the loaded condition.

MAIN ENGINE STARTING INTERLOCKS

 Main Engine is started from LOCAL ( EMERGENCY STAND), ECR & BRIDGE position. Starting interlocks must be verified .
They are as follows:-

 1. TURNING GEAR INTERLOCK:(By operating LIMITSWITCH) This device prevents engine from being started if the turning
gear is engaged. The turning gear is provided to turn the engine during maintenance only. When this device is left
engaged ,this will stop high pressure air from reaching the air start control valve.

 2. Correct running direction interlock ie AHD /AST:(By operating LIMIT SWITCH) This interlock prevents the fuel supply
if the running direction of the engine does not coincide with the telegraph position .The telegraph position and the
Running direction of the engine are sensed electrically and in case they donot corrspond, fuel is cut off via a puncture
valve and wrong way alarm is triggered off.

 3. Main LUB OIL PRESSURE : Be maintained between 5-6 kg/cm.

Piston oil Cooling pressure,
Jacket cooling water pressure .
Sufficient main air pressure
Sufficient fuel pressure
All must be above the required minimum value as per instructional manual.

 4. Sufficient Spring air pressure , Control air pressure , Safety air pressure :Must be above the required minimum. Ie 7
kg/cmsq

 5. Aux Blowers interlock: Must be in Auto mode. The auxiliary blower is provided in case scavange pressure is not
enough. The auxiliary blowers would provide sufficient scavenge air pressure during slow speed running , which is
essential for proper combustion.

 M/E are started and reversed( AHD & AST ) by compressed air , a pressure of around 30 kg/ sq cm.This air is applied on
top of the piston by start air v/v to push it down so that sufficient torque is achieved. Acceleration is achieved by Fuel
Injection. Desired indications are monitored on the ECC desk. After release of minimum fuel , the start air is shut off.

 6. SCAV Air Limiter is a mean of governor control for release of fuel depending upon the availability of scav air in the
desired ratio required for good combustion. As the Scav air pressure increases, a proportional fuel is released. Scav air
limiter can be over ridden .

 7.STARTING AIR DISTRIBUTER IN END POSITION: By Limit switch action

 Air is supplied to the starting air distributer and main starting v/v , causing slow turning v/v to open order to start in
AHD or ASTERN directions. Also electrical signal is fed to another valve which leads air to the reversing cylinder which
reverses to AHD position, causing reversing of the start air distributer and roller of the fuel pumps.Thus the engine
propellor rotates..

DIFFERENT SHUT DOWN SITUATIONS

 Lube oil inlet pressure to engine is very low <1 bar.

 Cam shaft Lube oil pressure is very low < 1.5 bar

 Very high Jacket cooling water temperature >95 deg C

 Low Jacket cooling water pressure < 0.1 bar

 No flow of Cylinder lube oil

 Thrust block temperature very high > 90 deg C

 Lube oil inlet pressure for turbocharger is low < 0.8 bar
 Over speed of the engine which activates shut down at 107 % of Max. continuous rating MCR

 EXH V/V SPRING AIR LOW PRESSURE TRIP ( 5.5 Bar)

 Emergency stop : From BRIDGE, ECR & LOCAL MANOVRING STAND

MAIN ENGINE SLOW DOWN

 1.LUB OIL CROSS HEAD LOW PRESSURE.( 1.7 Bar )

 2. JACKET COOLING WATER LOW PRESSURE LOW.

 3. JACKET WATER OUT LET HIGH TEMPERATURE. (95 Deg C)

 4.LUB OIL M/E INLET HIGH TEMP. (60 Deg C)

 5.OIL MIST DETECTOR IN CRANK CASE.

 6.EXH GAS CYL 1-9 OUT LET HIGH TEMP(450 Deg C)

 7.SCAV FIRE NO 1 – 9 UNIT.( 65 Deg C)

 8.EXH VALVE SPRING AIR LOW PRESSURE.

 9.CYLINDER OIL NON FLOW NO1 – 9 UNIT.

 10.PISTON LUB OIL OUT LET 1 – 9 HIGH TEMP.( 75 Deg C)

DIFFERENT ENGINE SLOW DOWN SITUATIONS

 In this situation the main engine will come to dead slow RPM i.e. below 30 RPM as the slow down protection gets
activated. Following are different slow down situation for main engine:

 Lube oil pressure falls to 1.5 bar

 Cam shaft pressure falls below 2 bar

 There is no flow of piston cooling media (water or oil)

 Oil mist detector or Main bearing sensors has been activated

 Lube oil temperature at the inlet of engine is high > 60 deg C

 Piston Cooling temperature is high > 75 deg C

 Jacket water Temperature is high > 88 deg c

 Engine cylinder exhaust temperature is high > 450 deg C

 Scavenge air temperature is high > 65 deg C

 Thrust block temperature is high > 75 deg C

 Low flow of Cylinder lube oil

 Control air pressure is low < 5.5 bar

MAIN ENGINE ALARMS

• GROUP 1- 01 M/E LO system

• GROUP 2- 02 M/E FO system

• GROUP 3 – M/E CW ( SW + FW ) System

• GROUP 4 - M/E EXHAUST GAS + SCAV System

• GROUP 5 – CONTROL AIR & Safety System

VARIOUS ALARMS ON M/E

1.M/E INLET LUB OIL PRESSURE LOW. - By Pressure Transducer

2.FUEL OIL PRESSURE LOW. - By Pressure Transducer

3.LUB OIL FILTER DIFF PRESSURE HIGH.- BY Differential Pressure Transmitter

4.M/E CONTROL AIR PRESSURE LOW. - By Pressure Transducer

5.M/E START AIR PRESSURE LOW. -- By Pressure Transducer

6.TURNING GEAR ENGAGE/DISENGAGE. -- By Limit Switch

7.M/E LUB OIL INLET TEMPERATURE HIGH.- By Temperature Transducer

8.EXH GAS CYLINDER DIVIATION ALARM --- By relay contacts in Control Circuit

9.FUEL OIL LEAKAGE TANK HIGH LEVEL ALARM – By float switch or by Electronic module

10.FUEL OIL VISCOSITY HIGH/LOW - By Differential Pressure Cell

11.LO T/C 1&2 TURBINE SIDE HIGH TEMP.-- . By Temperature Transducer

12.LO. T/C 1&2 BLOWER SIDE HIGH TEMP.--- . By Temperature Transducer

13 WRONG WAY ALARM- By Control circuit relay contacts

14.CROSS HEAD LO LOW PRESSURE.-- By Pressure Transducer

15.JACKET COOL FW INLET LOW PRESS.-- By Pressure Transducer

16. M/E SAFETY AIR LOW PRESSURE.--- By Pressure Transducer

17 F.O.INLET LOW TEMP.-- By Temperature Transducer

18. CRITICAL SPEED ALARM./BARRED SPEED: The range of speeds ( RPM) of the engine at which the resonant condition
occurs,is referred to as the critical speed or barred speed. High amplitude of viberation starts to build up when the M/E
RPM approaches this range and do not come back to some safe value until it crosses the barred speed range. Unsafe
stresses ocure in this range. This range is usually marked in red colour on the engine tachometer.

19 .M/E LO SUMP TANK LOW LEVEL. --- By Float Switch

20. FUEL CAM ABNORMAL ALARM -- By limit /microswitch

21. SENSOR ABNORMAL --- By Control circuit relay contacts

22. ENGINE START FAIL ALARM – (after three attempts) By Control circuit

ELECTRICAL GOVERNOR

 Since the hydraulic governors has operational problem such as , Low oil level, incorrect viscosity airlock, wrong
adjustments, excessive oil temperature and erratic linkages movements. Therefore Electric Governor came into
operation.

 The electric governor uses a combination of electrical and mechanical components in its operation.

 The speed sensing device is a small magnetic pick-up coil. The rectified, or d.c., voltage signal is used in conjunction
with a desired or set speed signal to operate a hydraulic unit.

 This unit will then move the fuel controls in the appropriate direction to control the engine speed.
BASIC ARRANGEMENT OF M/E ELECTRICAL GOVERNOR

 1.Load increase on engine causes speed drop momentarily.

• 2. The speed drop is sensed by the speed measuring device and is compared with the set value.(SPEED SETTING).

• 3. The deviation in speed is converted into an out put and controls the servo amplifier, which is a hydraulic device.

• 4.The output of this controls the servo motor,which simply, quickly and effectively controls the fuel injection by
positioning the fuel rack, thus increase the fuel to meet the increase in load.

DESCRIPTION OF ELECTRICAL GOVERNOR

• Speed signal is obtained from proximity switch. . Proximity Switch converts Frequency- pulses and ,converted by the
rectifier to d.c voltage proportional to speed .

• -Reference d.c voltage of opposite polarity, which is known as desired operating speed is fed to the controller.

• -These two voltages are connected to the input of electric amplifier.

• -If these voltages are equal and opposite, they cancel., thus no output is from the amplifier.

• -If they are different, then the amplifier sends a signal through the controller to Electro Hydraulic convertor which in
turn control the servo motor and reposition the fuel racks.

• -The function of the load sensing feed to the governor is to correct the fuel supply to the prime mover before a speed
change. Load sensing device anticipate the change in load. A signal is sent to the governor if load change has
taken.LOAD sensing is done electronically.

HYDRAULIC GOVERNOR Vs ELECTRIC GOVERNOR

• Unfortunately, the simple hydraulic governor has a serious defect, which prevents its practical use. It is inherently
unstable; that is, it keeps moving continually,making unnecessary corrective actions. In other words it hunts. The cause
of this hunting is the unavoidable time lag between the moment the governor acts and the moment the engine
responds. The engine cannot comeback to the speed called for by the governor.
Most hydraulic governors use a speed droop to obtain stability. Speed droop gives stability because the engine
throttle can take only one position for any speed.Therefore, when a load change causes a speed change,the
resulting governor action ceases at a particular point that gives the amount of fuel needed for a new load. In this way
speed droop prevents unnecessary governor movement and overcorrection (hunting)
 STEERING SYSTEM

• METHODS OF RUDDER CONTROL

1- NON FOLLOW UP MODE (NFU) ( By Selector Switch)

Selector Switch or push button is pressed, to energise the steering gear PORT or STBD solenoid Hydraulic valve so
that the rudder moves in one direction – either to port or stbd. It de-energises automatically at its mechanical limit
normally 30 deg to 35 deg.

2. Follow up Mode : (By Steering/ Helms wheel). In this mode the existing error between the helm and the rudders
true position is compared with the help of comparator.

This error is amplified and fed to the rudder control unit, thus the rudder moves to port/stbd. This process is
controlled by negative feedback signal.

3- AUTO MATIC CONTROL (GYRO CONTROL- ie Auto Pilot)

Gyro heading (True Course) is fed to the control unit, for automatic steering & correcting the course automatically.

AUTO PILOT- ELECTRONIC STEERING

 1.An Auto pilot on a ship is driven by the gyro compass or the Magnetic Compass and keep the vessel on a set course.
The gyro compass is not magnetic but works on the principle of gyroscopic inertia and points towards true north. Once
set, the gyro compass will steer the ship in a straight line until turned off. It has adjustments for sensitivity in case it's
too windy.

 2. Gyro Compass keeps the ship on a pre determined course using the autopilot, but the GPS input corrects for set,
drift and other external forces that might 'push' the ship off course.

 4.Auto pilot is used when a ship has to steer on a set course for a long time without any alteration.

 5.If the ship deviates from the set course, corrective action is taken By PID immediately and requisit amount of helm is
given to rudder to bring the ship back to the set course.

 6.The course to steer is compared with the ships heading obtained from the gyro or magnetic compass.

 7. Any difference between these two will cause an error and correcting helm is applied to the rudder so that ship is
brought back to the same value of the set course. Other vise the ship steers in zig zag manner.

 8.The course to steer is selected by the course selector knob, while the present heading is indicated on the gyro. Any
difference between the two signals is given to the comparator which has P I D control circuits. The error signal is fed
to the error amplifier , which also gets feedback from the rudder. The output from the error amplifieris is fed to the
telemotor or torque motor. Which in turn operate the rudder in opposite direction for correction.

 9.In an open sea , the ship is subjected to wind and weather, which causes ship to yaw. In rough weather larger
deviation of course are experienced.

 10.The linear filter is provided in the control unit to correct all these disturbances. This is called as KALMIN FILTER.
Description:-

• In case steering system using Auto Pilot mode , then the helms man is not required.

• The auto pilot mode is used when a ship has to steer a set course for a long time without alteration because any
deviation from the set course is controlled electronically and automatically and the ship comes back to its set course.

• The set course is compared with the ships heading obtained from the gyro or magnetic compass. Therefore any
difference between these two will cause an error and correcting helm is applied to the rudder such that the ships
heading is brought to the same value as set course.

• In this way automatic steering reduces the zig zag movement , thus the fuel consumption is considerably reduced.

• Maneuvering of a ship depends upon : type of a ship, length, beam, trim, loading and weather conditions.

• The steering is controlled by a change over switch and present heading of the ship is indicated on the gyro.

• The output from the gyro and manual set course is fed to the comparator in the control unit.

• This is referred as proportional, Integral & derivative control, which analyses the signal from the gyro and the course
selector.

• The summing amplifier is used to obtain a resultant error signal from these three controls.

• This error signal is sent to the error amplifier which also gets feedback from the rudder position

• The output of the error amplifier is fed via telemotor to the steering gear hydraulic unit which inturn operate the
rudder.

• Telemotor Transmitter is fitted in the Bridge Control unit and receiver is fitted in the steering gear compartment.

• How the PID control action works during Auto pilot mode

• The deviation signal is generated under following conditions :

• 1. When ship deviates from the set course. OR

• 2. When the set course is altered.

• In both cases the ships heading from gyro and set course signal are fed to the control unit. The control unit calculates
the rudder angle on the basis of PID control.

• The output of the control Unit is given to the Error Amplifier. Also the error amplifier gets feed back from the rudder.
The error amplifier works out the signal to be given to rudder via tele motor system.
• Proportional Control causes the rudder to move by an amount proportional to the off course error, ie is ship will
oscillate to either side of the required course. The error occurs Thus the signal is applied opposite to the movement of
ship to alter so that the ship comes back to the set course. Thus (P) control determines the rudder angle.

• DERIVATIVE CONTROL: in derivative control, the rudder is shifted by an amount proportional to the rate of change of
ships deviation from the course.

• Thus Derivative Control gives the counter helm to the rudder.

• Thus when P+D are acted, then the course to steer comes to the set course.

• INTEGRAL CONTROL is applied because of the errors due to design parameters, like shape of the hull & bow going to
port and the thrust on the propellor shaft

• Thus integral action takes care of the ships parameters.

• Thus this way (P+I+D) is a combined action which control the accuracy of the set course.

• KALMAN FILTER

 In an open sea , the ship is subjected to wind and weather, which causes ship to yaw. In rough weather larger deviation
of course are experienced.

 The linear filter is provided in the control unit to correct all these external disturbances and stable output is obtained .

Steering System ALARMS AS PER SOLAS reg 29 &30

• Indicators for Monitoring the Operating Conditions of the Steering Gear. Alarms are displayed in wheel House & ECC.

• The indicators for monitoring the operating conditions of the steering gear, provided in the wheel house and ECR are
designed to comply with SO LAS Regulations 29 and 30. The Hydraulic pump motor do not stop

• They are as follows:

• (a) No Volt Alarm – In case of power failure to the system

• (b) Phase failure - in case of single-phasing of the pump's motor, an alarm is activated

• (c) Motor overload- especially when the winding is overheated (the motor's control circuit is to have short circuit
protection)

• (d) Isolation (auto shut-off) valve operated e.g., in case of excessive flow rates

• (e) Hydraulic Oil tank level low

• (f) High oil temperature

• One steering is supplied from mains Power ie MSB and second Steering supplied from Emergency power source (ESB)
in case of total power failure

AIRCOND MACHINERY STARTING INTERLOCKS

• 1. Accomodation Blower - ON

• 2. Low Suction Pressure Switch - ON

• 3. High Discharge Pressure Switch - ON

• 4. Lub Oil Differential Pressure Switch - ON

• 5. Sea Water Pressure Switch- ON

• 6. Unloader Valve energised.

• 7. Accomodation Thermostat –ON

• 8. Motor over load relay contact - ON

 SAFETY TRIPS /SHUT DOWN

• LOW SUCTION PRESSURE TRIP.

• HIGH DISCHARGE PRESSURE TRIP

• LOW LUB OIL PRESSURE TRIP.

• MOTOR OVERLOAD TRIP

WHAT IS MARINE GROWTH PREVENTION SYSTEM

 Ships while sailing use seawater for several purposes. Seawater is used in the ship’s system and discharged after the
use.

 Sea water contains both macro and micro marine organisms such as sea worm, molluscs, barnacles, algae, hard shells
like acorn barnades etc.

 The fouling problem arises when barnacles, mussels and other forms of marine life as larvae enter into pipe-work
systems and settle on the internal surface of pipes where they rapidly grow and multiply. In the most extreme cases,
complete seawater lines can become blocked, affecting the safety and operational capability of the ship. In other
instances, the gradual restriction in the flow of seawater through cooling systems can impair engine efficiency, leading
to increased fuel usage.

 If preventive measures are not taken, the Marine growth can cause damage to the particular part in the long run.

 At times it becomes so serious that flow of sea water gets obstructed. Specially the GS & Fire line if gets choked, it
would lead to a dangerous situation with fire fighting equipments.

 Cleaning of blocked pipes or replacement of complete piping can be time consuming and expensive if required to be
replaces.

 This MGPS is very effective for A/C and Refrigeration machineries.

 To avoid formation of marine growth. MGPS or marine growth preventive system is used onboard ship.

 Description and working of MGPS is as follows.

• Basic principle on which MGPS runs is electrolysis. The process involves usage of copper, aluminum and ferrous anodes.
The anodes are normally fixed in pairs in the main sea chest or in such place where they are in the direction of the flow
of water.

• The system consists of a control unit which supplies impressed current to anodes .

• Due to the impressed current, the aluminum/ferrous anode produces ions, which spread over the system and produce
a anti corrosive film over the pipes, heat exchanger, valves, refrigeration and ac unit etc, internally.

• MGPS anodes are fitted with specially designed safety cap which helps in removing the anode for replacement on
board ship. Normally MGPS have a design life which coincides with the dry dock of the vessel.
 CATHODIC PROTECTION

• An electric cell is formed by the immersion of two dissimilar metals in the electrolyte.

• Sacrificial anode are mounted on the external part of the hull and insulated from the hull.

• The sacrificial anode is referred as corrosion cell which corodes away as current flows through it.

• When current flows in the sacrificial anode it liberates positvely charged ions & negatively charged ions remain there,
which forms a polarising film on the cathode and protects the hull. This process is called cathodic protection.

• When the ship is under way and water is passing by, a fresh supply of oxygen (dissolved in the water) reacts with the
hydrogen film forming water molecules. This destroys the hydrogen film and correspondingly increases the flow of
anodic current; there is increase of corrosion. The anode current thus starts increasing from 0-300 amps during ship are
in FW channel.

• In other words in hull electron flows from anode to cathode leaving positively charged iron ions at the anodic area and
at a the cathode the effect of arrival of electron is to produce negatively charged hydroxyl ions (OH) by electrolysis i.e.
seawater. These negative ions flows through the sea to the anodic area where they combine with the positive ions of
iron to form ferrous hydroxide Fe (OH) . This ferrous oxide is further oxidized by dissolving oxygen to form ferric
hydroxide Fe (OH)3 which is rust. Thus the anodic area is gradually corroded away whilst no corrosion takes place at the
cathodic area.

Consists of :

• Reference Electrodes.- Silver /silver chloride Electrodes.

• An Amplifier.( Magnetic Amplifier Or Thyristor controlled Amplifier.

• Transformer & Rectifiers.

• Sacrifcial Anodes

MODES OF OPERATION

• 1. Stand by mode. : When no current flowing.

• 2. Manual Mode: Output current going to the sacrificial anodes is controlled manually.

3. Automatic Mode: The potential difference between the hull & reference electrode is constantly monitored &
output current is controlled.

4. The confguration Mode : The control current set point is adjusted as per the speed of the ship.

The amount of current required depends upon :

1 Area beneath the water line.

2. Temperature of sea water.

3.Speed of the ship. 4. Quality & state of the paint work.

 PROPELLOR SHAFT EARTHING DEVICE

• Even on ships fitted with ICCP or sacrificial anode systems, propeller shaft bearings are vulnerable to corrosion.

• This is because turning propeller shafts are electrically insulated from the hull by the lubricating oil film in the bearings
and by the use of non-metallic bearing materials in the tail shaft.

• The problem can be eliminated if the shaft is earthed to the hull using a propeller shaft slipring. Corrintec supply
complete shaft earthing assemblies consisting of a pair of high silver content/graphite compound brushes mounted in a
balanced brush holder, running on a copper slipring with a solid silver inlay track.

• This combination has been proved to give the optimum electrical continuity. The number of brushes depends on the
size of the vessel. Smaller craft have a single brush holder. Installation

• The shaft slipring is supplied as two matched halves, complete with band and clamping arrangement and can be readily
installed by competent engineering personnel.

• The balanced brush holder is supplied ready for fitting to a shipyard-supplied 20mm diameter rod and mounting
bracket.

• Each brush holder has an adjustable tensioner to ensure good electrical contact and maximum brush utilisation.

Protection Of Propellers, Propeller shaft

 Local galvanic action takes place between the hub area and blade tip. This is caused by high peripheral tip speed as
compared with the hub speed. The hub becomes cathodic and the blades tip becomes anodic and consequently
corrodes.

 The moving propeller and shaft is generally electrically insulated from the ship’s hull by the film of oil in the bearing and
gears. Since these parts are not directly connected to the ship’s hull they are left unprotected. To overcome this they
are connected to ship’s hull through the slip rings and silver graphite brushes. The grounding cables are also provided
to complete the cathodic protection to the ship’s rudder. A periodic inspection of such earthing is worthwhile as the
brushes wear away and may occasionally stick in their brush holders.

 Measurement shall regularly log together with the ship operating conditions. e.g. location, draught, water temperature,
etc.

OXYGEN ANALYZER

• This O2 Analyzer measures the O2 content of the flue gas on the discharge side of the blowers. The exhaust gases
affected by the combustion efficiency of the boiler or introducing proportion of surplus air. The alarm starts flickering
when O2 content is more than 5% and audible alarm sounds when the content is more than 8%.

• There are various types of measuring instruments used on board ships for measuring different parameters as salinity,
oil contamination in feed water.

• An oxygen analyzer is very important equipment as it is used to measure the oxygen content especially during
situations of enclosed space entries and the presence of sufficient oxygen (21%) is an indicator that a space or tank is
safe to get into.At the same time this very oxygen needs to be minimised during inert gas operations on tankers . Also
inert gas systems use exhaust gases which must be monitored to ensure that their oxygen content is below 5%.

PRINCIPLE OF WORKING OF O2 ANALYSER

• Oxygen is attracted into a strong magnetic field. Most other gases are not.

• The main property of oxygen which helps in its detection and measurement of its percentage in the given sample of air
is that of Para-magnetism. Basically this means that oxygen gets attracted towards a magnetic field. The set up for
measuring oxygen content using this property can be understood from the image shown below.

• It is based upon the principle of PARAMAGNETISM. which means that it is attracted by a magnetic field.

• This paramagnetism is used to obtain fast, accurate oxygen measurements.

WORKING OF OXYGEN ANALYSER

• There are two platinum resistance wires which are exposed to two different chambers.
 • In the first chamber there is the air in which the oxygen content needs to be monitored plus there is an artificially
created magnetic field.

• While the second chamber there is the same air but there is no magnetic field present in this chamber.

• The platinum wires form a part of the Wheatstone bridge circuit . The Wheatstone bridge is used to measure an
unknown resistance by obtaining a balance between two legs of the circuit.

• Hence while one chamber of the meter attracts oxygen and the reference chamber attracts only air.

• This causes a difference in the temperature of the two wire sets because of the difference in thermal conductivity of
oxygen with respect to air.

• This causes imbalance in the resistance of the bridge legs and the degree of this imbalance is in proportion to the
oxygen content in the sample to be measured.

CALIBERATION

• The meter is calibrated to show this difference in resistance as a percentage of the oxygen in the given sample, thus
allowing the ship staff to note the oxygen content in the given space.

• False readings are likely if the gas sample contains another paramagnetic gas such as NO2.

• Therefore the instrument is calibrated.

• ZERO POSTION CHECK : ‘ZERO’ position setting can be done by using a pre calibrated sample. Test with 100% Nitrogen.
( In Emergency CO2 can be used). Open the control valve for three minutes, to obtain the zero setting.

• Now the instrument with atmospheric air to obtain 20.8% reading for which span control can be adjusted if necessary.

STARTING INTERLOCKS FOR STARTING THE MAIN HYDRAULIC PUMP

• 1. Confirm the power is ON from MSB.

• 2. All joysticks of ( Hoist, Luff & Slew mode) must be in neutral position.

• 3. Cooling Fan door is open and it is running.

• 4. Hydraulic Tank has oil upto the desired level.

• 5. All abnormalities in the motor circuit are reset. Such as overload, safety limits.

• 6.Emergency stops are reset.

SALINOMETER

 ELECTRICAL CIRCUIT

 The AC mains is fed to the circuit through main Switch & fuses and fed to the transformer. A pilot lamp on a 24 volts
secondary winding indicates the power supply is available.

 Voltage is applied across the electrode cell & the indicator. The indicator shows the salinity by measuring in the current
in( mAmp) which at preset value actuates the alarm through warning relay.

 The current from the rectifier divided into two paths.

 One path through a temperature compensator with in the sensing probe via resistor R2.

 The other path through the alarm relay potentiometer indicating MA and R3.

 The indicator is protected from O/L by a rectifier (zenor diode) as a shunt.

 When the water temperature is low, then the total resistance of the compensator(Thermister) is in the circuit.When
the temperature of the water rises, it reduces the resistance of the compensator device. Hence a large current flows
through the ammeter
  As the temperature of water increases the resistance of the compensator drops. Hence large current flows in the
circuit.

 The compensator therefore ensures that the alteration in the

 balance of the resistances of the two paths corresponds to the increased water conductivity due to the rise in
temperature and correct reading is thus obtained over the compensated range.

 The alarm setting is adjustable, and contacts of the warning relay closes and light a warning lamp ( Red) and sound
the audible alarm.

 The salinometer also controls the solenoid operated valve which dumps the unaccepted feed water to the bilges or
recirculate. The salinometer and valve reset automatically when the alarm condition clears. at the potentiometer.

SAFETY LIMIT DEVICES ON DECK CRANES

• HOIST MODE : LIMIT SWITCHES

• 1.The hook upper limit switch may for instance be tested by hoisting the hook slowly upwards until automatic stop is
imposed by the limit switch.

• 2.Distant Limit- Keep Distant between Hook & Jib Top.

• 3.Rope Wire Slack Over prevention Limit: In case the cable turns slack when the crane's hook reaches the bottom of
the hold or similarly, touches the deck and the cable continues to be paid out, there is a possibility of fouling or slipping
off the pulley and further complications when hoisting. The same could be the case when the rope snaps and there is
no tension on the cable. Lower Limit – Drum End.

• 4.Over Load Limit

• 5.Operation Lever “0” – Main Motor cannot start unless Joystick handle is positioned at neutral position.

• 6.Emergency stop – Stop in all position.

• LUFFING

• 1.Jib Upper Limit – Minimum Radius. Jib at highest position.

• 2.Jib Lower Limit -- Maximum Radius – Jib at lowest angle position, possible to by pass till lowest limit.

• 3.Jib Lowest Limit -- Drum End.

• 4.Operation Lever “0” notch Interlock . Motor in interlocked to start.

 • SLEW Mode – Slewing End Position 360 degrees.

BRIDGE CONTROL OF ME

 BRIDGE CONTROL SYSTEM takes into consideration the following:

 1.Starting and reversing of the engine.

 2.Critical running zone is by passed.

 3.Movement of telegraph at stop position checks the following:

(a) Turning Gear is disengaged.

(b) Starting air is available at correct pressure.

( c) Cooling water, luboil, & Fuel oil supplies are in order.

 4. Starting sequence will include the following:

(a) Cam shaft is correctly positioned.

(b) Starting air is admitted and shaft runs in right direction. .

(c ) Shaft has gained sufficient speed to cause sufficient compression pressure

required for combustion.

(d) Fuel is admitted and LOADUP program commences.

(e) Starting air is shut off.

(f) Speed is adjusted as per control

 5. If the initial firing not reached with in fixed time, then cycle is repeated. Start repeat alarm is initiated.

BRIDGE CONTROL SYSTEM- COMPONENTS

Bridge Control System consists of :-

• 1. Engine order Telegraph: for the control of Ahead and Astern movement with speed position like dead slow, slow, half
ahead, full ahead and navigational full ahead. The desired speed is transmitted as a current signal to an electro -
pneumatic convertor. The pneumatic signal is sent to the governor through the amplifier.

• 2. Speed sensing unit: getting a speed signal from proximity switches situated at the engine fly wheel.

• 3. Load programming unit.

• 4. Solenoid controls( Start, Stop, Ahead, Astern) fitted in the E/Room.

• 5. INSTRUMENTATION & ALARMS :- Bridge panel has the gauges and alarms such as :

1. Low Starting Air Pressure. 2. Lub Oil Pressure Low Alarm

3. Jacket Cool Water Pressure & Temperature. 4. Fuel Oil Pressure Low.
5. Scavange air pressure LOW alarm

BRIDGE CONTROL- PROCEDURE

• After preliminary checks of M/E, the M/E is blown through and tested on fuel. Then control shifted to Bridge Control by
pressing a button on the ECR and which is acknowledged on the bridge.

• All safety interlocks confirmed.( ie LOW LO Pr, Overspeed, Emcy Stop etc)

• In case of failed start , the start air is kept on. Three to four starts are allowed in case of start failure.

• Then Scav air pressure from control line is supplied to the scavenge air limiter, so that more fuel is injected for better
start .
• Once the engine is started, the speed is increased as per bridge order Accelerating limiter ensures no rapid
variation of engine speed occur. Limiters are provided for Slow down, shut down,
emergency stop, critical speeds.

• Critical speed range ( around 8-12 % of MCR speed): automatic jumping over the critical speed range Is done by
releasing more fuel. Other wise engine will slow down. Critical speed is a crank shaft speed at which resonance may
occur. An excessive vibration of shaft may occur. Critical speed is measured by torsion meter. And recorded on the
tortion graph. Torsion vibrations are due to varying torques and propellor thrust.

BRIDGE CONTROL OF MAIN ENGINES

• BRIDGE CONTROL OF MAIN ENGINES:

• Automatic control of the starting of the main engine can be done from the bridge as well as in Engine control room. The
automatic controls employed in starting the engine is by the following sequence:

• Automatic control used in correctly positioning of the cam shaft.

• Admitting starting air

• Admitting fuel

• Starting air shut off

• Speed adjustment to the value required

• Thus the engine is started and the various parameters like temperature, pressure, flow and tank level have to measured
at every watch to make sure that the engine is running safely.

• Temperatures of lube oil, JCW, exhaust gas, etc. are measured.

• Pressures of lube oil, JCW, fuel oil, and starting air etc. are measured.

• Flow of fuel oil is measured while running.

• Tank levels of Heavy fuel oil, diesel oil, and lube oil are measured.

• For measuring the parameters we make use of the transducers, in turn sending the input signal to the automatic
control system.

AUTOMATIC EMERGENCY SLOWDOWN

• Automatic emergency slow down(0perate in case of the bridge control only)

• Function of automatic emergency slow down

• In case under any of the following conditions and such abnormal condition continued for a preset time, the main engine
is slowed down automatically to a preset speed.

• Q(SL-1) Main L.O. high temp.

• @(SL-2) Piston cooling oil high temp.

• @(SL-3) Piston cooling oil low press.

• @(SL-4) Thrust pad high. temp.

• @(SL-5) Camshaft L.O. high temp.

• @(SL-6) Cylinder L.O. non flow

• a(SL-7) Cylinder C.F.W. low press.

• @(SL-8) Cylinder C.F.W. high temp.

• @(SL-9) Scavenging air box fire

• @(SL-10) Exhaust gas high deviation/ hiah temp.

• @(SL-11) Crankcase oil mist high density

• If the automatic emergency slow down operates, the alarm of "AUTO.EMERGENCY SLOW DOWN" is given and the each
cause indicator LED lights in the control room safety panel..

ELECTRICAL CONNECTIONS OF COOKING RANGE HEATING ELEMENTS