Class 4 Q & A part - 2

101 What is the purpose of Rocker Gear on an Engine?

The purpose of the Rocker Gear is to operate the Inlet and Exhaust Valves on the Cylinder Head.

102 Explain what would happen if you were to lose a Generator.

First the Standby Generator set would start up and automatically put itself on the Board.  If this did not happen, the Ship would "Black Out" and after a time delay, usually 30 seconds, the Emergency Generator would start up and supply the Emergency Switchboard, which supplies essential equipment.

103 What would you consider a minimum Insulation Reading Resistance?

Insulation Resistance must be kept above at least 1MW, the higher the Insulation Resistance the better.  Companies have their own Regulations, but most Companies only allow readings above 5MW.

104 What is a Shipboard use of Stainless Steel and the Properties that make it appropriate?

Stainless Steel could be used for Seawater Pump Shafts. 

It has good corrosive properties and also good wear properties.

105 Sketch and describe a Dry Powder Fire Extinguisher.

The outer container contains a sodium bicarbonate powder.  A capsule of carbon dioxide gas is located beneath a plunger mechanism in the central cap.  On depressing the plunger the carbon dioxide gas forces the powder up a discharge tube and out of the discharge nozzle.

106 How many PPM can be Pumped in Marpol Restricted Areas?

15 ppm.

107 What can you tell me about Halon Systems, with regards to new installations and existing ones?

SOLAS prohibits the installation of new or portable systems in all ships from 1st October 1994 and providing existing fixed installations and portable extinguishers remain serviceable and fit for purposes, they may remain in place (Ref: MGN 80 (Aug 1998)).

108 What is Loop Scavenging in a 2-Stroke Engine?

Loop Scavenging is where the Incoming Air passes over the Piston Crown, then rises towards the Cylinder Head forcing Exhaust Gases down and out the Exhaust Ports, just above the Inlet Port.  The advantage of Loop is that no Exhaust Valve is required.

109 Name Main Engine Shutdowns.

Low Lub Oil Pressure

High Jacket Water Temperature

High Main Bearing Temperature

Overspeed

Oil Mist Detection

110 What Safety Devices are fitted to the Main Engine Crankcase?

Explosion Door/Relief Valves and Oil Mist Detectors.

111 Regarding steel, what are three types of heat treatment ?

Hardening;

This involves heating the steel until it is 30 - 50 degrees C above upper critical temperature range ( 850 - 950 degrees C ), followed by rapid quenching. The hardest possible condition for the steel is thus produced and the tensile strength is increased.

Tempering;

This is employed to relieve quenching stresses and involves reheating the steel to around 650 degrees C ( lower critical temperature range ). Note the higher the tempering temperature, the lower the tensile properties of the material. Once tempered the metal is rapidly cooled by quenching.

Annealing and normalizing;

Normalizing, this is where the steel is heated to around 850 - 950 degrees C depending on it's carbon content and is then allowed to cool in air. A hard strong steel with refined grain structure is produced.

Annealing, again the steel is heated to around 850 - 950 degrees C but is cooled slowly, either in a furnace or an insulated space. A softer more ductile steel than that of normalized condition.

112 Describe the Boiler Hot Well and Cascade Tank.  Why is it Fitted and how would you Trace an Oil Leak?

The Boiler Hot Well is where the Condensate Drains return from the Condensor.  This Condensate may be contaminated as some of the Drains are from Fuel Oil Heating Systems or Tank Heating Systems.    Normally these Drains will pass to the Hot Well via an Observation Tank, which permits Inspection of Drains and their Discharge to an Oily Bilge if contaminated.  The Hot Well Tank is also arranged with Internal Baffles to bring about preliminary Oil Separation from any Contaminated Fuel or Drains.  The Feed Water is then passed through Charcoal or Cloth Filters to complete the Cleaning Process.  Any overflow from the Hot Well passes to the Feedwater Tank, which provides additional Feedwater to the System when required.  Feed Pumps take Suction from the Hot Well to the Boiler.

To Trace an Oil Leak to the System, various Heating Coils to Tanks would be shut off in turn until the Leak stopped, thus indicating which Heating Coil was Leaking.

113 What is the Pressure between an Engine Fuel Pump and Injector?

250-350 bar.

114 Explain the procedure for lowering a Lifeboat with Gravity Davits.

The Lifeboat is held in against a cradle by ropes called gripes and the cradle is secured by pins. With the gripes and securing pins (sometimes known as harbour pins) are removed and released, the winch handbrake can be released to enable the cradle to slide down and over the Ship's side.

A "Tricing-in Pennant (wire)" brings the Lifeboat close to the Ship's side to enable it to be boarded. 

The Bowsing Lines which fasten to each end of the Lifeboat are then used to hold it in to the Ship's side, the "Tricing-in Pennants" then being released.

A Painter is then led from the forward end of the Lifeboat and attached somewhere forward of the lifeboat on the ship.  Lifeboat plugs are then secured.

Once the Crew are on board the Lifeboat the bowsing lines are released and the Lifeboat is lowered to the water.  The Engine is started, Falls released and then the Painter.

115 How is the Signal from the Bridge when the Helm is Moved Transmitted to the Hydraulic Rams in Steering Flat?

When the Helm on the Bridge is moved, electrical impulses are produced.  These impulses are transmitted via an amplifier or control unit to the Steering Flat.  In the Steering Flat, these impulses are relayed to a servomotor (telemotor) which drives an adjusting gear and floating lever which puts the steering gear variable delivery pump on stroke, thus creating hydraulic pressure in the system which moves the Rams, thus moving the Tiller and Rudder.

The Pump is only required to deliver Oil when the Helm is moved i.e. once rudder has matched the Helm Angle, the Control Lever will put the Pump Off Stroke.

116 What are the advantages of CO2 Systems compared to Halon Systems?

CO2 is more Environmentally Friendly also Halon Systems are being phased out.

117 What type of valves are ship side valves ?

Ship side valves are Screw Down Non Return valves.

118On what type of Fire would you use a Dry Powder Fire Extinguisher?

The Dry Powder can be used on all classes of Fire, but it has no cooling effect.

119 Give a Shipboard use of Aluminium Bronze and the Properties that make it suitable for this use.

Pump Impellers.

It has good wear, fatigue and corrosive properties.

120 What would happen to the amps of a Centrifugal Pump if it were run with the discharge valve shut?

The amps would drop, as there would be no load on the pump.

121 What is a Water Fog based Fire-fighting Installation?

Unlike conventional sprinkler systems utilising water under low pressure in heavy large diameter pipes, the Water Fog Extinguishing System operates by using water under very high pressure in small bore pipes.  This reduces the weight and volume of the system and permits easy installation on board.

The Water Fog System produces micro-droplets of water; thus a very large cooling surface is created with only small quantities of water.  With this system the amount of water required for successful fire extinguishing is much less than conventional sprinkler systems.  This allows for the use of fresh water as the medium.  Also with the Water Fog System, the Water Fog is propelled into hidden spaces just like Halon or CO2, providing the most reliable Fire-extinguishing.

In accommodation areas this system can use a dual-purpose nozzle which incorporates a quartazoid bulb for detection and extinguishing.

The Water Fog System is also suitable for Engine Rooms.

122 What are the Pipes, used for Pumping Fuel around the Ship, Protected by?

Quick Closing Valves:  which can be operated remotely.  In most cases from the Bridge or a remote location from the Engine Room.

123 What are the dangers of excessive lubrication in Start Air Compressors?

There is a danger that excessive cylinder lubrication in Start Air Compressors could lead to explosions in Air Start Lines/Manifolds. 

Excessive lubrication can lead to carry over with compressed air, being deposited in the Receiver then transferred to the Air Start Manifold, where a leaking Air Start Valve may allow hot gases from combustion into the Air Start Manifold, ignite the oil vapour, causing an explosion. 

124 What is Boundary Cooling and the reasons for it?

It should be remembered that a Fire exists in three dimensions and therefore has six sides, therefore can be transmitted through bulkheads due to radiant heat, i.e. causing combustible materials in adjacent compartments to catch Fire.   Therefore, this radiant heat is prevented by Boundary Cooling of all sides of the compartment on fire, using water spray hoses.

125 What does AFFF stand for and where would you use this type of Extinguisher?

AFFF stands for:  Aqueous Film Forming Foam.

This would be used on Class B Fires, fires burning liquids such as lubricating oils and fuels.

126 Where would you find Heat Detectors and why?

Heat type Fire Detectors would be used in places such as the Galley, where other types of Detectors would give false alarms.

127 What precautions are to be taken are returning the engine into proper service prior to bottom end bearing survey?

Precautions to be taken before returning the engine to proper service are;

The oil flow to the piston should be checked ie, there should be a good flow returning from the underside of the piston to the sump, this is done with the lubricating pumps running and the crankcase doors off, some crankcase doors on larger engines will have a smaller inspection door that will facilitate this. The bottom end clearance must be within manufacturers specifications, bottom end float must be checked, connecting rod bolts must be torqued correctly and all locking devices fitted.

The engine must then be run on test; this will consist of first running the engine for 5 minutes with no load, checking for signs of overheating and listen for any strange noises, the engine is then stopped and crank case doors for that particular unit removed, the bottom end bearing is felt for signs of overheated, any signs of white metal coming away, the bottom end float will be checked. If everything is satisfactory, the engine is then run for 15 minutes and 30 minutes respectively, carrying out the same checks.

When these checks have been carried out satisfactorily, the engine will then be run on 25% load for one hour, then 50% and so on, keeping a close eye on temperatures and pressure and for signs of overheating until able to put on full load, manufacturers running instructions will vary from engine to engine and should be followed.

Once satisfied that the engine is run in, it maybe returned to service.

128 What is, and where would you find, the International Shore Connection?

This is a standard size Flange which is fitted with a suitable coupling suitable for the Ships Fire Hoses.  The Flange is slotted in order to fit any shore side Fire Main and enable water to be brought on board Ship lying alongside.  Usually located on the Bridge.

129 What is the Regulation regarding use of Evaporators Inshore?

Evaporators should not be used within 20 miles from Shore, due to risk of pollutants being taken into the Freshwater System.

130 If no testing equipment was available, explain how the condition of the lubricating oil could be assessed on board.

If no test equipment is available on board, lubricating oil condition can be determined by a few simple tests;

Crackle test for water, this is where a sample of  lubricating oil is take and placed in a test tube, the test tube is then heated, any water droplets will make a crackling noise due to the formation of bubbles, this will only detect small amounts of water, for larger amounts, a simple settling test can be used.

TBN can be tested by placing a drop of indicator solution on to blotting paper, this being followed by a drop sampled lubricating oil in the centre of the blotting paper.

A colour change should take place around the surrounding area of the drop i.e. if the colour is red, this shows acid is present, green / blue show s alkaline presence.

Note: filters will also give a good indication of the lubricating oil quality.

131 How would you test a double bottom tank for watertight intergrity?

Double bottom tanks are tested by filling them completely with water, including the sounding pipe, by doing this, a small head of pressure is applied to the tank, adjacent tanks, cofferdams around the tank being tested would be checked.

132 What are the Advantages and Disadvantages of Alkaline Batteries?

The Advantages of Alkaline Batteries are that they retain charge on open circuit and even if discharged, it can be left for long periods without adverse effect.

The Disadvantages are that they require a greater number of cells to produce a particular Voltage.

They are also more expensive than Lead Acid Batteries.

133 List possible Impurities in Heavy Fuel Oil?

Impurities in Heavy Fuel Oil come in the form of Solids and Liquids:

Solids:  dirt, rust and sand

Liquids:  water and sludge.

134 What Speed does the Centrifugal Brake on a Lifeboat Winch limit the Speed of Fall of the Lifeboat to?

The Centrifugal Brake on a Lifeboat will not allow the Lifeboat to fall faster than 36m/min.

135 How are star and delta connections combined to produce a star / delta starter for an electrical motor?

Star and delta connections are combined to produce a star / delta starter for an electric motor by having both ends of each phase for the motor starter windings taken to the starter.

In the start position, the windings are connected in star, the voltage across each phase winding being 58% line voltage, with a subsequent reduction in the starting current. The starting torque is also reduced to a third that of a direct on line starter.

As the motor then reaches normal running speed, a timer / relay will change the windings over to the delta connection for normal running.

136 What would you do if you had a High Chloride Level in the Boiler?

To reduce the Chloride Level in the Boiler, the Boiler would be Blown Down, thus allowing Fresh Feed to the Boiler.

137 What minimum current can be regarded as Fatal?

A shock current as low as 15mA ac or dc can be fatal.

138 Name the Trips found on a Generator Circuit Breaker.

Over Current

Under Voltage

Reverse Power.

139  How does an Oil Mist Detector Work?

The Oil Mist Detector uses a Photoelectric Cell to measure small increases in Oil Density.  A Motor driven Fan continuously draws samples of Crankcase Oil Mist through a measuring tube.  An increased meter reading and an Alarm will result if any Crankcase sample contains excessive Mist when compared to either Clean Air or to the other Crankcase Compartments.  The Rotary Valve, which draws the sample, then stops to indicate the Suspect Crankcase Compartment.

The Alarm will cause an Engine Slow Down or Shut Down.

140 What is the Critical and Barred Range on an Engine?

This is where the Speed of an Engine in rpm, at which the resonant condition occurs, and is referred to as Critical Speed.

The high stresses associated with resonant condition start to build up as Critical Speed is approached and do not come back to a safe value until speed is beyond Critical Speed.  The unsafe stresses either side of Critical Speed are known as Flank Stresses, this is known as the Barred Speed Range.

The Engine must not be continuously operated at speeds within the Barred Range.

141  How is crankshaft main bearing clearance measured?

Crankshaft main bearing clearance can be measured in the following ways;

By using a set of feeler gauges ( swedish feelers for better access ).

By means of lead wire, the main bearing cap is removed, as is the top shell, a piece of soft lead wire ( @ 0.5mm thick ) is then placed on the crankshaft journal. The shell and bearing cap are then replaced and torqued to the makers setting. The cap and shell are then removed again and the lead wire is gauged using a micrometer to get the clearance.

Another method is by measuring the crankshaft diameter and then the inside diameter of the bearing shell, this is probably the most accurate but can prove to be the most difficult.

142  What could start a Scavenge Fire?

The main cause of a Scavenge Fire is the Fouling of Scavenge Spaces by the blow by of products of incomplete combustion caused by incorrect cylinder lubrication, faulty fuel injection equipment, accumulation of such mixtures in the Scavenge Space can be set alight by sparks or flame blow by.

143  Sketch and describe the Mechanical Foam type Fire Extinguisher.

The outer container is filled with water.  The central container holds a carbon dioxide charge and a foam solution.  A plunger mechanism with a safety guard is located above the central container.  When the plunger is depressed, the carbon dioxide is released and the foam solution and water mix.  They are then forced out through a special nozzle, which creates the Mechanical Foam.  This Extinguisher has an internal pipe and is operated upright.

144  With regards CO2 Extinguishers, what testing and maintenance is carried out?

Being a pressure vessel, the CO2 Extinguisher is initially tested to 207 bar and after every ten years and after two such tests, every five years.

Carbon Dioxide Extinguishers should also be weighed every six months to check for leakage.

145  What are the Safety Devices fitted to an Air Compressor?

Low Lub Oil Pressure Shut Down

High Air Temperature Shut Down

1st Stage Relief Valve

2nd Stage Relief Valve

A Fusible Plug is fitted after the 2nd Stage Cooler, Set at 120°C

If Water Cooled, a Jacket Water Safety Valve is fitted.

146 Where would you expect to find a Soda Acid Extinguisher (Water)?

Accommodation areas.

147 What is the Purpose of a Fusible Plug on an Air Receiver and at what Temperature is it Designed to Melt

The purpose of the Fusible Plug is to act as a Safety Feature to Release Compressed Air from the Receiver in the event of a Fire in the Vicinity.  The Fusible Plug is designed to melt at 150°C.

148 What is meant by Preference Tripping?

Preference Tripping is the tripping of non-essential loads when an overload condition occurs on a Generator.

If a Generator Overload develops the Preference Trip Relay operates an  Alarm and acts to trip selected non-essential loads.  These loads may trip at set intervals depending on how essential the load is, i.e.  1st trip 5 seconds, 2nd trip 10 seconds

149 What are the Properties of Heavy Fuel Oil?

The Properties of Heavy Fuel Oil are:   High Viscosity, Long Ignition Delay i.e. Low Cetane Index

150 What would prevent Water rushing out of the Boiler if the Gauge Glass were to break?

A Ball Valve is fitted below the Gauge Glass Tube to shut off the Water.

151 Why is an Alarm Sounded when CO2 is released into the Engine Room?

An Alarm is sounded to inform personnel in the Engine Room that the release of CO2 is imminent.  The type of Alarm will be visual and sound different from Engine Room Alarm and General Alarm.

CO2 can not support Life.

152 Explain the Bilge System from Bilge Wells to Overboard

The Bilge Pump (Positive Displacement Pump) takes Suction from the Bilge Well via a Strum Box, then via a Strainer before entering the Pump where it is then discharged to the Bilge Holding Tank.

From the Bilge Tank the Oily Water Separator takes Suction, Bilge Water passes through the Separator before being discharged overboard via 15ppm Monitoring Unit, which will automatically stop the Oily Water Separator Pump and give an Alarm if the Oily Water Mixture exceeds 15ppm.

153 How would you test shell plating for watertight intergrity?

Shell plating can be tested for watertight integrity by a vacuum test, where in drydock, a sealed box is placed over welds and evacuated of air, loss of vacuum showing leaks, welds on ships plating may also be x-rayed to check the integrity of the weld.

154 Briefly describe the test for chlorides,

Phenophalein alkalinity test;

Take a 100ml sample of boiler feed water, add 1ml of phenophalein indicator, the solution should turn pink. Then add drops of sulphuric acid drop by drop until the colour turns clear;

PPM= 10x drops added

Chloride test;

Using the above solution, add 2ml of sulphuric acid, then2  20 drops of potassium chromate indicator, then add drops of silver nitrate, drop by drop until the colour turns brown,

PPM Chlorides = 10 x drops added

155 How is Lub Oil Temperature Controlled?

Lub Oil Temperature is Controlled by means of a Thermostatically Controlled Valve, which will allow Lub Oil to by-pass the Cooler when too cold and divert Lub Oil through the Cooler when too Hot.  Pre-set Wax Elements being incorporated in these Valves for this purpose.

156 When would a Star/Delta Starter be used on a Motor?

Where a slow moving high inertia load is involved the starting time must be considered because of the heating effect of the starting current and in this case a Star/Delta Starter would be used.

The Star/Delta Starter first connects the Starter Windings in Star and when running changes over to Delta.  The Star connection results in about 58% Line Voltage being applied to each Phase with therefore a reduction in Starting Current.  The Starting Torque is also reduced to about 1/3 of its direct on-line valve.

157 What is the Purpose of a Volute Casing in a Turbo Charger?

The purpose of a Volute Casing in a Turbo Charger is to change the Air Velocity in to Pressure.  It also ensures a Constant Velocity of Air leaving the Turbo Charger by accommodating for the gradual increase in quantity of Air that builds up at the circumference of the Compressor.

158 Explain your Company's Bunkering Procedures.

Most Companies will have a Bunkering Procedure which will consist of a check list containing Procedures such as:

Ensure vessel is securely moored

Scuppers are plugged

There are communication between both parties

No smoking signs placed

No hot work is taking place in the vicinity

Oil spill gear is available

Correct valves are opened for bunkering

The overflow tank is empty

This check list is then signed by both parties plus the Chief Engineer

The time of bunkers starting and finishing are then recorded

The amount to each tank

Place of bunkering

Type of Fuel Oil Bunkered, this is also recorded in the Oil Record Book.

Note:  Before Bunkering a set of soundings should be taken;  also during Bunkering to ensure Fuel is going to correct tanks;  and at the end of Bunkering.

Samples of Fuel Bunkered should be taken throughout Bunkering for Analysis.

159 What is the Bilge Injection Valve?

The Bilge Injection is a valve that enables the Engine Room Bilges to be pumped out directly overboard in the event of an emergency such as flooding.  The valve is normally fitted to the end of a branch connection with the main sea-water suction line.  This enables large main sea-water cooling pumps to be used as a bilge pump in an emergency.

160 Describe how a Self Excited A C Generator would work.

The Self Excited A C Generator basically consists of a Synchronisis Generator, where the 3-phase supply is generated, an A C Exciter and a Rotary Rectifier and a Static Excitation Device.

The Rotating Diodes change A C into D C for the D C Excitation Current, which is supplied through Brushes.   The Exciter in conjunction with the A V R is used to monitor the correct Voltage under Load Changes.

161 How do you carry out a Face Seal Check on a Breathing Apparatus Set?

Don Face Mask, tighten straps properly and turn air supply on.  Then switch air supply off and breath in, the mask should stick to face.  Note, pressure gauge should not drop rapidly either.  Switch air supply back on.

162 What are Crankcase Pressure Relief Valves for?

These Valves act as a Safeguard to relieve excessive Crankcase pressures, which may occur from Oil Vapour igniting in the occurrence of an Engine Component overheating.  They also prevent flames from being emitted from the Crankcase and must also be self closing to stop the return of atmospheric air into the Crankcase.  

163 What causes Black Smoke from Combustion i.e. in the Exhaust?

Black Smoke would indicate Faulty Fuel Injection Equipment or it would indicate Insufficient Air Supply.

164 What is the purpose of the Cylinder Relief Valve and Operating Pressure?

The Cylinder Relief Valve is designed to Relieve Pressures in Excess of 10%-20% above normal.

The Operation of this Device Indicates a fault in the Engine, which should be discovered and corrected immediately.

165 What type of Clutch is used on an Electric Windlass?

The type of Clutch used is a Dog Clutch.

166 What is the duration and range of a 136L Trolley Foam Extinguisher?

The duration of a 136L Foam Trolley Extinguisher is 15 minutes approximately with a range of around 18m.

167 How do you Start Up, run Parallel a Generator?

First check Engine Oil Levels, such as Lub Oil Sump, T/C Oil Level, Governor Oil Level, Rocker Arm Bank Oil Level (if fitted).

Check Jacket Water Header Tank Level

Ensure Indicator Cocks are Open, Start Lub Oil Priming Pump then bar Engine over (ensure Turning Bar is removed).

Kick Engine on Air.  Close Indicator Cocks.

Start the Engine.

Check all Parameters are correct:  Lub Oil Pressure/Temperature, Jacket Water Temperature/Pressure, Check Sea Water Cooling Pressure and Rocker Arm Lub Oil Pressure.

Allow Engine to warm up and when satisfied that everything is okay, Engine may be paralleled as follows:

Ensure the Voltage of the Machine to be paralleled is the same as the Bus-bar Voltage.  Ensure the Frequencies of both Machines are the same (the Frequency of the Incoming Machine can be adjusted using the Speed Control).

Select the Machine to be paralleled on the Synchroscope Selector.

The Synchroscope should then start to Rotate, it should be rotating in a clockwise direction slowly.  If it is rotating in an anti-clockwise direction, this means the speed of the Incoming Machine is too slow or if it is rotating Fast Clockwise, the speed of the Incoming Machine is too fast, this is adjusted using the Speed Control.

When the Needle of the Synchroscope is Rotating in the Clockwise Direction Slowly, the Breaker of the Incoming Machine should be Closed.  When the Needle of the Synchroscope is at the Five to Twelve Position, this will allow the Incoming Machine to take a slight amount of load when coming on the Switchboard and also prevent the Machine tripping on Reverse Power.

The Load is then shared equally between both Machines.

168 What sort of Starting Current do you get with a Direct On-Line Starter?

6-8 times Full Load Current.

169  What would happen if the Lub Oil Pressure dropped to Low on a Pump?

If the Lub Oil Pressure were to drop too low on the Lub Oil Pump, the Stand By Lub Oil Pump would cut in.   

170 What can you do to prevent Scavenge Fires?

Conscientious maintenance of the Engine and regular inspection and cleaning of Scavenge Air Spaces will help prevent Scavenge Fires.

171 How can cylinder liner wear be kept within limits given by the manufacturer?

Cylinder liner wear may be kept within engine makers limits by using good quality cylinder lubricating oil and fuels, lubricating oils with a high TBN.

Running the engine within it's limits.

Keeping good control of jacket water temperature and chemical treatment.

Also keeping a good maintenance schedule.

172  What is meant by Protection Discrimination?

This is the ability of a Protection System to disconnect only Faulty Circuits and to maintain the Electrical Supplies to Healthy ones.

Discrimination is achieved by co-ordinating the Current Ratings and the Time Settings of the Fuses and Over-current Relays used between the Generator and the Load.

The Devices nearest the Load having the lowest Current Rating and shortest Operating Time;  those nearest the Generator having the highest Current Rating and longest Operating Time.

i.e.  a Motor Fault on a Centrifugal Pump would not cause the Generator Breaker to Trip.

173 State why some centrifugal pumps have a double volute casing or a diffuser ring?

Some centrifugal pumps have a double volute casing to provide a rotational balance and this reduces wear on radial bearings.

A diffuser ring is fitted to high-pressure centrifugal pumps to covert the kinetic energy into pressure, this ring is fixed in the casing around the impeller in such a way that passages are formed around the vanes.

174 When working on Batteries, what precautions should be taken?

Ensure the space is well ventilated, do not smoke or use naked lights and also wear protective clothing such as apron, gloves and face shield.

175 Halon Fire-fighting System, describe it.

In a Halon Fire-fighting system, Halon bottles are strategically placed around the Machinery Space. The amount of Halon (1301) required for Fire-fighting is very little.  Each bottle has its own definition mechanism. This is operated from a remote location outside the Machinery Space.

On opening the Halon release cabinet, this will sound the Halon Alarm in the Engine Room, which will let personnel know that the release of Halon is imminent and that the Space should be evacuated.  Ventilation to the space should then be stopped and space sealed.  Before release of Halon, all personnel should first be accounted for.

176 What does SOLAS stand for?

Safety of Life at Sea.

177 How would you know a Refrigeration System was Undercharged?

Undercharge will show as a Low Compressor Pressure and large bubbles in the Liquid Line Sight Glass.

178 What Loads are considered Non-essential?

Loads considered as Non-essential are:   Air Conditioning and Ventilation, Laundry, Galley, Refrigeration and Deck Equipment.

179 Crankcase Inspections:  Frequency, Procedure and Reasons they are carried out.

The Frequency may vary from different Engine Manufacturers but is roughly around 5000 hrs.

Also Inspections are carried out after any work has taken place in the Crankcase.

Procedure is as follows:

Remove Crankcase Doors from both sides of the Engine.  Relief Valves can be checked at the same time as the Doors are off.

Inspect condition of all bolt locking devices, replace any damaged components.

Turn Engine over using Turning Gear, ENSURE NO-ONE is in Crankcase while doing this and that the Indicator Cocks are Open, check condition of Camshaft Drive Gears.

Start Main Lub Oil Pump and check Oil Flow from Bearings and Piston Cooling Parts.  Check for any Leakage from Internal Oil Pipes and Galleries.

Check for any damage of Camshaft Lobes

Check for any evidence of Water Leakage from Lower Cylinder Liner "O" Rings.

Replace any damaged Crankcase Door Joints.

Record any Defects.

180 How do you ensure that Batteries are always in good working order?

Where Lead Acid Batteries are used, they require a constant trickle charge, but for both types of Battery a regular charge up is necessary. 

Check state of Battery using a Hydrometer;  Lead Acid - S G 1270®1285   Alkaline is 1190 but S B for Alkaline Batteries does not change much during charge or discharge.

Ensure cells are covered with electrolyte, if not, top up with distilled water.

Keep batteries dry and clean Terminals should be smeared with Petroleum Jelly.

181 What would cause an Excessive High Pressure in a Refrigeration System?

Faults that would cause over pressure are; lack of cooling to the condenser, remedy is to increase cooling water flow through the condenser, or unblock any fouling on the cooling water side of the condenser.

Choked expansion valve, which could be caused by dirt impurities in the system, or freezing of the expansion valve, caused by water in the system, remedy is to clean expansion valve, clean system of impurities, rid system of moisture.

      

182 How often is the Emergency Steering Tested?

Emergency Steering is Tested at least once every 3 months.

183 What is meant by the Term, Type Ex'p'?

Ex'p' = Pressurisation.

This is where Equipment is Pressurised to prevent any gases entering Equipment.

184 Describe three on board tests for main engine lubricating oil.

The flow stick test; this is where the viscosity of the lubricating oil is tested.

Two samples of oil are used for this test, one from the system, and the other, fresh new oil. The flow stick contains two reservoirs, one for the system sample and one for the new fresh oil, these reservoirs are filled and the samples are allowed to reach the same temperature.

The flow stick is then tilted from the horizontal and the oil flows down two parallel channels, when the fresh oil reaches a reference point, the flow stick is returned to the horizontal.

The distance traveled by the used system oil is compared to that of the new, fresh oil and if the used oil is between the two used oil comparison points, the used system oil is still in good condition.

The % water in oil test is used to give an indication if any of water in the lubricating oil, here a fixed amount of oil is sampled from the system, which is 5ml and placed in a capsule where there is a 15ml solution of white and reagent. A lid incorporating a pressure gauge that is calibrated to read % water in oil is then screwed onto the capsule to form an air tight seal.

The capsule is then shaken vigorously for 1 minute, then left to stand, any water in the lubricating oil will react with the white spirit and reagent causing a rise in pressure that will be read on the pressure gauge as % water in the lubricating oil

See Sketch

Another test is; Microbiological degradation of oil test, this test will give an indication of an infestation of microbiological organisms in the lubricating oil.

The test makes use of slides that are coated with a special gel, which is dipped in the sample of lubricating oil, the slide is then placed in a test tube, sealed and left to incubate, any growth that comes

About in the incubation period is then compared to a chart to indicate any infestation by microbiological organisms.

185 What is Cross Flow Scavenging

In Cross Flow Scavenging, the Incoming Air is directed upwards, pushing the Exhaust Gases before it.  The Exhaust Gases then travel down and out of the Exhaust Port.  Advantage is no Exhaust Valve.

186 What would you do if the Lub Oil Temperature started to Rise?

Inform Bridge and reduce load on Engine, Investigate Problem, which could be a Fouled Cooler.

187 How can you Reverse the Direction of a Motor?

By swapping any two supply line connections over.

188 At what Temperature does the MCA state that Fuels must be kept in Storage Tanks?

14°C under their Flash Point.

189 What Safety Equipment should there be at a Bunker Station

Safety Equipment that should be found at a Bunker Manifold are a Foam Fire Extinguisher, Oil Spill Gear such as Spill Absorbent and there should also be communications of some sort.

190 How would you test a watertight door for watertight intergrity?

A watertight door is checked for watertight integrity by means of a simple hose test, but on construction are hydrostatically tested.

191 With regards flammable mixtures, explain lower and upper flammable limits.

The meaning of lower flammable limits is where the mixture is below the flammable range and is too lean and incapable of burning.

As where upper flammable limit is where the mixture is too rich and incapable of burning.

Between these limits is the flammable range.

192 What is the function of the High Pressure cut out in a refrigeration system?

The function of the HP cut out is to shut the compressor down in the event of an over pressure on the condenser side of the compressor, and can only be manually reset.

193 Briefly explain how High Expansion Foam is produced.

High expansion foam is produced by means of a Foam Generator, where from Foam Concentrate and Seawater, 1000 times quantity is achieved.  The generator blows air through a net sprayed with foam concentrate and water.  The vastly expanded foam is then diverted away to the space to be protected.  The foam is an insulator and an absorber of radiant heat; it also excludes oxygen from the fire.

194 What precautions should be taken when working aloft?

Where possible, staging or a ladder should be used and secured firmly. A safety harness and lifeline must be used. If possible a safety net should be rigged.

Tools should be carried up in secure containers or belts specially designed for carrying tools to prevent them falling and causing injury to anyone.

The area below the work site is to be roped off with warning signs, people working aloft.

Care should also be taken when working aloft that tools are placed in secure positions to prevent them dropping on anyone.

Hazards should be identified, such as, ships whistle, radars, antennas, which should all be isolated while aloft and do not operate signs placed.

195 How is Leakage in the High Pressure PipeLine between the Fuel Pump and Injector, detected?

Leakage between the Double Skin/Wall of the High Pressure PipeLine between the Fuel Pump and Injector is detected as this space between the Double Skin/Walled Pipe is led via Drain Line to a Small Tank fitted with a Level Alarm.

196 What is the Importance of "M" Notices?

M" Notices are important as they convey very useful information such as:

Merchant Shipping Notices (MSNs):  which will only be used to convey mandatory information, which must be complied with under British Legislation.

Merchant Guidance Notes (MGNs):  which will provide advice and guidance to relevant parties in order to improve the Safety of Shipping and of Life at Sea.

Marine Information Notes (MINs):  which will provide information to a more limited audience such as Training Establishments or Equipment Manufacturers.

197 What Limit does the MCA state that the lower limit of Flash Point of Fuels used on board Ship should be?

65°C

198 Why is Overlap necessary on Air Start Valves?

Overlap is necessary as if there was no Overlap it would be possible for the Engine to stop in a position where no Valves are Open, i.e. unable to Start.

199 What is the Principle Operation of a Flame Detector?   

As Flame has a characteristic Flicker Frequency of 25Hz, use is made of this fact to trigger an alarm.  Flickering radiation from flames reaching the detector lens/filter unit, which only allows infra-red rays to pass and be focused upon the cell.  The signal from the cell goes into the selective amplifier, which is tuned to 25Hz, then to a time delay unit (to minimise incidence of False Alarms) then to an alarm circuit.

200 What is the composition of inert gas after the Scrubber Tower on an Inert Gas System.

Oxygen:  0-1% (Alarm at 5%)

Carbon-monoxide:  0

Carbon Dioxide:  14-15%

Nitrogen:  85

201 Sketch and describe the Battery CO2 System.

The system shows a Battery CO2 System for a Machinery Space.  On opening the release cabinet, this will sound the alarm in the Engine Room, warning personnel that release is imminent and that they should vacate the Engine Room.  Opening of the cabinet will also stop ventilation.  Before release of CO2, a head count must be done to see all personnel are accounted for and the Machinery Space must be sealed.

When the operating handle is pulled, this opens a set of CO2 starting bottles, which in turn supply CO2 to an operating piston via a safety valve.  The piston in turn allows the battery of CO2  bottles to be released to the Engine Room.  This is known as a "One Shot" method.

202 Where are CO2 Extinguishers not permitted ?

CO2 Extinguishers are not permitted in the accommodation, because of their oxygen depleting effect in enclosed rooms.

203 What %/Ratio Halon is required to extinguish a Fire in a Compartment?

5%

204 Why are CO2 Extinguishers not permitted in the accommodation.

Because if used in a confined space, it could be lethal.

205 What is the purpose of the Crankcase Oil Mist Detector?

The purpose of the Oil Mist Detector is to detect the build up of Oil Mist in the Crankcase, generated from a Hot Spot.  The Detector will then give an Alarm, either Shut Down or Slow the Engine Down and give and indication of which Unit the Oil Mist is generated.

206 How would you test a hollow rudder for watertight intergrity?

A hollow rudder would be tested in drydock by filling the rudder with water and checking it for leaks, a small pressure may be applied to aid this, ie a head of pressure from a stand pipe of 2metres or 0.2 BAR air pressure.

207 In an air conditioning system, describe the conditions that could lead to legionella growth and list the precautions in the maintenance of an air conditioning system to reduce the risk of legionnaires disease being contracted.

The conditions that could lead to legionella bacterial growth are dirty air filters at the air inlet, pools of water below the evaporator that become stagnant, or water becoming stagnant in the humidifiers of the water type.

Precautions necessary in the maintenance of AC systems to reduce the risk of legionnaires disease

being contracted is to ensure the system is clean, i.e. . provide adequate drainage below evaporators for the removal of water. Weekly inspections of the system and cleaning of air filters, when necessary with super chlorinated solution, drainage areas also being cleaned with this solution at least every three months. If using water type humidifiers, regular sterilization of them is required. ( steam humidifiers being the preferred choice ).

208 Give a Shipboard use of Cupro-Nickel and the Properties that make it suitable for this use.

Heat Exchanger Tubes.

It has good corrosive qualities and very good heat transfer qualities.

209 What is the Pressure of a Start Air Receiver?

25-40 bar depending on the type of Engine.

210 How is the Bilge Injection Valve brought into Operation?

To bring the Bilge Injection Valve into operation during an Emergency, the Valve is opened fully and the Sea Injection or Suction Valve is fully closed.  After it is established the Bilge Injection Valve is capable of lowering the water level in the Engine Room, the Sea-water  Injection Valve or Suction Valve may be opened slowly.  This should be done in stages so that the Tank Tops are not pumped dry, as this would cause the sea water pump to loose suction.

211 What is Compression and Explain what Happens.

Compression is where the Air that is drawn into the Cylinder is compressed on the upward Stroke of the Piston, both Inlet and Exhaust Valves being closed on this Stroke.  As the Air is compressed by the Rise of the Piston, the Air Temperature is consequently raised.  As the Piston reaches the TDC, Fuel is Injected, causing Ignition and very rapid rise in Pressure of the Gases forcing the Piston down.

212 What type of Fire Detection Equipment did you have on board your Ship?

Flame Detector

Smoke Detector

Heat Detector

213 What testing and maintenance is done regarding Soda Acid and Foam Extinguishers?

The extinguisher containers are pressure vessels, therefore require testing.

Containers are initially tested to 25 bar every year for five years and thereafter at four yearly intervals to 20 bar.

On Soda Type Extinguishers 20% of contents should be discharged per year and replenished with Foam Type 50%.

Where practical the operating mechanism of portable extinguishers should be examined every three months.

214 What would be your first indication that there was water in the Sump?

Your first indication would be from your Lub Oil Purifier.

Or even possibly from water in Lub Oil Tests, if done Regularly.

215 Sketch and describe a CO2 Extinguishers.

A CO2 Extinguishers consists of a very strong container that is used to store liquid carbon dioxide under pressure.  A central tube provides the outlet passage for the carbon dioxide, which is released either by a plunger-bursting disc or a valve operated trigger.  The liquid changes to a gas as it leaves the Extinguisher and passes through a swivel pipe or hose to a discharge horn.

216 On what type of Fire would you use a Soda Acid Extinguisher (Water)?

This type of Extinguisher would be used on Class A Fires:  Fires burning wood, glass fibre, upholstery and furnishings.

217 Explain how the Emergency Generator starts up in the Event of Total Power Failure.

The Start-up of the Emergency Generator is initiated by an Electrical Relay, which monitors the normal Mains Power Supply.  Falling Mains Frequency or Voltage causes the "start-up" relay to operate the Generator Starting Equipment.  The Prime Mover may be electrically cranked from it's own 24V battery and starter motor or air started from it's own air reservoir fitted local to the Generator Engine.  A manual start-up may also be initiated by push buttons in the Main Control Room and in the Emergency Generator Room.

Also when power loss occurs, the Breaker feeding the Emergency Switchboard from the Main Switchboard opens.  This Breaker is interlocked with the Emergency Generator Breaker, which is normally open under normal circumstances, but in the event of Total Power Failure, this breaker will close when the Breaker feeding the Emergency Board from the Main Board opens.  Thus the Emergency Generator will feed the Emergency Switchboard.

218 What are the two Brakes on a Lifeboat Winch?

The two brakes on a Lifeboat are a centrifugal brake and a weighted brake known as a "Dead-Man's Brake" i.e. once you let go of the braking lever, the brake will come into action stopping the fall of the Lifeboat.

219 What would you do if you had High Jacket Water Cooling Temperatures?

Inform Bridge and then reduce Engine Load and Investigate Problem:

Which could be insufficient Flow through Cooler due to Fouled Cooler or Faulty Thermostatic Valve.

220 What are the two types of CO2 Fixed Installations used on board ships for Fire Fighting?

The two types of systems are:  Battery System and Bulk System.

221 Sketch and describe the Chemical Foam type of Extinguisher.

The main container is filled with sodium bicarbonate solution and a long inner polythene container is filled with aluminium sulphate.  The inner container is sealed by a cap, held in place by a plunger.  When the plunger is unlocked by turning it, the cap is released.  The extinguisher is then inverted for the two liquids to mix.  Carbon dioxide is produced by the reaction, which pressurises the container and forces out the foam.

222 Name the two most common types of Coolers.

Shell and Plate type Coolers

Shell being where a Tube Stack is used and Fitted into a Shell and closed at either end with end covers.

Plate type being made up of a number of pressed plates surrounded by seals and held together in a Frame.

223 Why is a Gear type Pump used for pumping Oil, while a Centrifugal Pump is used for pumping Water?

A Gear Pump is used for pumping Oil as it has a high suction lift, is self priming, able to produce the discharge pressure required by the System and can handle large amounts of Vapour or Entrained Gases.  It is also able to pump High Viscous Fluids.

A Centrifugal Pump is used for pumping Water, as it is unable to pump High Viscous Fluids such as Oil, the Centrifugal Pump is not Self-Priming.

224 How is the main bearing bottom half shell extracted ?

Assuming bearing cap and top shell have already been removed, the bottom shell is removed in the following manner; The crankshaft is turned using the turning gear until the oil hole is showing on the journal for the bottom shell to be removed. A tool for removing the bottom shell is then inserted in the oil hole as shown on the sketch, the tool consisting of a cylindrical piece that fits securely into the oil hole, attached to the cylindrical piece is a bit of flat bar that is the same thickness as the shell, this protrudes from the oil hole. The engine is then turned using the turning gear, this tool will come into contact with the bottom bearing shell and the bottom shell is pushed around and turned out, great care must be observed when carrying out this procedure. Also advisable to use plenty of oil for lubrication when turning bottom shell out.

225 How would you get water in the Combustion Spaces?

From Cracked Exhaust Valve Cages

Cracked Cylinder Head or Liner

Fuel Contamination via Fuel Injector

Undercooling of the Charge/Scavenge Air.

226 State the capabilities of a Ships Main Fire Pump.

It must be capable of supplying water to, at least two hoses and nozzles in the Ship and they must produce a good jet of water simultaneously.

227 How are a set of crankshaft deflections obtained?

A set of crankshaft deflections are obtained by placing a dial indicator between crankwebs of every unit and rotating the crankshaft, taking readings at various set positions of the crank throw.

First the crankcase temperature is taken and recorded. The dial indicator has set marks on the crankwebs where it is to be situated. The indicator is placed in this position, ensuring there is enough play in the indicator bending of the crankshaft,ie opening and closing of the crank webs as the engine is turned.

The engine is then turned to near enough B.D.C and the dial indicator is zeroed, the engine is then turned in it's normal direction of rotation, readings being taken at 30 degrees (which is zero position ), 90,180,270,and 330 degrees.

This procedure is carried out on every unit and recorded.

Note: the two readings that are taken at 330 and 30 degrees when the crank throw is near B.D.C are divided by two to get the mean value of the crank throw at B.D.C

228 Describe the procedure for pulling a piston?

First check that all lifting gear for the procedure is certified and well within safe working limits. Ensure the engine is isolated, starting air system shut down and manifold drained, all other systems such as jacket water, fuel valve cooling, lubricating oil, fuel oil systems are shut down and isolated and signs placed, also the jacket water and fuel valve cooling for particular unit should be isolated.

Assuming that the cylinder head has been removed. The engine is then turned using the turning gear, ensuring indicator cocks for the other cylinder heads are open, also ensuring no one is working in the crankcase working on the bottom end of the piston being removed, so that the piston is in a position that allows the wear ridge at the top of the liner can be removed to allow ease of removal of the piston. The wear ridge can normally be removed using air driven wire brush or emery clothe.

Once the wear ridge is removed, the piston is then turned to TDC, the lifting bolt hole in the piston crown is then checked and the lifting bolt is fitted, ensuring the shoulder of the lifting bolt bottoms out. A chain block is then fitted between the lifting bolt and the engine room crane, the weight is then taking up using the chain block.

The bottom end bearing bolts are then removed, first bolt locking devices are removed, depending on the size of the engine, the bottom end bearing cap may have to be supported by a chain block, also bottom end bolts may be of the hydraulically tensioned.

Once bolts are removed the bearing cap is removed, taking care not to damage or drop the bearing shell, the engine is now turned so that the crank pin comes away from the connecting rod, the chain block taking the total weight of the piston, the top bearing shell should now be removed before lifting the piston.

Also before lifting the piston, clamps are placed on the liner to prevent it from moving when the piston is lifted.

The piston can now be lifted out of the cylinder using the chain block, once the piston is clear, the crane can be used to lift the piston clear.

229 What can be fitted over Relief Valve Vents to give an indication of leakage?

Balloons

230 What are the Safety Features fitted to a Battery CO2 System?

A Stop Valve to stop discharge of CO2 to the Machinery Space.

A Safety Valve between the Starting Cylinders and Operating Piston.  This is to prevent operation of the System due to leaking Starting Bottles.

Pressure Alarm in discharge line to give an indication of an accidental escape or leaking CO2 bottle from the Battery.

231 Where are Infra-Red type Fire Detectors best situated?

They are best situated in machinery spaces and boiler rooms, where there is a high risk of fire.

232 In the occurrence of an Oil Spill, what do you do?

Stop the flow of oil.  If possible contain the spill on Deck and start clean up procedure using appropriate oil spill equipment and raise the alarm.  There will be a set Drill for Oil Spill Procedure.

If the oil has spilt into the Sea, if in Port, the Port Authorities must be informed, if at Sea, the Coastguard must be informed.

The time, place or position, type of oil and approximate quantity must be recorded in the Engine Room Log, Bridge Log and Oil Record Book.  Circumstances of spill must also be recorded.

233 Why should the boiler not be blown down on finding oil contamination?

The boiler should not be blown down, as this will cover all heating surfaces with oil i.e. insulating the tubes, heating surfaces.

234 What is the Function of a Circuit Breaker?

The Circuit Breaker is an Isolating Switch that also acts as a Fuse.  It has two designed ratings;  one of normal safe working current, and the other against overload, which may also have a time delay.

235 What is the purpose of the hunting gear regards steering gears?

The purpose of the hunting gear is, if  the rudder were to be displaced by heavy sea through lifting of the relief valves, the hunting gear is moved by the rudder stock, this will put the  steering gear variable speed delivery pump on stroke and rudder angle will be restored.

Also it is the  hunting gears requirement to put the pump on and off stroke via a floating lever which is operated  by the telemotor control.

236 How would you know an Air Start Valve was Leaking or Passing?

The adjacent Start Air Line for that Valve would become very hot.

237 Once a Fire Detector has detected or sensed a fire, what happens?

Associated with Fire Detectors is a Circuit connected to an Alarm Panel, which is usually situated on the Bridge, where the Alarm is accepted, usually there is a Repeater Panel in the Engine Control Room.  The Panel giving an indication on which Deck and Zone the Detector was activated.  Someone will then be sent to investigate and verify if it is a Fire or a False Alarm.

238 How is "Water Hammer" prevented?

In order to prevent water hammer it is necessary to open up drains on steam lines being brought into use.  The water must be completely drained so it leaves the line clear.  The steam valve is then cracked open so the line is heated and brought up to near working temperature.  Any condensate found during this process drains out of the line via the drains previously opened.  The valve may then be opened and drains closed.

239 What is the Purpose of the Fuel Oil Settling Tank?

The purpose of the Fuel Oil Settling Tank is to allow any water to separate from the Fuel Oil due to its higher density.  Heating Coils in the Tank aid this and the water is then drained from the tank using Sludge Cocks/Drains.

240 What are two types of abnormal cylinder liner wear?

Two types of abnormal cylinder liner wear are;

" Cloverleafing", this is where TBN is inadequate to neutralise cold corrosion, ie The TBN alkalinity is used up before it reaches ands of the oil ways around the cylinder liner, allowing acidic attack to take place as shown in the sketch;

Another type of abnormal wear is where more wear occurs at the bottom of the liner, this would indicate some sort of piston misalignment, or slackness of cross head guides, or slack running gear of that particular unit is slack.

241 What pumps in the Engine Room would supply the Fire Main?

As well as the Main Fire Pump, several pumps are arranged to supply the Fire Main, their number and capacity set by legislation (MCA for UK registered Ships).

These pumps are normally:  ballast pumps, general service pumps.

242 What are the Four Principle Types of Portable Fire Extinguishers found on board ships?

Soda acid type extinguishers

Foam extinguishers

Dry powder type extinguishers

Carbon dioxide extinguishers.

243 Sketch an Automatic Sprinkler System for the Ships Accommodation and explain.

The sketch shows an Automatic Sprinkler System, which provides a network of Sprinkler Heads throughout Protected Accommodation Zones.

The Sprinkler Heads in the Accommodation both detect and extinguish fires.  The Sprinkler Head is closed by a quartazoid bulb, which contains a liquid that expands considerably on heating, i.e. in the event of a Fire.  When excessively heated, the liquid expands, shatters the bulb and water will issue from the sprinkler head.  A deflector plate on the Sprinkler Head causes the water to spray out over a large area.

The water is supplied initially from a tank pressurised by compressed air and fresh water.  Once the tank pressure falls, as a Sprinkler Head issues water, a salt water pump cuts in automatically to maintain the water supply as long as possible.  The system is initially charged with fresh water to reduce corrosion effects.

Each Sprinkler Zone has a Flow Alarm, which will be set off when a Sprinkler Head operates. This will sound an alarm and give an indication of which Zone on an Alarm Panel, normally on the Bridge.

244  With respect to turbochargers, what are the advantages and disadvantages of roller bearings?

The advantage of ball or roller bearings are they have low frictional drag and are lubricated by their own self-contained gear type pumps driven off the rotor shaft. But the disadvantage of ball or roller bearings are they are very susceptible to vibration and fatigue, both when the engine is running and also from outside sources when the engine is stopped. They also have an finite life of around 20000hours.

245 What are the Disadvantages and Advantages of a Lead Acid Battery?

The Advantages of a Lead Acid Battery are;  they require fewer cells to achieve particular voltage and are reasonably priced.

The Disadvantages are that they require regular attention to keep fully charged, always require a trickle charge and they discharge on open circuit.

246 What would you do if you found an Engineer in Electric Shock?

First raise the alarm then isolate or switch off the current.

If this is not possible, pull or push the victim away from the source, taking care not to make electrical contact with the victim or the electrical source, i.e. use something non-conductive.

Once the victim has been removed from the electrical source, if the breathing is feeble or ceased, artificial respiration should be started at once.  Delay in starting artificial respiration can prove fatal.

Note:  If artificial respiration is started at once, 70% of the victims recover.  If there is 3 (three) minutes delay, only 20% of victims recover.

247 Sketch and describe a Bulk CO2 System

The sketch shows a Bulk CO2 System.  The System consisting of a large insulated vessel which holds CO2 at a working pressure of 21 bar at around -20°C.  To maintain this pressure and temperature a refrigeration circuit is required, one in standby, the other in operation.  As it is essential to maintain pressure in the vessel, a heater is also incorporated.  The System will discharge into the Engine Room and Hold via a main discharge valve, opening of this valve will shut down ventilation and activate the CO2 alarm, warning personnel of the imminent discharge of CO2, all personnel must then be accounted for and space sealed before discharge of CO2

With this System, the actual line to the Engine Room and Other Spaces, where the CO2 is discharged to, will have an individual manual valve and as the System is a Bulk System and the Spaces being discharged to will have different areas, a Chart will pre-determine how long each valve will be opened for, to give proper discharge coverage for each space.

248 What causes Blue Smoke in Combustion i.e. in the Exhaust?

Blue Smoke would indicate that Excessive Lub Oil was being burnt in Combustion.

249 What is Reverse Power Protection for?

Generators intended to operate in Parallel must have a Reverse Power Protection Trip.  A Reverse Power Relay monitors the direction of power flowing between the Generator and the Switchboard.

If a Prime Mover Failure occurred the Generator would act as a Motor.  The Reverse Power Relay detects this fault and acts to trip the Generator Circuit Breaker.

250 What is the Function of the Condenser in a Refrigeration System?

The function of a Condenser in a Refrigeration System is to condense and sub cool the refrigerant below Saturation Temperature.

251 What should you do to ensure that there is no Water Leakage into the Engine Cylinder before preparing Main Engine for Sea?

The Engine should be Turned using Turning Gear with Indicator Cocks open, keeping a close eye on the Cocks for any signs of Water Discharge.

Immediately prior to Starting, the Engine should be Kicked on Air.

Note:  2 Stroke Engines should be Turned at least one Revolution, where a 4 Stroke should be Turned two Revolutions

252 How would you Test for a Leaking Air Start Valve in Port?

First ensure all the Engine Indicator Cocks are Open for all Cylinders, then Isolate the Air Supply to the Timing Valves, this will ensure no Pilot Air is supplied to the Air Start Valves when the Auto Valve is Opened.

Then Operate the Auto Valve, any air discharge from the Indicator Cocks will indicate a leaking or Passing Air Start Valve.

253 What is the Diffuser Plate in a Turbocharger?

The Diffuser Plate in a Turbocharger is found on the Compressor side, it converts the Velocity/Kinetic Energy from the Compressor into Pressure.

254 How is Fuel supplied from Fuel Pump to the Injector?

Through Double Wall/Skin High Pressure Pipes.

255 What are the various cut-outs and alarms in a Funnel Inert Gas System?

High oxygen level (above 5%)

Loss of sea-water pressure/flow

Fan/blower failure

High gas temperature alarm.

256 What is the Principle Operation of a Smoke Detector?

Most smoke detectors are of the light scatter type using a photo cell separated by a barrier from a semi-conductor intermittently flashing light source housed in an enclosure whose containment allows smoke but not light inside.  When smoke is present in the enclosure, light is scattered around the barrier on the photocell and an alarm is triggered.

257 What would you do if Lub Oil Temperature started to Fall?

Reduce Sea Water Cooling Flow through the Lub Oil Cooler by throttling the Sea Water Discharge Valve from the Cooler.

258 Regarding the Emergency Bilge Injection Valve, what is its relevant size compared to the Main Sea Water Injection Valve?

The valve size of the Emergency Bilge Injection Valve must not be less than 2/3 the size of the Main Sea-water Injection Valve

259 In drydock, as a second engineer, what work would ensure was carried out first ?

As second engineer, my first priorities would be to ensure any work involving tailshafts, propellers, ship side valves, seawater suctions were carried out first.

260 What would cause a Crankcase Explosion?

A Crankcase Explosion could be caused by the formation of a Hot Spot i.e. the overheating of a bearing, which in turn could cause an oil mist to be generated.  If this Oil Mist is allowed to build up, an explosive condition could occur where the Oil Mist can be ignited by Piston Blow By or the Hot Spot itself.

261 What is the purpose of the Deck Seal on an Inert Gas System?

The purpose of the Deck Seal is to act as a non-return valve and prevent the back flow of gases, i.e. hazardous to non-hazardous.

262 How would you know if you had a Cracked Liner or Cylinder Head?

Your Jacket Water Header Tank would start to Fall.

Possibly higher Temperatures on that Unit

On a medium speed 4 Stroke Engine, if the Liner was cracked, you would get Water Contamination of the Sump.

On a 2 Stroke Engine there would be possible Water Leakage from Stuffing Box Drains.

263 What are the Essentials supplied by the Emergency Switchboard?

Essentials are:  Emergency Lighting, Alarms, Communications, Watertight Doors and other services necessary to maintain safety and to permit safe evacuation of the Ship by Lifeboats.  Also you will find that a Steering Gear Motor, Emergency Air Start Compressor and Emergency Fire Pump Motor are supplied from the Emergency Switchboard.

264 What type of valves do you find in a bilge system ?

The type of valves you find in a bilge system are screw down non return valves.

265 Why should a four stroke engine be turned two revolutions?

A four stroke engine should be turned two revolutions as the cam shaft makes half a revolution compared to one turn of the engine, therefore to properly check there was no  water leakage from the cylinder head into the combustion space, then engine would have to be turned twice to ensure opening of all inlet and exhaust valves.

266 How many Starts do you require to get from an Air Receiver without Recharging?

On a Reversible Engine:   12 Starts

On Engines with CPP Propellers:   6 Starts.

267 How would you go about finding an Earth Fault in the System?

Finding an Earth Fault would be by the process of elimination i.e. circuit breakers would be opened and closed until earth fault disappeared, taking care which breakers were being opened and closed as they maybe supply essential loads at the time.  It would be good practice to start with places such as the Galley and Laundry where faults are common.

268 How would you test a bulkhead for watertight intergrity?

Bulkheads would be tested by means of a simple hose test. On construction, bulkheads are hydrostatically tested.

269 When taking main engine thrust clearance, what figure of clearance are you looking for?

An approximate figure for thrust clearance is 1mm clearance for every 500mm of shaft diameter

270  Give four reasons why the temperature of the oil in a steering gear system would become excessive?

Four reasons why the temperature of the oil in the steering gear may become excessive are;

Not enough oil in the system

Air in the system

High load on the system due to heavy weather

Wrong grade of oil in the system, ie too viscous

271 Sketch and explain a Foam Fire-fighting Installation.

Here an Automatic Foam Induction System is shown.  The Automatic Inductor Unit ensures the correct mixing of Water and Foam compound which is then pumped to hydrants, deck or machinery space for use.  The foam compound tank is sealed to protect the contents from deterioration and has linked compound supply and air vent valves.  To operate the system, these two linked valves are opened and the Fire Pump started.  Foam mixing is carefully metered by the automatic inductor unit.  The Fire Pump and compound tank must be located outside the protected space.

272 Describe three good insulating materials suitable for permanent electrical wiring.

PVC; which is a very good insulator and commonly used.

Mica; this is another good insulator and is able to with stand high temperatures.

Rubber; which is another good insulater, it can with stand moderate temperatures.

Silicon rubber; this is also a very good insulator and can with stand high temperatures.

273 What are the Alarms and Trips on a Lub Oil System for the Main Engine?

Alarms and Trips on a Lub Oil System on a Main Engine are as follows:

High Lub Oil Temperature Alarm

Low Lub Oil Pressure Alarm

High Lub Oil Filter Differential Alarm

Low Lub Oil Sump Level Alarm

Low Lub Oil Pressure Shut Down Alarm

Stand By Lub Oil Pump Cut In Alarm

274 What are the reasons for not enough Scavenge/Charge Air?

Blocked Air Filter on Turbo Charger,

A Faulty Turbo Charger.

275  Why are pressure / vacuum valves fitted to tanks ?

The valve is to prevent over pressure and under pressure of the oil cargo tanks, as a moderate pressure acting on large surface areas of liquid cargo tanks are sufficient to rupture the tank. Similarly pressure drop on the inside of the tank can cause damage due to greater atmospheric pressure, therefore pressure / vacuum valves are fitted.

276 What type of Detector should be fitted in conjunction with an Infra-Red type Fire Detector?

It should be used in conjunction with a Smoke Detector, to give an early warning of fire.

277  How does the Overspeed Trip Work

The Overspeed Trip works by shutting the Fuel Off to the Engine.

There are various types of Trips, Mechanical Types, which work on the principle of Fly-weights, or Electrical Types, which work on the principle of a Speed "pick-up" operating a Stop Solenoid

278  What would you do in the Event of an Oil Spill?

Raise the Alarm, Inform Bridge and Chief Engineer. 

There should be a Set Drill for Oil Spills, which is practised regularly.

If possible contain the Spill on deck and start clean up procedures using appropriate Oil Spill Equipment.

If the Oil has Spilt into the Sea:-  If in Port, Port Authorities should be informed.  If at Sea, Coastguard should be informed.

The Time of Spill should be Recorded with the Place or Position of Ship at the Time of Spill along with Approximate quantity and Type of Oil.

Circumstances of Discharge or Escape would be Logged in Oil Record Book and Engine Room Log Book.

279 What is the Re-entry Procedure once a Machinery Space has been Flooded with  CO2 or Halon?

Once CO2 or Halon Flooding has taken place, the Space should be continued to be Boundary Cooled.

Only when the Extinguished Fire has been left long enough to cool down, can the Space be re-entered.  Note:  early re-entry can lead to re-ignition.

Re-entry should be done by personnel wearing breathing apparatus, taking water spray hoses with them to cool down any hot surfaces.  Note:  Re-entry should also take place from the lowest point remote from the seat of the Fire, if possible.

Cooling and smoke dispersal are the first priorities to provide an atmosphere in which others can operate and gradually bring machinery back into service. 

Where the Machinery Space Fire involves electrical equipment then only Dry Powder of Carbon Dioxide Extinguishers can be used until the equipment is isolated.

280 What Trips are there on a Generator?

The Trips on a Generator are:  Lub Oil Low Pressure Shut Down, Jacket Water High Temperature, Overspeed Shut Down.

281 What is the Function of the A V R?

The function of the A V R is to regulate the Exciter Field Current automatically, comparing the Generator Terminal Voltage with the Standard Set Voltage and thus maintaining the Generator Terminal Voltage to a Constant Value, regardless of Load Changes.

282  How is 15ppm reached in an Oily Water Separator?

15ppm is achieved in an Oily Water Separator by normally passing through a Two Stage Separator where in the first stage Oil/Water is passed into the coarse separating compartment. Here some oil will rise to the top of the Compartment due to its lower density, Heating Coils may aid this.  The remaining Oil/Water will flow down into the Fine separating Compartment and moves slowly between Catch Plates.  More Oil will separate out onto the underside of these Plates and travel outwards until free to rise to the oil collecting space.  The almost Oil Free Water (usually being at 100ppm at this stage) will then pass to the second stage of the separator, which is a Filter Unit comprising of two Filter Units.  The first Filter Stage removes Physical Impurities present and promotes some Fine Separation.  The second Stage Filter uses Coalescer Inserts to achieve the final De-oiling, Oil/Water Mixture leaving this Stage at less than 15ppm.

283  With respect to turbochargers, what are the advantages and disadvantages of plain sleeve bearings?

The advantages of plain sleeve bearings are that they are quite resilient towards vibration and fatigue, but the disadvantage of plain sleeve bearings are that they require external lubrication system with fine filtration if using engine oil.

284 Describe different types of Cooling Systems i.e. Seawater Cooling System and Central Cooling System.

A Seawater Cooling System is an arrangement that uses individual Coolers for Lub Oil, Jacket Water and the Piston Cooling System.  Each Cooler being circulated by Sea Water.

As where some modern Ships use a Central Cooling System with only one large Sea Water Circulated Cooler.  This cools a supply of Fresh Water, which then circulates to the other individual Coolers.  With less equipment in contact with Sea Water, the corrosion problems are much reduced in this System.

285 After a bottom end bearing has been opened up for survey, what are the nature and the cause of defects that may be encountered on inspection of the bottom end pin and bearing?

The defects found on inspection of the bottom end bearing and pin are; bearing shells may have signs of fretting on the reverse side, there may also be signs of wear or overheating on the shells or signs of pitting on the face or on the back of the shells if they have n't been seating correctly, they should also be checked for signs of pitting or cavitation.

Signs of overheating maybe due to overloading of the engine or lack of oil or from the oil being too hot, cavitation or pitting can be caused by impurities in the oil due to poor filtration, other reasons for poor bearing shell condition are oil dilution from fuel.

The crank pin should be checked for signs of scores which could be from impurities in the hole, the oil hole should be checked to see if it is clear and also the area around the hole should be checked for signs of cracking as this point is a stress raiser.

Other areas to check are the connecting rod bolts, these should be gauged to check for signs of elongation. Also serrations on the mating faces of the bearing cap and connecting rod should be checked for signs of cracks.

Cracks can be located using the dye penetrent method.

286  With reference to steering gears explain how the ship may be steered in each of the following circumstances;

Destruction by fire of the primary supply cable;

Destruction by fire of the telemotor lines;

Bearing failure in the running pump;

Steering gears require to have a separate power supplies and motors, one supply for each pump. The primary supply from the main switchboard, and the secondary or emergency supply from the emergency switchboard.. So if the primary supply was to be destroyed by fire in this case, the secondary or emergency supply would still be in operation.

If telemeter lines were destroyed by fire, the emergency steering arrangement would have to be used where the ship is navigated from the steering flat, using communications between bridge and steering flat. Emergency steering designs vary from ship to ship.

If there was bearing failure on the running pump and the pump were to stop, the standby pump would start up automatically, and steering would resume as normal from the bridge. The pump that bearing failure occurred on would be isolated.

287 What Preventative Maintenance should be Frequently done to Diesel Engine Start Air Receivers?

They should be drained of Accumulated Moisture.

288  Sketch, showing how a propeller is mounted using the pilgrim method.

The sketch shows a Pilgrim nut, which is in effect a threaded hydraulic jack which is screwed onto the tailshaft and provides a predetermined frictional grip between the propeller and it's shaft.NOTE: Propeller is tightened according to a table which takes into account ambient temperature.

289  What Action would you take in the event of the Main Engine Oil Sump Level Rising?  What could be the Problem and how would you fix it?

The action to be taken would depend on how fast the level was rising and what was causing it to rise.

It could be due to the Lub Oil Filling Valve being left open.

But, if it were due to Water or Fuel entering the Sump, the Engine would have to be Stopped as soon as it was Safe to do so.

Tests would be carried out to tell if it were Water or Fuel.

If it were Fuel, you can normally smell this in the Oil, but a Flow Stick Test can be done.

Water has a tendency to form the colour of the Oil, depending on extent of contamination.

f it were Fuel, the most likely cause would be a faulty Injector; therefore it would be changed.

If it were Water, it could be coming from a Cracked Liner or Liner 'O' Rings, therefore possible Liner change to solve the Problem.

The Oil may have to be changed, depending on extent of Contamination, but the Lub Oil Purifier may be able to cope with it.

290  What causes White Smoke from Combustion i.e. in the Exhaust?

White Smoke would indicate the presence of Water.

291 How is main bearing weardown checked?

Main bearing weardown is checked by means of bridge gauge. The main bearing cap and top shell are removed. The bridge gauge is then situated across the journal, a set of feeler gauges are then used to measure the clearance between the journal and gauge to obtain the weardown. On the bridge gauge is marked the initial readings for all bearings. In most cases weardown should not be more than 0.15 mm from initial reading.

292 What is meant by the Term, Type Ex'e'?

Ex'e' = Increased Safety Equipment.

Increased Safety Equipment is based primarily on the elimination of  "open sparking", i.e. equipment that does not have contacts.

293  Describe how an A C Motor works.

Most A C Motors on Ships are of the Induction or Squirrel Cage Motor types, the principle of operation for which is as follows:  The Starter is made up of three separately phased Windings, to which a 3-phase supply is connected.  The Rotor has a series of Copper Conductors along its Axis, which are joined by rings at the ends to form a Cage.  When the motor is started, the Rotating Magnetic Field induces an E M F in the Cage and thus a Current Flow.  The Current carrying Conductor in a Magnetic Field produces the Motor effect, which turns the Rotor.  The Motor Speed builds up to a value just less than the Speed of Rotation of the Magnetic Field.  The Motor Speed depends upon the E M F induced in the Rotor and this depends upon the difference in Speed between the Conductors and the Magnetic Field.

A number of different Fixed Speeds are possible by changing the number of Poles (Conductors).

294 What type of Water Tests would you do on a Low Pressure Auxiliary Boiler/Economiser?

Chlorides test

PH-alkalinity test

Total dissolved solids test - using hydrometer

Phenolphthalein Alkalinity test

Hardness test

Phosphate reserve.

295  On what type of vessel would you expect to find a Bulk CO2 System and what is normally incorporated into these systems?

You would normally expect to find a Bulk CO2 System on a Cargo or Ro-Ro type vessel where hold areas need Fire-Fighting Protection and the Cargo Space System is normally arranged for smoke detection, alarm and CO2 flooding.

Small air sampling pipes from the individual cargo holds are led into a cabinet on the Bridge.  Air is drawn from each hold by a small fan and each pipe is identified for its particular hold.  If smoke is drawn into the cabinet from one of the holds it will set off an alarm.  The smoke is also passed into the Wheelhouse where it can be detected by personnel on watch.

The location of the fire can be identified in the cabinet and the hold distribution valve below the cabinet is operated.  This valve shuts off the sampling pipe from the cabinet and opens it to the CO2 Main, leading to the Bulk CO2 discharge manifold.  A chart indicating the amount of time the release valve is to be opened for and this is done by first opening the main discharge valve to the manifold, setting off CO2 alarms.

296 What is Load Sharing?

Load Sharing is the equal balance of loads between Generators irrespective of Load Changes.

297  What survival equipment would you expect to find in a Lifeboat?

Survival equipment would include oars, a boathook, a compass, distress rockets, first aid equipment, rations and fresh water.

298 Explain Regulations regarding Power Supplies for Steering Gears.

The Electrical Power Supply must be from two widely separate supplies i.e. one from the Main Switchboard and the other from the Emergency Board. 

Electrical leads and fuses are to allow 100% overload, giving only short circuit protection.

If failure does occur on one system, the stand-by system will cut in within 45 seconds.

The Steering Motors will have sequential starting.

 

299 What are the advantages of the pilgrim method?

The advantages of the Pilgrim method are; that engine torque maybe transmitted without loading the key, where fitted.

Also thrust produced is transmitted through a hydraulically pressurised nitrile tyre, which is applied to the propeller to force it onto the shaft.

300 Give possible reasons why the Engine Room Bilge Pump may not be able to Empty Bilges.

The Strum Box from the Bilge may be Fouled.

Bilge Pump Suction Strainer may be blocked.

A Valve may be left open from an Empty Bilge.

There could be a hole in the System on the Suction Side of the Pump.

Depending on type of Bilge Pump, the Pump Suction or Discharge Valves may need overhauling.

301 What safety precautions should be observed when preparing to open up a cylinder liner for inspection?

Safety precautions to be observed when preparing to open up a cylinder liner for inspection are;

Ensure the engine starting system is isolated, do not start signs placed, valves locked in closed position and the bridge is informed, note, it is also good practice to drain the air start manifold.

Ensure that the fuel system is isolated, same with the lubrication system.

The jacket water and fuel valve cooling to the particular unit is isolated and drained.

Turning gear should be engaged and isolated when in use.

Ensure all lifting gear that is to be used is well within it's safe working limits and that it is also certified and certification is within date.

302 What are the alarms fitted to a Bulk CO2 System?

Low level Alarm (loss of 5% volume)

High Level Alarm (increase of contents over 98% volume)

Leakage Alarm past Main Discharge Valve

Alarm when Main Discharge Valve is opened.

303 Why Purge a Boiler Furnace?

A Boiler Furnace is purged before burner operations to ensure that there is no unburned fuel or gases in the Furnace, which may cause a blowback.  Purging should be carried out for at least two minutes.

304 What are the advantages of Halon Systems over CO2 Systems?

Less Halon is needed to extinguish a Fire than CO2 therefore less storage space is required.

Also the atmosphere in a Halon flooded Space is not toxic, although does contain some highly irritant gases when extinguishing.

305 On what type of Fire would you use a CO2 Extinguisher?

Class B and C Fires and Electrical Fires.

306 Why are Weighted Cocks fitted to Sounding Pipes of Fuel Oil Tanks?

Weighted Cocks are fitted to Sounding Pipes of Fuel Oil Tanks to prevent Fuel Oil spills from overflows.  They also prevent vapours escaping from Tanks.

307 Give a Shipboard use for Grey Cast Iron and the Properties that make it suitable for this use.

Freshwater Pump Casings.

It has fairly good machining qualities and is also inexpensive.

308 What is the purpose of a cofferdam?

The purpose of cofferdams are to prevent leakage of one tank or double bottom to another ie, there would be a cofferdam betweeen fuel tanks and fresh water tanks. They also allow for inspection of tanks, cofferdams should also be sounded regularly to check for leaks.

309 What Gas is given off by Batteries while Charging?

Hydrogen.

310 What maximum weardown limit would you be looking for on a sterntube bearing?

Around 2mm maximum.

311 Why carry out Boiler Feed Water Tests?

Boiler Feed Water Tests are carried out to prevent and detect contamination of the Feed Water i.e. a build up of scale occurring, which could reduce Boiler efficiency and can cause serious overheating.

Also to prevent corrosion.

Prevent Carry Over - where soluble salts and suspended solids are carried over with Steam.

312  In the event of turbocharger failure, how can an engine be arranged to operate safely?

In the event of turbocharger failure with one of the above systems, an engine could still be arranged to operate safely by fitting blanking plates which are specially designed for this purpose and are supplied in the spares with the turbocharger.

To fit these blanking plates, the compressor end is removed as well as the blower side and exhaust side bearings / pumps, rotor shaft.

The blanking plates are then fitted, cooling water is still supplied to the turbocharger unless the fault is due to a cooling water leak.

The engine can only be run at reduced power and load, according to manufacturers instructions.

313 Why is a Hydrostatic Release fitted to a Liferaft?

In the event of the Vessel sinking, the hydrostatic release operates at a predetermined water depth, releasing the Liferaft lashings, allowing the Liferaft to float free and inflate.

314 What is done to ensure the Emergency Generator is Always Available and Will Start?

The System should be checked regularly and operated weekly to ensure it's availability if required.  Fuel tanks should be kept full, ample cooling water in radiator cooling system and starting equipment should be functional, i.e. batteries should be fully charged or air receivers full.

315 What are possible defects that may be found with main bearing shells?

Possible defects that might be found on main bearing shells are;

Signs of wiping on bearing surface - signs of metal to metal contact as lubrication is reduced to boundary ( oil too hot, oil starvation, fuel dilution ).

Signs of scoring - due to abrasive contaminants entering oil wedge and there diameter being thicker than the oil wedge thickness ( due to poor or defective filtration )

Signs of pitting, corrosion due to reduced TBN - hence acid attack

Fretting between shell and housing - insufficient tension or vibration. 

316  What is the function of the impeller and the volute casing in a centrifugal pump?

The function of the impeller is to increase the liquids velocity by it's rotation, thus increasing the energy, some of the energy being partially converted to pressure energy by the suitable design of  the impeller  vanes. Suction in the pump being created by the difference in pressure between the suction and discharge side of the impeller.  

The function of the volute casing is to convert most of the liquids kinetic ( velocity ) energy from the impeller into pressure

317  How does Generator Lub Oil cope with Blow By?

Generator Lub Oil copes with Blow By, by having a TBN of 20-30 (TBN standing for Total Base Number which is an indication of the quantity of Alkali, i.e. base, which is available to neutralise acids from blow by).

318 What is the expected suction lift of a centrifugal pump?

The suction lift expected by a centrifugal pump should be around 4metres in theory,but may vary due to the conditions.

319  Explain a Main Engine Lub Oil System

Lub Oil for an Engine is stored at the bottom of a Crankcase known as the Sump, or in a Drain Tank located beneath the Engine.  The Oil is drawn from this Tank through a Strainer by one of two Pumps in parallel, one Pump being on Stand-by.  The Pump discharges the Oil into one of a pair of Fine Filters, it is then passed through a Cooler before entering the Engine and being distributed to the various Branch Pipes.  The Branch Pipe for a particular unit may feed the Main Bearing, for instance.  Some of this Oil will pass along a Drilled Passage in the Crankshaft to the Bottom End Bearing and then up a Drilled Passage in the Con-rod to the Gudgeon Pin in a Trunk Piston Engine or Crosshead Bearing in a Crosshead Engine.

An Alarm at the end of the Distribution Pipe ensures that adequate Pressure is maintained, by the Pump.  Pumps and Fine Filters are arranged in duplicate with one as standby.  After use in the Engine, the Lub Oil drains back to the Sump or Drain Tank for re-use.

320  What does the opening of the CO2 release cabinet do?

It sets off an Alarm in the Engine Room to warn personnel that the release of CO2 is imminent.

It also stops all ventilation.

321  If only one inch of water was observed in the Gauge Glass after blow down (only one Gauge Glass) after Blowing Down Gauge Glass, what would you do?

Reduce Firing Rate of Burner and increase Feed Water Flow to Boiler by starting another Feed Pump.

322  What is the duration of a 9L Foam Fire Extinguisher?

Approximate duration of around 50 seconds.

323  What is the procedure involved in the replacement of a turbocharger bearing?

The procedure for replacing turbocharger bearings is as follows;

First ensure the engine is isolated, ie starting system shut down and do not start signs placed.

Starting on the compressor end, remove drain plug from the bearing housing and drain the oil.

Then remove the pump assembly.

Then using the bearing extractor tool, the bearing assembly is removed while the shaft is supported.

All dismantled parts should be wrapped in waxed paper and kept clean.

The bearing chamber should be thoroughly cleaned before inserting the new bearing, the bearing assembly is then replaced on the shaft, the pump is now placed.

The turbine end bearing is now changed in the exact same way.

Before the bearing housings are reclosed and filled with oil, the "K" value must be measured and checked that it is the same as the "K" value that is stamped on the plate of the turbocharger.

Note; this value should also be checked before dismantling the turbocharger for a bearing change.

True running of the turbo charger shaft should also be checked with a dial indicator for trueness after bearing renewal.

The turbocharger bearing housings end covers are now replaced and refilled with fresh oil.

324  Describe and sketch a Soda Acid Extinguisher.

The container of the Extinguisher holds a sodium bicarbonate solution.  The screw on cap contains a plunger mechanism covered by a safety guard.  Below the plunger is a glass phial containing sulphuric acid.  When the plunger is struck, the glass phial is broken and the acid and sodium bicarbonate mix.  The resulting chemical reaction produces carbon dioxide gas, which pressurises the space above the liquid, forcing it out through the internal pipe to the nozzle.

325  What is the Difference between a Clarifier and a Purifier?

A Purifier removes Water as where a Clarifier removes Solid Impurities.

In some cases, both are used for separation purposes, firstly the Oil is purified, then clarified.

326  Give reasons why Protection Equipment is essential in an Electrical Distribution System.

To disconnect and isolate faulty equipment in order to maintain the power supply to the remaining healthy circuits in the system.

To prevent damage to equipment from the thermal and magnetic forces that occur during short circuit and overload faults.

To protect personnel from electric shock.