engineering - tutorial questions

Engineering Tutorial Questions

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TUTORIAL QUESTIONS

1. What is the popular machinery used for main propulsion. Diesel Engine Steam Turbine Gas Turbine

Suggest a suitable propulsion system for and give reasons: (a) Container Ship - slow speed direct drive diesel engine are best suited they have large power outputs, ability to burn low grade fuels, very efficient horsepower/ fuel consumed, can be direct drive thus eliminating the need for CPP or gearbox. (b) Cruise Ship diesel electric propulsion is popular on cruise ships. The main reason being, that the engine room is basically run as a power generation plant and as more speed is required another generator would be put on line. The same power plants can be used for thrusters and general ship board use. (c) Passenger Ferry The use of medium speed diesels coupled to CPP, gearbox or azimuth drive units provides good power and maneuverability. The smaller height, size and weight enable the engine to be easily installed in the vessel.

2. With regards to diesel engines explain the following:

(a) Scavenging is the process whereby air at a greater pressure than atmospheric pressure is used to press the exhaust gas out of the cylinder of an engine. Air enters the cylinder around BDC and sweeps or scavenges the exhaust gas from the cylinder. 2 stroke engines with the exhaust valve in the cylinder head are known as uniflow scavenged engines because the air is scavenged in one direction. (b) Pressure charging is the use of pressurized air to increase the mass of air in the combustion process. This is generally achieved by use of a turbo charger to compress the air which is cooled to increase its density. At low speeds, 2 stroke engines use an electric driven blower to supply air until the turbo kicks in. (c) Scavenge fires caused by the blow- by of products of incomplete combustion past the pistons and through the scavenge ports into the air chambers. Use of poor fuel and/or poor maintenance of the fuel injection system will lead to the piston rings jamming, which will further result in an accumulation of fuel/oil mix getting blown into the scavenge space and being set alight by sparks or blow-by. (d)Crankcase explosions occur when lubricating oil is vaporized on contact with hot spots or over heated parts within or adjacent to the crankcase. The vaporized oil can be ignited by hot spots, sparks, piston blow-by, or fires in adjacent compartments e.g. scavenge space.


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3. Explain the diesel cycle. The cycle on a 2 stroke is completed in two strokes (1 revolution of the crankshaft) the downward power stroke when reaching near BDC the exhaust valve opens and soon after the scavenge ports are opened as the piston continues its downward stroke driving out the exhaust gases. The scavenge port is closed as the piston travels up on its compression stroke and soon after the exhaust valve is closed and the air is compressed as it moves to the top to complete its cycle where fuel is injected and combustion forces the piston down for another cycle. The 4 stroke cycle is completed in 4 stokes of the piston or 2 revolutions of the crankshaft. The 4 distinct strokes are known as the inlet, compression, power and exhaust.

What is the difference between 2 stroke and 4 stroke? The main difference between a 2 and 4 stroke is the power developed. The 2 stroke having 1 power stroke /rev and the 4 stroke having 1 power stroke/2 revolutions, theoretically giving twice the power when in fact due to inefficiencies in scavenging and other losses is more like 1.8 times. For a particular power rating the 4 stroke is considerably lighter, can operate efficiently at high speeds and direct power take off are possible. 2 stroke engines on the other hand do not require the complicated valve operating mechanism found on 4 strokes, are claimed to have lower operating cost and specific fuel consumption and do not require a reduction gear box to the propeller shaft.

4. Name three basic groups the ships electric power is divided. Give five items included in each group. Make a sketch to show how the emergency generator is connected to the system. The three basic groups that the ships electrical supply is divided into are: (1) Non Essential, (2) Essential, (3) Emergency Non Essential Items: The items not required for the safe navigation of the vessel. These items are the first to be automatically isolated to prevent electrical blackout. The following are considered non essential items. - Galley equipment Domestic fridge and freezers Domestic fresh water pumps Domestic water heaters Cabin heating General lighting Accommodation lighting Air conditioning Sewerage system pumps Engine lube oil and cooling heaters Water heaters Lifts Essential Items: The items considered essential for ship safety typically are - Steering gear Boiler fans and fuel pumps Engine fresh water pumps Engine sea water pumps Lube oil pumps Bilge pumps Navigation lights Gyro compass Engine room lighting Fire detection equipment. Emergency Items: As name implies are items required for emergency situations. Power is supplied from the main switchboard under normal conditions and when a power failure occurs, supply is from the emergency switchboard. Items typically found in this category are Lifeboat and life raft boarding lights Water tight doors Radio communications General alarm Emergency fire pump if electric Emergency generator starting circuits Intercom.


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5. Explain what is meant by turbo charging. A turbo charger is an air compressor driven by exhaust gases. The single shaft has a exhaust gas turbine one end and air compressor the other end. The exhaust gas may enter the turbine directly or via a constant pressure chamber. The compressed air is cooled to increase the charge air density and then delivered to the engine via the air intake manifold or scavenge air receiver. What are the advantages of turbo charging? The advantages of turbo charging has that it utilizes otherwise wasted energy from the exhaust gases thus not creating any extra load on the engine, to compress air as to increase the mass in the combustion process and by adding fuel at the correct mixture will increase the power output.

6. What are the main parts of a diesel engine Lube Oil system? The main parts in the lube oil system are the purifier, heater, filters with by-pass valves, strainers, pumps, oil cooler, controller and relays, sump tank possibly fitted with heater element. Give reasons for using a different type of oil for cylinder liner lubrication in big engines. Slow speed diesel engines are provided with separate lubrication for cylinder liners which is injected between the liner and piston by mechanical lubricators. In addition to lubricating, the oil assists in forming a gas seal and contains additives to keep the cylinder liner clean. The oil used is of a special type and is not recovered.

7. What are the main parts of the diesel engine cooling system? The jacket water cooling system consists of 2 pumps (one sufficient to operate the system alone and the other on standby), water cooler, header tank, water pre-heater, air vents, strainer, various valves and monitoring and alarm system. Large two stroke engine generally have a drain tank fitted for draining the cooling water into to facilitate maintenance and reuse the water.

Give two reasons for cooling diesel engines. (1) The properties of metal will deteriorate if temperatures are to high. (2) To maintain clearances between parts as specified.

Give three operational problems with this system. (1) The first operational problem would be low water level due to leaks in the system, and to ensure that all alarms and monitoring system is operational. (2) The use of corrosion inhibitors and additives in the cooling water need to be closely monitored to avoid corrosion and blockages within the system. Also the use of sacrificial anodes needs to be monitored. (3) The sea water side of the water cooler should be closely monitored as to avoid excessive buildup of marine growth and scale that would affect the efficiency.

8. Name and explain two types of boiler.

There are basically 2 types of marine boilers: (a) Fire or Smoke Tube Boilers where tubes are surrounded by water and hot gases pass through the inside of these tubes. (b) Water Tube Boilers where the water flows through the inside of the tubes and hot gasses pass over the external surfaces.


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List ten boiler mountings and clearly explain there functions. (1) Safety Valves - are fitted to protect the boilers from the effects of over pressure. 2 safety valves are fitted with 3 on high pressure boilers (2) Main Stop Valves - enables the boiler to be isolated from the main steam line if 2 or more boilers are fitted to the line. The valves should be screw down non return type. (3) Auxiliary Stop Valves are basically a smaller version of the main stop valve used to isolate boilers from the auxiliary steam line. (4) Feed Check Valves - are fitted to give final control over the entry of feed water to the boiler. (5) Feed Water Regulator maintain the water level to a predetermined level (maximum and minimum) (6) Water Level Indicators are two gauge glasses fitted directly to the boiler and a remote reading indicator placed at a convenient control position. (7) Low Water Alarms and High Water Alarms (8) Blow Down Valves are fitted to the water drum to enable the drum to be blown down to reduce the density. The valve can be used to drain the drum. Two valves are fitted. (9) Scum Valves are mounted on the steam drum having an internal fitting in the form of a shallow pan situated just below the normal water level, which is used to remove oil and scum from the surface. The valves discharge down the blow down line. (10) Drain Valves to drain the boiler (11) Air Vents to release air from the drums, either when filling or rising steam. (12) Salinometer Valve used to draw off a sample of water without flashing off for testing purposes. (13) Pressure Gauge Connections

9. Explain with sketches the impulse and reactions turbine operation.

Impulse Turbine Reaction Turbine


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Give five turbine protection devices. (1) Over speed alarm (2) Low oil pressure alarm (3) Vacuum Failure

(4) Low steam pressure (5) Motoring (6) Thrust bearing failure (7) Excessive vibration at bearing pedestals (8) Overheating due to excessive temperature differentials

10. What is the common fixed fire fighting systems used on ships?

The most common system in use is the CO2 total flood system which must be capable of discharging 85% within 2 minutes giving 40% saturation of the compartment Explain one of them (with a sketch) suitable for machinery space of a large ship.

Explain the procedure of the operation of the system. 11. To burn successfully in diesel engines and boilers without damaging parts, you

have to know certain properties of bunker fuel. Explain four such properties. (1) Water Content (2) Viscosity (3) Type of fuel e.g. HFO, MGO, DO, Blend (4) Chemical properties e.g sulphur content, other metallic impurities. (5) order to CIMAC standard


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12. Make a list of the things to be carried out before and during bunker operations. The list will vary from ship to ship depending upon the arrangements, the main procedures being: (1) Bunker plan to be drawn up and posted. Soundings taken. (2) Ship securely moored and safe access between ship and shore. (3) Adequate crew available to perform bunkering operations (4) Fire fighting equipment ready, signs noting bunkering operations and no smoking, oil spill gear readily available (5) Check condition of hoses, connections and blank off unused cargo and bunker connections. Cargo and bunker lids closed. (6) Scuppers plugged and drip trays, save alls clean and in place (7) Confirmed communication between ship and shore and onboard change over of tanks. Confirm emergency procedures and stopping arrangements (8) Confirm quantity to be taken, rate of flow, pressure, available capacity of tanks, use of overflow tanks, vent pipes clear (9) Inform Port Authority, B flag, Red at night, check for any oil slicks present prior to starting bunkers and all checklists comleted and OK. (10) Start pumping at slow rate, check for leaks, correct tanks being filled, check emergency stop, cont. pumping and slowly buildup to agreed rate. (11) Monitor tank levels, check hoses and connections for leaks, vent pipes clear (12) Ensure tanks have enough capacity to drain lines and tanks not to be filled above 95%. What action would you take if you find out that you have received poor quality bunkers? Immediately stop bunkering operations. Notify the fuel provider of the situation. Take 3 samples, 1 for the fuel provider, 1 to be kept on board and the other to an independent analyzer. Soundings taken of tanks contaminated and isolate from good fuel. Lodge Note of Protest. Log all events and have signed by 2 witnesses. Report to owner, agent, lawyer and fuel supplier.

13. On completion of bunker operations you have out that the fuel oil was

contaminated. Explain what actions you would take. As Above

14. With regards to steering gear explain (a) Transmitter is located in the wheelhouse. In the case of a all hydraulic

system, hydraulic oil is transmitted to the receiver by rams operated by the helm.

(b) Receiver is located in the steering flat. Impulse oil from the transmitter is received which in turn is connected by linkage to the pump control rod.

(c) Power transmission to rudder stock The receiver activates the control arm that directs the oil to the required ram to move the rudder stock in the required direction.


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Give five SOLAS requirements for steering gear. (1) Every ship is to have a main and auxiliary steering gear. Failure of one side

must not make the other side inoperable. (2) Relief valves must be fitted to all sections that can be isolated. (3) The main steering gear and rudder stock must have adequate strength and

be capable of moving from 35 degrees P to S at maximum draught and speed and be capable of moving from 30 to 35 (P to S) in 28 seconds.

(4) The auxiliary steering gear shall be of adequate strength and capable of moving from 15 degrees P to S in less than 60 seconds at maximum draught and half maximum speed or 7 knots (which ever is greater).

(5) Main and auxiliary power units shall automatically start after a blackout, operate from the bridge the change over, on and off and provide audio and visual alarm if power fails.

15. Explain the steering gear checks carried out before starting a voyage. Within 12 hours prior to departure, the steering gear shall be check and tested by the ships crew. The tests shall include where applicable the operation of the following:

(a) The main steering gear. (b) The auxiliary steering gear (c) The remote steering controls system (d) The steering position on the bridge (e) The emergency power supply (f) Rudder angle indicators in relation to the actual position of the rudder (g) Remote steering gear power failure alarms (h) Automatic isolating arrangements and other automatic equipment (i) The full movement of the rudder according to the required capabilities of

the steering gear. (j) Visual inspection of the steering gear and its connecting linkages (k) The operation and means of communication between the bridge and

steering flat. You have observed slow and sluggish the rudder movement. Give reasons for this situation. There are several causes to this problem, some of which are bypass valve not shut - relief valve leaking - pump drive below speed - abnormal internal leak in pump - leak across worn control valve - abnormal load on actuator due to seizure or damage to rudder or rudder post check if movement normal in local control but slow in manual control of auto-pilot unit.

Explain two methods of emergency steering operation. (1) In the event of failure of the telemotor: - Reduce ships speed to 7 knots Establish communications between bridge and steering flat Turn off power supply to control box Change over to hand operated screw mechanism to control pump stroke Operate the steering gear by turning the pump control and observing the

rudder indicator. (2) Other method encountered when a problem between the telemotor and

receiver has arisen is to operate the solenoid valves manually from the steering flat. Communication with the bridge as to how much rudder to apply.


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16. Explain common methods used to reduce rolling of a vessel. Bilge Keels consist of fins running fore and aft on the turn of the bilge. As the ship rolls the fins create a resistance that reduces the amplitude of the roll and increases the roll period. They are cheap, require no machinery but are subject to damage. Passive Tank Systems usually consist of interconnected tanks port and starboard partially filled with water. The interconnecting duct is fitted with a valve to restrict the flow to ensure that the moment produced by water moving across the ship are out of phase with the inclining moment caused by the wave thus reducing the angle of roll. Controlled Passive Tanks are fitted with a gyroscopic sensor controlled valve in the air duct of a closed system to achieve a greater degree of control. Active Controlled Tanks have a CP Impeller fitted in the water duct to control the flow of water. The pitch is controlled by a gyroscopic sensing unit. Activated Stabilizing Fins consist of fins port and starboard automatically controlled to turn in opposite directions as the rolls in order to produce moments opposing the roll.

17. Sketch and describe a pump used on a large ship and name for which system the pump is used.

Centrifugal Pump characteristics are decided at the design stage when the energy exchange from shaft work to fluid energy is fixed by pump speed and impeller diameter. This pump has many applications on board, this one being to discharge crude oil.

Give reasons why such a pump is suitable for the system? The centrifugal pump is very efficient in that it can discharge large volumes of cargo at rates in excess of 5000m3 and is simple in design.


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Discuss the common defects and maintenance of the pump? The pump is not self priming and when used on duties requiring suction lift they need external priming arrangements. Is limited to how much head it can pump and the viscosity of the fluid. There are few moving parts so maintenance is mainly concerned with inspecting the impeller and checking seal ring clearances and bearings. Impellers are subject to to corrosion and erosion due to cavitation, particularly pumps used for sea water.

Give hazards of bilge water. The 3 main hazards of bilge water are:

Reduced stability due to free surface effect Fire hazard from oil in bilges Toxic gases produced from bacteria contamination

18. Explain the bridge controls system of a direct drive diesel engine. The bridge control is a closed loop circuit where the governor acts as a speed sensor and controller. The desired value of speed is transmitted to the governor via the bridge telegraph. Minimum instruments are provided showing critical readings lube oil and coolant pressures, exhaust temperature and rpm. Only critical alarms are fitted. Control to engines is handed over to the bridge from the engine room and must be accepted before controls can be used. A bridge control direct drive engine is not starting (not turning on compressed air) from the bridge. What options have you to start the engine? Notify engine room and use emergency telegraph controls. Engine can be operated from the control room or from local controls situated on the engine, depending upon the problem with bridge controls. If you have no air then we all have a problem.

19. You are keeping watch on a very large container ship single screw, 70000hp diesel engine. Ship is in the middle of the Atlantic doing 26 knots. Explain the correct action to take and give reasons if you encounter the following situation (a) Main engine high cooling water alarm Reduce speed, ensure that engine has received alarm, check position in relation to any relevant dangers and traffic.

(b) Main engine low lubricating oil alarm Reduce speed, ensure that engine room has been notified, and plot ships. position and traffic. (c) Crankcase oil mist alarm

Reduce speed immediately and stop engine. Assess the situation in regards to sea room, location, anchoring etc. Look at having a fire team on standby should a fire or explosion eventuates.

(d) High temperature alarm in the scavenge space Reduce speed by approx. half, and locate source of fire. A request will come from the engine room to stop the engine and the OOW should assess the situation in regards to sea room, possibilities of anchoring etc.


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20. Discuss additional requirements for SOLAS for UMS operation. (1) All essential machinery for propulsion, control and safety must be available at the remote control station. (2) All control system must be independent or failure of ones system must not make the other redundant (3) Indication of shaft speed and direction of propeller thrust and propeller pitch if applicable. (4) Single control device for each propeller to be provided, with aprevention for over loading. (5) Main machinery stopping device (6) propulsion machinery orders from the bridge must be indicated in the machinery control room and the engine maneuvering position. (7) Transfer of control must only be possible from the engine room to the bridge. (8) A manual override to be provided to override automatic control. (9) Alarm to be provided on the bridge and machinery space to show low starting pressure. If automatic starting in use, the number of attempts must be limited to save sufficient air for local engine start.

21. Compare the stern power available for diesel main propulsion ship and steam turbine main propulsion ship.

22. Sketch and describe a bilge system.

What types of valves are used in the above system and give reasons for the selection? Screw down non-return globe valves are used on bilge suction lines to prevent water returning down the line creating a siphoning affect.

Discuss the importance of having a bilge injection valve. Bilge injection valves are used for emergency bilge pumping.


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23. What are the regulations of discharging water/oil mixture from machinery spaces? (1) The oil content of machinery space discharges mufor tankers and all vessels over 400GT must not exceed 15ppm (2) The vessel must be proceeding on a voyage, outside any special area and equipped with an approved and operational oily water separator or oil filtering equipment. (3) The vessel is more than 12 nm from the nearest land. (4) Bilge water is not to originate from tanker cargo pump rooms and is not mixed with cargo oil residues. (5) Must have approved oil content monitoring equipment on board. (6) Discharge must be recorded in oil record book.

Explain with sketches how the oily water separator functions in service.

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