APRIL 2019

EXAMINATION OF MARINE ENGINEER OFFICERFunction: Marine Engineering at Management LevelMARINE ENGINEERING KNOWLEDGE (GENERAL)TIME ALLOWED - 3 HOURS

Q1. Sketch and describe the refrigeration system of a container carrying bananas only. How does the controlled atmosphere of the container extend the green life and shelf life of bananas? How is the airflow system designed? 2019/APR

Answer :-

Individual containers with their own refrigeration plant (Figure ) are connected to the 440 or 220 a.c. sockets provided on deck. These containers mat be arranged for ships’ systems with either 440 or 220 V by provision of a direct connection for a 220 V supply to the self-contained refrigerator and a 440 V connection through a step down transformer. The refrigeration system is similar to the Freon gas compressor system with air cooled system for coling the gas to liquid after compression. The system is shown in the sketch. For bananas the recommended temperature is between 11 to 16 degrees centigrade with a good supply of circulation air . This will prevent the bananas from ripening during the voyage and till delivery of the containers.

Air Cooler fans

Fans may be either centrifugal or of the propeller type; the air circulation system being based on a pressure requirement of about 50mm W.G.(water gauge). All of the electrical energy of the fan motors is dissipated in the form of heat and has to be removed by the refrigeration plant. Fan output should be variable so that it can be reduced as heat load diminishes. There is no problem with d.c. motors but with a.c. either the motors are two speed, or each cooler has a number of fixed speed fans which can be switched off individually to suit the load. In the latter case, provision must be made to blank off the stopped fans to prevent ait loss.

The capacity of the fans is determined by the number of air changes per hour required in the cargo chamber, and this is influenced by the maximum calculated heat load. In a system using air coolers and fans, all the heat load must be carried away by the circulating air and the difference between delivery and suction air temperature is directly proportional to the weight of air being circulated. Since the temperature difference is limited by the allowable temperature spread in the cargo chambers and maximum temperature spread in the cargo chambers and maximum load can be estimated, the selection of suitable fans is straightforward.

In most installations the number of air change required per hour, based on an empty chamber, varies between 40 for dead cargoes such as frozen meat or fish and 80 for fruit cargoes, such as bananas which evolve heat freely.

Q2. You have been appointed as the Second Engineer of an eight years old vessel, recently purchased by your shipping company. Write a report to the engineering superintendent covering the inspection of main propulsion machinery carried out by you, to ensure its trouble free operation. Answer:- (Note for information) The handing over and taking over operation is done in one day during the port stay when cargo is being discharged or loaded. The sellers are not bound to leave any of their own records, except all drawings, manuals and statutory books and certificates for the operation of the ship. So no past records such as repair records or dry docking records as well as engine overhaul records. These will be taken out of the ship by the sellers. Hence because of the shortage of time and because of no previous records available , the inspection will be prolonged and done as deemed necessary as the situation warrants.

The least inspection that can be carried out is crank case inspection of all units and crank shaft deflections . The time available may be just sufficient for this activity.

Report:- During the voyage the indicator cards and Draw cards of all units have been taken. During the port stay when cargo was being loaded, the crank case inspection of all units have been carried out. The running clearances of all the bearings are within the satisfactory range. The tie rod pinching screws are all tight and no metallic debris found in the crank case. The locking arrangement of all the bearing bolts are satisfactory.

The indicator cards display sheet with their individual draw cards are enclosed with this report. The power balance is in order with the peak pressures in all units uniform and power produced in each unit the same.

I have taken an inventory of main engine spares and we need urgently 6 fuel injector guides and plunger sets . An indent for the same is included in the enclosures to this report

Q3. Describe with the aid of sketches where necessary a vane type steering gear showing how to weight of the rudder and stock are carried and the arrangement that allow for wear down; OCT 2017/SEP 2017/NOV 2018/FEB 2019/APR

Answer:- Repeat Question. Refer to Q4 FEB 2018 EKG.

Q4. Cast iron is most widely used after steel in Marine Engineering. Most cast irons consist of graphite in steel like matrix. Discuss the variation of properties that may arise with reference to pearlitic greycast iron and spherical grey cast iron. Describe briefly the treatment necessary to produce these two types of Irons. 2019/AP

Answer:- Cast iron is a ferrous alloy that is made by re-melting pig iron in a cupola furnaceuntil it liquefies. The molten iron is poured into molds or casts to produce casting iron products of the required dimensions.

Based on the application of cast iron, the alloying elements added to the furnace differ. The commonly added alloy elements are carbon followed by silicon. The other alloying elements added are chromium, molybdetitanium, vanadium, etc.

1.White cast iron

*When the white cast iron is fractured, white coloured cracks are seen throughout because of the presence of carbide impurities.

*White cast iron is hard but brittle. It has lower silicon content and low melting point. The carbon present in the white cast iron precipitates and forms large particles that increase the hardness of the cast iron.

*It is abrasive resistant as well as cost-effective making them useful in various applications like lifter bars and shell liners in grinding mills, wear surfaces of pumps, balls and rings of coal pulverisers, etc.

2.Grey cast iron or pearlitic cast iron is the most versatile and widely used cast iron. The presence of carbon leads to formation of graphite flakes that does not allow cracks to pass through, when the material breaks .Instead, as the material breaks the graphite initiates numerous new cracks. The fractured cast iron is greyish in colour, which also gives it the name. The graphite flakes make the grey cast iron exhibit low shock resistance. They also lack elasticity and have low tensile strength. However, the graphite fakes gives the cast iron excellent machinability ,damping features as well as good lubricating properties making them useful in many ship board applications. The graphite microstructure of the cast iron has a matrix that consists of ferrite, pearlite or a combination of two. The molten grey iron has greater fluidity and they expand well during the solidification or freezing of cast iron. Lastly the silicon content in grey cast iron or pearlitgic cast iron is limited to 0.4 percent whereas in white or spherical cast iron it is lower and as much as 0.1 percent which adds to the hardness.

Q5. Reverse osmosis is the modern alternative for shipboard production of drinking water.A. Describe using simple diagrams if necessary, the principle of reverse osmosis. B. Sketch a line diagram showing a single pass system for producing fresh water from sea water and Describe such a system./JAN 2018/JULY 2018/OCT 2018/NOV 2019/APR

Answer:- Repeat question. Refer to Q9 JAN 2018 EKG.

Q6. With reference to Gear pumps used for lubricating oil transfer. (a) Sketch and describe a gear type pump indicating the flow of fluid.(b) state the materials that gear type pump components may be manufactured from.(c) specify THREE applications that are suitable for the employment of gear types pumps.

Answer:-The simple gear pump (Figure ) has rotors and shaft which are integrally forged of nitralloy steel. They are hardened all over and ground finished after hardening. Close grained grey cast iron is used for the casing and bearing housing . The shaft of the pump shown are supported in white metal bearings but needle roller bearing are an alternative. Lubrication is provided by the oil passing through. The liquid being pumped, is forced out after being carried around between gear teeth and housing as the teeth mesh together. It is certain that the centrifugal effect contributes to the pumping action. There is no side thrust with straight gear teeth.

Side thrust produced by single helical gears, causes severe wear and in one pump opened for examination bronze bearing bushes exhibited wear to a depth of 3mm so that gears had become displaced axially. Despite the excessive clearance due to wear, it was noted that the pump continued to be effective when repaired as far as possible (no spares being available).

To gain the benefit of using helical gears, a double helical is necessary. This larger pump is of the type used for large, slow speed engine lubrication system spring loaded relief valves are usually fitted and may be of the adjustable calibrated type to facilitate the setting of delivery pressure.

(1)The gear pumps are used widely for engine lubrication.

(2) For transfer of lub oil and fuel oil in ships.

(3) For hydraulic power transmission in deck machinery.

Q7. With reference to Refrigeration system onboard your vessel:(a) Sketch and describe high pressure cut-out in a refrigeration system.(b) The refrigeration compressor has stopped due to operation of the h.p cut-out explain.(i) The possible cause.(ii) How these causes would be found and possible remedies. (c) What steps are taken if the compressor “short-cycle” on low pressure cut-out?

Answer:-

In the event of over pressure on the condenser side of the compressor , the high pressure cut-out will cause the compressor to shut down. The device is reset by hand.

The bellows in the cut-out is connected by a small bore pipe between the compressor discharge and the condenser. The bellows tends to be expanded by the pressure and this movement is opposed by the spring. The adjustment screw is used to set the spring pressure.

During normal running the switch arm is held by the switch arm catch and holds the electrical circuit in place. Excessive pressure expands the bellows and moves the switch arm catch around its pivot. The upper end slips to the right of the step and releases the switch arm so breaking the electrical contact and causing the compressor to cut out. The machine cannot be restarted until the trouble has been remedied and the switch reset by hand.

(b)The possible causes for the operation of the HP cut-out are:

(1)Condenser cooling water supply failure. Pump should be restarted.

(2) Ineffective cooling because of excessive scale formation on tube surfaces. Condenser needs cleaning.

(3) Excessive air in the system causing high pressure. Air should be removed from the system.

(4) refrigerant overcharged leaving less space in the receiver. The excess gas must be taken back in the refrigerant bottles.

((c) If compressor short cycles on low pressure, the causes are:

The liquid flowing out after the expansion valve is not evaporating fully so that the wetness in the gas is excessive causing liquid to enter the compressor suction and thereby actuating the LP cut-out. The flow of liquid through the evaporator coils is caused by either excessive frosting on the evaporator coils so preventing heat transfer to the refrigerant. Defrosting the coils is necessary. Excessive liquid can flow through the coils if the expansion valve is damaged allowing the liquid to pass through without throttling. In this case the defective expansion valve must be renewed.

Q8. With reference to Flue gas Inert gas system:

a. Sketch a line diagram showing a typical 'Inert Gas System' used for inerting the cargo tanks of oil tankers, labelling the component parts. b. Describe the system. c. State what oxygen content you would expect in the flue gases if good combustion is achieved. 2019/MAR 2019/APR

Answer:- Repeat Question.

Q9. With reference to auxiliary boiler safety valve: A. Describe, with aid of a Sketch the safety valves for an auxiliary boiler; B. Identify, with reasons, the part that require particularly close attention during overhaul; C. Describe how the safety valves are reset after an overhaul. 2019/APR

Answer:- (a) The sketch given below is a ordinary spring loaded high lift safety valve as fitted in marine auxiliary boilers. This valve gives uninterrupted constant lift of D/24 and is suitable for low pressure auxiliary boilers. The lift of the valve is resisted by the spring compression which can be set to lift to the required pressure.

Safety valve (Fig.68)

(b) With the safety valves completely dismantled, the following parts need

close inspection.

(1) Valve spindle:- generally inspect the spindle for any damage particularly cracks on the surface. Particularly check for bends if any and this can be done by verification of trueness by centering on the lathe.

(2) Springs:- the permanent set or deformity can be checked by

comparing their heights with the spare spring on board. Springiness may be checked by bouncing them on the floor. Ring the springs to

detect for any cracks.

(3) Valve and valve seats :- Check the valve and valve seats for any indentation or grooving marks. If so the valves and valve seats will need machining. Valve and valve seat need lapping with very fine emery paste or jewellers rouge since they very rarely come into operation.

(4) Valve chest, spring casings and covers:- Check for cracks by tapping them and listening to the metallic sound.

(5) Compression nut:- Try the compression nut on the cover and check for radial and axial play.

(6) Check the drain from bottom of chest is clear, as well as the connecting pipe up to scupper is clear.

(7) Other parts require close inspection for deformity and cracks.

BOILER SAFETY VALVE SETTING PROCEDURE:

1) A Gagging tool is used alternatively on the valve to prevent simultaneous

lifting of the valves at the set pressure.

2) Use the standard boiler gauge brought by the surveyor if the boiler pressure gauge is not caliberated.

3) Remove the caps keep the valve spindle of one valve (port) gagged. The

other valve will be se first (stbd).

4) Keep the compression nut screwed down, on the valve to be set, till the previous marks.

5) Raise steam pressure slowly and bring pressure to set pressure.

6) A slight hissing sound will be heard. This is the floating condition of the valve. In this condition the valve will sit on its seat by slight pressure on the spindle with the palm of the hand and will not come back unless tapped.

7) Reduce pressure, remove gagging tool and fit out the other valve. Repeat

above operation on this valve for setting.

8) When both valves are set remove gagging tool. Fire the boiler at maximum capacity. Note full flow of waste team from waste steam pipe. Note pressure on gauge. The pressure should not exceed 10% of the set pressure. On satisfactory completion of setting, refit caps, cotters, locks and easing gear. Test easing gear and following safety alarms and cut outs: -

(a) H.P cut off and alarm

(b) Low water alarm and cut off

(c) High water alarm and cut off

NOTE:- For purpose of answering in the examination the sketch reproduced from Reed’s vol 8 may be drawn.

(Fig.70)