MARCH 2017

MARINE ENGINEERING PRACTICETIME ALLOWED - 3 HOURSInstructions1.Answer any SIX questions.2.All questions carry equal marks.3.Neatness in handwriting and clarity in expression carries weightage4.Illustration of an answer with clear sketches ? diagrams carries weightage5.All unused pages of answer script must be cancelled out by two lines (x) across the pageQ1. Accidents regularly occur due to premature or accidental release of Co2 into machinery spaces W.R.T. this enumerate the procedure or arrangement that you as 2nd engineer would adopt W.R.T the following

A. Contractors working on Co 2 system; B. Understanding between bridge and engine room in the event of a machinery space fire; C. Familiarizing staff with the system; D. What checks and test would you carry out before putting system in operation?

Answer:-(A) The following conditions must be

adhered to when contractors are working on the CO2 system*The contractors must be licensed by the class or the administration and the leader of the team must show valid proof when asked for.*minimum number of persons must be engaged in the work , only what is essential.*The persons working on the system should be properly trained and must be

aware of the dangers that can be encountered. The normal jobs that is carried out on the system are:

(1)Weighment of bottles-----once in 5 years.

(2) Pressure testing of the pipe lines -------------once every 10 years(3)Strain test of the bottles ---------once in twenty years.

(4)Occasional refilling of leaky bottle/bottles.

When carrying out (1) job , it is necessary that each bottle is safely disengaged from the gang release mechanism and then lifted to record the weight. After the recording of the weight, the reconnection must also be done in a safe manner. This the leader of the team must be able to demonstrate to gain the second engineers confidence. When carrying out job (2) the gang release mechanism must be completely disengaged from the individual bottkes ..All the exposed openings where the seals are fitted must be closed by special screw caps which the contractor must provide. After this is arranged the pressure testing of the pipe sections can proceed safely. When carrying out (3) job and (4) job the disconnected bottles must be immediately be fitted with the screwed safety caps.

(B) The chief Engineer is in command of the Engine room and the master is in command of the ship. All communication with the office and other outside agencies such as administration, port authorities and classification society must be directed through the master , where as all communication to the engine room staff should be directed through

the chief Engineer . If this is strictly adhered the possibility of a wrong communication or mis-communication can be avoided

(C) The staff under the second enginner must be made thoroughly familier with the system and for this the Saturday routines for testing the system along with the pperformance of mock drills will make the staff not only familier but also proficient in their actions. They are to be instructed on the possible mishaps that can occur when checking and how to avoid them. One definite instruction is ever not to try out the gang release .

(D) The checks to be carried out to the CO2 system are: All bottles are properly clamped and

properly supported on their wooden grating..

The gang release properly connected to the individual cylinders as well as the main actuating piston and bottle/bottles.

The two torn horn is to be tested . The pipe lines are tested by blowing

through compressed air through the testing connection and verified that air comes out freely from every spreader.

The mater valve is to be tested for correct operation.

.Q2. Under CSM bottom end bearing of a large 2stroke slow speed engine is due for survey A. As 2nd eng explain the procedure involved in complete inspection of a bottom end bearing; B. List the precaution to be taken; C. Indicate the reasons for possible defects which could be encountered and state how they may be rectified; D. What test are carried out on completion of survey and reassembly.

Answer:- (A) and (B)- Precautions :- (1) At least 20 minutes must elapse before crank case doors are opened ,if the engine is working.

(2) Obtain propeller clearance from deck department till completion of the job.

(3) Carry out safety check list for C/C entry.

(4) Thoroughly clean clean crank case free of oil, so that no one slips inside whilst working.

Preparation :- (1) Attach lifting gear at correct locations to dismantle bearing half and to remove it out of crank case.

(2) Ensure hydraulic opening tools are in good order.

Procedure :- Before dismantling the bearing , the bearing clearance is checked with crank at bottom centre using long feeler gauge.

(2) Take crank to top centre,attach hydraulic unfastening device and slacken the holding nuts. Support the lower half bearing on the attached chain blocks and lower bearing to bottom of crank case. Transfer the lower half bearing outside crank case using a chain block attached to support outside the crank case. Refer to sketch FIG:1

(3) Fit Guide bars on both guides to prevent the cross head from lowering whilst turning the crank.

(4) Wrap a sling around the bottom of con-rod and attach to a chain block supported on side of crank case.. Refer to fig (2) Turn enginein the direction of the attached sling, while pulling the sling using the chain block till the top half bearing clears the crank pin.Ensure top half of bearing is locked tight on con-rod palm so that the tpo half will not fall off.

(5) The crank can now be turned to bottom so that the top half of bearing is fully exposed . Refer to fig (3). If needed it can be removed from con-rod by dismantling the lock plates..

FIG: 1

FIG:2

(c) The bearing metal should be tapped with the wooden handle of the hammer to check that the metal is well bonded. This is in the case of thick shell bearings. In thin shell bearings look for excessive wear indicated by exposure of the back strip metal. The oil channels may need dressing especially in thick shell bearings. Also look for cracks in the white metal especially in thick shell

bearings. The crank pin is to be gauged by an outside micrometer . this instrument is provided by the engine builders and measurements taken in top-bottom , and P-S directions at at least 4 locations and recorded for future reference. This is the check for ovality of the crank pin.

D) After survey the bearing is to be assembled with copious smearing of lub oil on the crank pin. The crank is taken to BDC and oil clearance checked and recorded. The crank is turned to port side , and using a long crow bar the webs are to be pinched in both directions to ensure that the bearing shifts either easily and is not being held tight. The lub oil pump started and the crank turned through one full revolution to see the leak off flow of oil from the bearing clearance. This activity is done after clearing all gear and equipment from the crank case.

It is a good practice to stop the ship for a few minutes after the pilot has been dropped outside the port limit , and feel the bearing for any early sign of overheating.

Q3. A. State the circumstances owing to which it may be necessary to renew a cylinder liner; B. Explain how the liner is removed; C. Explain how a new liner is fitted; D. State the important checks to be made after fitting.

Answer:- The circumstances are:

*Excessive wear of the liner when

exceeded the allowable limit of wear.

*If the liner is cracked.

*If the liner is scored heavily at some

locations caused by seizure.

(B) After taking the regular precautions applicable to

all crank case jobs, including the routine unit decarb

job the engine cylinder head, piston with piston rod are

removed and rested in their locations firmly.

For the removal of the liner the makers

provide a strong back with jacking devise and this

gear is designed as per the models requirement and

hence varies from engine to engine. Using this device

the liner is forced out, lifted and placed firmly on the

engine floor plate..

(1)The new spare cylinder liner be removed safely

from its stowed position and made to rest on wooden

packings in a vertical position to enable proper cleaning and

removal of the protective coating from the liner inner

surface. The liner is to be gauged at the usual locations in

fwd---aft and P---S directions using the calibration template.

(2) The internal space in entablature, especially the cooling water space around the liner to be thoroughly

cleaned , by removing the accumulated sludge and descaled thoroughly, and the space painted using a recommended anti corrosive coating .Particular attention to be paid to the location of the rubber rings , which should be descaled thoroughly.(3)The liner is now to be lifted and inserted into the jacket(entablature) and made to rst on its flange seat on the entablature. When inserting the liner it should be made to coincide with the markings or locating dowel/s. After the liner rests on the entablature, the following checks must be made from the scavenge space:- * the cylinder lubrication quill holes coincide correctly. *The scavenge ports coincide with corresponding ports in the entablature.(where such design features exist). * The height from end of liner to the diaphragm surface is same throughout. This should be checked with a steel flat scale. This confirms that the liner is sitting squarely.(4)The liner is removed and layed in its previous location. The rubber sealing rings are fitted ensuring they are not twisted. To ensure they are not twisted, the mould line on the rings must be expose , the rings stretched while lifting them and released at the groove location. The Garlock square cord is to be lightly caulked in its groove. This cord is usually placed above the rubber rings. The rings are to be smeared with soft soap for easy entry. (5)The liner is lifted placed correctly on the entablature after checking the dowel marks and then forced in using the cylinder head or any device provided

for this purpose(depending on design of engine). An inspection must be made from the scavenge space to confirm that the liner is fitted and seated as per the original seating when fitted without the rubber rings. Checks:- (1) cooling water tightness check:- The jacket outlet is to be blocked , the jacket space filled with fresh water and the space subjected to a pressure of 2 kg/sq cm, using a hand hydraulic pump. The pressure to be maintained for 30 minutes and during this time the scavenge space examined for signs of leakage from the fitted liner. (2) The liner is to be gauged in all locations using the micrometer and template . This is to ensure that the liner bore has not been strained. This can happen if the liner dimensions are not correct.In such a situation the liner should not be used and the old liner is to be refitted. (3) The piston with the piston rod is to be inserted without the rings and tightened on the cross head. The crank is made to rotate and the clearance between the piston and liner bore measured using long feeler gauge in 4 locations ie fwd, aft, P and S should not exceed 1mm . this measurement is taken at TDC, MID TRAVEL POSITION and BDC This check assures that the vertical alignment is in order. The unit is now ready to be assembled with the running gear and made ready for sailing.

Q4. Describe the procedure to be under taken when upon a routing schedule for changing fuel injector on a main engine it is found that the injector body is seized and cannot be removed using conventional means

Answer:-Routine schedule is planned maintenance and

this work is normally carried out in port and not at

sea.

The gap or space between the injector pocket and the injector body is very small and in most designs the injector fits in as a sliding fit. Due to the high temperature attained in this region , the space between the injector and the pocket gets jammed by carbon soot and caked very hard.

As a first attempt a rag quite large can be soaked with any patented release oil normally carried on board and the rag posirttioned around the fuel body , so that the oil penetrates into the space and loosens the caked soot . For the oil to penetrate and loosen the soot it may take about an hour. After which the injector may be levered out using a long and heavy pinching bar or crow bar.

If this fails an attempt using dry ice ( carbon di oxide flakes) should be tried and this should do the job.

For the dry ice to be effective the dry ice should be in place on the injector body for at least half hour or one hour so that the injector gets sufficiently cold and shrinks , when it can be levered easily. To maintain the dry ice in place , a sufficiently large dia pipe piece is

placed around the affected fuel injector to hold the dry ice. The temperature of the dry ice is approximately -- 60 to –70 degrees and must be handled with rubber gloves . If handled with bare hands it can cause frost bite.. The dry ice is not carried on board and hence has to be ordered from ashore. Normally the ship chandler will be able to supply it at short notice. . At least 5 kgs of dry ice will be required

Q5: Briefly describe your action plan on following exigencies:

A. Leaky economizer tube, while at sea ; B. Leaky intercooler of main air compressor, while manoeuvring.

Answer:- (A) There are two alternatives available depending on the circumstances of the location of the ship. If the residual voyage period is only about two days to reach port , then the repair maybe dealt by postponing the repair till berthing of the ship., and for this purpose, the engine exhaust is by-passed to the engine uptake , thereby bypassing the economiser. and operating the boiler on oil fire. This can nbe done only if this provision is fitted on board. If this provision is not there , then the repair must be done at sea , with the engine stopped The casing covers are opened and the wash tray fitted in place. Using the fire hose and sea water connected to the hydrant in engine room, the finned tubes are thoroughly hosed with sea water till the fins were cleared of all the oily soot which has caked in between the fins of the tubes. A final hosing down with fresh water is carried out to rinse the tubes of any salt adhering to the surface of the tubes. Testing procedure :- The casing plates are fitted with new joints and the drain valve on the wash tray kept shut. Fresh water is filled to the top of the tubes through the inspection door in the casing plate. The inspection doors on the water and steam boxes opened. The leaky tube is identified by evidence of water flowing out of the tube., which is plugged using brass taper plugs made on board. Before fitting the casing doors finally, a leak test is carried out by circulating water from the boiler back to boiler using the circulating pump and observing the tubes from the gas side. The casing plates can now be fitted and the economiser is ready for operation.(B) Most ships have two main air compressors. So if one main air compressor inter cooler is leaking the repair can easily be post poned until the shi[pp has berthed on arrival at port or after the pilot has disembarked and the ship is enroute

But if there is only one main air compressor and it is not possible to stop the ship, the repair will have to be postponed till either FWE is rung or the engine is in FULL AWAY status. All modern air compressors are fresh water cooled and this will involve some consumption of fresh water. The defect will be observed by the burst of the bursting disc, indicating the intercooler tube within the intercooler box is leaking. The location of the leak is noticed by the air under pressure leaking out of the hole. The hole can be blocked by suitable brazing. After testing the inter cooler which is now reassembled with new bursting disc the compressor can be put into service.

Q6. Explain in detail how you would isolate one of sprinkler system for routine maintenance. Describe all tests and inspections you would make and how you would return the system to service

Answer:-. Any maintenances on a section is carried out with the stop valve closed. The test valve can be opened to create flow and cause the non- return section alarm valve to open to test the alarm.

Regular maintenance of the system consists of greasing the various valves and checking their freedom of movement , logging the pressure gauge reading, before and after each alarm valve ( thus checking the tightness of the non-return valves) and checking the alarm system. The latter is done by opening the test valves and checking that the audible and visual alarms work . the pressure tank level is checked and recharged, if necessary , with fresh water and air. The centrifugal salt- water pump should also be tested by closing the isolating valves and draining the pressure switch circuit. When the pump should start automatically.

Q7. During normal engine operation a turbocharger rapidly loses speed and the speed reduction is accompanied by appreciable noise,

 A. State with reasons the possible causes; B. Explain in

detail how the engine might be safely operated if the damage caused by this incident is such that the turbocharger cannot function; C. State with reasons the factors which may limit engine operating speed with the turbocharger out of action.

Answer:- (A) The situation is typical of a scavenge fire. When a scavenge fire occurs , the air manifold is full of smoke at higher pressure causing a high back pressure on the compressor of the turbocharger and hence the sudden reduction of speed of the TC. The noise is caused by the pu;lsation of the air and smoke mixture in the manifold or scavenge space.(B) The main engine is run in the normally aspirated condition by putting the TC out of operation. For this the rotor is removed and the air and exhaust spaces in the TC properly isolated so that the air supply to the engine is maintained pure. since the TC is out of action, the engine will run on lower power about 80 percent load and the fuel control will be accordingly reduced. The speed is so adjusted till combustion conditions in each unit is optimised to give colourless exhaust and the exhaust temperatures are normal. The sketch shows how the passages are isolated

Q8. Severe engine vibration has recently become evident when the main engine for which you are responsible operates within a certain speed range.

A. State, with reasons, the possible causes of such vibration; B. State the consequences of operating the engine under such vibratory conditions; C. Describe the procedure you, as Second Engineer, would implement in order to investigate and rectify the problem.

Answer:- - (a) When the main engine is running at a particular RPM, the forcing frequency or firing frequency is given by N*RPM vibs/min If it is a 4-stroke engine it will be N*RPM/2 vibs/min These forcing torsional amplitudes are noticed as a small flicker of the tacho meter needle. It cannot be seen with the naked eye, but

can be captured on an oscilloscope.. These torsional amplitudes are small and do not cause any harm.. When the engine is running in a normal condition at constant RPM, it is in almost non-resonant condition.

The problem appears when this non-resonant condition moves into a partial resonant condition torsionally., and this happens when the steady state condition is disturbed. The equation of motion for a particular forcing frequency and the accompanied natural frequency of torsional vibration is given by :

T Cos θ = I d 2 θ + f d θ + Q θ dt2 dt

Where T is the mean firing torque, I is rotational mass of any equivalent rotor,say the propeller and any reciprocating mass like piston and piston-rod with part of con-rod

considered as rotor at the crank position ,Q is the torsional stiffness of the shaft.’ and f is the natural damping constant.

This steady state equation for a non resonant condition will deteriorate into a partial resonant condition if either T changes or I changes. Normally I will not change as the rotational masses are constant.. I will only change if the propeller is damaged which is a rare occurrence.. What frequently happens is that T changes because of imbalance in power produced in each unit with corresponding difference in peak pressures. This is therefore the cause for noticeable vibration levels to increase (b) If the engine is continued to run in this mode the condition will deteriorate. It may start initially with loosened foundation bolts, proceed with loosened tie-rods and end up with fatigue cracks appearing on the shaft at critical locations. (c)By taking power cards and Draw cards of all units and by comparison the power produced and peak pressure in each unit can be made the same by suitable adjustments to fuel rack positions of individual fuel pumps . If all is well the vibrations or excessive disturbing amplitudes will disappear .The further corrective action would be to tighten all the foundation bolts when the ship reaches port. If the vibrations were very severe it may also need loosening of all tie-rods and retensioning them in accordance with instructions given in the manual. If however the problem is not solved, the propeller needs to be checked for damage. This can be done only when ship is anchored or berthed in ballast condition. The propeller can be checked by trimming the ship forward , and by standing in the life boat moored aft of the ship , each propeller blade can be brought up and examined for noticeable damage. The mass of propeller is considerd as the mass of propeller together with entrapped water. In damaged condition of propeller the entrapped water mass changes and hence the propeller mass changes. The damaged propeller can be suitably repaired in dry dock

Q9. A. Sketch a transmission shaft coupling which enables the propeller shaft to be withdrawn outward;B. (i) describe the coupling and method fitting and dismantling; (ii) state how the grip of the coupling can be checked when fitted; (iii) why should coupling bolts be interference fits (iv) State what precaution should be taken when dismantling the coupling. (V) State with reasons

why the metal that the intermediate and tail end transmission shaft are made of.

Answer:- (A)

(B) This type of coupling is called a muff coupling and is common on all twin screw ships especially tugs , off-shore vessels and ferry ships utilising twin screws. The muff coupling enables the shaft to be withdrawn outwards since there is no interference aft of the ship as the rudder is placed between the two propellers. The coupling fits on a taper which has a taper ratio of 1:14 if keyed or 1:18 if not keyed. The method of fitting and dismantling is by hydraulic jacking with suitable rigs specially provided for the same and these are sketched as under. The method of withdrawal and fitting is given in the two sketches given below.

(2) The force of the grip is estimated from a graph drawn with the jacking force on the Y axis and the corresponding displacement on the X axis. The displacement is measured in mm by the dial gauge. The push-up force is increased in steps with corresponding displacement occurring and measured by the dial gauge. The push-up is continued in steps to take up the strain till the coupling reaches its initial location already marked before withdrawal.

(3) Coupling bolts need an interference fit to prevent lateral slackness in the bolt holes. The slackness will induce shear stress on the bolts when transmitting torque which under varying conditions can cause fatigue in the bolt material and fatigue failure of the bolts can occur

(4) The intermediate shaft and the tail shaft are made of alloy steel , the chemical composition of which is : Carbon--------0.6 percent max Silicon---------0.45 percent max Manganese---0.3---1.5 percent Sulphur--------0.04 percent max Phosphorous-0.04 percent max

Residual elements Copper---------0.3 percent max Chromium------0.3 percent max Molybdenum---0.15 percent max Nickel------------0.4 percent max The specified minimum tensile stress is 400- 600N/mm2

With a longitudinal percentage elongation of 12percent.

The reasons for the above specified values is governed by the heavy and varying stress that the shafting is subjected to when in service and for its prolonged life.

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