OCTOBER 2017

MARINE ENGINEERING KNOWLEDGE (GENERAL)

TIME ALLOWED - 3 HOURS

Instructions 1. Answer SIX questions only. THREE Questions from each section 2. All questions carry equal marks. 3. Neatness in handwriting and clarity in expression carries weightage 4. Illustration of an answer with clear sketches / diagrams carries weightage

Q1. With reference to oil / water separators: A. Describe, will the aid of a sketch, the circuit for an interface detector; B. Explain the consequences if the interface position is incorrect.Answer:- (A) The diagram shows a level sensor/transducer of the capacitance type that is used to detect the level of an oil-water interface in an oily water separator.

Detection of the interface is achieved by variation in charge in a capacitoitance which is accomplished by alteration in dielectric strength. One plate of the capacitor is a probe, possibly made of stainless steel, the other is the separator shell and both are connected to a.c. bridge which is supplied with high frequency low voltage alternating current. As the oil-water interface

moves down (a to b) the dielectric strength (relative permittivity ) alters, the solenoid controlled relay valve is moved up and this causes an oil discharge valve to open on the separator and a water discharge valve to close(B) If the interface position is different from the actual interface position in the separator, either oil can go out with the water or water will go into the oil collecting tank and is as follows: * If the actual interface level is higher than the indicated interface level, water will go with the oil into the oil collecting tank. * If the actual interface level is lower than the indicated interface level oil will go out into the sea with the water and may cause an infringement in the permitted oil discharge criteria which will sound the alarm and cause the auto stop to stop the discharge.

Q2. With reference to the carriage and pumping of liquefied gas cargo: A. Sketch a suitable pumping system labeling the component parts; State; B. Why submerged hydraulically driven pumps are not used; C. How overheating of pump drive shaft bearings is avoided; D. How tank is rendered safe both in loaded & unloaded condition. E Why at the end of discharge about

2% of liquid cargo is left in the tank. F. State, how the risk of fire and explosion in cargo tanks is obviated both in the loaded and discharged conditionAnswer:- Repeat Question. Refer Q 2 EKG JAN 2017

Q3. State with reasons how cracking in EACH of the following location is caused rectified and avoided - 1. A-frame; 2. Bedplate longitudinal girder; 3. Bed plate transverse girder.Answer:-Repeat question. Refer to Q9 EKG APRIL 2017.

Q4. Describe how you, as Second Engineer, would prepare an auxiliary boiler for survey by a classification society.Answer:- To carry out the survey the boiler has to be blown down completely according to the blowing down procedure. After blowing down and before commencing the cleaning operation the boiler must be safely isolated to prevent any accidents occurring and for this the steam outlet connection to the main steam line must be blanked using a strong spoon flange at the connection to the main steam manifold. Similarly the common feed line must be blanked to prevent accidental entry of feed water in the boiler under survey. These precautions are necessary to be observed in ships where there are two or three boilers connected to a common steam manifold. Cleaning procedure:- The boiler’s fire side smoke side and water/steam side have to be thoroughly cleaned and made free of all deposits so that the bare metal surface is exposed. In water tube boilers rotary

descaling heads mounted on a flexible shaft is very effectively used for descaling the internal surfaces of the water tubes where scaling occurs. In smoke tube boilers the external surfaces are descaled manually. In small package boilers where entry into the boiler is not possible, chemical cleaning or descaling is done by warming up the boiler with a very weak acid solution which loosens the scale and breaks it. The scale collected is flushed out. All the 10 listed mountings are dismantled, overhauled and surveyed. The furnace lining is suitably repaired by renewing broken bricks, the fire cement wherever cracked is suitably excavated and fire cement mortar mix made and filled up.

Q5. Damage has occurred to the main engine exhaust valves and the fuel supplied at a particular port is suspected. The owner’s case/ however, in the ensuing dispute may be weak because the fuel was ordered specifying only type and viscosity. A. Apart from fuel specification, describe how you, as Second Engineer, should have assisted the owners’ case when receiving the suspect fuel. B. Describe a recognized fuel standard that may be used when ordering bunker fuel. C. Explain how the correct standard selected D.Suggest with reasons, why particular mention should be made of certain elements that might not be included in the fuel standardAnswer:- Repeat question. Refer to Q5 EKG APRIL 2017

Q6. With reference to feed regulation: A. Describe, with the aid of sketches, the operation of a boiler feed water regulator controlled by at least two other parameters besides water level in the drum; B. Give reasons for the

inclusion of the other elements besides water level in controlling feed flow; C. Deduce the possible effects on the system w3hen the drain valve in the constant leg in the level transmitter starts to leak.Answer:-

(a) Three element control gives the highest value of performance. Feed flow is compared to steam flow for the correct 1: 1 ratio. If the ration is incorrect then an out of balance signal is given to the controller. Drum level again acts as a trimming device on a wide proportional band with integral action. Three element actions are illustrated in Fig. (b) The reason for including the other elements steam flow and level is to make the feed controller sufficiently sensitive to prevent the effects of “shrink ”and “swell” Which occur during manoeuvring periods. (c) If the drain in the constant leg of the level transmitter leaks, the level seen in the level indicator will be false and erroneous because of the steady leakage from the constant head leg.

(a) There element control gives the highest value of performance. Feed flow is compared to steam flow for the correct 1: 1 ratio. If the ration is incorrect then an out of balance signal is given to the controller. Drum level again acts as a trimming device on a wide proportional band with integral action. Three element actions are illustrated in Fig.65 (b) The reason for including the other elements steam flow and level is to make the feed controller sufficiently sensitive to prevent the effects of “shrink ”and “swell” Which occur during manoeuvring periods.

(c) If the drain in the constant leg of the level transmitter leaks, the level seen in the level indicator will be false and erroneous because of the steady leakage from the constant head leg.

Q7. Sketch a sealing arrangement for an oil lubricated stern tube. A. Identify the common form of seal failure; B. State how oil loss due to seal failure can be restricted whist on passage; C. What material is used for sealing ring and propeller shaft liner?Answer:- Repeat question. Refer Q7 EKG APRIL 2017

Q8: A. State the laboratory tests that may be carried out On specimens of steel for ships’ plate giving reasons for the tests. B. The basic compositions of two ships’ plates are given in Table below one is an example of modem practice whilst the other is a specification of a 1940’s tanker that split in two due to brittle fracture. Compare these two specifications critically and explain

which of these two steels would be most resistant to brittle fracture

M Si S P AI N Steel’A’

0.18%

0.70%

0.30%

0.04%

0.04%

0,015%

0,005%

Steel “B”

0. 19%

0.57%

0.03%

0.029%

0.042%

0.005%

0.008%

Answer:- (a) The destructive tests required and their reasons are as follows:

(1) Tensile test along with percentage elongation. In the range of the ultimate tensile test we obtain the elastic limit which gives the permissible strength, and the percentage elongation, which gives a measure of its ductility quality.

(2) Charpy impact notch test to give its impact or shock resisting strength.

(3) Bend test to ensure its ductility quality in cold condition which is necessary for cold fabrication of the steel, especially for cold rolling to give necessary curvature to the plates.

(b) Sulphur - is usually an undesirable impurity in steel rather than an alloying element. Sulphur should not exceed 0.04 %, and if it increases above 0.04 % the steel becomes brittle and will fracture. Hence type A steel is the defective steel.

Q9. Draw a diagram of a four ram electro-hydraulic steering gear showing: 1. Pump isolating valves 2. Relief / Shock valves 3. Bypass

valves B. Explain the operation of the system sketched in A; C. Indicate in the diagram (A) the valve positions for the operation of the system when one pump is isolated and the unit is operating on two rams only.

Answer:- The four ram steering arrangement is a duplication of the two ram steering gear, thereby increasing the turning speed of the rudder. The two sets are rams (1) and (2) and its pump placed above ram (3) . the other set is rams (3) and (4) with its pump above ram (4). With all rams working and two motors working , the floating lever is connected to both pumps, the shock valves of both the sets are activated by keeping the by-pass valves A and F shut. and the valves B,C,D,and E open.

If for some reason one set say set number one is not in use , then therams (1) and (2) are non operational, the by-pass valve A will be kept open to allow free flow of oil between rams (1) and(2) and the valves Band C shut since these rams are non operational. The floating lever will be disconnected from the respective pump.

Similarly if the second set is out of operation, the by-pass valve F will be kept open for free flow of oil in the rams (3) and (4) which are not operational. The valves D and E will be kept shut and the floating lever will be disconnected from the non- operational pump.

This system is called 100 % redundant because when one set is not in use even if it is in good working condition, then that set becomes redundant amounting to the full component gear. It is designed that in normal sea condition , with vessel steaming at its maximum service speed the speed of rotation of the rudder is as per REG 29 of SOLAS chapter 2 with one set of rams and one pump in operation. When both sets are in operation the speed of rotation is almost doubled.

Another reason why it is called 100% redundant is that the change over of the respective valves and the disconnecting of the floating lever is done manually.