DieselShip's Online Content Library

Q7. A. Describe the effect of Cavitation on; The thrust and torque; The propeller blades B.A ship 120m long displaces 10500 tonne and has a wetted surface area of 3000m2. At 15 knots the shaft power is 4100KW, propulsive coefficient 0.6 and 55% of the thrust is available to overcome frictional resistance; calculate the shaft power required for a similar ship 140m long at the corresponding speed.   = 0.42 and n = 1.825

Q9. A. What is leakage flux as it applies to the iron-core transformer? How is it considered in the analysis of the transformer? (6)

B. Three conductors fitted side by side in the stator of a salient-pole alternator. Each generates a maximum voltage of 200V (sinusoidal). The angle subtended at the centre of the stator between adjacent conductors is 20 electrical degrees. If the three conductors are connected in series, find (i) the r.m.s. value of the effective voltage and (ii) the ‘breadth factor’. Using the theory that is the basis of this problem, give one reason why three-phase current has been introduced. (10)

Q7. A. Explain how to distinguish between list and loll and describe how to return the ship to the upright in each case.  (B) A ship 90 long displaces 5200 tonne and floats at draughts of 4.95m forward and 5.35 m aft when in sea water of 1023 kg/m3. The water plane area is 1100m2, GML 95m, LCB 0.6m forward of midships and LCF 2.2m aft of midships. Calculate the new draughts when the vessel moves into fresh water of 1002 kg/m3

Q9. A. Describe the effects of changes in speed, rotor current and torque as load is applied to an induction motor. How does the motor adjust its stator current with changes in mechanical load?

B. A shunt motor runs at 900 rev/min when connected to a 440 V supply, the armature current being 60 A and armature resistance 0.4 ohm. At what speed will it run on a 220 V supply with an current of 40 A. Assume 60 percent reduction in flux for the 220 V connection.

Q8. A. Why is it important in a tender ship to keep the double bottom tanks pressed up?

B. The fuel consumption of a ship at 17 knots is 47 tonne/day. The speed is reduced and the consumption is reduced to 22 tonne/day. At the lower speed, however, the consumption per unit power is 13.2% greater than at 17 knots. Find the reduced speed and the percentage saving on a voyage of 3000 nautical miles.

Q9. A. What is Prismatic Co-efficient (CP). Derive the formula CP =

, where

= Co-efficient of fineness and

= midship section area co-efficient. (6)
B) The ½ ordinates of a water plane at 15m intervals, commencing from aft, are 1, 7, 10.5, 11, 11, 10.5, 8, 4 and 0m. Calculate:

(a). TPC;

(b). Distance of the centre of flotation from midships.

(c). Second moment of area of the water plane about a transverse axis through the centre of flotation.  (10)

Q8. a) Explain why the iron losses in a transformer are substantially independent of the load current. (6)

b) The equivalent circuit for a 200/400-V step-up transformer has the following parameters referred to the low-voltage side. (10)

Equivalent resistance = 0.15 W; Equivalent reactance = 0.37 W

Core-loss component resistance = 600 W; Magnetising reactance = 300 W

When the transformer is supplying a load at 10 A at a power factor if 0.8 lag, Calculate,

i) the primary current

ii) secondary terminal voltage.

Q8. (a) Explain various powers and efficiencies in the Propulsion plant of a ship (6)
(b) A vessel with a displacement of 12250 t burns 290 t of fuel while travelling at a speed of 15 knots on a voyage of 2850 nautical miles. On a voyage of 1800 nautical miles at a speed of 13 knots and a displacement of 14200 t, estimate the quantity of fuel that will be burnt. (10)

Q7.  The pitch of a propeller is measured by means of a batten and cord. The horizontal ordinate is found to be 40 cm while the vertical ordinate 1.15 m at a distance of 2.6 m from the centre of the boss. calculate the pitch of the propeller and the blade width at that point. (16)

Q6. A. What are the characteristics of PN junction diode? Point out its specifications. Also point out the significance of dynamic and static resistances. (6)

B. A 72 KVA transformer supplies a heating and lighting load of 12 KW at unity power factor and a motor load of 70 kVA at 0.766 (lagging) power factor: Calculate the minimum rating of the power-factor improvement capacitors which must be connected in the circuit the ensure that the transformer does not become overloaded. (10)

Q7. a) Describe the principle of variable-capacitance transducer. (6)

b) A coil of resistance 10 ohms and inductance 100mH is connected in series with two parallel capacitors each of value 100 mF across a 250 V, 50Hz supply. determine (10)

i) The circuit current

ii) The total power factor

iii) The power taken from the supply.

Q9. a) What is meant by the term ‘back e.m.f.’ as applied to an electric motor? (6)

b) A 40 kW,220V shunt motor has a full-load efficiency of 90 per cent, an armature resistance of 0.075 ohms and a shunt motor-field resistance of 55 ohms. When ‘at starting’, the starter handle is moved onto the first stud, it is desired to limit the current, through the armature to 1.5 times the value which it has when the motor is on full load. What must be the total value of the starting resistance? If, on overload, the speed falls to 90 per cent of its normal full-load value. What would be the armature current? Neglect the effect of armature reaction. (10)