DieselShip's Online Content Library

Q7. A. What is back emf? Derive the relation for the back emf and the supplied voltage in terms of armature resistance.

b) An 8kw, 230V, 1200 rpm d.c shunt motor has Ra = 0.7W. The field current is adjusted until, on no-load with a supply of 250V, the motor runs at 1250 rpm and draws armature current of 1.6 amps. A load torque is then applied to the motor shaft which causes la to raise to 40 A and the speed falls to 1150 rpm. Determine the reduction in the flux per pole due to the armature reaction.

Q8. a) Describe the process of correcting a negative GM. (6)

B. A ship 120 m long displaces 10500 tonne and has a wetted surface area of 3000 m2. At 15 knots the shaft power is 4100 kW, propulsive coefficient 0.6 and 55% of the thrust is available to overcome frictional resistance; calculate the shaft power required for a similar ship 140 m long at the corresponding speed.  = 0.42 and n = 1.825  (10)

Q9. a) Describe briefly the inclining experiment and explain how the results are used. (6)

b) A ship of 14900 tonne displacement has a shaft power of 4460 Kw at 14.55 knots. The shaft power is reduced to 4120 Kw and the fuel consumption at the same displacement is 541 kg/h. Calculate the fuel coefficient for the ship. (10)

Q7. (a) What are the various resistances acting against the motion of the ship? (6)

(b) A vessel of 10000 t displacement burns 25 t of fuel per day when her speed is 12 Knots. Calculate the probable consumption of fuel over a voyage of 3000 nautical miles at a speed of 11 knots with a displacement of 11000 t. (10)

Q7. A ship of 6400 t displacement is floating in salt water. The ship has to proceed to a berth where the density of the water is 1008 kg per cubic meter. Find how much cargo must be discharged if she is to remain at the salt water draft. (16)

Q6. a) State why cargo ships must have collision bulkheads. (6)

b) A double bottom tank is 1.2 m deep and has a sounding pipe extending 11 m above the tank top. The tank is filled with oil (rd 0.89) to the top of the sounding pipe. The double bottom floors are spaced 750 mm apart and are connected to the tank top by riveted angles, the rivets having a pitch of 7 diameters. If the maximum allowance stress in the rivets is 30 MN/m2, calculate the pressure in kN/m2 on the outer bottom and the diameter of the rivets. (10)

Q9. a) Explain Fleming's Right hand rule. (6)

b) A one-turn armature coil has an axial length of 0.4m and a diameter of 0.2m. It is rotated at a speed 500 rev/min in a field of uniform flux density of 1.2 T. Calculate the magnitude of the e.m.f. induced in the coil. (10)

Q9. A wooden ring having a mean diameter of 200 mm and a cross-sectional area of 400 mm2 is wound uniformly with a coil of 300 turns. If the current passed through the coil is 5 A calculate the value of flux produced in the coil. (16)

Q8. (a) Explain how fluorescent tubes power factor is improved. (6)

(b) A fluorescent lamp taking 80W at 0.7 power factor lagging from a 230V, 50-Hz supply is to be corrected to unity power factor. Determine the value of the correcting approach required. (10)

Q10.a) Draw the complete phasor diagram of the transformer under no-load conditions. (6)

b) The following results were obtained on a 50 KVA transformer: open circuit test-primary voltage, 3300 V; secondary voltage, 415 V; primary power, 430 W. Short circuit test primary voltage, 124 V; primary current, 15.3 A; primary power, 525 W; secondary current full load value. Calculate: (10)

(i) The efficiencies at full load and at half load for 0.7 power factor

(ii) The Voltage regulations for power factor 0.7 (i) lagging, (ii) leading

(iii) The secondary terminal voltages corresponding to (i) and (ii)

Q8. (a) Explain what is meant by 'assigned summer freeboard' (6)

(b) A box-shaped vessel 60m long, 10m beam, and 6m deep, is floating in salt water at drafts 4m Forward and 4.4 m. Aft. Find how far forward of amidships a weight of 30 tonnes must be loaded if the draft aft is to remain at 4.4m. (10)

Q6. (a) Sketch an arrangement showing the principal of a proportional plus Integral (P + I) control loop. (6)

(b) Compare the series and parallel resonance circuits. Find the frequency at which the following circuit resonates. (10)