DieselShip's Online Content Library

Q9. A ballast tank is 15 m long, 12 m wide and 1.4 m deep and is filled with fresh water. Calculate the load on the top and short side, if: (16)

(a) The tank is just completely full

(b) There is a head of 7m of water above the tank top.

Q9. (a) Shunt generators having drooping characteristics are best suited for parallel operation. Discuss (6)

(b) Two 220 V D.C. generators each having linear external characteristics, operated in parallel. One machine has a terminal voltage of 270 V, on no-load and 220 V at a load current of 35 A, while the other has a voltage of 280 V at no-load and 220 V at 50 A. Calculate the output current of each machine and the bus bar voltage when the total load is 60 A. What is the kW output of each machine under this condition. (10)

Q6. (a) Define Centre of Flotation. What happens to the draught and trim of a ship if a small mass is added to the ship at the Centre of Flotation? (6)

(b) A ship of displacement 10010 tonnes has KM 6.7m and GM 0.76m. A mass of 10 tonnes having KG 7.6m is shifted transversely. The deflection of a pendulum of length 7.6m is 0.125m. Find the distance through which the mass is shifted. Also find the position of the new centre of gravity above the keel due to the removal of the same mass. (10)

Q7. (a) Compare constant current method and constant voltage method of charging batteries. (6)
(b) A 24V emergency battery is to be charged from the 110V ship's mains when the e.m.f. per cell has fallen to a minimum value of 1.8V. The battery consists of 12 cells in series, has a capacity of 100 Ahr at a 10 hr rate and the internal resistance is 0.03Ω/cell. If charging continues until the voltage per cell rises to 2.2V, find the value of the variable resistor needed to control the charging. The charging current can be assumed to be equal to the maximum allowable discharge current (10)

Q8. The loads of a 4-wire, 3-phase systems are:

Red line to neutral current = 50 A, power factor of 0.707 (lagging)

Yellow line to neutral current = 40 A, power factor of 0.866 (lagging)

Blue line to neutral current = 40 A, power factor 0.707 (leading).

Determine the value of the current in the neutral wire. (16)

Q7. (a) What are the different types of stern used in ship construction? (6)

(b) A ship consumes 360t of fuel, stores and water when moving from sea water of 1.025 t/m3 into fresh water of 1.000 t/m3 and on arrival it is found that the draught has remained constant. Calculate the displacement in sea water. (10)

Q4. a) Why is a synchronous motor not self-starting? What are the various ways in which it can be started? (6)

b) A coil has a resistance of 4 ohms and an inductance of 0.00954 henry. Calculate the power the coil will absorb and its power factor when it is connected to a 100-volts 50-cycle supply. (10)

Q7. a) Explain what do you understand by the term ‘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.

Q6. A 100 KVA, 2400/240 V, 50 Hz, 1-phase transformer has no- load current of 0.64 A and a core loss of 700 W, when its high voltage side is energized at rated voltage and frequency . calculate the two components of no-load current. If this transformer supplies a load current of 40 amp at 0.8 lagging power factor at its low voltage side, determine the primary current and its power factor. Ignore leakage impedance drop. (16)

Q6.a) Derive an expression for the emf induced in an a.c. generator. (6)

b) A 3000 KVA, 6-pole alternator runs at 1000 r.p.m. in parallel with other machines on 3300V bus-bars. The synchronous reactance is 25%. Calculate the synchronizing power for one mechanical degree of displacement and the corresponding synchronizing torque. (10)

Q9. (a) What are the water pressure loads on the ship's hull. (6)

(b) The water plane area of a ship at 8.4 m draught is 1670 m². The area of successive water planes at 1.40 m intervals below this are 1600, 1540, 1420, 1270, 1080 and 690 m² respectively. Calculate the displacement in fresh water at 8.4 m draught and the draught at which the ship would lie in sea water with the same displacement. (10)

Q7. A. Describe the no-load saturation characteristic of a d.c. generator.

B. A d.c. motor takes an armature current of 110 A at 480 V. The resistance of the armature circuit is 0.2 . The machine has six poles and the armature is lap-connected with 864 conductors. The flux per pole is 0.05 Wb. Calculate;

(i) The speed;

(ii) The gross torque developed by the armature.