DieselShip's Online Content Library

Q8. (a) Compare fixed pitch with controllable pitch propellers. (6)

(b) A ship of 12400 tonne displacement is 120 m long, 17.5 m beam and floats at a draught of 7.5 m. The propeller has a pitch ratio of 0.75 and, when turning at 100 rev/min, produces a ship speed of 12 knots with a real slip of 30%. Calculate the apparent slip, pitch and diameter of the propeller. The wake fraction w may be found from the expression. w = 0.5Cb - 0.05 (10)

Q4. With respect to circuit breakers:

a) Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse. (6)

b) A coil having a resistance of 10 ohm and an inductance of 0.15 H is connected in series with a capacitor across a 100 V, 50 Hz supply. If the current and the voltage are in phase what will be the value of the current in the circuit and the voltage drop across the coil? (10)

Q5. A) By means of a schematic circuit diagram illustrate the peak rectifier. If the supply voltage is v(t) = Vm Sinwt, what is the voltage across the load resistor? (6)

b) A battery-charging circuit is shown below in fig. The forward resistance of the diode can be considered negligible and the reverse resistance infinite. The internal resistance of the battery is negligible. Calculate the necessary value of the variable resistance R so that the battery charging current is 1.0 A. (10)

Q4.a) Explain the construction and principle of operation of permanent magnet moving coil instrument. (8)

b) A permanent magnet moving coil instrument has a coil of dimension 15 mm × 12mm. The flux density in the air gap is 1.8 × 10-3 wb/m2 and the spring constant is 0.4 × 10-6 Nm / rad. Determine the number of turns required to produce an angular deflection of 900 when a current of 5 mA is flowing through the coil. (8)

Q4. a) A 440 V, 10KW 0.8 pf phase load is supplied as shown.

Calculate short circuit fault current at the load and at the main switch board (8)

b) Explain the safe working procedure that you will follow while working in live MSB bus bar. (8)

Q8. A. What is back emf? Derive the relation for the back emf and the supplied voltage in terms of armature resistance.

B. A three- phase induction motor is wound for four poles and is supplied from a 50 Hz system. Calculate.

i. The synchronous speed; (4)

ii. The speed of the rotor when the slip is 4 per cent; (3)

iii. The rotor frequency when the speed of the rotor is 600 r/min. (2)

Q9. A. Explain how the efficiency and regulation of a transformer can be assessed by open circuit and short circuit tests?

B. A 25 kVa signal phase transformer 2200:200V has a primary and secondary resistance of 1Ω and 0.01 Ω respectively. Find the equivalent secondary resistance and full load efficiency at 0.8pf lagging, if the iron losses of the transformer are 80% of the full load copper losses.

Q2. Two Alternators running in parallel with D/G # 1 having 2000 KW capacity with 4 % speed droop and D/G # 2 having 1000 KW capacity with 4% speed droop. The no load frequency is 62 Hz. How much KW load shared by each alternator if total ship load is 1200 KW?

Q6. A. Describe with the aid of a sketch, an isolator for a 3 phase 440V, 20-amp electric supply List the safety features of the isolator described in the sketch. B. A moving coil ammeter, a thermal ammeter and a rectifier are connected in series with a resistor across a 110 V sinusoidal a.c. supply. The circuit has a resistance of 50 to current in one direction and, due to the rectifier, an infinite resistance to current in the reverse direction. Calculate: (i) The readings on the ammeters; (ii) The form and peak factors of the current wave.

Q10. Evaluate for a frequency of 15 kHz, the amplification and the phase difference between input and output signals of a voltage amplifier using a triode having an amplification factor of 48 and a mutual conductance of 1.2 m A/V with an anode-load resistant of 160 k . The output p.d. is fed by a coupling capacitor of negligible reactance to a subsequent circuit of resistance 480 k and the total shunt capacitance is 90µ F.

Q6. A. Describe how the force on the ship’s bottom and the GM vary when grounding takes place.

B. A ship of 8,000 tonnes displacement takes the ground on a sand bank on a falling tide at an even keel draft of 5.2 metres. KG 4.0 metres. The predicted depth of water over the sand bank at the following low water is 3.2 metres. Calculate the GM at this time assuming that the KM will then be 5.0 metres and that mean TPC is 15 tonne.

Q10.  The breadth of the upper edge of a deep tank bulkhead is 12 metres. The vertical heights of the bulkhead at equidistant intervals across it are 0, 3, 5, 6, 5, 3 and 0 metres respectively. Find the depth of the centre of pressure below the waterline when the tank is filled to a head of 2 metres above the top of the tank.