DieselShip's Online Content Library

Q6. a) What is back emf? Derive the relation for the back emf and the supplied voltage in terms of armature reactance. (6)

b) Two earth lamps at 120 V, 15 W are used on a 110 V distribution circuit. Due to damage to a motor, the resistance of the positive line is reduced to 10 ohm and that of the negative line to 5 ohm. Find the voltage across each lamp and the extra load on the generator due to the fault. (10)

Q5. With Reference to different types of transformers used onboard.

a) Discuss the basic principle of operation of a transformer (5)

b) Enumerate the different types of transformers used onboard also state their functions for which they are used. (5)

c) A 440/110 V single phase transformer supplies a load of 5kW at 0.8 power factor load. Calculate the primary and secondary currents. (Ignoring transformer power losses)? (6)

Q10. a) Describe the effect of cavitations on the propeller blades. (6)

b) The following data are available from the hydrostatic curves of a vessel.

Calculate the TPC at a draught of 5.05m. (10)

Q9 a) Explain the preference for a 60 Hz system. Describe the dangers of running a 50 Hz system from a 60 Hz supply. (6)

b). A ring-main, 900m long, is supplied at a point A at a p.d. of 220V. At a point B, 240m from A, a load of 45A is drawn from the main, and at a point C, 580m from A, measured in same direction, a load of 78A is taken from the main. If the resistance of the main (lead and return) is 0.25 ohm per kilometre, calculate the current which will flow in each direction round the main from the supply point A and the potential difference across the main, at the load where it is lowest. (10)

Q8. A. Why is it important to maintain high efficiency of operation?  And low values of voltages regulation for power transformers?

B. A 100 KVA transformer has 400 turns on the primary and 80 turns on the secondary. The primary and secondary resistances are 0.3 and 0.01 respectively, and the corresponding leakage reactance’s are 1.1 and 0.035 respectively. The supply voltage is 2200 V. Calculate:

(i) The equivalent impedance referred to the primary circuit;

(ii) The voltage regulation and secondary terminal voltage for full load having a power factor of (i) 0.8 lagging and (ii) 0.8 leading.

Q6. An alternator having 8 pole driven by 900 rpm Diesel engine supplies power to load of Synchronous motor having 24 poles and Induction motor of 8 poles and 2 % slip. A) Calculate the frequency and speed of Synchronous Motor. B) Calculate the frequency and Speed of Induction Motor

Q10. A 100 kW, 460 V shunt generator was run as a motor on no load at its rated voltage and speed. The total current taken was 9.8 A, including a shunt current of 2.7 A. The resistance of the armature circuit at normal working temperature was 0.11  Calculate the efficiencies at i. Full load; ii. Half load. (16)

Q9. The ½ ordinates of a water plane at 15m intervals, commencing from aft, ar. 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.

Q8. A ship 150 m in length, 24 m breadth, displaces 25000 tonne when floating at a draught of 9 m in sea water of density 1025 kg/m³. The ship’s propeller has a diameter of 5.8 m, a pitch ratio of 0.9 and a blade area ratio of 0.45. With the propeller operating at 2 rev/sec, the following results were recorded:

Apparent slip ratio = 0.06

Thrust power = 3800 kW

Propeller efficiency = 64%

The Taylor wake fraction is given by: WT = 0.5CB - 0.05

Calculate EACH of the following for the above condition:

(a) The ship’s speed

(b) The real slip ratio

(c) The thrust per unit area of blade surface

(d) The torque delivered to the propeller.

Q6. A ship 75m long has semi ordinates at the load water plane commencing from forward as follows: 0, 1, 2, 4, 5, 5, 5,4, 3, 2 and 0 metres respectively.

The spacing between the first three semi-ordinates and the last three semi-ordinates is half of that between the other semi-ordinates. Find the position of the Centre of Flotation relative to amidships.

Q7. (a) The residuary resistance of a 1/25 scale model of a ship is 6.35 N when tested at 1.543 m/s in fresh water of density 1000 kg/m3. The frictional resistance of the ship at 12 knots in sea water of density 1025 kg/m3 is 145 kN. Frictional resistance can be assumed to vary with speed to the power 1.825. Calculate the effective power (naked) for the ship at the speed corresponding to the model test.

(b) The following additional data apply to the ship operating in service at the corresponding speed calculated in Q6 (a) with a propeller having a pitch of 4.6 m.

Appendage and weather allowance = 22%

Quasi-propulsive coefficient (QPC) = 0.7

Propeller speed = 1.75 rev/s

Taylor wake fraction = 0.32

Propeller thrust = 565 kN

Calculate EACH of the following:

(i) The torque delivered to the propeller; (ii) The propeller efficiency; (iii) The real slip ratio.

Q6. (a) Explain what is meant by floodable length. B. (i) Construct a graph from the following information:

(ii) From this graph find the TPC's at draft of 3.2m; and 4.3m; (iii) If the ship is floating at a mean draft of 4m, and then loads 50 tonnes of cargo, 10 tonnes of fresh water, and 25 tonnes of bunkers, whilst 45 tonnes of ballast are discharged, find the final mean draft.