DieselShip's Online Content Library

Q7. (a) What is Freeboard of a Ship? Why oil tankers have less freeboard? (6)

(b) A box barge 25 m long and 4 m wide floats in fresh water at a draught of 1.2 m and has an empty mid length compartment 5m long. The bottom of the barge is lined with teak (rd 0.805) 120mm thick. After grounding all the teak is torn off and the centre compartment laid open to the sea. Calculate the final draught. (10)

Q6. A) With the aid of delta and star connection diagrams, state the basic equation from which the delta-star and star- delta conversion equation can be derived. (6)
B) Three batteries A, B, and C have their negative terminals connected together. Between the positive terminals of A and B there is a resistor of 0.5 ohm and between B and C there is a resistor of 0.3 ohm
Specifications of the three batteries are given below.
Battery A 105 V, Internal resistance   0.25 ohm
Battery B 100 V, Internal resistance   0.2 ohm
Battery C   95 V, Internal resistance   0.25 ohm
Determine the current values in the two resistors and the power dissipated by them. (10)

Q4. (a) Describe the normal criteria used for setting thermal protection relays and their

advantage compared to magnetic types. (6)
(b) The low-voltage release of an a.c. motor-starter consists of a solenoid into which an iron plunger is drawn against a spring. The resistance of the solenoid is 35 Ω. When connected to a 220V, 50Hz, a.c. supply the current taken is at first 2A, and when the plunger is drawn into the ‘full-in” position the current falls to 0.7A, Calculate the inductance of the solenoid for both positions of the plunger, and the maximum value of flux-linkages in weber-turns for the “full-in” position of the plunger. (10)

Q5. a) What is leakage flux as it applies to the iron-core transformer? How is it taken into account in the analysis of the transformer? (6)

b) The following results were obtained on a 50 kVA transformer: open circuit test-primary voltage, 3300 V; Second 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, to be assumed at full load value. Calculate:

(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) (10)

Q4.a) List the factors that determine the starting torque of the three-phase induction motor. How does this torque generally compare with the value of the rated torque (6)

b) An 18.65 KW, 6 Pole, 50 Hz, 3 phase slip ring induction motor runs at 960 rpm on full load with a rotor current per phase of 35 A allowing 1 KW for mechanical losses, find the resistance /phase of three-phase winding. (10)

Q8. The half-ordinates of a ship’s water-plane, which is 80 m long, commencing from forward at equal intervals, are as follows: 0.2, 4.0, 5.0, 5.2, 5.0, 4.0 and 0.2 m respectively. Calculate the area of the water-plane using Simpson’s First Rule.

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

B. Draw the circuit of Half-wave rectifier and its output waveform. A diode whose internal resistance is 20 is to supply power to 1000 load from 110 V (RMS) source. Calculate

(i) peak load current, (ii) DC load current, (iii) AC load current.

Q7. With reference to adjoining circuit calculate following. (a) Current in each branch of circuit. (b) Total current.

Q7. A. Describe how protection against short circuit is provided in a 3 phase induction motor circuit.

B. Explain how rotating magnetic field is produced in three phase winding with three phase supply. A 4-pole, 3-phase induction motor operates from a supply whose frequency is 50 Hz. Calculate

(i) Speed at which the magnetic field of the stator is rotating,

(ii) speed of the rotor when the slip is 0.04,

(iii) the frequency of the rotor current when the slip is 0.03.

Q10. A. How does change to frequency affect the operation of the transformer? What makes this ratio different from the ratio of transformer? B. A 550 KVA, 50 Hz single phase transformer has 1875 and 75 turns in the primary and secondary windings respectively. If the secondary voltage is 220 V, calculate (i)Primary voltage; (ii)Primary and secondary currents; iii. Maximum value of flux.

Q8. The armature and filed resistances of a 220 V shunt motor are 0.25 ohm and 110 ohm respectively and when running on load, the motor takes 6 A. Calculate the losses attributable to iron, friction and windage and assuming this value to remain constant on loads, determine the efficiency when the current supplied is 62 A.

Q9. With respect to Ship Propulsion:

a. Explain the various efficiencies associated with propeller and shafting arrangement.

b. When a propeller of 4.8 m pitch turns at 110 rpm, the apparent slip is found to be —S % and the real slip is 1.5 S %. If the wake speed is 25 % of the ship speed, calculate the ship speed, apparent slip and the real slip.