DieselShip's Online Content Library

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. (a) Define longitudinal centre of gravity (LCG) and longitudinal centre of buoyancy (LCB). (6)

(b) The immersed cross-sectional areas of a ship 120m long, commencing from aft are 2, 40, 79, 100, 103, 104, 104, 103, 97, 58 and 0 m². Calculate:

(i) Displacement

(ii) Longitudinal position of the centre of buoyancy. (10)

Q9. A) Describe the effect of cavitations on the propeller blades. (6)

B) A propeller 4.6m diameter has a pitch of 4.3m and boss diameter of 0.75 m. The real slip is 28% at 95 rev/min. Calculate the speed of advance, thrust and thrust power.  (10)

Q8. A ship of 9,900 tonnes displacement has KM=7.3 m and KG=6.4 m she has yet to load two 50 tonne lifts with her own gear and the first lift is to be placed on deck on the inshore side (KG 9 m and center of gravity 6m out from the center line). When the derrick plumbs the quay its head is 15m above the keel an 12m out from the center line.

Calculate the maximum list during operation.

Q2. The half-ordinates(m) of a waterplane, which are 6m apart, are given by: 11,16,24,84,39,42,47,52,40,23,26,46,13,23.

Calculate and compare the areas of waterplane as given by the 1,4,1 rule, the 1,3,3,1 rule and the trapezoidal rule

Q6. a) Describe how the distribution of mass within the ship affects the rolling period. (6)

b) The righting moments of a ship at angles of heel of 0, 15°, 30°, 45°, and 60° are 0, 1690, 5430, 9360 and 9140 kN-m respectively. Calculate the dynamical stability at 60°. (10)