DieselShip's Online Content Library

Q9. A piece of aluminium has a mass of 300 g and its volume is 42 cm3

Calculate

a) its density in kg/m3

b) the relative density

c) the mass of 100 cm3 of aluminium (16)

Q7. a) Define TPC. Explain why TPC for a given draught will vary with the density of the water in which the ship floats? (6)

b) The pitch of a propeller is measured by means of a batten and cord. The horizontal ordinate is found to be 40 cm while the vertical ordinate 1.15 m at a distance of 2.6 m from the centre of the boss. Calculate the pitch of the propeller and the blade width at that point. (10)

Q6. The open-circuit voltage of a cell as measured by a voltmeter of 100 Ω resistance, was 1.5V, and the p.d. when supplying current to a 10 Ω resistance was 1.25V, measured by the same voltmeter. Determine the e.m.f. and internal resistance of the cell. (16)

Q4. a) Sketch and describe a star-delta starter for starting an induction motor (10)

b) Three similar coils, each having a resistance of 10 ohms and an inductance of 0.02 H are connected in

i) Star

ii) Delta to a 3-phase, 50-Hz supply with 500V

Calculate the total power absorbed and the line current in each case. (6)

Q9. (a) Explain about non-linear resistors with some examples and illustration on how they differ from linear resistor. (6)

(b) A half-wave rectifier is used to supply 50V d.c. to a resistive load of 800Ω. The diode has a resistance of 25 Ω. Calculate a.c. voltage required. (10)

Q7. (a) Define Density, Relative Density (6)

(b) A bilge holding tank of 5 m length, 3 m width and 1.8 m depth has water of density 1.020 t/m3 up to a sounding of 1.3 m and oil of density 0.86 t/ m3 is floating on top of water up to an ullage of 0.3 m. Calculate the mass of water and oil in the tank. (10)

Q8. (a) Derive the formula for Admiralty Coefficient. (6)

(b) A ship travels 900 nautical miles at a speed of 12.5 knots and burns 150t of fuel over the voyage. Estimate the distance the ship could travel at a speed of 13.5 knots on 250t of fuel. (10)

Q4. a) What is a commutator? Discuss its rectifying action in detail. (6)
(b) Determine the line current taken by a 440 V, three-phase, star-connected motor having an output of 45 Kw at 0.88 (lagging) power factor and an efficiency of 93 per cent. (10)

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)