DieselShip's Online Content Library

Q7. a. By means of a schematic circuit diagram illustrate the peak rectifier. If the supply voltage is v(t) = Vra Sin wt, what is the voltage across the load resistor? (6)

b. A D.C. motor takes an armature current of 110 A at 480 V. The resistance of the armature circuit is 0.2𝛀. The machine has six poles and the armature is lap-connected with 864 conductors. The flux per pole is 0.05 Wb. Calculate:

(i) The speed.

(ii) The gross torque developed by the armature. (10)

Q6. A. Describe how water tightness is maintained where bulkheads are pierced by longitudinal beams or pipes.

B. A propeller has a pitch ratio of 0.95. When turning at 120 rev/min the real slip is 30%, the wake fraction 0.28 and the ship speed 16 knots. The thrust is found to be 400 KN, the torque 270 KN-m and the QPC 0.67. Calculate:

i. The propeller diameter;

ii. The shaft power;

iii the propeller efficiency;

iv. The thrust deduction factor.

Q6. a) With respect to Buoyancy of a vessel:

What do you understand by reserve buoyancy what happen if the lost buoyancy is greater than the reserve buoyancy? (6)

b) A triangular bulkhead is 7 m wide at the top and has a vertical depth of 8 m.  Calculate the load on the bulkhead and the position of centre of pressure if the bulkhead is flooded with sea water on only side:

(i) to the top edge,

(ii) with 4 m head to the top edge. (10)

Q6. A. Define following terms with reference to alternating currents - Cycle; Time-period; Frequency; Peak factor

B. A heater unit of inductance has a resistance of 6.5 ohms and is intended for use with 100V mains. For what 50Hz voltage would it be suitable when placed in series with an external apparatus, of negligible resistance, having an inductance of 0.01H. If the frequency rises by 5 per cent and this voltage remains constant, what constant, what would be the resulting change or voltage at the heater terminals?

Q6. (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 angle, measured at a distance of 2m from the centre of the boss, was found to be 21.5  Calculate the pitch of the propeller (10)

Q6. A vessel of 10000 t displacement burns 25 t of fuel per day when her speed is 12 Knots. Calculate the probable consumption of fuel over a voyage of 3000 nautical miles at a speed of 11 knots with a displacement of 11000 t. (16)

Q9. a) Explain what is meant by synchronous or resonant vibration (6)

b) A ship's speed is increased by 20% above normal for 8 hours, reduced by 10% below normal for 10 hours and for the remaining 6 hours of the day the speed is normal. Calculate the percentage variation in fuel consumption in that day from normal. (10)

Q8. Find the length of manganese wire required to make a 15.7 Ω resistor, if the diameter is 0.315 mm and the resistivity is 407 μΩ mm (16)

Q6. a) Describe a simple single-phase transformer. (6)

b) A 15 KVA, 440 / 110- volt, 50 Hz cycle/sec, single-phase transformer has primary and secondary resistance of 0.12 ohm and 0.0077 ohm respectively. The iron loss of the transformer is 0.16 kW. Calculate the efficiency of the transformer (10)

i) On full load unity power factor

ii) on 80 per cent full load at a power factor of 0.9 lagging

Q9. (a) Explain why the TPC for a given draught will vary with the density of the water in which the ship floats. (6)

(b) A box shaped ship with 12m beam is floating upright at a draft of 6.7 m. Find the increase in draft if the vessel is now listed 18 degrees. (10)

Q9. (a) List the causes for impairment of stability of a vessel. (6)

(b) A box-shaped vessel floats upright on an even keel as shown in fresh water of density 1000 kg per cubic meter, and the center of buoyancy is 0.50 m above the keel. Find the height of the center of buoyancy above the keel when the vessel is floating in salt water of density 1025 kg per cubic meter. (10)

Q5. (a) On what factors does the capacitance of a parallel-plate capacitor depend? (6)

(b) A tuned circuit consisting of a coil having an inductance of 200µH and a resistance of 20Ω in parallel with a variable capacitor is connected in series with a resistor of 8000Ω across a 60 V supply having a frequency of 1 MHz. Calculate: (10)

(a) The value of C to give resonance.

(b) The dynamic impedance and the Q factor of the tuned circuit.

(c) The current in each branch