DieselShip's Online Content Library

Q6. A. Explain distribution factor and pitch factor for alternator windings.

B. A 3phase, 4pole 24 slot alternator has its armature coils short pitched by one slot. Find the distribution factor and pitch factor.

Q8. A. What is meant by “Resonance” in RLC circuits? Compare the series and parallel resonance circuits.

B. Find the frequency at which the following circuit resonates.

Q7. Two 10 MVA 3 phase Alternator operate in parallel to supply at 0.8 power factor with lagging load of 15 MVA. If the output of one Alternator is 8 MVA at 0.9 lagging. A. Calculate the output of second Alternator. B. Calculate the value of Power factor of second Alternator.

Q9. Sketch a graph of starting current, and torque against the speed of rotation for a single cage motor.  B. A 230V motor, which normally develops 10Kw at 1000 rev/min with an efficiency of 85%, is to be used as a generator. The armature resistance is 0.15Ohm and the shunt field resistance is 220Ohm. If it is driven at 1080 rev/min and the field current is adjusted to 1.1A by means of the shunt regulator what output in Kw could be expected as a generator, if the armature copper loss was kept down to that when running as a motor.

Q7. A. Describe stability requirement for dry-docking.

B. A ship of 8000 tonne displacement floats upright in seawater. KG = 7.6m and GM = 0.5m. A tank, KG is 0.6m above the keel and 3.5m from the centre line, contains 100 tonne of water ballast. Neglecting the free surface effect, calculate the angle which the ship will heel, when the ballast water is pumped out.

Q6. (a) Describe how bulkheads are tested.

(b) A double bottom tank containing seawater is 6m long, 12m wide and 1m deep. The inlet pipe from the pump has its center 75mm above the outer bottom. The pump has a pressure of 70 kN/m2 and is left running indefinitely. calculate the load on the tank top:

 (i) If there is no outlet.

(ii) If the overflow pipe extends 5m above the tank top.

Q8. A. Describe the stability requirements of a ship for dry-docking.

B. A ship 130m long displaces 14000 tonne when floating at draughts of 7.5m forward and 8.10m aft. GML – 125m, TPC – 18,LCF-3m aft of midships. Calculate the final draughts when a mass of 180 tonne lying 40m aft of midships is removed from the ship.

Q10. A ship of 10000 tonne displacement floats in sea water of density 1025 kg/m3 at a draught of 6m. A rectangular tank 10m long and 8m wide is partially full of oil fuel of density 900 kg/m3. In this condition, the KG of the ship is 6.25m.

Other hydrostatic data for the above condition are:

Centre of buoyancy above the keel (KB) = 3.325m

Transverse metacentre above the centre of buoyancy (BM) = 4.865m

Tonnes per centimetre immersion (TPC) = 20.5

Calculate the change in effective metacentric height when a rectangular tank 12m long, 10m wide and 6m deep, with its base 1 m above the keel, is filled to a depth of 5m with sea water ballast.

NOTE: Assume the ship to be wa11sided over the affected range of draught

Q7. A. Explain how to distinguish between list and loll and describe how to return the ship to the upright in each case. B. A ship 120m long has a light displacement of 4000 tonne and LCG in this condition 2.5m aft of midships.  The following items are then added:

Using the following hydrostatic data, calculate the fine draughts:

Q10. A. Explain how to distinguish between list and loll and describe how to return the ship to the upright in each case. B. A ship of 5000 tonne displacement has a double bottom tank 12m long. The ½ breadths of the top of the tank are 5, 4 and 2m respectively. The tank has a watertight centreline division. Calculate the free surface effect if the tank is partially full of fresh water on one side only.

Q7. A. Describe the effect of Cavitation on; The thrust and torque; The propeller blades B.A ship 120m long displaces 10500 tonne and has a wetted surface area of 3000m2. At 15 knots the shaft power is 4100KW, propulsive coefficient 0.6 and 55% of the thrust is available to overcome frictional resistance; calculate the shaft power required for a similar ship 140m long at the corresponding speed.   = 0.42 and n = 1.825

Q9. A. What is leakage flux as it applies to the iron-core transformer? How is it considered in the analysis of the transformer?

B. Three conductors fitted side by side in the stator of a salient-pole alternator. Each generates maximum voltage of 200V (sinusoidal). The angle subtended at the centre of the stator between adjacent conductors is 20 electrical degrees. If the three conductors are connected in series, find

(i) the r.m.s. value of the effective voltage and

(ii) the ‘breadth factor’. Using the theory that is the basis of this problem, give one reason why three-phase current has been introduced.