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Q9. A) Describe the stability requirements of a ship for dry-docking. (6)

B) The ½ ordinates of a waterplane at 15m intervals, commencing from aft, are 1, 7, 10.5, 11, 11, 10.5, 8, 4 and 0m. Calculate:

(a) TPC.

(b) Distance of the centre of flotation from midships.

(c) Second moment of area of the waterplane about a transverse axis through the centre of flotation. (10)

Q7. a) Describe how water tightness is maintained where bulkheads are pierced by longitudinal beams or pipes. (6)

b) A ship of 15000 tonne displacement has an Admiralty Coefficient, based on shaft power, of 420. The mechanical efficiency of the machinery is 83%, shaft losses 6%, propeller efficiency 65% and QPC 0.71. At a particular speed the thrust power is 2550 kW. (16)

Q8. A. What is back emf? Derive the relation for the back emf and the supplied voltage in terms of armature resistance.

B. A three- phase induction motor is wound for four poles and is supplied from a 50 Hz system. Calculate.

i. The synchronous speed; (4)

ii. The speed of the rotor when the slip is 4 per cent; (3)

iii. The rotor frequency when the speed of the rotor is 600 r/min. (2)

Q9. A. Explain how the efficiency and regulation of a transformer can be assessed by open circuit and short circuit tests?

B. A 25 kVa signal phase transformer 2200:200V has a primary and secondary resistance of 1Ω and 0.01 Ω respectively. Find the equivalent secondary resistance and full load efficiency at 0.8pf lagging, if the iron losses of the transformer are 80% of the full load copper losses.

Q2. Two Alternators running in parallel with D/G # 1 having 2000 KW capacity with 4 % speed droop and D/G # 2 having 1000 KW capacity with 4% speed droop. The no load frequency is 62 Hz. How much KW load shared by each alternator if total ship load is 1200 KW?

Q6. A. Describe with the aid of a sketch, an isolator for a 3 phase 440V, 20-amp electric supply List the safety features of the isolator described in the sketch. B. A moving coil ammeter, a thermal ammeter and a rectifier are connected in series with a resistor across a 110 V sinusoidal a.c. supply. The circuit has a resistance of 50 to current in one direction and, due to the rectifier, an infinite resistance to current in the reverse direction. Calculate: (i) The readings on the ammeters; (ii) The form and peak factors of the current wave.

Q10. a) (i) What is direct-connected alternator? (3)

(ii) How is a direct-connected exciter arranged in an alternator? (3)

b) Find the synchronous impedance and reactance of an alternator in which a given field current produces an armature current of 200 A on short circuit and a generated e.m.f. of 50V on open- circuit. The armature resistance is 0.1 ohm. To what induced voltage must the alternator be excited if it is to deliver a load of 100A at a p.f. of 0.8 lagging, with a terminal voltage of 200V. (10)

Q8. A. Define longitudinal centre of gravity (LCG) and longitudinal centre of buoyancy (LCB). (6)

B. A ship 120m long floats has draughts of 5.50m forward and 5.80m aft. MCT1 cm 80 tonne m, TPC 13, LCF 2.5m forward of midships. Calculate the new draughts when a mass of 110 tonne is added 24m aft of midships. (10)

Q10.A. Describe briefly the significance of the factor of subdivision.

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 centreline, 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.

Q10. A. Explain the use of KN curves. B. A ship of 6000 tonnes displacement has drafts 7m. f and 8m. A. MCT 1cm. 100 tonnes-m. TPC 20 tonnes, centre of flotation is amidships. 500 tonne of cargo is discharged from each of the following four holds.

No.1 hold, center of gravity 40m forward of amidships

No.2 hold, center of gravity 25m forward of amidships

No.3 hold, center of gravity 20m forward of amidships

No.4 hold, center of gravity 50m forward of amidships

The following bunkers are also loaded:  150 tonnes at 12m forward of amidships 50 tonnes at 15m aft of amidships Find the new drafts forward and aft.

Q4. (a) List the components of residuary resistance. (b) A ship model 6m long has a total resistance of 40N when towed at 3.6 knots in fresh water. the ship itself is 180m long and displaces 20400 tonne. the wetted surface area may be calculated from the formula S= 2.57, Calculate ePn for the ship at its corresponding speed in sea water. f (model)fw =0.492; f (ship)sw =0.421; n=1.825.

Q6. A. Describe the factors to consider in order determining whether a list is due to a negative GM or to uneven distribution of masses in a ship. (6)

B. A vessel of 8000 tonne displacement has 75 tonne of cargo on the deck. It is lifted by a derrick whose head is 10.5m above the centre of gravity of the cargo, and placed in the lower bold 9m below the deck and 14m forwarded of its original position. Calculate the shift in the vessel’s centre of gravity from its original position when the cargo is: i. Just clear of the deck; ii. At the derrick head; iii. In its final position. (10)