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Q9: A. Explain how trim occurs, and explain the effect of trim on tank soundings. B. A ship 150 metres long arrives at the mouth of a river with drafts 5.5m.  F and 6.3m A MCT 1 cm. 200 tonnes-m.  TPC 15 tonnes.  Centre of flotation is 1.5m. aft of amidships.  The ship has then to proceed up the river where the maximum draft permissible is 6.2m.  It is decided that SW ballast will be run into the forepeak tank to reduce the draft aft to 6.2m.  If the canter of gravity of the forepeak tank is 60 metres forward of the center of flotation, find the minimum amount of water which must be run in and also find the final draft forward.

Q8. (a) Explain what is meant by left and right handed propellers, and also explain the rotation of propellers in a twin-screw ship.

b) A ship 120m long displaces 8000 tonne, GML is 102m, TPC 17.5 and LCF 2m aft of midships. It arrives in port with draughts of 6.3m forward and 6.6m aft.

During the voyage the following changes in loading have taken place:

Fuel used          200 tonne         18m forward of midships

Water used        100 tonne         3m aft of midships

Stores used        10 tonne           9m aft of midships

Ballast added     300 tonne         24m forward of midships

Calculate the original draughts. (10)

Q10. A. What is back emf? Derive the relation for the back emf and the supplied voltage in terms of armature resistance. (6)

B. Find the synchronous impedance 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)

Q6. a) Define centre of buoyancy and show with the aid of sketches how a vessel which is Stable will return to the upright after being heeled by an external force (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. (10)

Calculate:

(i) Indicated power

(ii) Effective power

(iii) Ship speed.

Q7. A ship consumes 360 t of fuel, stores and water when moving from sea water of 1.025 t/m3 into fresh water of 1.000 t/m3 and on arrival it is found that the draught has remained constant.

Calculate the displacement in sea water. (16)

Q7. a) Explain with the aid of a simple sketch ullage and sounding of a tank. (6)

b) A deep tank 10 m wide and 10 m deep has a rectangular manhole of 1.2 m X 0.6 m at the forward end. The longer sides of the manhole are horizontal and its lower edge is 0.7 m from the bottom of the tank. Find the thrust experienced by the manhole cover when the tank has oil of RD 0.8 to an ullage of 1 m. (10)

Q7. a) What is Kirchoff’s current Law. (6)

b) Calculate the value of I2 in the circuit, when I1= 3A. (10)

Q8. Find the p.d between A-B and B-C shown in the figure below. (16)

Q8. A 24 V emergency battery is to be charged from the 110 V ship’s mains when the e.m.f. per cell has fallen to a minimum value of 1.8 V. The battery consists of 12 cells in series, has a capacity of 100 Ahr at a 10 hr rate and the internal resistance is 0.03 ohm/cell. If charging continues until the voltage per cell rises to 2.2 V, find the value of the variable resistor needed to control the charging. The charging current can be assumed to be equal to the maximum allowable discharge current. (16)

Q6.a) What is the effect on the field flux of an alternator current in the synchronous motor that leads the terminal voltage. (6)

b) A 1,000-kVA, 11,000-V, 3-ϕ, star-connected synchronous motor has an armature resistance and reactance per phase of 3.5 Ω and 40 Ω respectively. Determine the induced e.m.f. and angular retardation of the rotor when fully loaded at (a) unity p.f. (b) 0.8 p.f. lagging (c) 0.8 p.f. leading. (10)

Q8. (a) Compare fixed pitch with controllable pitch propellers. (6)

(b) A ship of 12400 tonne displacement is 120 m long, 17.5 m beam and floats at a draught of 7.5 m. The propeller has a pitch ratio of 0.75 and, when turning at 100 rev/min, produces a ship speed of 12 knots with a real slip of 30%. Calculate the apparent slip, pitch and diameter of the propeller. The wake fraction w may be found from the expression. w = 0.5Cb - 0.05 (10)

Q4. With respect to circuit breakers:

a) Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse. (6)

b) A coil having a resistance of 10 ohm and an inductance of 0.15 H is connected in series with a capacitor across a 100 V, 50 Hz supply. If the current and the voltage are in phase what will be the value of the current in the circuit and the voltage drop across the coil? (10)