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Q6. A. Describe the normal criteria used for setting thermal protection relays and its advantage compared to magnetic types.

B. The low-voltage release of an a.c. motor-starter consists of a solenoid into which an iron plunger is drawn against a spring. The resistance of the solenoid is 35 ohm. When connected to a 220 V, 50 Hz, a.c. supply the current taken is at first 2A, and when the plunger is drawn into the “full-in” position the current falls to 0.7 A. Calculate the inductance of the solenoid for both positions of the plunger, and the maximum value of flux-linkages in weber-turns for the “full-in” position of the plunger.

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).

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.

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.

Q6. A. With reference to dynamical stability, describe the effect of an increase in wind pressure when a vessel is at its maximum angle of roll to windward.

B. A ship of 15000 tonne displacement has righting levers of 0, 0.38, 1.0, 1.41 and 1.2 m at angles of hell of 0 , 15 , 30 , 45  and 60  respectively and an assumed KG of 7.0 m.  The vessel is loaded to this displacement but the KG is found to be 6.80m and GM 1.5m –

(i) Draw the amended stability curve; (ii) Estimate the dynamic stability at 60

Q5. A single screw vessel with a service speed of 15 knots is fitted with an unbalanced rectangular rudder 6 m deep and 4 m wide with an axis of rotation 0.2 m forward of the leading edge. At the maximum designed rudder angle of 35° the centre of effort is 30% of the rudder width from the leading edge. The force on the rudder normal to the plane of the rudder is given by the expression: Fn = 20.2 A v2α newtons

Where: A = rudder area (m2) v = ship speed (m/s)   α = rudder helm angle (degrees)

The maximum stress on the rudder stock is to be limited to 70 MN/m².

Calculate EACH of the following: (a) the minimum diameter of rudder stock required; (b) the percentage reduction in rudder stock diameter that would be achieved if the rudder was designed as a balanced rudder, with the axis of rotation 1.0 m aft of the leading edge.

Q7. A. what is the effect on fuel consumption per unit time, if the ship’s speed is outside its operation range? B. The frictional resistance of a ship in fresh water at 3m/s is 11N/m2.  The ship has a wetted surface area of 2500m2 and the frictional resistance is 72% of the total resistance and varies as speed 1.92.  If the effective power is 1100Kw, calculate the speed of the ship.

Q10. Describe with sketches the arrangement of a power operator sliding water light door. B. A watertight bulkhead 7.5m high has vertical stiffeners 0.75m apart, connected at the bottom by brackets having 10 rivets 20mm diameter in each arm. The bulkhead is flooded to the top on one side only with seawater calculate. (i) Shearing force at top and bottom; (ii) Position of zero shear; (iii) Shear stress in the rivets; Draw the load and shearing force diagrams.

Describe the effect of cavitation’s on

(i) The thrust and torque

(ii) the propeller blades.

(b) A ship of 355190 tonne displacement is 325 m long, 56m wide and floats in sea water of density 1025 kg/m3 at a draught of 22.4 m. The propeller has a diameter of 7.4 m, a pitch ratio of 0.85, and when rotating at 1.5 rev/s the real slip is 48.88% and the fuel consumption is 165 tonne per day.

The taylor wake fraction Wt=0.5Cb-0.05.

Calculate

a) The speed in knots

b) The reduced speed at which the ship should travel if the fuel consumption in a voyage is to be halved.

C) the length of the voyage if the extra time on passage is six days when travelling at the reduced speed.

d) The amount of fuel required onboard before commencing on the voyage at the reduced speed.

Q7. A. What factors influence the frictional resistance of a ship and what formula is used to calculate the resistance?

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.  f= 0.42 and n = 1.825