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Q6. Explain why the bilging of empty double-bottom or deep tanks below the waterline leads to an increase in GM. B. A ship of 10,000 tonnes displacement has GM=0.5 metres. The period of roll in still water is 20 seconds. Find the new period of roll if a mass of 50 tonnes is discharged from a position 14 metres above the centre of gravity.

Q8. A. List the factors that determine the starting torque of the three-phase induction motor. How does this torque generally compare with the value of the rated torque? (6)

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

i. The synchronous speed.

ii. The speed of the rotor when the slip is 4 per cent.

iii. The rotor frequency when the speed of the rotor is 600 r.p.m. (10)

Q4. A. Explain why the GM must remain positive until the critical instant at which the ship takes the blocks overall. B. A Ship of 5000 tonnes displacement enters a dry dock trimmed 0.45m by the stern. KM=7.5m., KG=6.0m. MCTC=120 tonnes-m.  The centre of flotation is 60m. Frome aft. Find the effective metacentric height at the critical instant before the ship takes the blocks overall, assuming that the transverse metacentre rises 0.075m.

Q7. A 3-phase slip ring induction motor gives a reading of 60V across the slip rings on open circuit, when at rest with normal stator voltage supplied. the motor is star connected and has an impedance of 0.6 + j6 ohms/phase. find the rotor current and its power factor when the machine is 1. At standstill with slip-rings joined to a star connected starter with a phase impedance of 5+j4 ohm 2. Running normally with a 4% slip.

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 of 12000 tonne displacement has a rudder 15 m2 in area, whose centre is 5 m below the waterline. The metacentric height of the ship is 0.3 m and the centre of buoyancy is 3.3 m below the waterline. When travelling at 20 knots the rudder is turned through 30 degree. Find the initial angle of heel if the force Fr perpendicular to the plane of the rudder is given by:

Fr=577Av2 Sin  a N

Allow 20% for the race effect. (10)

Q7. a) Describe the stability requirements of a ship for dry-docking. (6)

B. An oil tanker 160m long and 22m beam floats at a draught of 9m in seawater. Cw is 0.865. The midships section is in the form of a rectangle with 1.2m radius at the bilges. A midships tank 10.5m long has twin longitudinal bulkheads and contains oil of 1.4 m3/t to a depth of 11.5m. The tank is holed to the sea for the whole of its transverse section.  Find the new draught. (10)

Q7. A resistor of ohm value 3 ohms is connected in series with a coil of inductance 0.1 H and resistance 1 ohm. If 100 V at a frequency of 50 Hz is applied to the circuit find the current flowing.

Q7. (a) Explain clearly the meaning of the term ‘reserve buoyancy' (6)
(b) When a mass of 6 t is moved transversely through a certain distance on a ship of 4300 t displacement, the deflection of an 11 m pendulum is found to be 120 mm. The transverse meta-centre is 7.25 m above the keel and KG 5.46 m. Find the distance through which 6 t was moved (10)

Q6.  A double bottom tank is 1.2 m deep and has a sounding pipe extending 11 m above the tank top. The tank is filled with oil (rd 0.89) to the top of the sounding pipe. The double bottom floors are spaced 750 mm apart and are connected to the tank top by riveted angles, the rivets having a pitch of 7 diameters. If the maximum allowable stress in the rivets is 30 MN/m2, calculate the pressure in kN/m2 on the outer bottom and the diameter of the rivets. (16)

Q7. a) What is a right-handed and a left-handed propeller? (6)

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

Q9. A 105V, 3kW d.c. shunt motor has a full-load efficiency of 82 percent. The armature and field resistances are 0.25 Ω and 90 Ω respectively. The full-load speed of the motor is 1000 rev/min. Neglecting armature reaction and brush drop, calculate the speed at which the motor will run at no load if the line current at no load is 3.5A. calculate the resistance to be added to the armature circuit, in order to reduce the speed to 800 rev/min, the torque remaining constant at full-load value. (16)

Q7. a) Name the three main types of A.C. motor and explain the use to which they are put in marine engineering. (6)

b) A four-pole motor is fed at 440V and takes an armature of 50 A. The resistance of the armature circuit is 0.28 ohm. The armature winding is wave connected with 888 conductors and the useful flux per pole is 0.023 Wb. Calculate the speed. (10)