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Q7. A ship of 2890 tonne displacement and speed of 14 knots has a machinery mass of 410 tonne. The mass of ship’s machinery is given by the formula: m=  V3 tonne;(i) Calculate the mass of the machinery of a similar ship of 3000 tonne displacement at the corresponding speed; (ii) if the 2890 tonne ship required 2920 Kw shaft power, calculate the shaft power required by the 3000 tonne ship.

Q7.A. By means of a schematic circuit diagram illustrate the peak rectifier. If the supply voltage is v(t) = Vra Sin wt, what is the voltage across the load resistor?

B. A d.c. motor takes an armature current of 110 A at 480 V. The resistance of the armature circuit is 0.2?. The machine has six poles and the armature is lap-connected with 864 conductors. The flux per pole is 0.05 Wb. Calculate;

(i) The speed;

(ii) The gross torque developed by the armature.

Q6. A. Describe how water tightness is maintained where bulkheads are pierced by longitudinal beams or pipes.

B. A propeller has a pitch ratio of 0.95. When turning at 120 rev/min the real slip is 30%, the wake fraction 0.28 and the ship speed 16 knots. The thrust is found to be 400 KN, the torque 270 KN-m and the QPC 0.67. Calculate:

i. The propeller diameter;

ii. The shaft power;

iii the propeller efficiency;

iv. The thrust deduction factor.

Q6. a) With respect to Buoyancy of a vessel:

What do you understand by reserve buoyancy what happen if the lost buoyancy is greater than the reserve buoyancy? (6)

b) A triangular bulkhead is 7 m wide at the top and has a vertical depth of 8 m.  Calculate the load on the bulkhead and the position of centre of pressure if the bulkhead is flooded with sea water on only side:

(i) to the top edge,

(ii) with 4 m head to the top edge. (10)

Q6. A. Define following terms with reference to alternating currents - Cycle; Time-period; Frequency; Peak factor

B. A heater unit of inductance has a resistance of 6.5 ohms and is intended for use with 100V mains. For what 50Hz voltage would it be suitable when placed in series with an external apparatus, of negligible resistance, having an inductance of 0.01H. If the frequency rises by 5 per cent and this voltage remains constant, what constant, what would be the resulting change or voltage at the heater terminals?

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)

Q8. (a) State the relationship between impedance, voltage and current (6)

(b) The filament of a 230V lamp takes a current of 0.261A when working at its normal temperature of 2000° C. The temperature coefficient of the tungsten filament material can be taken as 0.005 ohms/ohms at 0ºC/ºC. Find the approximate current which flows at the instant of switching on the supply to the cold lamp, which can be considered to be at a room temperature of 20° C (10)

Q6. (a) Explain in brief the term 'bulwark" and 'freeing port'. (6)

(b) A ballast tank is 15 m long, 12 m wide and 1.4m deep and is filled with fresh water. Calculate the load on the top and short side, if: (10)

(i) The tank is just completely full

(ii) There is a head of 7m of water above the tank top.