DieselShip's Online Content Library

Q10. (A). Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse.

(B) An AC Voltage Of 24 V is connected in series with the silicon diode and load resistance 500 Ohm having forward resistance 1O Ohms. Calculate the peak output voltage.

Q 7. With reference to Synchronous Motors.

A. Draw and explain the principle of operation Synchronous Motors.

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 200 V.

Q4. A) Calculate the Line and Phase current at full load of a 50 kW, 440 Volt 3 phase deltas connected motor having full load efficiency 90% and power factor O.8 lagging. B) Calculate the starting current if motor is started by star/delta starter and Auto transformer starter which has transformer tapping 65 %

Q8. A. What is Silicon controlled rectifier (SCR)? How is the breakover voltage of the SCR defined? (6)

B. A d.c. motor takes an armature current of 110 A at 480 V. The resistance of the armature circuit is 0.2𝛀. The machine has six poles and the armature is lap-connected with 864 conductors. The flux per pole is 0.05 Wb. Calculate: (a) The speed; (b) The gross torque developed by the armature. (10)

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

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.

Q9. 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.

Q10. With reference to fixed pitch propellers:
a. Explain Propeller Slip and Propeller Thrust. (6)
b. The shaft power of a ship is 3000 KW, the ship’s speed V is 13.2 knot. Propeller rps is 1.27. Propeller pitch is 5.5m and the speed of advance is 11 Knots. Find:
i. Real Slip
ii. Wake fraction
iii. Propeller thrust, when its efficiency, η = 70% (10)

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 movement of a ship with negative metacentric height. (b) A ship of 8000 tonne displacement has its centre of gravity 4.5m above the keel and transverse metacenter 5m above the keel when a rectangular tank 7.5m long and 15m wide contains seawater. A mass of 10 tonne is moved 12m across the deck. Calculate the angle of heel:(10) (i) If there is no free surface of water. (ii) if the water does not completely fill the tank.

Q9. A. Describe briefly the inclining experiment and explain how the results are used. B. A ship of 8500 tonne displacement has a double bottom tank 11m wide extending for the full breadth of the ship, having a free surface of seawater. If the apparent loss in metacentric height due to slack water is 14cm, find the length of the tank.

Q6. a) Derive the expression for current and voltage relations between line and phase values in the star and delta cases. Draw vector diagram.

b) Three impedances Z=5+j4 are connected in the form of a delta to the three loads of a balanced 3-phase circuit. The line voltage is 120 Volts.

Find (a) The phase current, (b) Power factor, (c) The volt-ampere in the circuit.