DieselShip's Online Content Library

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

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 100V, 50Hz 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?

Q6. A. Explain what is meant by the terms wave form, frequency and average value.

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.

Q6. A. Describe the effect of the following loads on power factor: -

(i) Induction motors; (ii) Transformers; (iii) Partly loaded motors; (iv) Cage type motors.

B. In a 50-Kav, star-connected, 440-V, 3-phase, 50-Hz alternator, the effective armature resistance is 0.25 ohm per phase. The synchronous reactance is 3.2 ohm per phase and leakage reactance is 0.5 ohm phase. Determine at rated load and unity power factor:

(a) Internal e.m.f Ea (b) no-load e.m.f E0 (c) percentage regulation on full-load (d) value of synchronous reactance which replaces armature reaction.

Q8. The armature and filed resistances of a 220 V shunt motor are 0.25 ohm and 110 ohm respectively and when running on load, the motor takes 6 A. Calculate the losses attributable to iron, friction and windage and assuming this value to remain constant on loads, determine the efficiency when the current supplied is 62 A.

Q9. With respect to Ship Propulsion:

a. Explain the various efficiencies associated with propeller and shafting arrangement.

b. When a propeller of 4.8 m pitch turns at 110 rpm, the apparent slip is found to be —S % and the real slip is 1.5 S %. If the wake speed is 25 % of the ship speed, calculate the ship speed, apparent slip and the real slip.

Q9. (a) Describe how thrust power is determined. (6)

(b) The following information relates to a model propeller of 400mm pitch:

(i) Plot curves of thrust and torque against rev/min

(ii) When the speed of advance of the model is 150 m / min and slip 0.20, calculate the efficiency.

Q8. The speed of a ship is increased to 18% above normal for 7.5 hours, and then reduced to 9% below normal for 10 hours. The speed is then reduced for the remainder of the day so that the consumption for the day is the normal amount. Find the percentage difference between the distance travelled in that day and the normal distance travelled per day.

Q8. A. Explain the reasons for fitting bulbous bow. B. When a ship is 800 nautical miles from port its speed is reduced by 20%, thereby reducing the daily fuel consumption by 42 tonne and arriving in port with 50 tonne on board. If the fuel consumption in t/h is given by the expression (0.136+0.001 V3) where V is the speed in knots, estimate: (i) The reduced consumption per day; (ii) The amount of fuel on board when the speed was reduced; (iii) The percentage decrease in consumption for the latter part of the voyage;

(iv) The percentage increases in time for this latter period.

Q6. 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 5.0m 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 i. If there is free surface of water ii. If the water doesn’t completely fill the tank.

Q10. A. Explain the considerations which govern the size and shape of a rudder. B. A ship of 12000 tonne displacement has a rudder 15m2 in area, whose centre is 5m below the waterline.  The metacentric height of the ship is 0.3m and the centre of buoyancy is 3.3m below the waterline.  When travelling at 20 knots the rudder is turned through 30 .  Find the initial angle of heel if the force Fn perpendicular to the plane of the rudder is given by: Fa=577 Av2 sin  N, Allow 20% for the race effect.

Q10. A. List the components of residuary resistance. B. The following data are available for a twin-screw vessel:

Calculate the service speed if the brake power for each engine is 3500Kw. The transmission is 3% and the allowances for weather and appendages 30%.

Q9. A) Define longitudinal centre of gravity (LCG) and longitudinal centre of buoyancy (LCB).(6) B) A vessel, when floating at a draught of 3.6 m has a displacement of 8172 tonne, KB 1.91 m and LCB 0.15 m aft of midships. From the following information, calculate the displacement, KB and position of the LCB for the vessel when floating at a draught of 1.2rn. (10)