DieselShip's Online Content Library

Q8. A. Sketch an arrangement showing the principal of proportional plus integral (P+I) control loop.

B. Compare the series and parallel resonance circuits. Find the frequency at which the following circuit resonates.

Q7. A. Which of the following three motors has the poorest speed regulation: shunt motor, series Motor or cumulative compound motor? Explain.

B. A 440V shunt motor takes an armature current of 30A at 700 rev/min. The armature resistance is 0.7ohm. If the flux is suddenly reduced by 20 per cent, to what value will the armature current rise momentarily? Assuming unchanged resisting torque to motion, what will be the new steady values of speed and armature current? Sketch graphs showing armature current and speed as functions of time during the transition from initial to final, steady-state conditions.

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.

Q9. Sketch a graph of starting current, and torque against the speed of rotation for a single cage motor.  B. A 230V motor, which normally develops 10Kw at 1000 rev/min with an efficiency of 85%, is to be used as a generator. The armature resistance is 0.15Ohm and the shunt field resistance is 220Ohm. If it is driven at 1080 rev/min and the field current is adjusted to 1.1A by means of the shunt regulator what output in Kw could be expected as a generator, if the armature copper loss was kept down to that when running as a motor.

Q6. A. What is Prismatic Co-efficient (C_P). Derive the formula C_P = C_b/C_m , where  C_b= Co-efficient of fineness and C_m = midship section area co-efficient.

B. The length of a ship is 18 times the draught. while the breadth is 2.1 times the draught. At the load water plane, the water plane area co-efficient is 0.83 and the difference between the TPC in sea water and the TPC in fresh water is 0.7. Determine the length of the ship and the TPC in fresh water.

Q10. (a). Explain the various efficiencies associated with propeller and shafting arrangement.

(b) A propeller 6m diameter has a pitch ratio of 0.9, BAR 0.48 and, when turning at 110 rev/min, has a real slip of 25% and wake faction 0.30. If the propeller delivers a thrust of 300 KN and the propeller efficiency is 0.65. Calculate:

i. Blade area;

ii Ship speed;

iii. Thrust power;

iv Shaft power

v. Torque.

Q8. With the aid of sketches:
a. Explain various lines plan.
b. The half -breadths of waterplane of a ship of 120m length ad 15m breadth are given below:

Calculate i) Water plane area ii) TPC in salt water iii) Cw iv) LCF from Mid-ship

Q10. A ship of 10000 tonne displacement floats in sea water of density 1025 kg/m3 at a draught of 6m. A rectangular tank 10m long and 8m wide is partially full of oil fuel of density 900 kg/m3. In this condition, the KG of the ship is 6.25m.

Other hydrostatic data for the above condition are:

Centre of buoyancy above the keel (KB) = 3.325m

Transverse metacentre above the centre of buoyancy (BM) = 4.865m

Tonnes per centimetre immersion (TPC) = 20.5

Calculate the change in effective metacentric height when a rectangular tank 12m long, 10m wide and 6m deep, with its base 1 m above the keel, is filled to a depth of 5m with sea water ballast.

NOTE: Assume the ship to be wa11sided over the affected range of draught

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 120m long has a light displacement of 4000 tonne and LCG in this condition 2.5m aft of midships.  The following items are then added:

Using the following hydrostatic data, calculate the fine draughts:

Q10. A. Explain how to distinguish between list and loll and describe how to return the ship to the upright in each case. (6)

B. A ship of 5000 tonne displacement has a double bottom tank 12m long. The ½ breadths of the top of the tank are 5, 4 and 2m respectively. The tank has a watertight centreline division. Calculate the free surface effect if the tank is partially full of fresh water on one side only. (10)

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)