DieselShip's Online Content Library

Q6.a) Derive an expression for the emf induced in an a.c. generator. (6)

b) A 3000 KVA, 6-pole alternator runs at 1000 r.p.m. in parallel with other machines on 3300V bus-bars. The synchronous reactance is 25%. Calculate the synchronizing power for one mechanical degree of displacement and the corresponding synchronizing torque. (10)

Q9. A. Discuss different methods of speed control of a d.c. series motor by adjusting field ampere turns.

B. A 230 V, d.c. shunt motor runs at 1000 r.p.m and takes 5 amperes. The armature resistance of the motor is 0.025𝛀 and shunt field resistance is 230𝛀. Calculate the drop in speed when the motor is loaded and takes the line current of 41 amperes. Neglect armature reaction.

Q8. A. Explain the significance of the root mean square value of an alternating current or voltage wave form; Define the form factor of such a wave form.

B. Two 10 MVA 3 phase Alternator operate in parallel to supply at 0.8 power factor with lagging load of 15 MVA. If the output of one Alternator is 8 MVA at 0.9 lagging.

1. Calculate the output of second Alternator.

2. Calculate the value of Power factor of second Alternator.

Q5. Fig Q3 shows a single stage transistor amplifier. The voltage between base and emitter is 0.3 V and the d.c. voltage at the output terminals is 8 V. (a) Calculate EACH of the following, assuming the base current is small enough to be neglected: (i) The voltage between emitter and collector; (ii) The power developed in the 150Ωresistor; (iii) The power dissipated in the transistor. (b) Sketch the circuit diagram and show the additional components needed to make the amplifier suitable for amplifying small a.c. signals.

Q10. the following loads are supplied by two alternators running in parallel 1. 1400kw@pf 0.86 lagging 2. 900 kw @ pf 0.8 lagging. 3. 800 kw @ pf unity 4 500kw @pf0.8 leading. If the load on one machine is adjusted to 2100kw @ pf of 0.92 find the load and p.f of the other machine.

Q7. A. Distinguish between power efficiency and all-day efficiency. Why is all-day efficiency considered more reasonable basis for comparison than ordinary efficiency? B. The no-load current of a transformer is 5.0 Amps, power factor 0.25 when supplied at 235 V, 50 Hz. Turns on the primary winding is 200. Calculate A. the maximum value of flux in the core, B. the core loss.

Q10. (a) Explain what is meant by left and right handed propellers, and also explain the rotation of propellers in a twin-screw ship.

(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.

Q7. A box barge 45 m long and 15 m wide floats at a level keel draught of 2 m in sea water, the load being uniformly distributed over the full length. Two masses, each of 30 tonne, are loaded at 10 m from each end and 50 tonne is evenly distributed between them. Sketch the shear force diagram and give the maximum shear force.

Q6. The following data applies to a ship operating on a particular voyage with a propeller of 6 m diameter having a pitch ratio of 0.95:

Propeller speed = 1.8 revs/s

Real slip = 34%

Apparent slip = 7%

Shaft power = 10000 kW

Specific fuel consumption = 0.22 kg/kW-hr

Calculate EACH of the following:

(a) The ship speed in knots;

(b) The Taylor wake fraction;

(c) The reduced speed at which the ship should travel in order to halve the voyage consumption;

(d) The voyage distance if the voyage takes 3 days longer at the reduced speed;

(e) The amount of fuel required for the voyage at the reduced speed.

Q1. A RO-RO ferry of length 80 m has a displacement of 3800 tonne in sea water of density 1025 kg/m3 with BM = 3.4 m. The breadth of the ship at the waterline, between sections 3 and 7 is constant at 13 m. To increase stability, sponsons, 1.8 m deep and of constant plan area are to be fitted as shown in Fig Q1.

The sponsons extend over the midships length between sections 3 and 7, with sponson widths as shown in Table Q1.

For the new condition, there is no change in draught and the load waterline is at mid-depth of the sponson. Calculate the increase in BM due to the sponsons.

Q6. A. What factors influence the frictional resistance of a ship and what formula is used to calculate the resistance? 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:  Fn=577 Av2 sin  N, Allow 20% for the race effect.

Q6. A propeller has a pitch of 4.57m. At 100rev/min the real slip is 20 percent and wake speed is I knot.  Calculate the apparent slip percentage