DieselShip's Online Content Library

Q8. Find the p.d between A-B and B-C shown in the figure below. (16)

Q7. A 24V emergency battery is to be charged from the 110V ship's mains when the e.m.f. per cell has fallen to a minimum value of 1.8V. The battery consists of 12 cells in series, has a capacity of 100 Ahr at a 10 hr rate and the internal resistance is 0.03Ω/cell. If charging continues until the voltage per cell rises to 2.2V, find the value of the variable resistor needed to control the charging. The charging current can be assumed to be equal to the maximum allowable discharge current (16)

Q7.a) Explain the process of voltage buildup in a self-excited shunt generator. (6) 

b) A shunt-wound generator has a magnetisation-curve given by the figures below. The total resistance in the field circuit is 20 Ohm and the armature resistance is 0.02 Ohm. With the machine on load, estimate the e.m.f. generated and the armature current when the terminal voltage of the machine is 140V. (10)

Field current

(I)_amperes
1.2
2.8
5.0
7.0
7.7
9.0
11.0
Generated e.m.f. (e)_Volts
46
88
126
149
154
162
168
 

Q9. (a) Describe water pressure loads on the ship's hull. (6)

(b) The 1/2 ordinates of a waterplane 120 m long are as follows: (10)

Section AP 1/2 1 1½ 2 3 4 5 6 7 8 8½ 9 9½ FP

½ ord 1.2 3.5 5.3 6.8 8.0 8.3 8.5 8.5 8.5 8.4 8.2 7.9 6.2 3.5 0 m

Calculate:

(a) Waterplane area

(b) Distance of centroid from midships.

Q10. A. Why is a synchronous motor not self-starting? What are the various ways in which it can be started?

B. A 500V, single phase synchronous motor gives a net output mechanical power of 7.46kW and operates at 0.9 power factor lagging. Its effective resistance is 0.8 . If the iron and friction losses are 500 w and excitation losses are 800w, calculate the armature current and the commercial efficiency.

Q9. A. Briefly describe the maintenance routines carried out for emergency batteries onboard.

B. A power of 36 W is to be dissipated in a register connected across the terminals of a battery, having emf of 20V and an internal resistance of 1Ω. Find (i) What value of resistance will satisfy this condition. (ii) The terminal voltage of the battery for each of the resistances and (iii) The total power expenditure in each case.

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.

Q8. A. Explain the purpose of interlopes and state their magnetic polarity relative to the main poles of both generators and motors.

A 200V, long-shunt compound-wound generator has a full-load output of 20kW. The various resistances are as follows; armature (including brush contact) 0.15 ohm, series field 0.025 ohm, interpole field 0.028 ohm, shunt field (including the field-regulator resistance) 115 ohm. The iron losses at full load are 780W, and the friction and wind age losses 590W. Calculate the efficiency at full load.

Q10. (a) What is meant by Quasi Propulsive Coefficient?

A ship of 15000 tonne displacement has mechanical efficiency of the machinery is 83%, shaft losses 6%, propeller efficiency 65% and QPC 0.71. At a particular speed the thrust power is 2550 KW. Calculate: (i) Indicated Power; (ii) Effective power.

Q8. A. Why is it important in a tender ship to keep the double bottom tanks pressed up?

B. A ship of 6000 tonne displacement has a wetted surface area of 2500 m2 and a speed of 15 knots.

(i) Calculate the corresponding speed and wetted surface area of as similar ship of 2000 tonne displacement.

(ii) If the ship resistance is of the form R=0.45 S V1.83 N; find the resistance of the 6000 tonne Ship.

Q7. A ship of length 120 m displaces 11750 tonne when floating in sea water of density 1025 kg/m3. The center of gravity is 2m above the center of buoyancy and the waterplane is defined by the following equidistant half-ordinates given in Table Q1:

Calculate EACH of the following:

(a) The area of the waterplane;

(b) The position of the centroid of the waterplane from midships;

(c) The second moment of area of the waterplane about a transverse axis through the centroid;

(d) The moment to change trim one centimeter (MCT1cm).