DieselShip's Online Content Library

Q7. (a) Explain why the draught of a ship decreases when it passes from fresh water to seawater and vice versa. (6)

(b) A lock gate which is 15m wide has salt water on one side to a depth of 8m and fresh water on the other side to a depth of 9m. Find the resultant thrust on the lock gate and state on which side of the gate it acts. (10)

Q9. A piece of aluminium has a mass of 300 g and its volume is 42 cm3

Calculate

a) its density in kg/m3

b) the relative density

c) the mass of 100 cm3 of aluminium (16)

Q7. a) Define TPC. Explain why TPC for a given draught will vary with the density of the water in which the ship floats? (6)

b) The pitch of a propeller is measured by means of a batten and cord. The horizontal ordinate is found to be 40 cm while the vertical ordinate 1.15 m at a distance of 2.6 m from the centre of the boss. Calculate the pitch of the propeller and the blade width at that point. (10)

Q6. The open-circuit voltage of a cell as measured by a voltmeter of 100 Ω resistance, was 1.5V, and the p.d. when supplying current to a 10 Ω resistance was 1.25V, measured by the same voltmeter. Determine the e.m.f. and internal resistance of the cell. (16)

Q4. a) Sketch and describe a star-delta starter for starting an induction motor (10)

b) Three similar coils, each having a resistance of 10 ohms and an inductance of 0.02 H are connected in

i) Star

ii) Delta to a 3-phase, 50-Hz supply with 500V

Calculate the total power absorbed and the line current in each case. (6)

Q7. (a) Describe the function of the stern frame. (6)

(b) A ship displacing 10000 tonne and travelling at 16 knots has a fuel consumption of 41 tonne per day. Calculate the consumption per day if the displacement is increased to 13750 tonne and the speed is increased to 17 knots. Within this speed range, fuel consumption per day varies as (speed)^3.8 (10)

Q8. (a) What are the effects of adding mass to draught and trim of a ship? (6)

(b) The half ordinates of the waterplane area of a ship of 8200 t displacement, 90 m long are 0, 2.61, 3,68, 4.74, 5.84, 7.00, 7.30, 6.47, 5.35, 4.26, 3.16, 1.88 and o m respectively. It floats in sea water of 1.024 t/m3. Calculate the change in mean draught when moving into water of 1.005 t/m3 (10)

Q4. a) What design factor limits the maximum torque of a d.c. motor? (6)

(b) A shunt motor runs on no load at 700 r/min off a 440 V supply. The resistance of the shunt circuit is 240Ω. The following table gives the relationship between the flux and the shunt current:

Shunt current (A):      0.5   0.75   1.0   1.25   1.5   1.75   2.0

Flux per pole (mWb): 6.0   8.0   9.4   10.2   10.8   11.2   11.5

Calculate the additional resistance required in the shunt circuit to raise the no-load speed to 1000r/min (10)

Q5. a) Describe the effects of changes in speed, rotor current and torque as load is applied to an induction motor. How does the motor adjust its stator current with changes in mechanical load? (6)
b) A 20 KVA, 2000/220V, single-phase transformer has a primary resistance of 2.1 Ω and a secondary resistance of 0.026 Ω. The corresponding leakage reactance’s are 2.5 Ω and 0.03 Ω. Estimate the regulation at full load under power-factor conditions of:
(i) Unity

(ii) 0.5 (lagging)

(iii) 0.5 (Leading) (10)

Q4. a) Explain the preference for a 60 Hz system. Describe the dangers of running a 50 Hz system from a 60 Hz supply. (6)
b) A transistor amplifier stage comprises a transistor of parameters hie = 800  hfe = 5O and hoe = 20µ S, and bias components and coupling capacitors of negligible effect. The input signal consists of an e.m.f. of 60 mV from a source of internal resistance 2.2 k , and the total load on the stage output is 4 k . Determine the current, voltage and power gains of the amplifier stage. (10)

Q4. A) With reference to voltage variation profiles caused by load changes imposed on alternating current generators when starting large motors online:

a) Sketch a voltage dip, showing an acceptable recovery time. (2)

b) State salient factors that cause the variation in part (a) (3)

c) Outline salient factors that assist recovery from the deviation shown in part (3)

B) A three-phase induction motor is wound for four poles and is supplied from a 50 Hz System calculate:

a) The synchronous speed

b) The speed of rotor when the slip is 4 per cent.

c) The rotor frequency when the speed of the rotor is 600 r/min (8)