DieselShip's Online Content Library

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

(B) An AC Voltage Of 24 V is connected in series with the silicon diode and load resistance 500 Ohm having forward resistance 1O Ohms. Calculate the peak output voltage.

Q 7. With reference to Synchronous Motors.

A. Draw and explain the principle of operation Synchronous Motors.

B. Find the synchronous impedance reactance of an alternator in which a given field current produces an armature current of 200 A on short circuit and a generated e.m.f. of 50V on open circuit. The armature resistance is 0.1 ohm. To what induced voltage must the alternator be excited if it is to deliver a load of 100A at a p.f of 0.8 lagging, with a terminal voltage of 200 V.

Q4. A) Calculate the Line and Phase current at full load of a 50 kW, 440 Volt 3 phase deltas connected motor having full load efficiency 90% and power factor O.8 lagging. B) Calculate the starting current if motor is started by star/delta starter and Auto transformer starter which has transformer tapping 65 %

Q8. A. What is Silicon controlled rectifier (SCR)? How is the breakover voltage of the SCR defined? (6)

B. A d.c. motor takes an armature current of 110 A at 480 V. The resistance of the armature circuit is 0.2𝛀. The machine has six poles and the armature is lap-connected with 864 conductors. The flux per pole is 0.05 Wb. Calculate: (a) The speed; (b) The gross torque developed by the armature. (10)

Q8. A. What is meant by the Admiralty Coefficient and the Fuel Coefficient? (6)

B. A ship of 14900 tonne displacement has a shaft power of 4460 kW at 14.55 knots. The shaft power is reduced to 4120 kW and the fuel consumption at the same displacement is 541 kg/h. Calculate the fuel coefficient for the ship. (10)

Q7. A. Describe the stability requirements of a ship for dry-docking.

(b) A double bottom tank containing seawater is 6m long, 12m wide and 1m deep. The inlet pipe from the pump has its center 75mm above the outer bottom. The pump has a pressure of 70 kN/m2 and is left running indefinitely. calculate the load on the tank top:

 (i) If there is no outlet.

(ii) If the overflow pipe extends 5m above the tank top.

Q6. (a) Describe the relationship between frictional resistance and

(i) Ship’s speed;

(ii) the wetted area;

(iii) surface roughness;

(iv) The length of the vessel.

b) A ship 150m long and 8.5m draught has a rudder whose area is one sixtieth of the middle-line plane and diameter of stock 320mm. Calculate the maximum speed at which the vessel may travel if the maximum allowable stress is 70 MN/m? the centre of stock 0.9m from the centre of effort and the maximum rudder angle is 35 degrees. (10)

Q8. A ship consumes an average of 70 tonne of fuel per day on main engines at a speed of 17 knots. The fuel consumption for auxiliary purposes is 8 tonne per day. When 800 nautical miles from port it is found that only 140 tonne of fuel remains on board and this will be insufficient to reach port at the normal speed. Determine, using a graphical solution, the speed at which the ship should travel to complete the voyage with 20 tonne of fuel remaining.

Q8. (a) Define coefficient of fineness of waterplane area, block coefficient and midship coefficient. (6)

(b) A box shaped vessel has length 100m and breadth 12m and floats at a range of drafts from 1m to 10m. Produce curves of KB1, BM and KM. (10)

Q8. A. Describe the fundamental principle of a propeller. (6)

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 (10)

Q9. A. Describe the effect of cavitaion on: i. The thrust and ordque; ii. The propeller blades.

B. A ship 150m long and 19m beam floats at a draught of 8m and last a block coefficient of 0.68 i) if the admicatry coefficient is 600 calculate the shaft power required at 18 knots; ii) If the speed is now increased to 21 knots, and within this speed range resistance varies as speed find the new shaft power.

Q4. In some circumstances electrical current may be induced into the shafting of rotating machinery.

a) State the problem that may be caused by this current. (6)

b) Explain with aid of sketches, how currents may be avoided or reduced in the following instances:

(i) D.C machines

(ii) Main shafting fitted with a bronze propeller (5X2)