DieselShip's Online Content Library

Q8. A. What is back emf? Derive the relation for the back emf and the supplied voltage in terms of armature resistance.

B. A three- phase induction motor is wound for four poles and is supplied from a 50 Hz system. Calculate.

i. The synchronous speed; (4)

ii. The speed of the rotor when the slip is 4 per cent; (3)

iii. The rotor frequency when the speed of the rotor is 600 r/min. (2)

Q9. A. Explain how the efficiency and regulation of a transformer can be assessed by open circuit and short circuit tests?

B. A 25 kVa signal phase transformer 2200:200V has a primary and secondary resistance of 1Ω and 0.01 Ω respectively. Find the equivalent secondary resistance and full load efficiency at 0.8pf lagging, if the iron losses of the transformer are 80% of the full load copper losses.

Q2. Two Alternators running in parallel with D/G # 1 having 2000 KW capacity with 4 % speed droop and D/G # 2 having 1000 KW capacity with 4% speed droop. The no load frequency is 62 Hz. How much KW load shared by each alternator if total ship load is 1200 KW?

Q6. A. Describe with the aid of a sketch, an isolator for a 3 phase 440V, 20-amp electric supply List the safety features of the isolator described in the sketch. B. A moving coil ammeter, a thermal ammeter and a rectifier are connected in series with a resistor across a 110 V sinusoidal a.c. supply. The circuit has a resistance of 50 to current in one direction and, due to the rectifier, an infinite resistance to current in the reverse direction. Calculate: (i) The readings on the ammeters; (ii) The form and peak factors of the current wave.

Q10. Evaluate for a frequency of 15 kHz, the amplification and the phase difference between input and output signals of a voltage amplifier using a triode having an amplification factor of 48 and a mutual conductance of 1.2 m A/V with an anode-load resistant of 160 k . The output p.d. is fed by a coupling capacitor of negligible reactance to a subsequent circuit of resistance 480 k and the total shunt capacitance is 90µ F.

Q6. A. Describe how the force on the ship’s bottom and the GM vary when grounding takes place.

B. A ship of 8,000 tonnes displacement takes the ground on a sand bank on a falling tide at an even keel draft of 5.2 metres. KG 4.0 metres. The predicted depth of water over the sand bank at the following low water is 3.2 metres. Calculate the GM at this time assuming that the KM will then be 5.0 metres and that mean TPC is 15 tonne.

Q10.  The breadth of the upper edge of a deep tank bulkhead is 12 metres. The vertical heights of the bulkhead at equidistant intervals across it are 0, 3, 5, 6, 5, 3 and 0 metres respectively. Find the depth of the centre of pressure below the waterline when the tank is filled to a head of 2 metres above the top of the tank.

Q6. A. With reference to dynamical stability, describe the effect of an increase in wind pressure when a vessel is at its maximum angle of roll to windward.

B. A ship of 15000 tonne displacement has righting levers of 0, 0.38, 1.0, 1.41 and 1.2 m at angles of hell of 0 , 15 , 30 , 45  and 60  respectively and an assumed KG of 7.0 m.  The vessel is loaded to this displacement but the KG is found to be 6.80m and GM 1.5m –

(i) Draw the amended stability curve; (ii) Estimate the dynamic stability at 60

Q5. A single screw vessel with a service speed of 15 knots is fitted with an unbalanced rectangular rudder 6 m deep and 4 m wide with an axis of rotation 0.2 m forward of the leading edge. At the maximum designed rudder angle of 35° the centre of effort is 30% of the rudder width from the leading edge. The force on the rudder normal to the plane of the rudder is given by the expression: Fn = 20.2 A v2α newtons

Where: A = rudder area (m2) v = ship speed (m/s)   α = rudder helm angle (degrees)

The maximum stress on the rudder stock is to be limited to 70 MN/m².

Calculate EACH of the following: (a) the minimum diameter of rudder stock required; (b) the percentage reduction in rudder stock diameter that would be achieved if the rudder was designed as a balanced rudder, with the axis of rotation 1.0 m aft of the leading edge.

Q7. A. what is the effect on fuel consumption per unit time, if the ship’s speed is outside its operation range? B. The frictional resistance of a ship in fresh water at 3m/s is 11N/m2.  The ship has a wetted surface area of 2500m2 and the frictional resistance is 72% of the total resistance and varies as speed 1.92.  If the effective power is 1100Kw, calculate the speed of the ship.

Q10. Describe with sketches the arrangement of a power operator sliding water light door. B. A watertight bulkhead 7.5m high has vertical stiffeners 0.75m apart, connected at the bottom by brackets having 10 rivets 20mm diameter in each arm. The bulkhead is flooded to the top on one side only with seawater calculate. (i) Shearing force at top and bottom; (ii) Position of zero shear; (iii) Shear stress in the rivets; Draw the load and shearing force diagrams.

Describe the effect of cavitation’s on

(i) The thrust and torque

(ii) the propeller blades.

(b) A ship of 355190 tonne displacement is 325 m long, 56m wide and floats in sea water of density 1025 kg/m3 at a draught of 22.4 m. The propeller has a diameter of 7.4 m, a pitch ratio of 0.85, and when rotating at 1.5 rev/s the real slip is 48.88% and the fuel consumption is 165 tonne per day.

The taylor wake fraction Wt=0.5Cb-0.05.

Calculate

a) The speed in knots

b) The reduced speed at which the ship should travel if the fuel consumption in a voyage is to be halved.

C) the length of the voyage if the extra time on passage is six days when travelling at the reduced speed.

d) The amount of fuel required onboard before commencing on the voyage at the reduced speed.