DieselShip's Online Content Library

Q9. (a) Define longitudinal centre of gravity (LCG) and longitudinal centre of buoyancy (LCB). (6)

(b) The immersed cross-sectional areas of a ship 120m long, commencing from aft are 2, 40, 79, 100, 103, 104, 104, 103, 97, 58 and 0 m². Calculate:

(i) Displacement

(ii) Longitudinal position of the centre of buoyancy. (10)

Q9. A) Describe the effect of cavitations on the propeller blades. (6)

B) A propeller 4.6m diameter has a pitch of 4.3m and boss diameter of 0.75 m. The real slip is 28% at 95 rev/min. Calculate the speed of advance, thrust and thrust power.  (10)

Q8. A ship of 9,900 tonnes displacement has KM=7.3 m and KG=6.4 m she has yet to load two 50 tonne lifts with her own gear and the first lift is to be placed on deck on the inshore side (KG 9 m and center of gravity 6m out from the center line). When the derrick plumbs the quay its head is 15m above the keel an 12m out from the center line.

Calculate the maximum list during operation.

Q7. A Ship of 3,000 tonnes displacement is 100m long has KM=6m, KG=5.5m.  The centre of floatation is 2m.aft of amidships.  MCTC=40 tonnes-m.  Find the maximum trim for the ship to enter a dry dock if the metacentric height at the critical instant before the ship takes the blocks forwarded and aft is to be not less than 0.3m.

Q8. A) Explain how the distribution of masses affects rolling and pitching. (6)

B) A ship turns in a circle of radius 100 metres at a speed of 15 knots. The GM is 2/3 metres and BG is 1 metre. If g = 981 cm/sec2 and 1 knot is equal to 1.8532 Km/hour, find the heel due to turning. (10)

Q9. A. Describe the general precautions to be taken against capsizing. State the recommended criteria for passenger and cargo ships.  B. The ½ ordinates of a water plane at 15m intervals, commencing from aft, ar. 1, 7, 10.5, 11, 11, 10.5, 8, 4 and 0m. Calculate: i. TPC; ii. Distance of the centre of flotation from midships; iii. C. Second moment of area of the water plane about a transverse axis through the centre of flotation.

Q7. A. Describe the effect of Cavitation on; The thrust and torque; The propeller blades B.A ship 120m long displaces 10500 tonne and has a wetted surface area of 3000m2. At 15 knots the shaft power is 4100KW, propulsive coefficient 0.6 and 55% of the thrust is available to overcome frictional resistance; calculate the shaft power required for a similar ship 140m long at the corresponding speed.   = 0.42 and n = 1.825

Q9. A. What is leakage flux as it applies to the iron-core transformer? How is it considered in the analysis of the transformer? (6)

B. Three conductors fitted side by side in the stator of a salient-pole alternator. Each generates a maximum voltage of 200V (sinusoidal). The angle subtended at the centre of the stator between adjacent conductors is 20 electrical degrees. If the three conductors are connected in series, find (i) the r.m.s. value of the effective voltage and (ii) the ‘breadth factor’. Using the theory that is the basis of this problem, give one reason why three-phase current has been introduced. (10)

Q7. A. Explain how to distinguish between list and loll and describe how to return the ship to the upright in each case.  (B) A ship 90 long displaces 5200 tonne and floats at draughts of 4.95m forward and 5.35 m aft when in sea water of 1023 kg/m3. The water plane area is 1100m2, GML 95m, LCB 0.6m forward of midships and LCF 2.2m aft of midships. Calculate the new draughts when the vessel moves into fresh water of 1002 kg/m3

Q9. 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?

B. A shunt motor runs at 900 rev/min when connected to a 440 V supply, the armature current being 60 A and armature resistance 0.4 ohm. At what speed will it run on a 220 V supply with an current of 40 A. Assume 60 percent reduction in flux for the 220 V connection.

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

B. The fuel consumption of a ship at 17 knots is 47 tonne/day. The speed is reduced and the consumption is reduced to 22 tonne/day. At the lower speed, however, the consumption per unit power is 13.2% greater than at 17 knots. Find the reduced speed and the percentage saving on a voyage of 3000 nautical miles.

Q9. A. What is Prismatic Co-efficient (CP). Derive the formula CP =

, where

= Co-efficient of fineness and

= midship section area co-efficient. (6)
B) The ½ ordinates of a water plane at 15m intervals, commencing from aft, are 1, 7, 10.5, 11, 11, 10.5, 8, 4 and 0m. Calculate:

(a). TPC;

(b). Distance of the centre of flotation from midships.

(c). Second moment of area of the water plane about a transverse axis through the centre of flotation.  (10)