DieselShip's Online Content Library

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.

Q6. For the network shown in Fig.Q1 calculate each of the following: (a) The current drawn from each battery; (b) The potential difference across the 40Ωresistor and across the 50Ωresistor; (c) The power dissipated in the 60Ωresistor.

Q9.  A. Explain how the voltage regulation of a transformer is defined. Is this quantity large or small for the iron-core transformer? Explain B. A single-phase transformer has 480 turns on the primary and 90 turns on the secondary. The mean length of the flux path in the core is 1.8m and the joints are equivalent to an air gap of 0.1mm. The value of the magnetic field strength for 1.1T in the core is 400 A/m, the corresponding core loss is 1.7W/Kg at 50Hz and the density of the core is 7800 Kg/m3

Q7. A. Derive an expression for the e.m.f induced in an a.c. generator. B. A 3000 KVA, 6 pole alternators runs at 1000 r.p.m in parallel with other machines on 3300 V bus-bars. The synchronous reactance is 25%. Calculate the synchronizing power for one mechanical degree of displacement and the corresponding synchronizing torque.

Q8. A ship 160m long and 8700 tonne displacement floats at a waterline with

While floating at this waterline, the ship develops a list of 10° due to instability. Calculate the negative metacentric height when the vessel is upright in this condition

Q7. A. Describe stability requirement for dry-docking. B. A ship of 8000 tonne displacement, 110m long, floats in sea water of 1.024t/m3 at draughts of 6m forward and 6.3 m aft. The TPC is 16, LCB 0.6 m aft of midships, LCF 3m aft of midships and MCT1cm 65 tonne m, the vessel now moves into fresh water of 1.000t/m3. Calculate the distance a mass of 50 tonne must be moved to bring the vessel to an even keel and determine the final draught.

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).

Q2. The ‘wall sided formula’ gives an expression for righting lever (GZ) as follows:  GZ = sin θ (GM + ½ BM tan2 θ) (a) Derive an expression for the `angle of loll' of a ship which is initially unstable in still water, using the wall sided formula. (b) A box shaped vessel designed to carry timber, is 80 m long, 12 m wide and floats at a draught of 5 m in sea water of density 1025 kg/m3 with a KG of 4.815 m. A beam wind acts on the exposed area of the vessel causing it to heel to an angle of 15°. The heeling moment caused by the wind is given by the expression: Heeling moment = 0.85 A b v2 cos2 θ Nm

where:  A = exposed area = 627 m2 b = lever = 6.5 m      v = wind speed in m/s                                        θ = angle of heel in degrees.

Calculate the wind speed in knots, using the wall sided formula for GZ.

Q8. A. Describe the procedure for speed, Power and fuel consumption trials. B. An oil tanker has LBP 142m, beam 18.8m and draught 8m. It displaces 17000 tonne in seawater of 1.025 1/m3. The face pitch ratio of the propeller is 0.673 and the diameter 4.8m. The results of the speed final show that the true slip may be regarded as constant over a range of speeds of 9 to 12 knots and is 35% the wake fraction may be calculated from the equation: W=0.5Cb = 0.05. If the vessel uses 20 tonne of fuel per day at 12 knots and the consumption varies as speed. Find the consumption per day at 100 rev/min.

Q8. A box barge of 60m long and 10m wide floats at a level keel draught of 3m. Its centre of gravity is 2.5m above the keel. Determine the end draughts if an empty, fore end compartment 9m long is laid open to the sea.

Q8. A. Explain the use of KN curves.

B. The half breadths of the load waterplane of a ship 150 m long commencing from aft, are 0.3. 3.8. 6.0, 7.7, 8.3.9.0,8.4.7.8, 6.9.4.7 and 0 m respectively. Calculate: (a) area of waterplane (b) distance of centroid from amidships (c) second moment of area about a transverse axis through centroid.