DieselShip's Online Content Library

Q9. (a) Describe the effect of running an induction motor on reduced voltage (6)

(b) A 90V D.C. generator is used to charge a battery of 40 cells in series, each cell having an average e.m.f. of 1.9 V and an internal resistance of 0.0025 Ω. If the total resistance of the connecting cells is 1Ω, calculate the value of the charging current (10)

Q7. (a) What is Freeboard of a Ship? Why oil tankers have less freeboard? (6)

(b) A box barge 25 m long and 4 m wide floats in fresh water at a draught of 1.2 m and has an empty mid length compartment 5m long. The bottom of the barge is lined with teak (rd 0.805) 120mm thick. After grounding all the teak is torn off and the centre compartment laid open to the sea. Calculate the final draught. (10)

Q6. A) With the aid of delta and star connection diagrams, state the basic equation from which the delta-star and star- delta conversion equation can be derived. (6)
B) Three batteries A, B, and C have their negative terminals connected together. Between the positive terminals of A and B there is a resistor of 0.5 ohm and between B and C there is a resistor of 0.3 ohm
Specifications of the three batteries are given below.
Battery A 105 V, Internal resistance   0.25 ohm
Battery B 100 V, Internal resistance   0.2 ohm
Battery C   95 V, Internal resistance   0.25 ohm
Determine the current values in the two resistors and the power dissipated by them. (10)

Q6. A. Explain distribution factor and pitch factor for alternator windings.

B. A 3phase, 4pole 24 slot alternator has its armature coils short pitched by one slot. Find the distribution factor and pitch factor.

Q8. A. What is meant by “Resonance” in RLC circuits? Compare the series and parallel resonance circuits.

B. Find the frequency at which the following circuit resonates.

Q7. Two 10 MVA 3 phase Alternator operate in parallel to supply at 0.8 power factor with lagging load of 15 MVA. If the output of one Alternator is 8 MVA at 0.9 lagging. A. Calculate the output of second Alternator. B. Calculate the value of Power factor of second Alternator.

Q9. Sketch a graph of starting current, and torque against the speed of rotation for a single cage motor.  B. A 230V motor, which normally develops 10Kw at 1000 rev/min with an efficiency of 85%, is to be used as a generator. The armature resistance is 0.15Ohm and the shunt field resistance is 220Ohm. If it is driven at 1080 rev/min and the field current is adjusted to 1.1A by means of the shunt regulator what output in Kw could be expected as a generator, if the armature copper loss was kept down to that when running as a motor.

Q7. A. Describe stability requirement for dry-docking.

B. A ship of 8000 tonne displacement floats upright in seawater. KG = 7.6m and GM = 0.5m. A tank, KG is 0.6m above the keel and 3.5m from the centre line, contains 100 tonne of water ballast. Neglecting the free surface effect, calculate the angle which the ship will heel, when the ballast water is pumped out.

Q6. (a) Describe how bulkheads are tested.

(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.

Q10. A) Describe the stability requirements of a ship for dry-docking. (6)

B) A ship 130m long displaces 14000 tonne when floating at draughts of 7.5m forward and 8.10m aft. GML – 125m, TPC – 18, LCF-3m aft of midships. Calculate the final draughts when a mass of 180 tonne lying 40m aft of midships is removed from the ship. (10)

Q10. A ship of 10000 tonne displacement floats in sea water of density 1025 kg/m3 at a draught of 6m. A rectangular tank 10m long and 8m wide is partially full of oil fuel of density 900 kg/m3. In this condition, the KG of the ship is 6.25m.

Other hydrostatic data for the above condition are:

Centre of buoyancy above the keel (KB) = 3.325m

Transverse metacentre above the centre of buoyancy (BM) = 4.865m

Tonnes per centimetre immersion (TPC) = 20.5

Calculate the change in effective metacentric height when a rectangular tank 12m long, 10m wide and 6m deep, with its base 1 m above the keel, is filled to a depth of 5m with sea water ballast.

NOTE: Assume the ship to be wa11sided over the affected range of draught

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 120m long has a light displacement of 4000 tonne and LCG in this condition 2.5m aft of midships.  The following items are then added:

Using the following hydrostatic data, calculate the fine draughts: