DieselShip's Online Content Library

Q10: A. What is meant by the Admiralty Coefficient and the Fuel Coefficient?

B. A rectangular watertight bulkhead 9 m high and 14.5 m wide bas sea water on both sides, the height of water on one side being four times that on the other side. The resultant centre of pressure is 7 m from the top of the bulkhead. Calculate:

i) The depths of water

ii)  the resultant load on the bulkhead

Q8. A. What are the factors which determine the synchronous speed of a motor?

B. Three conductors fitted side by side in the stator of a salient-pole alternator. Each generates 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.

Q10. (a) List the variables which affect the force on Rudder (6)

b) A ship of 15000 tonne displacement has an Admiralty Coefficient, based on shaft power, of 420. The mechanical efficiency of the machinery is 83%, shaft losses 6%, propeller efficiency 65% and QPC 0.71. At a particular speed the thrust power is 2550kW.

Calculate:

(i) Indicated power,  (ii) Effective power,   (iii) Ship speed.

Q9. A. Explain the effect of bilging a centreline compartment located away from amidships.

b) A ship of 4000 tonne displacement has a mass of 50 tonne on board, on the centre line of the tank top. A derrick, whose head is 18 m above the CG of the mass, is used to lift it. Find the shift in the ship's centre of gravity from its original position when the mass is

(i) lifted Just clear of the tank top

(ii) raised to the derrick head

(iii) placed on the deck 12 m above the tank top. (10)

Q9. a) What is the operational impedance of an R.C. Circuit? Describe its usefulness. (6)
B. A ring-main, 900m long, is supplied at a point A at a p.d. of 220V. At a point B, 240m from A, a load of 45A is drawn from the main, and at a point C, 580m from A, measured in the some direction, a load of 78A is taken from the main. If the resistance of the main (lead and return) is 0.25 ohm per kilometre, calculate the current which will flow in each direction round the main from the supply point A and the potential difference across the main, at the load where it is lowest. (10)

Q7. A. Explain how to distinguish between list and loll and describe how to return the ship to the upright in each case. (6)

B. A ship 120m long has a light displacement of 4000 tonne and LCG in this condition 2.5m aft of midships.  (10)

The following items are then added:

Cargo    10000 tonne      LCG 3.0 m          forward of midships

Fuel      1500 tonne        LCG 2.0 m          aft of midships

Water    400 tonne          LCG 8.0 m          aft of midships

Stores   100 tonne          LCG 10.0m         forward of midships

Using the following hydrostatic data, calculate the final draughts:

Draught (m) --- Displacement (t) --- MCTI cm (tm) --- LCB from midships (m) --- LCF from midships (m)
8.50 ---------- 16650 -------------- 183 ------------ 1.94 F ------------------ 1.20A
8.00 ---------- 15350 -------------- 175 ------------ 2.10 F ------------------ 0.60F

Q9. A hopper barge of box form 50 m long and 10 m wide floats at a draught of 2 m in seawater when the hopper, which is 15 m long and 5 m wide, is loaded with mud having relative density twice that of the seawater, to the level of the waterline. Doors in the bottom of the hopper are now opened allowing the mud to be discharged. Calculate the new draught. (16)

Q6. a) What are the various resistances acting against the motion of the ship? (6)

b) A vessel uses 300 t of fuel on a voyage of 3000 nautical miles at a speed of 12 knots when her displacement is 10000 t. Estimate the fuel required for an estimated voyage of 1500 nautical miles at a speed of 15 knots and displacement of 14000 t. (10)

Q9. a) Name the various types of capacitors? (6)

b) A 500W, 100V bulb is to be connected across 250V, 50Hz mains. Find the value of the capacitor required to be connected in series. (10)

Q7. Ten thousand cubic millimeters of copper are

a) Drawn into a wire 100 metres long,

b) Rolled into a square sheet of 100 mm side. Find the resistance of the wire and the resistance between opposite faces of the plate, if the resistance of the copper is 17 μΩmm or 1.7 x 10-8 ohms-metres. (16)

Q8. A 24 V emergency battery is to be charged from the 110 V ship’s mains when the e.m.f. per cell has fallen to a minimum value of 1.8 V. The battery consists of 12 cells in series, has a capacity of 100 Ahr at a 10 hr rate and the internal resistance is 0.03 ohm/cell. If charging continues until the voltage per cell rises to 2.2 V, find the value of the variable resistor needed to control the charging. The charging current can be assumed to be equal to the maximum allowable discharge current. (16)

Q6.a) What is the effect on the field flux of an alternator current in the synchronous motor that leads the terminal voltage. (6)

b) A 1,000-kVA, 11,000-V, 3-ϕ, star-connected synchronous motor has an armature resistance and reactance per phase of 3.5 Ω and 40 Ω respectively. Determine the induced e.m.f. and angular retardation of the rotor when fully loaded at (a) unity p.f. (b) 0.8 p.f. lagging (c) 0.8 p.f. leading. (10)