DieselShip's Online Content Library

Q7. A. What factors influence the frictional resistance of a ship and what formula is used to calculate the resistance?

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.  f= 0.42 and n = 1.825

Q10. A. If resistance S V2 and S 2/3, derive the Admiralty Coefficient formula. B. A ship 160m long, 22m beam and 9.2m draught has a block coefficient of 0.765. The Pitch of the propeller is 4m and when it turns at 96 rev/min the true slip is 33%, the wake fraction 0.335 and shaft power 2900 Kw.  Calculate the Admiralty Coefficient and the shaft power at 15 knots.

Q7. A. Explain the effect on GM during the filing of a double – bottom tank. (6)

B. An oil tanker 160m long and 22m beam floats at a draught of 9m in seawater. Cw is 0.865. The midships section is in the form of a rectangle with 1.2m radius at the bilges. A midships tank 10.5m long has twin longitudinal bulkheads and contains oil of 1.4 m3/t to a depth of 11.5m. The tank is holed to the sea for the whole of its transverse section. Find the new draught. (10)

Q6. A. Describe the stability requirements of a ship for dry-docking.

b) A ship of 12000 tonne displacement has a rudder 15 m2 in area, whose centre is 5 m below the waterline. The metacentric height of the ship is 0.3 m and the centre of buoyancy is 3.3 m below the waterline. When travelling at 20 knots the rudder is turned through 30 degree. Find the initial angle of heel if the force Fr perpendicular to the plane of the rudder is given by:

Fr=577Av2 Sin  a N

Allow 20% for the race effect. (10)

Q6. (A) Explain the concept of dynamical stability. (6)

b) A vessel of 8000 tonne displacement has 75 tonnes of cargo on the deck. It is lifted by a derrick whose head is 10.5m above the centre of gravity of the cargo and placed in the lower hold 9m below the deck and 14m forward of its original position. Calculate the shift in the vessel's centre of gravity from its original position when the cargo is: (10)

(i) just clear of the deck

(ii) at the derrick head

(iii) in its final position.

Q9. a) Explain the term Angle of loll and state the dangers it poses to a vessel. What action to be taken to correct angle of loll. (6)

B. A forward deep tank 12 m long extends from a longitudinal bulkhead to the ship’s side. The widths of the tank surface measured from the longitudinal bulkhead at regular intervals are 10, 9, 7, 4 and 1 m. Calculate the second moment of area of the tank surface about a longitudinal axis passing through its centroid. (10)

Q8. A ship 96 m long floating at 5 m fwd draft and 6.4 m aft draft. MCTC 180 tm, TPC 16. COF is 2 m abaft of midships. Find the location where a weight of 50 t should be placed so as to keep the aft draft constant. (16)

Q8. a) What is the effect of density of water on draught and TPC? (6)

b) A ship of 15000 t displacement floats at a draught of 7 m in water of RD 1.000. It is required to load the maximum amount of all to give the ship a draught of 7 m in sea water of RD 1.025. If the water plane area is 2150 m², Calculate the mass of oil required. (10)

Q6. a) State Ohm's Law. (3)

b) State the limitations of Ohm's Law. (3)

c) 3 resistors of value 2 Ω, 4 Ω and 8 Ω are connected in series across a supply of 42 V. Find the current taken from supply and voltage drop across each resistor. (10)

Q9. The following are the results of measurements taken at intervals over a half cycle of alternating voltage:

Time (t milliseconds)
0
0.45
0.95
1.5
2.1
2.5
3.1
3.9
4.5
5.0

Voltage (V volts)
0
20
36
40
37.5
33
32
31
20
0
Calculate the R.M.S value, average value and frequency of the wave. (16)

Q7. A 24V emergency battery is to be charged from the 110V ship's mains when the e.m.f. per cell has fallen to a minimum value of 1.8V. The battery consists of 12 cells in series, has a capacity of 100 Ahr at a 10 hr rate and the internal resistance is 0.03Ω/cell. If charging continues until the voltage per cell rises to 2.2V, 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)

Q7.a) Explain the process of voltage buildup in a self-excited shunt generator. (6)

b) A shunt-wound generator has a magnetisation-curve given by the figures below. The total resistance in the field circuit is 20 Ohm and the armature resistance is 0.02 Ohm. With the machine on load, estimate the e.m.f. generated and the armature current when the terminal voltage of the machine is 140V. (10)

Field current

(I)_amperes
1.2
2.8
5.0
7.0
7.7
9.0
11.0
Generated e.m.f. (e)_Volts
46
88
126
149
154
162
168