QUESTION BANK NAVAL ARCHITECTURE PART-3

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Q a) State why for dry-docking, a ship should have adequate initial metacentric height, be upright and have a small or moderate trim, normally by the stern.

b) What do you understand by reserve buoyancy? What will happen if the lost buoyancy is greater than the reserve buoyancy?

c) Explain why the amplitude of ship motion should be limited.

d) A ship of 8100 tonne displacement floats upright in the seawater. KG=7.5 m & GM=0.45 m. A tank, whose centre of gravity is 0.5 m above the keel & 4 m from the centerline, contains 100 tonne of the water ballast. Neglecting free surface effect, calculate the angle of heel when the ballast is pumped out.

Q a) Describe the fundamental principle of a propeller.

b) Explain what is meant by singing of the propellers.

a) A propeller 6m diameter has a pitch ratio of 0.9, BAR 0.48 and, when turning at 110 rev/min, has a real slip of 25% & wake faction 0.30. If the propeller delivers a thrust of 300 kN & the propeller efficiency is 0.65, calculate:

i. Blade area

ii. Ship speed

iii. Thrust power

iv. Shaft power

v. Torque

Q A box-shaped pontoon is 36 metres long, 4 metres wide & floats in salt water at drafts F-2.00 m , A-4.00 m. Find the new drafts if the pontoon now passes into fresh water.

Q The breadth of the upper edge of a deep tank bulkhead is 12 metres. The vertical heights of the bulkhead at equidistant intervals across it are 0, 3, 5, 6, 5, 3 and 0 meters respectively. Find the depth of the centre of the pressure below the waterline when the tank is filled to a head of 2 metres above the top of the tank.

Q A propeller has a pitch ratio of 0.95. When turning at 120 rev/min the real slip is 30%, the wake fraction 0.28 & the ship speed 16 knots. The thrust is found to be 400 kN, the torque 270 kNm & the QPC 0.67.

Calculate:

a) The propeller diameter

b) The shaft power

c) The propeller efficiency

d) The thrust deduction factor

Q a) Explain how increase of draught and of displacement influence rolling.

a) A pontoon has a constant cross-section as shown in Fig. Given below The metacentric height is 2.5 m. Find the height of the centre of gravity above the keel.

Q a) Describe how the force on the ship’s bottom and the GM vary when grounding takes place.

b) A ship of 8,000 tonnes displacement takes the ground on a sand bank on a falling tide at an even keel draft of 5.2 metres. KG 4.0 metres. The predicted depth of the water over the sand bank at the following low water is 3.2 metres. Calculate the GM at this time assuming that the KM will then be 5.0 metres & that mean TPC is 15 tonne.

Q a) Explain the term volumetric heeling moments.

b) A box barge 33 m long and 5.5 m wide has a light displacement and KG of 216 tonne & 2.75 m respectively. 80 tonne of machinery are put on board and in order to maintain stability 54 tonne of Ballast are at Kg 0.15 m. The final GM is 0.13 m. Calculate the Kg of the added machinery.

Q a) With reference to dynamical stability, describe the effect of an increase in the wind pressure when a vessel is at its maximum angle of roll to windward.

b) A ship of 15000 tonne displacement has righting levers of 0, 0.38, 1.0, 1.41 and 1.2 m at angles of hell of 0°, 15°, 30°, 45° and 60° respectively & an assumed KG of 7.0 m. The vessel is loaded to this displacement but the KG is found to be 6.80m and GM 1.5 m.

i. Draw the amended stability curve.

ii. Estimate the dynamic stability at 60°

Q a) Explain how wave profile affects the shear-force and bending moment curves.

b) A ship 125 m long displaces 12000 tonne. When a mass of 100 tonne is moved 75 m from forward to aft there is a change in trim of 65 cm by stern. Calculate:

i MCT 1 cm

ii The longitudinal metacentric height

iii The distance moved by the centre of gravity of the ship.

Q a) Explain the purpose of non-watertight longitudinal subdivision of tanks.

b) A ship 90 m long displaces 5200 tonne and floats at draughts of 4.95 m forward and 5.35 m aft when in sea water of 10233 kg/m3. The waterplane area is 1100 m2, GML 95 m, LCB 0.6 m forward of the midships & LCF 2.2 m aft of midships.

Calculate the new draughts when the vessel moves into fresh water of 1002 kg/m3.

Q a) Describe with sketches the arrangement of a power operator sliding water tight door.

b) A watertight bulkhead 7.5 m high has vertical stiffeners 0.75 m apart, connected at the bottom by brackets having 10 rivets 20 mm diameter in each arm. The bulkhead is flooded to the top on one side only with seawater. Calculate:

i. Shearing forces at top and bottom

ii. Position of zero shear

iii. Shear stress in the rivets

Draw the load & shearing force diagram

Q 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 & the first lift is to be placed on deck on the inshore side (KG 9 m and centre of gravity 6m out from the centre line). When the derrick plumbs the quay its head is 15 m above the keel and 12 m out from the centre line. Calculate the maximum list during operation

Q a) Explain the effect on GM during the filing of a double bottom tank.

b) A ship of 8,000 tonnes displacement has KM 7.5 m, and KG 7.0m. A double bottom tank is 12 meters long 15 meters wide &1 meter deep. The tank is divided longitudinally at the centre line & both sides are full of salt water. Calculate the list if one side is pumped on until it is half empty.

Q a) Explain the effect of trim on tank soundings.

b) A ship of 6600 tonne displacement has KG 3.6 m & KM 4.3 m. A mass of 50 tonne is now lifted from the quay by one of the ship’s derricks whose head is 18 m above the keel. The ship heels to a maximum of 9.5° while the mass is being transferred. Calculate the outreach of the derrick from the ship’s centreline.

Q a) Explain what is meant by:

i. Wave-making resistance

ii. Frictional resistance

iii. Eddy-making resistance

b) Explain the reasons for fitting bulbous bow.

c) When a ship is 800 nautical miles from port its speed is reduced by 20%, thereby reducing the daily fuel consumption by 42 tonne and arriving in port with 50 tonne on board. If the fuel consumption in t/h is given by the 0.136+0.001 V³) where V is the speed in knots, estimate:

i. The reduced consumption per day.

ii. The amount of fuel on board when the speed was reduced.

iii. The percentage decrease in consumption for the latter part of the voyage.

iv. The percentage increases in time for this latter period.

Q a) What do you understand by reserve buoyancy what happen if the lost buoyancy is greater than the reserve buoyancy?

b) A forward deep tank  of 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 & 1 m. Calculate the second moment of area of the tank surface about a longitudinal axis passing through its centroid.

Q a) Describe the effect of Cavitation on:

i. The thrust and torque

ii. The propeller blades

b) Describe the process of correcting a negative GM.

c) A ship 120 m long displaces 10500 tonne and has a wetted surface area of 3000 m² At 15 knots the shaft power is 4100 kW, propulsive coefficient 0.6 and 55% of the thrust is available to overcome frictional resistance. Calculate the shaft power required for a similar ship 140 m long at the corresponding speed.

f= 0.42 and n = 1.825

Q a) What is meant by the Admiralty Coefficient and the Fuel Coefficient?

b) A ship of 14900 tonne displacement has a shaft power of 4460 kW at 14.55 knots. The shaft power is reduced to 4120 kW and the fuel consumption at the same displacement is 541 kg/h. Calculate the fuel coefficient of ship.

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

Q a) Describe how thrust power is determined.

b) The following information relates to a model propeller of 400 mm pitch:

Rev/min        400 450 500 550 600

Thrust N      175 260 365 480 610

Torque Nm 16.8 22.4 28.2 34.3 40.5

i. Pilot curves of thrust and torque against rev/min.

ii. When the speed of advance of the model is 150 rev/min and slip 0.20, calculate the efficiency.

Q a) Explain how to distinguish between list and loll and describe how to return the ship to the upright in each case.

b) Explain the effect of bilging a centreline compartment located away from amidships.

c) A ship of 5000 tonne displacement has a double bottom tank 12 m long. The ½ breadths of the top of the tank are 5.4 & 2 m respectively. The tank has a watertight centreline division. Calculate the free surface effect if the tank is partially full of fresh water on one side only.

Q  a) Describe measures which may be taken to improve the stability or trim of a damaged ship.

b) A ship 85 m long displaces 8100 tonne when floating in seawater at draughts of 5.25 m forward & 5.55 m aft. TPC 9.0, GML 96 m, LCF 2 m aft of midships. It is decided to introduce water ballast to completely submerge the propeller & a draught aft of 5.85 m is required. A ballast tank 33 m aft of midships is available. Find the least amount of water required & the final draught forward.

Q a) Define hull efficiency and propeller efficiency.

b) A ship of 2890 tonne displacement and speed of 14 knots has a machinery mass of 410 tonne. A mass of ship’s machinery is given by the formula: m= k Δ2/3 V³tonne.

i. Calculate the mass of the machinery of a similar ship of 3000 tonne displacement at the corresponding speed.

ii. If the 2890 tonnes ship required 2920 kW shaft power, calculate the shaft power required by the 3000 tonne ship.

Q a) Explain how trim occurs, and how explain the effect of trim on tank soundings.

b) A ship of 150 metres long arrives at the mouth of a river with drafts 5.5 m. F and 6.3 m A. MCT 1 cm. 200 tonnes-m. TPC 15 tonnes. Centre of floatation is 1.5 m aft of amidships. The ship has then to proceed up the river where the maximum draft permissible is 6.2 m. It is decided that SW ballast will be run into the forepeak tank to reduce the draft aft to 6.2 m. If the centre of gravity of the forepeak tank is 60 metres forward of the center of flotation, find the minimum amount of water which must be run in and also find the final draft forward.

Q A vessel of 12000 tonne displacement has a length along the load water line of 140 m. The waterline lengths at 1 m interval of draught below this are 139, 138, 136.5, 134.5, 132 & 129 respectively. If the centre of lateral resistance is at the centroid of this immersed area calculate the angle to which the ship will heel due to centrifugal force when the vessel turns in a circle of 400 m diameter when travelling at 16 knots with KG 5 m & GM 0.4 m.

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

Q A propeller has pitch of 4.57 m. At 100 rev/min the real slip is 20% and wake speed is 1 knots. Calculate the apparent slip percentage.

Q a) Describe stability requirements for dry-docking.

b) A ship of 8000 tonne displacement, 110 m long, floats in sea water of 1.024 t/m³ at draughts of 6 m forward and 6.3 m aft. The TPC is 16, LCB 0.6 m aft of midships, LCF 3 m aft of midships and MCTI cm 65 tonne m. The vessel now moves into fresh water of 1.000 t/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.

Q a) Explain the effect on stability when a tank is partially filled with liquid.

b) A ship of 11200 tonne displacement has a double bottom tank containing oil, whose centre of gravity is 16.5 m forward & 6.6 m below the centre of gravity of the ship. When the oil is used the ship’s centre of gravity moves 380 mm. Calculate:

i. The mass of oil used

ii. The angle, which the centre of gravity moves relative to the horizontal

Q a) Explain why the bilging of empty double bottom tanks that are wholly below the waterline leads to an increase in GM.

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

i. Displacement

ii. Longitudinal position of the centre of buoyancy

Q The end bulkhead of the wing tank of an oil tanker has the following widths at 3 m intervals, commencing at the deck: 6.0, 6.0, 5.3, 3.6 & 0.6 m. Calculate the load on the bulkhead and the position of the centre of pressure if the tank is full of oil rd 0.8.

Q a) Describe briefly the inclining experiment and explain how the results are used.

b) A ship of 8500 tonne displacement has a double bottom tank 11 m wide extending for the full breadth of the ship, having a free surface of seawater. If the apparent loss in metacentric height due to slack water is 14 cm, find the length of the tank.

Q A ship 160 m long and 8700 tonne displacement floats at waterline with

Station        AP ½ 1 2 3 4 5 6 7 7½ FP

½ ordinate 0 2.4 5.0 7.3 7.9 8.0 8.0 7.7 5.5 2.8 0m

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.

Q The daily fuel consumption of a ship at 17 knots is 42 tonne. Calculate the speed of the ship if the consumption is reduced to 28 tonne per day, & the specific consumption at the reduced speed is 18% more than at 17 knots.

Q a) Describe the effect of Cavitation on:

i. The thrust and torque

ii. The propeller blades

b) A ship 150 m long and 19 m beam floats at a draught of 8 m and has a block coefficient of 0.68.

i. If the Admiralty Coefficient is 600, calculate the shaft power required at 18 knots.

ii. If the speed is now increased to 21 knots, and within this speed range resistance varies as speed³,

find the new shaft power.

Q a) State what is meant by floodable length illustrating your answer by drawing a typical curve of floodable length of a ship.

b) A vessel has a maximum allowable draught of 8.5 m in fresh water and 8.25 m in sea water of 1.026 t/m³, the TPC in the sea water being 27.5. The vessel is loaded in river water of 1.012 t/m³ to draught of 8.44 m. If it now moves into sea water, is it necessary to pump out any ballast and if so, how much?

Q a) Describe the ways in which an unstable ship can be made stable.

b) When a mass of 25 tonnes is shifted 15 m transversely across the deck of a ship of 8,000 tonnes displacement, it causes a deflection of 20 cm in a plumb line 4 m long. If the KM = 7 m, calculate the KG.

Q a) Explain why the bilging of empty double bottom tanks below the water line leads to an increase in GM.

b) A ship of 10,000 tonnes displacement has GM=0.5 meters. The period of roll in still water is 20 seconds. Find the new period of the roll if a mass of 50 tonnes is discharged from a position 14 meters above the centre of gravity.

Q A box shaped barge of uniform construction is 32 metres long and displaces 352 tonnes when empty, is divided by transverse bulkheads into four equal compartments. Cargo is loaded into each compartment & level stowed as follows:

No.1 hold – 192 tonnes No.2 hold – 124 tonnes

No.3 hold – 272 tonnes No.4 hold – 176 tonnes

Construct load & shearing force diagram, before calculating the bending moments at the bulkheads & at the position of maximum value, hence draw the bending moment diagram.

Q A ship 75 m long has semi ordinates at the load water plane commencing from forward as follows:

0,1,2,4,5,5,5,4,3,2 and 0 meters respectively.

The spacing between the first three semi-ordinates and the last three semi ordinates is half of that between the other semi-ordinates. Find the position of the Centre of the floatation relative to amidships.

Q A ship of 3,000 tonnes displacement 100 m 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 & aft is to be not less than 0.3m.

Q a) How the distribution of mass within the ship affects the rolling period?

a) A ship of 14000 tonne displacement is 125 m long and floats at draughts of 7.9 m forward and 8.5 m aft. The TPC is 19, GML 120 m and LCF 3 m forward of midships. It is required to bring the vessel to an even keel draught of 8.5m. Calculate the mass which should be added and the distance of the distance of the centre of the mass from midships.

Q a) Describe the procedure for speed, power and fuel consumption trials.

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 2550 kW. Calculate:

i. Indicated power

ii. Effective power

iii. Ship speed

Q a) Describe the factors to consider in order determining whether a list is due to a negative GM or to uneven distribution of masses in a ship.

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

i. Just clear of the deck

ii. At the derrick head

iii. In its final position