FEBRUARY 2017

NAVAL ARCHITECTURE
TIME ALLOWED - 3 HOURS

1. Answer SIX questions only. THREE from each section

2. All questions carry equal marks.
3. Neatness in handwriting and clarity in expression
carries weightage
4. Illustration of an answer with clear sketches /
diagrams carries weighAGE
5. All unused pages of answer script must be
cancelled out by two lines (X) across the page.

Q1. With reference to membrane tanks for the carriage of liquefied

gas at very low temperatures. A. Describe with a sketch one
method of building up the insulation; B. State which alloy is used
for the membrane and the reason; C. Explain why a secondary
barrier is installed. i) Longitudinally; ii) Transversely

Answer:-Membrane tanks are of rectangular form and rely on the

main hull structure for their strength. A very thin lining (0.5 mm to
1.2mm) contains the liquid. This lining must be constructed of low
expansion material or must be of corrugated form to allow for
changes in temperature. The lining is supported by insulation which
must therefore be load-bearing

Several types on insulation are acceptable, such as balsa wood,

polyurethane, pearlite, glass wool and foam glass
Indeed, the primary barrier itself may be constructed of
polyurethane which will both contain and insulate the cargo. Usually,
however, the primary barrier is of low-temperature steel or of
aluminium, neither of which become brittle at low temperatures

(b) The alloy used for the membrane tank is invar alloy,
because of its low thermal expansion coefficient and is stable
metallurgically at low temperatures. It is a 36 percent nickel iron
alloy having a low thermal expansion and able to withstand
temperatures as low as -4500C. This alloy is of weldable
quality and hence is used in the construction of the tank
primary barrier.

(c) The secondary barrier is the main support for the primary
barrier which is the membrane tank containing the liquefied
gas. The secondary barrier consists of the insulation together
with the internal steel framing for strength. If the gas leaks
into the secondary barrier the low temperature experienced
by the steel will cause brittle fracture to the steel framing
and hence the steel internal framing as well as the inner
bottom and side shell are made of Arctic steel which has
good resistance to brittle fracture occurring at low
temperatures. the internal framing consists of transverse(floors)
and longitudinal(intercostals) frames all of which are made of
Arctic steel.

Q2. With reference to dry docking define the responsibility of the

2nd engineer prior to dry dock; Whilst the vessel is in DRYDOCK;
Prior to flooding and leaving th
Answer:- (a)The second engineer’s supervision and check are
required in the following operations during docking.
  Observe the clinometers in engine room to see that ship
is upright during docking.

 Carry out any transfer of F/O, F/W or/and L/O in

accordance with instructions from MASTER.

 Keep list of jobs to shown to the repairs manager which

are to be carried out in D/D. The repair order giving the
list may be highlighted in colour for identification.

 Designate the 3rd engineer or 4th engineer to mark all

sea suction and discharge valves for overhaul and survey
to the repair staff section head .

 If there is a propeller shaft withdrawal for survey , then

get the special propeller withdrawal strong back set,
poker gauge and drawings ready for handing over to the
propeller withdrawal team section head.

 Instruct the ships electrical officer to supervise the shore

connection and also verify if the earth connection is
properly established. He should also note the shore
power meter reading before shore current commences.

(b)During the stay in dry dock he should personally

supervise the following jobs being carried out in the dry
dock.
* Sea suction and discharge valves
* High , low sea suction and emergency fire pump
sea suction boxes opening , cleaning, painting and final
refitting..
 * Rudder drop, pintle clearances, jumping
clearance.
and any repairs to rudder.
 Propeller drop and supervision during propeller
shaft withdrawal if carried out.
 propeller polishing and repairs to propeller blades
if any
(c)BEFORE AND WHILST UNDOCKING
(1) Bunkers should not be taken when the ship
is on the blocks. In cases where ships sail out
immediately after dry docking, bunkers are to
be supplied after the ship has undocked and
is floating.
(2) Shore power cables are to be connected after
the ship has docked and the dock is dry. The
cables should be disconnected before flooding
the dock.
(3) During flooding of the dock, the flooding is
stopped when the level of water in the dock
reaches just above the high suction box. All
the sea suction valves under the floor plates
should be checked for any leaks. In this
situation the ship is not floating and is still
sitting firmly on the blocks. This verification is
necessary to avoid any mistakes made by
shipyard staff whereby some valves have not
 been fitted their cover joints and gland
packings. A second docking can be avoided by
this check.
(4) The Master c/o , C/E and 2/E should visit
the dry dock before flooding and verify the
following before giving orders for flooding :-

(a) The rudder fastening bolts are

tight and cemented, the pintle
cover plates are in place and
welded.
(b) The propeller cone fitted and all
bolts cemented.
(c) The rope guard in place and
properly welded
(d) The sea suction box grids fitted
and locked with locking wire.
(e) Bilge keel repairs are
completed.
(f) Both anchors hoisted and
housed in their respective
hawse pipes.
F/W can be supplied in the dry dock as required , but it
should be ensured that the soundings of F/W tanks at
the time of un-docking is the same as soundings when
docking.
Q3. A. Sketch the cross-section of a bulk carrier with either deep or
shallow double bottom showing the type of framing used; B.
Describe the corrosion problems experienced with ballast tanks;
C.State how such tanks are protected against extensive corrosion.

Answer:-

(b) The bulkcarrier carries a large amount of ballast water

during the ballast leg of a voyage and the water being sea
water is acidic in composition and causes corrosion of the
internal surfaces of the tanks, especially wherever the
protective coating is destroyed. The tanks are alternately in
full and empty conditions . This leads to some amount of
erosion of the coating by frequent flow of the water in the
tank. Corrosion is basically caused by air present in the tank
leading to rust formation of the exposed portion of the
surfaces where the protective coating is damaged. Galvanic
corrosion is also present in small effect because of the
dissimilarity in the metal quality between frames and the
plating.

(c) Protection against corrosion is provided by the application

of coal tar epoxy to a good thickness after proper
preparation of the internal surfaces. Together with this the
tanks are fitted within zinc anodes internally to prevent
galvanic corrosion.

Q4. A. Describe the preparation necessary before the application

(in day dock) of sophisticated or approved long life coating to the
underwater surface of the hull; B. State the significance of the
roughness profile. C. List the different sophisticated coating which
are available.

Answer:- (b)The preparation necessary is as follows:

(1) The under water areas are scraped clean using stel
scrapers to remove the barnacle growth and sea weed sticking
to the underwater hull. This operation is best done when the
water from the dry dock is being pumped out before the
surface becomes dry.

(2) The heavily scaled areas or strakes are grit blasted till
the colour of the plate conforms to a standard as contracted.
The grade of grit blasting is based on Swedish colour code
composed by the association of ship coating contractors and
goes by the numbers SA2, SA2.5, SA3 , SA3.5. The corresponding
colour backgrounds are brown, black, grey and silver. The highest
grade indicates 100 percent scale removal. The grit pellets are
blasted on the surface at high velocity using an air gun. Grit is
pelletised mill slag.
(b) Measuring Hull Roughness

The hull roughness of the ship can be determined by a tool known as

hull roughness analyzer or similar instrument for those ship which are
not coated with silicon based foul release paint coating.

If the ship’s hull is coated with silicon based paint, speed trails are done
to determine hull roughness which gives changes in the performance
and speed of the ship. Understanding Hull Roughness
Analyzer

A Hull Roughness Analyser (HRA) consists of a portable

microprocessor along with a digital printout and display unit.

A computer is connected to the hand held carriage having a stylus

measuring head.

The stylus head is moved around the hull surface to measure and record
the hull roughness profile.The short wave roughness is the diameter of
the stylus tip. The long wave cut off is set at 50 mm.

Working of Hull Roughness Analyzer (b) Measuring Hull

Roughness

The hull roughness of the ship can be determined by a tool known as

hull roughness analyzer or similar instrument for those ship which are
not coated with silicon based foul release paint coating.

If the ship’s hull is coated with silicon based paint, speed trails are done
to determine hull roughness which gives changes in the performance
and speed of the ship.
Understanding Hull Roughness Analyzer Hull Roughness
Analyser (HRA) consists of a portable microprocessor along with a
digital printout and display unit
A computer is connected to the hand held carriage having a stylus
measuring head The stylus head is moved around the hull surface to
measure and record the hull roughness profile.The short wave
roughness is the diameter of the stylus tip. The long wave cut off is set at
50 mm
Working of Hull Roughness Analyzer
samples having length of 50 mm.
For each 50 mm sample, the micro processor will assess the mean
gradient through the peaks and valleys to give highest peak to lowest
valley measurement for that sample.One traverse of the head at any
point on the hull will collect information from 10 samples having length of
50 mm. For each 50 mm sample, the micro processor will assess the
mean gradient through the peaks and valleys to give highest peak to
lowest valley measurement for that sample.This measurement is known
as Rt (50).The roughness check covers approx 100 selected
locations which must include bow, stern, mid ship, and boot
topping area (area between load line and ballast water line).A
number of traverses for stylus will give ‘n’ readings, hence the
Mean Hull Roughness (M.H.R) at that station is average of
Rt (50) i.e.M.H.R = ∑Rt(50)/ n

(c) TABLE+: Paints used in various structures Area of Type of paint

system shops 1st choice 2nd choice 3rd choice I. Under water
Epoxide Oleoresinous Chlorinated rubber 2.Boot topping Chlorinated
Epoxide Oleoresinuos rubber 3. Top side Epoxide Oleoresinous
Chlorinated rubber and vinyl paints 4. Super Oleoresinous
Polyurethane -dostructure 5. Weather deck Epoxide Oleoresinous -
doPaint should conform to minimum specifications: (1) Freedom
from undue settlement, thickening or gas evolution on storage (2)
Freedom from skinning (3) Ease of application by brush or spray or
roller (4) Minimum drying time for repainting (5) Freedom from
unreasonable health or safety hazards. The coatings used in
underwater paint system and the minimum :hickness required are
given below: rype of paint Minimum DFT @I) -- -- I. Bitumen or pitch
pigmented with aluminium powder !. Oleoresinous I. Epoxide resin I.
Coar tar epoxide resin i. Vinyl resin 1. Chlorinated rubber High
performance protective paint systems The long periods in service
with short maintenance periods are necessary for economical
operation and for this high performance coating systems are
required These are based on the newer types of non-saponifiable
resins such as epoxies, vinyls and chlorinated rubber which resist the
alkaline conditions associated with cathodic protection and are in
general applied at a dry film thickness of 100 p per coat. The coatings
depend mainly ot their high film thickness for their protective
properties and provide resistance inhibition, chemical inhibitive
properties being of sccondary importance. Typical systems have a
total dry film thickn-ss of 300 - 400 u and are obtained by air-less
spray in 3 or 4 coats.

Q5. A. With regard to ship construction details for transverse

watertight bulkheads: - i. State the purpose of this type of
bulkhead; ii. State how the bulkheads are tested for water
tightness B. If it is necessary to penetrate the bulkhead, precaution
must be taken to ensure that the watertight integrity and the
strength of the bulkhead are maintained. With this in mind,
describe, using simple sketches, how the following pass through
bulkheads - i. Main transmission shaft; ii. Electrical cables; iii. Fuel
oil transfer pipes; iv. Air and sounding pipes.

Answer:- The purpose and usefulness of transverse bulk heads

are given under:

 They provide and improve the residual buoyancy

of the ship.
 They contribute to the shear strength of the hull
structure.
 They give separation to cargo and ;prevent mixing
of cargo.
 They isolate a fire in the cargo compartment and
so should be considered as a structural fire
protection.

(b) Water tight transverse and longitudinal bulk heads are

tested during construction of the ship by filling seawater
upto the main deck level with tghe other side of the hold
empty. This proves the water tight integrity of the bulkhead.
During the service life of the ship, if any part renewals of the
bulkhead are carried out, the part renewed is tested by sea
water hose pressure applied on the welding seams.
Q6. Describe how water tightness is maintained where bulkheads
are pierced by longitudinal beams or pipes.

Answer:-The longitudinal strength which resists bending

moments on the hull structure are critical and important for
the longitudinal strength opf the ship. Hence the longitudinal
deck girders must be maintained continuous and when
piercing the bulheads the bulk heads are to be cut accordingly
to allow the girder section to pass through. The ga[p
provided is then closed to water tight condition by suitable
welding.
 The sketch shown under is an example of the deck
girder passing through the trunk of the corrugated bulkhead.

For pipe passing through the bulkhead refer to sketch shown in

Q 5 of this same question paper
Q8. Describe the procedure adopted for the speed trials of a ship
and analysis of the results. What are the precautions to be taken?

Answer:- Answer:- Before proceeding on speed and

endurance trials , it is required that the weather is fine
and calm. These tests will not be conducted even in
moderate weather. The speed trials are done in
accordance with the MOU describing the methodology of
conducting the speed trials. In the building contract the
ships guaranteed speed at SCR in full loaded draft
conndition is given. . This condition however cannot be
fulfilled as the ship will be in ballast condition. In order to
satisfy the requirement of draft an acceptable empirical
formula to ogive the ballast speed condition related to the
SCR at loaded condition is derived and used as per the
empirical formula.
The speed test may be required to be done for SCR as
well as MCR and hence both the speed tests are done
concurrently.
The speed test is done for about 8 repeated runs
on a measured nautical mile in both directions so that the
effect of the tidal current is neutralised. The average of
the 8 runs or laps is the resultant speed
The measured mile is chosen by selecting two
land marks identified on the nautical chart and very close
to a nautical mile. The stop watches are used to start and
stop the clock when the vessel is abeam of the land
marks and this is verified by the compass Azimuth
repeaters placed on the ships bridge wings on port and
starboard side.
ENDURANCE TEST:- The endurance test lasts for about 4
hours and is carried out immediately after the speed trials
which last for about 2 hours.
During the endurance test the main engine is run at
SCR speed and accordingly the RPM of the engine is set.
The engine is sufficiently warmed up to be changed over
to heavy fuel. The speed trials are done on marine diesel
oil. During the endurance run the exhaust boiler will be
on. On the main engine the following readings are
recorded and becomes the part of the test report.

 Exhaust temperatures of each unit.

 C/W outlet temperature of each unit.
 Piston cooling oil outlet temperature of each unit.
 Lub-oil temperature and pressure., inlet to engine
and outlet from engine.
 Luboil cooler inlet and outlet temperature.
 JC/W inlet and outlet temperature.
 T/C RPM.
 T/C air cooler air temperature before and after
cooler
 Pressure drop across air cooler.
 Pressure drop across air filter.
 Scavenge air temperature and pressure.
*RPM counter reading of main engine at commencement
of endurance test.
* RPM counter reading at end of endurance test.
* fuel meter reading in liters at commencement of
endurance test.
* Fuel meter reading at end of test.
The indicator Power and Draw cards for each unit is
recorded to calculate the power produced during the
endurance test and from that the SFOC is calculated.
If it is contracted to prove the torsional vibration
characteristics calculations , then the electronic torductor
with the oscilloscope is fitted on the shaft and the
characteristics of the vibration amplitude at the critical
speed as well as the vibration amplitude at SCR is
recorded and verified that ithey are close to the calculated
results..

Q9. What do you understand by the effective power of a ship?

Describe the stages by which the power produced by the main
engine of the ship is transformed into the effective power. Discuss
the essential sea trials maneuvers (navigation trials) conducted and
typical objectives of each test.

Answer:- The power produced by the engine is the indicated power

Ip. The mechanical efficiency of the engine is usually between about
80% and 90% and therefore only this percentage of the ip is
transmitted to the shaft, giving the shaft power sp or brake power
bp.

Sp or bp = ip X mechanical efficiency

Shaft losses vary between about 3% and 5% and therefore the power
delivered to the propeller, the delivered power dp, is almost 95% of
the sp.
 dp = sp x transmission efficiency

The delivered power may be calculated from the torque on the shaft

dp = torque x 2∏n

The propeller has an efficiency of 60% to 70% and hence the thrust
power tp is given by:

Tp = dp x propeller efficiency

The action of the propeller in accelerating the water creates a

suction on the after end of the ship. The thrust exerted by the
propeller must exceed the total resistance by this amount. The
relation between thrust and resistance may be expressed in the form

R1 = T (1 - t)

Where t is the thrust deduction factor.

The thrust power will therefore differ from the effective power. The
ratio of ep to tp is known as the hull efficiency which is a little more
than unity for single screw ships and about unity for twin screw
ships.

Ep= tp x hull efficiency

In an attempt to estimate the power required by the machinery from

the calculation of ep, a quasi propulsive coefficient QPC is
introduced. This is the ratio of ep to dp and obviates the use of hull
efficiency and propeller efficiency. The prefix quasi is used to show
that the mechanical efficiency of the machinery and the transmission
losses have not been taken into account.

Ep = dp x QPC

The true propulsive coefficient is the relation between the ep and ip,
although in many cases sp is used in place of ip
 Ep = ip x propulsive coefficient

Ep = sp x propulsive coefficient.

The essential sea trial manoeuvres and their tests are

 Crash stop test

 Turning circle manoeuvre and its recording
*Anchoring test

Crash stop Test :-After the endurance test is completed the

crash test is carried out. The ship is running at the
service speed when the double ring astern is rung and
the time recorded. The position of the ship also marked
on the chart.
The engine room will take some time to respond ,
since the engine will respond to reverse movement only
after the engine has stopped turning. With engine now
responding at full astern speed , the progress of the ship
ahead is arrested and the time it comes to complete halt
is noted as well as the position. This record gives the
time taken for the crash stop and the distance travelled
ahead. This information is now mandatory and the results
are printed in bold letters and exhibited on the ships
wheel house for the guidance of persons piloting the ship
Steering Test and turning circle plot:_
Answer:- The turning circle for both port and starboard
turns with ship at full service speed and the rudder at
hard port and hard starboard are plotted on the chart and
a copy of the circles with the diameters scaled is exhibited
in the wheel house for the guidance of persons piloting
the ship.
Anchoring test:- After the ship retuns to the ship yard sea
front after completing the speed and endurance tests , the
anchoring test is done..
The anchor will be dropped and the chain will be
paid out for about 5 hackles amounting to a length of 450
feet. The captain may give an astern movement for the
catenary to form easily without taking the aid of the tide.
When the ship is stationary the anchor will be hauled in
by the windlass and the time taken to bring the anchor
just above the water noted in the stop watch. The rate of
hauling in should not be less than 9 meters per minute.
When the ship is restored to its course the speed of
movement of the rudder or the rudder turning test is
carried out. The ship is to be running at the service
speed , when the rudder is turned from mid-ships to hard
port and then hard starboard and the time of travel of the
rudder from mid-ship to hard port and to hard starboard
and finally to mid-ships is recorded and checked if the
time conforms to the Reg 29 rule requirement