March 10
12) With reference to structural fire protection in passenger ship accommodation
space
a) Define the meaning of Class A bulkhead
(3)
b) Discuss the design of ventilation systems to prevent the spread of smoke and
fire.
(5)
c) Where A class bulkheads have to be penetrated explain how the integrity of
the bulkhead is retained with respect to ventilation trunkings.
(2)
a) Class A Bulkhead
a. are constructed of steel or other equivalent material;
b. are suitably stiffened;
c. and are insulated with approved non-combustible materials such that
the average temperature of the unexposed side will not rise more than
140 C above the original temperature, nor will the temperature, at any
one point, including any joint, rise more than 180 C above the original
temperature, within 60 min.
b) Precautions must be taken to maintain the fire integrity of bulkheads and
decks through which trunking passes and to reduce the likelihood of smoke
and hot gases passing from one space to another. This is achieved by using
suitable materials, in conjunction with sleeves and dampers where ducts pass
through divisions. The dampers must operate automatically but must be
capable of being closed manually from both sides of the division. The damper
must be provided with an open-closed indicator .
c) Ducts with a cross sectional area exceeding 0.02 m2 passing through A Class
divisions must be fitted with an insulated steel sleeve unless the duct is of
steel in way of the division. Ducts with a cross sectional area exceeding 0.075
m2 must be fitted with fire dampers where they pass through A Class
divisions.
13)
a) Describe, with the aid of a sketch, how a hydraulically operated folding hatch
cover opens and closes.
(7)
b) Explain how the water tightness and security of the hatch cover sketched in
Q13a can be ascertained before proceeding to sea.
(3)
, a) The hatch illustrated comprises a pair of covers operated by an external
pinned hydraulic cylinder for opening and closing. An internal cylinder may be
fitted at cross joints between the panels.
when in the closed position a part of the rail can be retracted down so that the
end of the wheel lowers down and allows a neoprene seal in the hatch edge to
press down on the coaming rail bar to make the watertight seal.
The cross joints press together when it closes and a flat bar engages on
the neoprene seal for water tightness, a locator block ensures
alignment of the joint.
Weight
Cover Cleats are fitted to the hatch sides for sealing
bearing
pads Cleat
Neoprene
Coaming
b) Methods of checking weather tightness would be:
hose test - impact jet on seals from one metre distance - inspect
chalk test - on top of bar that the hatch sealing rubber rests
ultrasonic testers are available to check the seals
inspect from inside of the closed hatch for any light penetrating.
14) Explain the method adopted in modern shipbuilding practice to prevent hull
fractures due to corrosion fatigue, making reference to the sequence of assembly
of the plating and welding and the subsequent protection on completion of
construction.
(10)
In shipbuilding practise corrosion and fatigue are tackled individually.
,Regarding fatigue the design should be strong enough to exceed limiting values - of
loading and expected number of cycles. This will require a design with adequate
section moduli of structure, with respect to computer projected modelling and historic
best design.
In fabrication, minimise ignition points such as sharp edges on notches for
longitudinals passing through floors and webs, sharp corners radiused, rough edges
smoothed, fairing attachments removed and flushed, lifting lugs left on structure if
possible, if not, cut off smoothly. Butt welds should be used where possible instead
of fillet welds – it has been shown fillet weld are more susceptible to corrosion
fatigue.
Correct welding sequences reduce distortion and limits residual stress which
otherwise may encourage cracking. Generally when welding plates of units it is
better to weld central butts (vertical joints) and seams (horizontal joints) of the whip
than work outwards transversely and longitudinally. At cross joints, weld butts first,
gouge through the seam and weld. Stiffening structure across seams and butts are
welded after the shell has been welded.
Cleaning by abrasive blasting causes a peening effect on the surface which leaves a
fine layer of compressive stress which reduces the chances of fatigue crack initiation
– which requires tension.
Steel for construction should be blast cleaned and immediately primed prior to
fabrication to give the best subsequent paint protection, final protective coatings are
applied after fabrication – epoxy based coating are hard and give good protection.
Cathodic protection systems are fitted on completion of construction.
July 10
12) State with reasons, the actions to be taken if a vessel exhibits sluggish heavy
rolling and poor directional stability in a moderate sea, after enduring a period of
severe weather.
(10)
If the ship is heavily rolling (wallowing) after being in heavy seas there a likelihood of
structural damage to the hull, hatch covers, ventilators etc. This would allow water
ingress which could reduce stability (free surface effect). Sounding bilges will give
an indication of any such damage.
Free surface in ballast tanks could be eradicated by pumping out or pressing up
(load condition permitting).
Checking other spaces for water ingress e.g. chain (spurling) pipe covers to the
chain locker, air pipes and sounding pipes to tanks will indicate any structural
damage affecting the stability) and there may also be a problem of increased trim by
the head with more green seas being taken on forward, exacerbating the problems.
, Generally, even keel is the desirable sailing condition, but if there is a trim, it is better
to be by the stern. In this condition, there would be less likelihood of propeller/rudder
emerging, thus giving better power/steering.
A trim by the head would cause more green seas to be taken over the bows making
the condition worse. However, if flooding occurred aft, a severe trim by the stern
could make directional stability worse and broaching could occur.
Any list would reduce the roll angle at which deck edge immersion would occur,
hence any list should be corrected to provide the maximum angle off heel to deck
edge immersion
Reducing main engine speed would lessen the impact effect of the seas and thus
reduce the possibility of structural damage, particularly at the fore end. Ship motion
behaviour would generally be better and the change in speed would cause a change
in the periodic time of wave encounter which would reduce resonant motions if they
had been occurring.
13) Outline the essential information to be supplied to the drydock management prior
to drydocking a vessel.
(10)
Essential information that would be sent to drydock management prior to drydocking.
Name of vessel and IMO number and vessel specification
Date required to dock vessel and number of days to complete docking
Drydock repair contract, this would detail who would be legally responsible for all
aspects covering safety in dock. This would include gas freeing certificates, hot work,
staging and lifting.
Docking Plan
Drydock repair specification including all survey items to be completed
List of Specialised contractor to be employed by vessel directly
Contact numbers for vessel and technical manager in charge of repair
Number of personnel remaining on board
Shore power required and location of connection
Fresh water requirement and connection location
Cooling water requirement if staying on ships power
Sludge connection location
Access points to ship for gangways (2 points required)
Method of waste collection and disposal of shipboard generated waste.
Sewage disposal method to be adopted in dock
Essential information supplied to drydock management prior to docking (this
assumes that the company has awarded contract to yard, docking plan has been
followed and repair list has been approved) will include the following items;
Copy of Gas free certificates for empty fuel tanks, etc. that are to be worked in
drydock (for tanker vessels gas free certificate).
