LECTURE NOTES ON SHIP CONSTRUCTION Ship Construction – General General knowledge of the principal structural members of a ship and the proper name for the various parts is essential for controlling the operation of the ship and care for persons on board at the operational level and to Maintain seaworthiness of the ship and actions to ensure and maintain the watertight integrity of the ship are in accordance with accepted practice. Stability conditions comply with the IMO intact stability criteria under all conditions of loading. UNDERSTANDING THE VARIOUS STRUCTURAL MEMBERS: i. Bracket – support the girder, etc ii. Bulkheads – a vertical partition between compartments iii. Center girder – In lieu of longitudinal, provide longitudinal strength . Longitudinal framing in DB – iv. Floor – A vertical athwartships member in way of the double- bottom. It will run from the center girder out to the margin plate on either side of the vessel. v. Frame – Internal support member for the shell plating. Vessel may be framed longitudinally or transversely. vi. Gusset – triangular plate for joining angle bar to a plate vii. Intercostals Side girder – A side girder in the fore and aft line sited either side of the keel. Integral connection with the tank top and the ship’s bottom plating and rigidly connected by floors viii. Keels – center line plate from stem to the stern frame.
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LECTURE NOTES ON SHIP CONSTRUCTION
Ship Construction – General
General knowledge of the principal structural members of a ship and the
proper name for the various parts is essential for controlling the
operation of the ship and care for persons on board at the operational
level and to Maintain seaworthiness of the ship and actions to ensure
and maintain the watertight integrity of the ship are in accordance with
accepted practice. Stability conditions comply with the IMO intact
stability criteria under all conditions of loading.
UNDERSTANDING THE VARIOUS STRUCTURAL MEMBERS: i. Bracket – support the girder, etc
ii. Bulkheads – a vertical partition between compartments
iii. Center girder – In lieu of longitudinal, provide longitudinal strength
. Longitudinal framing in DB –
iv. Floor – A vertical athwartships member in way of the double-
bottom. It will run from the center girder out to the margin plate
on either side of the vessel.
v. Frame – Internal support member for the shell plating. Vessel may
be framed longitudinally or transversely.
vi. Gusset – triangular plate for joining angle bar to a plate
vii. Intercostals Side girder – A side girder in the fore and aft line sited
either side of the keel. Integral connection with the tank top and
the ship’s bottom plating and rigidly connected by floors
viii. Keels – center line plate from stem to the stern frame.
. Flat plate keels – Generally used keel. Center girder is
attached to the keel and inner bottom plating by continuous
welding and no scallops permitted
a. Duct keels – a form of flat plate keel with tow center girder.
Often fitted between collision bulkhead and forward engine
room bulkhead to provide tunnel for pipes and additional
buoyancy.
ix. Lightening holes – holes cut into floors or intercostals to reduce
weight and to provide access to tank areas
x. Longitudinal – A fore and aft strength member connecting the
athwartships floors. It must be continuous for ship > 215m.
Additional longitudinal are to be found in pounding area
xi. Margin plate – a fore and aft plate sited at the turn of the bilge. The
upper edge is normally flanged to allow connection to the tank top
plating, while the opposite end is secured to the inside of the shell
plate by an angle-bar connection. It provides an end seal to the
double bottom tanks, having all the floors joining at right angles,
up to the collision bulkhead.
xii. Panting beams – athwartships members in the forepart introduced
to reduce the in & out tendency of the shell plating, caused by
varying water pressure on the bow.
xiii. Panting stringers – internal horizontal plates secured to the shell
plating and braced �� athwartships by the panting beams.
xiv. Scantlings – used to indicate the thickness of plates, angles and
flanges.
xv. Sheer strake – the continuous row of shell plates on a level with
the uppermost continuous deck.
VARIOUS STRESSES ENCOUNTERED BY A SHIP
Bending, Shear, Hogging, Sagging, Racking, Pounding, Panting. DEFINITIONS: HOGGING When the peak of a wave is amidships, causing the hull to bend so the ends of the keel are lower than the middle. The opposite of sagging. SAGGING: When the trough of a wave is amidships, causing the hull to deflect so the ends of the keel are higher than the middle. The opposite of hogging.
PANTING:
The pulsation in and out of the bow and stern plating as the ship alternately rises and plunges deep into the water POUNDING: Pounding, as a boat will do in short seas when the bow lifts clear of the water then comes crashing down. The term is local to English ports on the North Sea. RACKING: The effect of distortion of a vessel into a parallelogram shape due to the low transverse strength of the vessel is called as racking. Racking stress occurs in a seaway when the vessel is sailing in heavy weather and encountered heavy accelerations due to roll and heave.
Racking stress and its causes
In a seaway as a ship rolls from one side to the other the different areas
of the ship have motion which are dependent on the nature of the subject
area. The accelerations are thus not similar due to the various masses of
the different sections (although joined together). These accelerations on
the ships structure are liable to cause distortion in the transverse
section. The greatest effect is under light ship conditions.
Local Stresses
Panting
This is a stress, which occurs at the ends of a vessel due to variations in
water pressure on the shell plating as the vessel pitches in a seaway. The
effect is accentuated at the bow when making headway.
Pounding:
Heavy pitching assisted by heaving as the whole vessel is lifted in a
seaway and again as the vessel slams down on the water is known as
pounding or slamming. This may subject the forepart to severe blows
from the sea. The greatest effect is experienced in the light ship
condition.
Stresses caused by localized loading
Localized heavy loads may give rise to localized distortion of the
transverse section.
Such local loads may be the machinery (Main engine) in the engine room
or the loading of concentrated ore in the holds.
xvi. Panting beams – athwartships members in the forepart introduced
to reduce the in & out tendency of the shell plating, caused by
varying water pressure on the bow.
xvii. Panting stringers – internal horizontal plates secured to the shell
plating and braced athwartships by the panting beams.
xviii. Sheer strake – the continuous row of shell plates on a level with
the uppermost continuous deck.
SOME IMPORTANT QUESTIONS & ANSWERS:
Q. describes racking stress and its causes
Q. describes what is meant by 'panting' and states which parts of the ship is affected
Q. describes what is meant by 'pounding' or 'slamming' and states which part of the ship is affected
Q. describes what is meant by 'hogging' and by 'sagging' and distinguishes between them
Q. describes the loading conditions which give rise to hogging and sagging stresses
1. Describe the circumstances which cause panting and pounding
stresses.
i. Panting stresses is an in and out motion of the plating in the
bows of a ship and is caused by unequal water pressure as the
bow passes through successive waves.
ii. Pounding stresses is exist when ships is pitching. Ship’s bows
lift clear of the water and come down heavily. It causes damage
to the bottom and girder at the bow.
2. Sketch a transverse section through the forward part of a large
cargo vessel, showing the structural arrangements which resist the
stresses.
i. Panting stress
Tiers of panting beams are fitted forward of the collision
bulkhead below the lowest deck. These are similar to deck
beam and are connected to frames by beam knees, but are
only fitted at alternative frames. Tiers of beams are spaced 2
meters apart vertically and supported by wash plates or
pillars.
Panting stringers, similar to deck stringers, are laid on each
tier of beams.
To stiffen the joint between each beam and the inner edge of
the stringer, the plate edge may be shaped or gussets fitted.
At intermediate frame without beams, the stringer is support
by a beam knee of half its depth.
At fore ends, the stringers are joined by flat plate called
“Breasthooks”.
ii. Pounding stress is resisted by strong cellular double bottom.
For a large cargo vessel, longitudinally framed bottom is used.
The outer bottom plating covering the flat of the bottom must
be thickened.
The connections of the shell and inner bottom girder-work
are made stronger
Plate floors are fitted at alternate frames
Longitudinal are stronger than normal
Side girders are no more than 2.1 meters apart.
Members compensating stress
Racking Heavy weight
Water pressure
Local Stress
Hoging & Sagging SF BM Dry-
docking Pounding Panting
Beam knee � � �
Beams � � � �
Bulkheads � � � � � �
Decks � � � � �
Floors � � � � � �
Frames � � � �
Long' girders � � � � �
Pillars � � � �
Shell plating � � � � � � � � � �
SOME MORE EXAMINATION QUESTIONS
i. Describe the circumstances which cause panting and pounding
stresses.
a. Panting stresses is an in and out motion of the plating in the
bows of a ship and is caused by unequal water pressure as
the bow passes through successive waves.
b. Pounding stresses is exist when ships is pitching. Ship’s
bows lift clear of the water and come down heavily. It causes
damage to the bottom and girder at the bow.
ii. Sketch a transverse section through the forward part of a large
cargo vessel, showing the structural arrangements which resist
the stresses in (1).
a. Panting stress
i. Tiers of panting beams are fitted forward of the
collision bulkhead below the lowest deck. These are
similar to deck beam and are connected to frames by
beam knees, but are only fitted at alternative frames.
Tiers of beams are spaced 2 meters apart vertically
and supported by wash plates or pillars.
ii. Panting stringers, similar to deck stringers, are laid on
each tier of beams.
iii. To stiffen the joint between each beam and the inner
edge of the stringer, the plate edge may be shaped or
gussets fitted.
iv. At intermediate frame without beams, the stringer is
support by a beam knee of half its depth.
v. At fore ends, the stringers are joined by flat plate
called “Breasthooks”.
b. Pounding stress is resisted by strong cellular double bottom.
For a large cargo vessel, longitudinally framed bottom is
used.
i. The outer bottom plating covering the flat of the
bottom must be thickened.
ii. The connections of the shell and inner bottom girder-
work are made stronger
iii. Plate floors are fitted at alternate frames
iv. Longitudinal are stronger than normal
v. Side girders are no more than 2.1 meters apart.
iii. Sketch a longitudinal section of a bulk carrier, showing and
naming all the main compartments. // Explain the reasons for
this arrangement of compartments.
a. Large, clear holds without tween deck – to load and
discharge cargo quickly
b. Large hatches with steel covers for safety
c. Engine place aft
d. Topside tank – enable water ballast to be carried high up to
reduce GM
e. Sloping side tanks at the bilge – assist in handling bulk
cargo since it helps the self-trimming of cargo
iv. List the structural members of a ship which are designed to
resist the main longitudinal stresses in a ships hull. // State
briefly how structural continuity is maintained in these
members to enable them to perform their designed function.
a. Longitudinal stress: hogging, sagging
b. Longitudinal work in the double bottom:
1. Deck stringer and sheer-strake thicken
2. Deck girder and longitudinal bulkhead
3. Special steel for sheer-strake and bilge strake
4. Longitudinal frames and beams in the bottom
and under the strengthen deck
5. Stress is greatest amidships, so strengths of the
parts is made greater amidships
c. Hull is strengthen at about the half-depth of the ship to
resist the shearing stress
v. It is useless to make one part very strong if an adjacent part which
has to resist the same stress is weak. Hence, it is important to
maintain structural continuity
vi. When material has to be cut away, compensations must be made
to preserve continuity of strength. Square corners should be
avoided as far as possible since it has been found that these are
always a source of weakness.
vii. Parts which are very strong compared to the neighboring parts
should not be ended suddenly, as there would be a tendency for
them to tear away where they end. They should be gradually
tapered off ���� and merge into the weaker parts.
viii. List the functions of : bilge wells, stern tubes.
a. Stern tube: to support the shaft and to make a watertight
joint where the shaft enters the hull.
i. Steel tube. The fore end with flange bolted to after
peak bulkhead and a large nut in aft end
ii. Inside tube, a brass bush which has grooves in it
iii. Strips of lignum vitae in grooves act as bearing for
shaft
iv. Studding box to prevent water getting into hull
b. Bilge well: when the cellular double bottom extends out to
the ship’s side there are no proper bilges. In this case the
holds drain into bilge well, which are sunken compartments
in the double bottom. It is to collect water from rain, cargo