SEA204B1
Trim, Stability and Stress I
Module 1: Shipbuilding Materials
• Steel is an alloy of iron and various other metals, which
are used to enhance the properties (strength, resistance
to corrosion, tolerance of heat, etc.) of iron
• Ship classification
• the process of verifying ship standards against a set
of requirements including the testing
• Ship’s construction and design, survey and approval
• Lifesaving Appliances and Fire Fighting Equipment
Module 1: Shipbuilding Materials
• Testing Procedure
• Through Thickness Tensile Tests
• Dimensions
• Plates and flats
• Bars and other similar products
Module 1: Shipbuilding Materials
• Mechanical Test specimens
• Tensile Test Specimens
• Impact Test Specimens
• Additional Number of Tensile Tests
Module 1: Shipbuilding Materials
• Grades of steel
• Grade A: for ship’s superstructures, bulkheads(<20mm)
• Grade B: wrought products(rods, plates and bars)
• Grade C: fabrication of carbon steel pressure vessels and
boilers, tanks
• Grade D&E: sheer strakes/hull (high tensile strength)
Module 1: Shipbuilding Materials
• Tensile strength –the strength of the material to counter
or resist the tension applied to it.
• Ductility – maximum deformation that can be imposed
on a metal without the occurrence of cracking
• Hardness - ability of a body to resist permanent
deformation
• Toughness – materials having high strength and fracture
resistance
Module 1: Shipbuilding Materials
• Stress - It is the force per unit area applied to the material
Tensile stress = tension ÷ cross sectional area
• Strain - It is the ratio of extension to original length
Strain = Extension / Length
Example: Calculate for the longitudinal strain with the ff given:
Original Length: 50 m
After Stretching: 50.4 m
To find the extension, subtract the original length (50m) to length of the body after it was
stretched (50.4m). You will get the extension of 0.4m. Apply the formula and you will get
0.008
Module 1: Shipbuilding Materials
• Limit of proportionality – means the size of the deformation is
directly proportional to the deforming force or load
• Elastic limit – beyond this point, it will not go back to its original
length
• Elastic behaviour – it occurs when a material returns to its
original length
• Plastic behaviour – it occurs when the stretched material does
not return to its original length
• Yield point – beyond this point, small increases in force give
much big increases in length
Module 1: Shipbuilding Materials
• Modulus of elasticity - a quantity that measures an object or
substance's resistance to being deformed elastically when a
stress is applied to it
• Toughness - refers to materials having high strength and
fracture resistance
• Brittle fracture - is an unstable failure process that occurs in
fiber-polymer composite materials, metals with high strength
and low ductility, and in some metal types at low temperature
(i.e. below the ductile/brittle transition temperature)
• Stress fracture - premature failure under the influence of tensile
stresses
Module 1: Shipbuilding Materials
• Casting - is a process of heating steel, aluminum and other
metals to turn them into a liquid which is called as molten
metal.
• Sand casting – uses a mould made out of sand. It is
traditionally used for its economical features.
• Die casting – uses metal mould. It is simplified and used for
complex shapes.
• Forging – steel is heated so that it becomes soft, it can be
forced into a mould, called a die, using a very large force
Module 1: Welding
• Arc welding - is a type of welding process using an electric
arc to create heat to melt and join metals. It uses DC or AC.
• Electroslag welding - is a generally fast welding process used
to join large materials such as thick plates.
• Tungsten Inert Gas welding - uses a tungsten current form and
is usually used in industries that work with stainless steel.
• Metal Inert Gas welding - is a process of welding that uses a
gas to shield the weld metal.
Module 1: Welding
•
Butt joints welding - these are joints between parts that are generally in
line.
•
Fillet welding - refers to the process of joining two pieces of metal
together when they are perpendicular or at an angle.
•
Full fillet weld – is a weld where the size of the weld is the same as the
thickness of the thinner object joined together
•
Single-pass weld - a weld made by depositing the filler metal with a
single pass
•
Multi-pass weld - the weld metal and the associated heat-affected
zone are subjected to repeated thermal cycling from successive
deposition of filler metals
Module 1: Welding
•
Back run weld - is an additional welding pass carried out from the
opposite side of the weld joint before the main passes are laid.
•
Tack welding - places small tack welds on one side of the joint with the
filler rod.
•
Lack of fusion - occurs when there is no fusion between the weld metal
and the surfaces of the base plate.
•
Lack of root penetration – occurs when there is Insufficient heat input
and improper joint preparation.
•
Slag inclusion - are nonmetallic particles trapped in the weld metal or at
the weld interface.
Module 1: Welding
•
Porosity - caused by the absorption of nitrogen, oxygen and hydrogen in
the molten weld pool which is then released on solidification to become
trapped in the weld metal.
•
Overlap - occurs when molten metal flows over the surface of the base
material and then cools without fusing with the base material.
•
Undercut - a groove or crater that occurs near the toe of the weld.
When this weld flaw occurs, the weld metal fails to fill in that grooved
area, resulting in a weak weld that is prone to cracking along the toes.
Module 2: Bulkheads
•
Transverse Bulkheads - a partition wall of planking or plating running in
an athwartship direction across a portion or the whole breadth of a ship,
or from side to side to create compartments.
•
Purpose:
•
subdivide a ship against flooding
•
Subdivide a ship against spread of fire
•
support decks & superstructures
•
resist racking stresses
•
Bulkhead deck - the uppermost continuous deck of a ship to which all main
transverse watertight bulkheads are carried. It is usually the freeboard deck.
•
Freeboard deck - is normally the uppermost complete deck exposed to the
weather & sea
Module 2: Bulkheads
•
Collision bulkhead - is watertight up to the freeboard deck and
positioned not less than 5% of the length of the ship (or 10 metres,
whichever is the less) and not more than 8% of the length of the ship.
•
•
Consideration:
•
Factor 1: Position based on flood-able length calculations
•
Factor 2: Position based on the classification society code books
•
Factor 3: Position based on SOLAS rule, which states that the collision
bulkhead should be located aft of the forward perpendicular at a
distance not less than 5 percent of the ship’s length of the ship or 10
meters (whichever is less). The distance must also not exceed 8 percent
of the ship’s length.
Collisions bulkhead protects the ship’s floodable length in case of collision.
Module 2: Bulkheads
•
Watertight bulkheads - are vertically designed watertight divisions/walls within
the ship’s structure to avoid ingress of water in the compartment if the
adjacent compartment is flooded due to damage in ship’s hull or collision.
•
The number of transverse bulkheads in a ship depends on her length and the
position of the machinery space. Example a ship of 105 m shall have 5 or 6
bulkheads depending on position of machinery spaces. A ship of 145 m shall
be fitted with 7 or 8 bulkheads
•
Corrugated bulkheads - are made of plates having uniform thickness, usage of
corrugated bulkheads come handy due to ease in fabrication and reduction
of welded joints on the bulkhead.
•
Aft Engine room bulkhead - is pierced to allow the propeller shaft to pass
through. A Watertight gland is fitted around the shaft. Also an opening is
provided for human passage by a water tight door.
Module 2: Bulkheads
•
Longitudinal bulkhead – is a partition wall running fore and aft, made of
planking or plating. It equally subdivide the tank into two equal space.
The division of the tanks reduces the adverse effect of the free surface
on the vessel’s metacentric height.
•
Free surface - is the surface of a fluid that is subject to zero parallel shear
stress, such as the interface between two homogeneous fluids, for
example liquid water and the air in the Earth's atmosphere.
•
When a vessel with a full tank is heeled, the liquid within the tank acts like a solid
mass
•
When a vessel with a partially-filled tank is heeled, the liquid will seek to remain
parallel with the waterline. The centre of gravity of the liquid, being the centre of its
volume, will move with the liquid and can have a considerable effect upon the
vessel’s stability. It will reduce the metacentric height thereby the stability.
Module 2: Watertight and Weather tight doors
•
Watertight doors - are installed to prevent the ingress of water from one
compartment to another during flooding. They are usually located at
the bottom part of the ship where the engines and shaft tunnel are
found. It is tested using pressure tank to apply hydrostatic pressure.
•
Weather tight doors - are located above the waterline of the vessel.
Designed to prevent the entrance of water from outside to inside. This
generally includes a insignificant head of water. It is tested using high
pressure hose.
•
Non watertight doors - these are normal doors inside watertight
compartments. Examples are store doors, machinery doors, cabin doors,
galley doors.
Module 2: Watertight and Weather tight doors
•
Screw Gear on Watertight doors
The ship’s planned maintenance system must be followed for carrying out routine
inspection and maintenance on watertight doors which should include the correct
functioning of the whole system and specifically:
•
Warning devices and alarms
•
The electric/hydraulic mechanism
•
Valves
•
Fluid level indicators
•
Seals
•
Lights
Module 3: Watertight and Weather tight doors
• Watertight Doors Drill on Ships
•
1. Drills for the operation of watertight doors shall take place every week.
Also, the doors should be checked before leaving the port.
•
2.All watertight doors, both hinged and power operated should be
operated daily during the rounds.
•
3. The door should be able to operate from both local and remote
places. i.e. bridge and ship control centre.
•
4. If the door is operated from a remote location, there should be an
audio and visual alarm during the closing,
•
5. There should be an indication of both open and close on the remote
place of operation
Module 3: Watertight and Weather tight doors
• Watertight doors and their mechanisms and indicators, all
valves the closing of which is necessary to make a
compartment watertight and all valves for damage-control
cross-connections must be inspected at sea at least once per
week. •
• Records of drills and inspections are to be entered in the log,
with a record of any defects found and need to be rectified
immediately. When the defect have been repaired or
rectified it has to be recorded in the log book
Module 3: Corrosion and its prevention
• Corrosion - occurs when a refined metal is naturally converted
to a more stable form such as its oxide, hydroxide or sulphide
state this leads to deterioration of the material. It is a process
through which metals in manufactured states return to their
natural oxidation states.
• Erosion of Metals - occurs upon the frictional rubbing of
surfaces, wear, and cavitation, as well as upon the action of
strong gas or liquid currents upon a surface, especially at high
temperatures
Module 3: Corrosion and its prevention
• Corrosion - occurs when a refined metal is naturally converted
to a more stable form such as its oxide, hydroxide or sulphide
state this leads to deterioration of the material. It is a process
through which metals in manufactured states return to their
natural oxidation states.
• Erosion of Metals - occurs upon the frictional rubbing of
surfaces, wear, and cavitation, as well as upon the action of
strong gas or liquid currents upon a surface, especially at high
temperatures
Module 3: Corrosion and its prevention
• Anode is an electrode through which conventional current
flows into the device from the external circuit. The electrode
of a battery that releases electrons during discharge is called
Anode.
• Cathode is an electrode through which conventional current
flows out of the device. The electrode that absorbs the
electrons is called the Cathode.
Module 3: Corrosion and its prevention
• Electrolyte - is a chemical compound that dissociates into ions
and hence is capable of transporting electric charge.
• Electrolytes can be solid, liquids, or solutions
• Galvanic corrosion (dissimilar-metal corrosion) is an
electrochemical process in which one metal corrodes
preferentially, when in electrical contact with a different type
of metal, and both metals are immersed in an electrolyte such
as water.
Module 3: Corrosion and its prevention
•
Corrosion can be prevented through using multiple products and techniques including:
•
Painting: The paint forms a barrier between the metal and the environment,
namely moisture.
•
Sacrificial anodes: Utilization of a metal lower on the Galvanic Series to be
attacked first, instead of the metal in use. The sacrificial anode can be
replaced as needed.
•
Passivation: Some corrosion processes will create solid metal compounds
that will coat the initial site of corrosion and prevent further corrosion at that
site.
•
Cathodic Protection: The iron is coated with a thin layer of zinc which is
acting as a sacrificial layer for the iron. Instead of the iron corroding, the Zn
acts as the sacrificial anode in the cell and protects the iron
Module 3: Corrosion and its prevention
Some of the parts highly exposed to corrosion by sea water are:
•
Ship’s external hull – exposed to water
•
Rudder
•
Ballast Tanks
Major methods of corrosion protection:
1. Cathodic Protection – ICCP (Impressed Current Cathodic Protection)
2. Cathodic Protection – Sacrificial Anodes
Module 3: Corrosion and its prevention
• Anti-fouling paint – is a underwater hull paints (also known as bottom
paints) It is a specialized category of coatings applied as the outer
(outboard) layer to the hull of a ship or boat, to slow the growth and/or
facilitate detachment of subaquatic organisms that attach to the hull
and can affect a vessel's performance and durability.
• Typical paint schemes for:
• Underwater Hull and Boottop - Coating systems for the underwater parts
of a ship should be corrosion-inhibiting, antifouling, abrasion-resistant,
smooth, and compatible with cathodic protection.
• Topside and superstructure - an aesthetic topcoat of aliphatic
polyurethane or aliphatic polyurethane/acrylic may be used.
Module 3: Corrosion and its prevention
Typical paint schemes for:
• Paint systems for decks should be very resistant to corrosion and the
influences of weather. They should be non-slip and resistant to impact,
scratching, and abrasion, as well as resistant to (sea) water, fuel oils,
lubricating greases, cleaning agents, and cargo spills.
• most common deck coating systems are twocomponent epoxies,
polyurethanes, and zinc silicates with a DFT of 250-300 µm for
epoxy/polyurethane systems and 75-100 µm for zinc silicates.
• Ballast Tanks - Coating systems for ballast tanks should be resistant to
(polluted) seawater, corrosion inhibiting, free from pores, and resistant to
the side effects of cathodic protection. Eg. epoxy coal tar coating,
bituminous coatings and solvent-free bituminous compositions
Module 3: Corrosion and its prevention
• Sacrificial Anodes – is a type of cathodic protection system. The anode is
made from a metal alloy with a more "active" voltage (more negative
electrochemical potential) than the metal of the structure it is protecting
(the cathode).
• Generally come in three metals: magnesium, aluminum, and zinc
• Fitted within the hull, and are often fitted in ballast tanks
• Impressed current cathodic protection (ICCP)
• the ultimate state-of-the-art, long-term solution to corrosion problems, and are
recognized as a superior alternative to sacrificial anode systems, which require
frequent replacement.
• the systems work by supplying a controlled amount of DC current to submerged
surfaces using highly reliable mixed metal oxide anodes and zinc reference
electrode
Module 4: Surveys and dry-docking
Annual Surveys
1. The purpose of an Annual Survey is to confirm that the general condition
of the hull is maintained at a satisfactory level.
2. 2. Generally as the ship ages, ballast tanks are required to be subjected
to more extensive overall and close-up surveys at Annual Surveys
3. Read in Module 4
• Hull – Items to be inspected, performance test, Hull & Machinery Items Check Points
• Shell plating, Rudder, Fore and Aft Ends of the Ship, Propeller and Stern tube
• Dry docking - is one of the best opportunity to carry out inspection of hull
and other parts like propeller, rudder, etc. which are mostly under water.
Module 4: Surveys and dry-docking
Hull Painting
Step 1. WASHING Shipyard personnel use (fresh water) high-pressure
washers to remove marine growth and chlorides from the ship side.
Step 2. BLASTING Blasting is done primarily to remove rust or defective
paint from the ship side. In this process, old paint in the defective areas is
removed entirely to expose the bare steel
Step 3. PAINTING Once the blasting is completed, the entire vessel is
cleaned and painted to protect the integrity of the steel and prevent future
corrosion. The underwater side is painted with anti-fouling paint to prevent
marine growth and ensures vessel operates close to its original design
speed and fuel consumption
Module 4: Surveys and dry-docking
Paint quantities for wetted surface
Solve the wetted surface first so that we will know the quantities
of paint to use
Wetted surface = 2.58 √ ∆ L
√ = square root
∆ = displacement
L = Length
Constant = 2.58
Module 4: Surveys and dry-docking
Paint quantities for wetted surface
Solve the wetted surface if the ship has LBP of 181 m. and
displacement of 58,136 tons.
Wetted surface = 2.58 √ ∆ L
= 2.58 √ 58,136 x 181
= 2.58 √ 10522616
= 2.58 x 3243.85
= 8369.15 sq mtrs
Module 4: Surveys and dry-docking
Paint quantities for wetted surface
Solve the required paints to used if the wetted surface is 8369.15
sq mtrs and if one gallon of paint can be used an average of
27.5sqmtrs/gallon.
No. of gallons to use for wetted surface = WS ÷Area per gallon
= 8369.15 sq mtrs / 27.5 qmtrs per gallon
= 304.3 gallons
Module 4: Surveys and dry-docking
Simpson’s Rule
Simpson's rule is one of the numerical methods which is used to evaluate the definite
integral. Usually, to find the definite integral, we use the fundamental theorem of calculus,
where we have to apply the antiderivative techniques of integration. It is commonly used
to calculate areas and volumes of irregular figure.
In Simpson’s First Rule: This can be used when there are odd
numbers of ordinates.
Area under the curve = h/3(a1, + b4, + c2 + d4 + e1)
h= common interval
1,4,2,4,1= Simpson’s multiplier
Module 4: Surveys and dry-docking
Ordinates
Length
Multiplier
Product
A
0.0m
1
0.0
B
7.0m
4
28.0
C
11.0m
2
22.0
D
15.2m
4
60.8
E
19.4m
1
19.4
Total
130.2m
Common Interval (h) = 6.5 m.
h/3(a1, + b4, + c2 + d4 + e1)
= 6.5/3(0 + 28, + 22 + 60.8 + 19.4)
= 6.5/3(130.2m)
= 2.16(130.2m)
Half Area = 282.1m
Total Area = Half area X 2
Total Area = 282.1m X 2
Total Area = 564.2m
Watch the video:
https://www.youtube.com/watch?v=rZ6A4lj8Kac&t=
56s
Module 5: Stability
Simpson’s second rule: The area between any four consecutive
ordinates is equal to the sum of the end ordinates, plus three
times each of the middle ordinates, all multiplied by three
eighths of the of the common interval.
A = 3h/8 (y1 + 3y2 + 3y3 +y4 )
h= interval length
1,3,3,2,3,3,1= Simpson’s multiplier
Module 5: Stability
Ordinates
Length
Multiplier
Product
A
1m
1
0.0
B
4.5m
3
13.5
C
9.2m
3
27.6
D
13.8m
2
27.6
E
9.0m
3
27.0
F
4.4m
3
13.2
G
0m
1
0
Total
108.9
Distance between ordinates (h) = 8 m.
Half Area = 3/8 x interval length(h) x (a1+b3+c3+d2+e3+f3+g1)
= 3/8 x 8 x 108.9
= 326.7m
Total Area = 326.7 x 2
= 653.4 sq mtrs
Watch the video
https://www.youtube.com/watch?v=RYfBtWZQTKs
Module 5: Stability
TPC for given mean draught and density of the dockwater
Ship floats on her mean draft 5.31 m. on density 1.009 t/m3. Table
TPC 48.7. Find the correct TPC for density 1.009.
Corrected TPC for density = (Table TPC x Given ɣ) ÷ 1.025 t/m3
= (48.7 t/cm x 1.009 t/m3) ÷ 1.025 t/m3
= 47.94 t/cm
Module 5: Stability
Fresh Water Allowance (FWA) = The amount by which the ship would
increase her draft when passing from salt water to fresh water. The unit of
fresh water allowance is expressed in millimeter.
FWA (mm) = Displ. ÷ (4 x TPC)
Ship has summer mean draft 11.93 m. with corresponding displ. 58,136 t. and TPC 53.8 t/cm.
Find the FWA and ship’s mean draft in fresh water.
FWA (mm) = 58,136 t. ÷ (4x53.8)
= 270 mm
270 mm./1000 mm. = 0.27 m.
Sea Water to fresh water – draft increases Fresh
water to sea water – draft decreases
Fresh Water Mean Draft = 11.93 m. + 0.27 m. = 12.20 m.
Note: Always remember that when ship is from sea water proceeding to fresh water, the
draft increases in fresh water
Module 6: Stability
Inertia is a property of matter by which it remains at rest or in uniform motion
in the same straight line unless acted upon by some external force.
Moment of Inertia (I) = Lb3 ÷ 12
I = Inertia
V = Volume of displacement
b = breadth
L = length
Module 6: Stability
The table shows that a ship has mean draft 8.00 m. with corresponding
displacement 37,624 t. and KM 14.45 m. LPP 181 m. Average Breadth 28.8
m. Solve the, Inertia, Volume of displacement, KB, BM and KM
3
Moment of Inertia (I) = Lb ÷ 12
= 181m X (28.8mX28.8mX28.8m)
12
I = Inertia
V = Volume of displacement
b = breadth
L = length
= 360,308.7
Volume of displacement = Table displacement ÷ 1.025 t/m3
= 37,624 t ÷ 1.025 t/m3
= 36,706.34 cu. m.
Module 6: Stability
BM = Inertia ÷ Volume of displacement
= 360,308.7 ÷ 36,706.34
= 9.81 m.
KM = KB+ BM
KM = Distance from keel to metacentre
KB = Height of the Center of Buoyancy
BM = Length of Metacentric Radius
KB is usually 0.55 to 0.60 of the ship’s draft.
KB is 0.58 of the ships mean draft = 8.00 m x .58 = 4.64 m.
KM = KB + BM
= 4.64 m. + 9.81 m
= 14.45 m
Module 6: Stability
Angle of deck immersion – means that as the angle of heel increases, there
comes a point when the deck of the ship immerses.
Angle of Vanishing Stability - represents a fundamental measure of the
boat's ability to recover quickly from the impact of a breaking wave.
Point of vanishing stability – is the point where the GZ curve meets the
horizontal axis
Range of stability - the distance between the origin and point of vanishing
stability
Angle of Loll – is the angle at which a ship with a negative
initial metacentric height will lie at rest in still water.
End of Presentation
Capt. Mico Mark L. Cruz, MM, MarAd, PhD, FRIMarM
LCDR
PCGA