Presentation on theme: "Principles of Ships Stability PETRAS PIKSRYS SHIPS STABILITY SHIPS STABILITY IS THE TENDENCY OF SHIP TO ROTARE ONE WAY OR THE OTHER WHEN FORCIBLY INCLINED."— Presentation transcript:
Principles of Ships Stability PETRAS PIKSRYS
SHIPS STABILITY SHIPS STABILITY IS THE TENDENCY OF SHIP TO ROTARE ONE WAY OR THE OTHER WHEN FORCIBLY INCLINED
WHAY IS STABILITY IS SO IMPORTENT ? IF THE SHIP LOST STABILITY WHAT WILL BE HAPPENED: 1. LOST OF MOBILE 2. LOST THE HUMANS LIFES 3. LOST THE SHIP 4. LOST THE CARGO 5. OIL POLLUTION
FUNDAMENTALS OF STABILITY STABILITY is the tendency of vessel to rotate one way or the other when forcibly inclined. IMPORTENT !! Ships stability cant catch directly Stability can define only by calculating
HOW CALCULATING SHIPS STABILITY AND CARCO PLAN ? 1.By previous similar cargo plan. 2.By standard cargo plan according STABILITY BOOKLET 3.By standard cargo plan forms 4.By special cargo plan computer 5.By standard PC with special cargo plan program 6.By special or standard hand calculator
SHIPS STABILITY CRITERIAS THERE ARE TWO SHIPS STABILITY CRITERIAS: 1 h>0 ships metacenter height always positive. 2 Z g < Z critical h = Z m – Z g Z g defined by calculating Z m define according hydrostatic curves Z g critical define according special diagram.
SHIPS STABILITY CALCULATING SHIPS STABILITY CALCULATING BY MOMENT FORMULAS. MAIN OBJECT OF CALCULATING TO DEFINE SHIPS STABILITY CRITERIAS: GM=h METACENTER HEIGHT Z g SHIPS GRAVITY HEIGHT MOMENT FORMULA: D 0 Z 0 +P 1 Z 1 +P 2 Z 2+…….+ P n Z n Z g = D 0 + P 1 + P 2 + …….. + P n
SHIPS STABILITY CALCULATING Z g critical CURVE Z g critical D
WHO CALCULATING SHIPS CARGO PLAN AND STABILITY? 1.CARGO OFFICER (ch.mate) 2.PORT CARGO OFFICER (supercargo) 3.SHIPS MASTER
STABILITY INITIAL STABILITY - The stability of a ship in the range from 0 to 7 /10 of inclination. OVERALL STABILITY - A general measure of a ship's ability to resist capsizing in a given condition of loading. DYNAMIC STABILITY - The work done in heeling a ship to a given angle of heel.
INITIAL SHIPS STABILITY Initial ships stability when ship inclinating from 7 till12 degrees. Ships underwater body did not change volume V 0 =V 1 C C1C1 G m V0V0 V1V1 wL W1W1 L1L1
INITIAL METACENTRIC FORMULA m G C M=D h sin Q Q st h D VgVg C 1 l st M=D l st l st =h sin Q
SHIPS STABILITY CALCULATING Initial stability calculating by ships stability triangle Calculating formula lst= h sinQ Overall stability calculating by hydrostatic ships body formula l f Dynamic stability is the area under the static stability curve Dynamic stability also potential energy available to return the ship to the upringing
STABILITY TRIANGLE Q m C G C1C1 l st =hsin Q l st h D Vg lflf l f
PHANTACORENS SHIPS BADY FORM STABILITY ARMS l f lflf DISPLACEMENT ARMS l f
METACENTRIC HEIGHT Metacentric height GM is calculated by subtracting KG From KM (GM=KM-KG), GM is a measure of the ship.s stability. KM=h. With initial stability(0 – 10 deg.) the metacenter does not move, and Sine function is almost linear(a straight line). Therefore, the size of the ship,s Righting Arm, GZ, is directly prportional to the size of the ships Metacentric Height, GM. IMPORTENT ! Thus, GM is a good measure of the ships initial stability.
METACENTRIC HEIGHT m G C h a W L a
MAIN STABILITY POINTS There are three main stability points: m- metacenter is the end of hydrostatic force when ship listing. G- centre of ship gravity C- centre of ship underwater body.
SHIPS STABILITY STABILITY REFERENCE POINTS G h a r C WOWO LoLo m Zc ZGZG ZmZm
MAIN STABILITY POINTS m metacenter G center of gravity C center of buoyancy m G h a C1C1 Q WoWo LOLO W1W1 L1L1 Q C
SHIPS STABILITY METACENTER m C0C0
SHIPS STABILITY METACENTRIC HEIGHT FORMULAS h=r-a h= z m – z G h= z c - r o - z G
METACENTRIC HEIGHT METACENTRIC HEIGHT MEENS SHIPS INITIAL STABILITY m G C h a W L r0r0
Three states of static equilibrium (a) Positive stability - m above G (b) Neutral stability – m and G in the same position ( c )Negative stability –m below G m a m G b G m G h>O h=O h
"name": "Three states of static equilibrium (a) Positive stability - m above G (b) Neutral stability – m and G in the same position ( c )Negative stability –m below G m a m G b G m G h>O h=O hO h=O h
POSITIVE SHIPS STABILITY Positive ships stability when m above G h>0 C C1C1 G m h W L W1W1 L1L1
SHIPS STABILITY CURVE L l st Q h 57, 3 Q POSITIVE SHIPS STABILITY h>0
NEUTRAL SHIPS STABILITY Neutral ships stability when m and G in the same position h=0 CC1C1 G m W L
SHIPS STABILITY NEUTRAL SHIPS STABILITY l st Q h=0
NEGATIVE SHIPS STABILITY Negative ships stability when m below G h<0 C C1C1 m G h WL W1W1 L1L1
h=-0 NEGATIVE SHIPS STABILITY h M st Q st
STABILITY CONDITIONS The positions of Gravity and the Metacenter will indicate the initial stability of a ship. Following damage, the ship will assume one of the following three stability conditions: 1. POSITIVE STABILITY. The metacenter is located above the ships center of gravity. As the ship is inclined, Righting Arm are created which tend to return the ship to its original, vertical position. 2. NEUTRAL STABILITY. The metacenter and the ships center of gravity are in the same location. As the ship is inclined,. there are no returing moment. 3. NEGATIVE STABILITY. The ship,s center of gravity is above the metacenter. As the ship is inclined, negative Righting Arms (called upsetting arms) are created which tend to capsize the ship.
METACENTRIC FORMULA h=Z m - Z G C C1C1 D m h l st M=( l f lst)D OVERALL Vg W0W0 L 0 W1W1 L1L1 lflf G Zm ZGZG M- UPSERTING MOMENT M
METACENTRIC HIGHT METACENTRIC HIGHT IS FIRST DERIVATIVE SHIPS STABILITY CURVE h 57,3 M st Q l st
METACENTER HEIGHT W L W1W1 L1L1 C C1C1 G m h Metacenter height GM is a determine of ships stability curve METACENTER MOMENT IS UPSERTING MOMENT M= D h sin Q
WL DYNAMIC STABILITY
SHIPS DYNAMIC STABILITY DYMAMIC MOMENT Q M M DYNAMIC MOMENT
SHIPS STABILITY STATIC MOMENT CURVE Q M
SHIPS DYNAMIC STABILITY MAXIMUM DYNAMIC ANGLE Q dyn Q static Q M Q dyn max S1S1 S2S2 Q dyn WHEN S 1 = S 2
SHIPS DYNAMIC CURVE SHIPS DYNAMIC STABILITY CURVES APPLICATES IS EQUVALENT STATIC CURVES AREA S M dyn S=M dyn Q M dyn
DYNAMIC STABILITY The dynamic stability is the area under the curve in metre-radians Multiplated by the ship,s displacement in tonnes. It is areas under the GZ Curve which are required for checking stability criteria which depending Upon the ship,s data may be expressed in metre-degrees or metre-radians. The area unde GZ curve also the potential energy available to return the Ship to the upringht. Principle of conservation of energy, the potential energy in converted into Rotation energy as the ship moves towards the upright.
MdMd M st Q max DYNAMIC STABILITY M st Q M din CURVE
STABILITY ELEMENTS THE LAW OF BUOYANCY THE LAW OF GRAVITY STABILITY REFERENCE POINTS LINEAR MESURMENTS IN STABILITY THE STABILITY TRIANGLE RIGHTING MOMENT STATIC STABILITY CURVE DYNAMIC STABILITY CURVE ROLLING PERIOD
Learning Objectives Comprehend the concepts of hydrostatics, buoyancy, and Archimedes' principle Comprehend static equilibrium of a floating vessel and the relationship of the centers of gravity and buoyancy to righting arms and stability Comprehend and identify positive, negative and neutral conditions of stability Comprehend the effects of movements of the centers of gravity and buoyancy on vessel stability Know how ship's stability curves are derived and comprehend their use in determining stability condition
Draft Freeboard Depth of hull Reserve buoyancy List / Trim Definitions
SHIPS HULL MARKINGS At XVIII hundred one Englishman called PLIMSOL in Great Britan Parlament filds for marcks on the hull to for Safe shipping. Now thats marks called PLIMSOL MARKS.
PLIMSOL DISC PLIMSOL DISC DIVAIDING SHIPS BODY IN TWO PARTS: 1. RESERVE BUOYANCY 2. DISPLACEMENT WL RESERVE BOYANCY DISPLACEMENT
FREE BOARD SHIPS MAIN FREE BOARD MEENS SHIPS RESERVE BUOYANCY DRAFT SHIPS MAIN DRAFT MEENS SHIPS DISPLACEMENT
RESERVE BUOYANCY MAINTAIN FREEBOARD – RASERVE BUOYANCY PRIOR TO PREVENT LIMITING DRAFTS ARE ASSIGNED TO EXCESIVE HULL STRESS AS A RESULT OF OVERLOADING
FREE BOARD WL FREE BOARD WNA W S F TF FREE BOARD MEENS RESERVE BUOYANCY
DRAFT MAIN DRAFT MEENS SHIPS DISPLACEMENT W L DRAFT
Archimedes' principle Calculations of displacement (W) The effect of salt water and fresh water on displacement (relate to draft) [1/35 vs 1/36] Buoyancy
Archimedes principle BOYAD A body immersed (or floating) in water will buoyed ARCHIMEDES FORCE By a force equal to the weight of the water displaced.
THE LAWS OF BUOYANCY 1.Floatating objects posses the property of buoyancy. 2.A floatating body displaces a volume of water equal in a body immersed (or floating) in water will be duoyed up by a force equal to the weight of the water displaced W L C VgVg D G D=Vg
SHIPS BUOYANCY D=V*g V*g D G C W L ARCHIMEDES FORCE
WNA W S T F TF PLIMSOL MARKS (Load lines) Markings of minimum allowable freeboard for registred cargo- Carryng ships.Located amidships on both the port and starboard sides the ship. Since the required minimum freeboard varies with water density and severity of weather, different markings are used for: - TF – Tropical Fresh Water - F - Fresh Water - T - Tropical Water (sea water) - S - Standard Summer - W - Winter - WNA-Winter North Atlantic
SHIPS HULL MARKINGS Calculative Draft Marks Used for determining displacement and other properties of the ship for stability and damage control. Those draft marks indicate the depth of the keel (baseline) below the waterline. TWO POSIBLE MARKING SYSTEMS: 1. Roman numerals in height 2. Arabic numerals in height
DRAFT IN FEETS 1 ft = m XIII XIV XV XVI XVII
DRAFT IN METRES 1 ft = m
SHIPS HULL MARKINGS Navigational Draft Marks Ships operational drafts. These draft marks include the depth of any projections below the keel of the ship. Limiting Draft Marks Limiting drafts are assigned to maintain reserve buoyancy (freeboard) prior to damage, and to prevent excessive hull stresses as a result of overloading.
DISPLACEMENT The weight of the volume of water that is displaced by the underwater portion of the hull is equal to the weight of the ships GRAVITY The force of gravity acts vertically downward through the ships center Of gravity. The magnitude of the force depends on the ships total weight. MOMENT The endency of a force to produce a rotation about a pivot point. This works like a torque wrench acting on a bolt.
DISPLACEMENT D=D LS + D S + D C D – Displacement D LS – Weight light ship D S - Weight supply D C - Weight cargo
GRAVITY THE FORCE OF GRAVITY ACTS VERTICALY DOWNWARD THROUGHT THE SHIPS CENTER OF GRAVITY W L G D= D L+ D C+ D S
SHIPS STABILITY METACENTER MOMENT =UPSERTING MOMENT M = D h sin O
RIGHTING MOMENT THE TENDENY OF A FORCE TO PRODUCE A ROTATION ABOUT A PIVOT POINT C0C0 G m C1C1 M = D h sin Q D Vg h
GRAVITY The force of gravity acts vertically downward throught the ships center of gravity. D=Vg W L VgVg D C G
Application of following terms to overall stability (a)Couple (b)Righting arm (GZ) (c)Righting moment (RM) - RM= GZ (W) (d)Upsertting moment
DEFINITIONS Couple. Since the forces of buoyancy and gravity are equal and act along parallel lines, but in opposite directions, a rotation is developed. Righting arm. The distance between the forces of buoyancy and gravity is know as the ships righting arm. Righting moment. The righting moment is equal to the ships Righting arm multiplied by the ships displacement. Metacentric height. The distance between center of gravity G and Metacener M.
The development of the static stability curve from the cross curves of stability Foctors involed : - G does not change position as heeling angle changes - C is always at the geometric center of the volume of the underwater hull - the shape of the underwater hull changes as heeling angle changes
Using curves,find (a) Maximum rigting arm (GZ) GZ=h (b) Angle of heel where maximum GZ arm ocurs l static maximum (c) Range of critical stability Q critical SHIPS STABILITY CURVE
SHIPS STABILITY STABILITY CURVES ELEMENTS l st Q h 57.3 l static max Q critical
STATIC STABILITY CURVE When a ship is inclined through all angles of heel,and the righting arm for each angle is measured, the statical stability curve is produced. This curve is a snapshotof the ships stability at that particular loading condition.Much information can be obtained from this curve, including: 1.Range of Stability: This ship will generate Righting Arms when inclined from 0 deg. Till to approximately 74 dg. 2.Maximum Righting Arm: The angle of inclination where the maximum Righting Arm occurs 3.Danger Angle:One half the angle of the maximum Righting Arms.
DRAFT DIAGRAM AND FUNCTIONS OF FORM The Draft Diagram is a nomogram located in Section II(a) of the Damage Control Book. It is used for determining the ships displacement, as well as other properties of the ship, including: - Moment to Trim One Inch (MT1); - Tons per Inch Immersion (TPI); - Height of Metacenter (KM); - Longitudinal Center of Flotation (LCF) - Longitudinal Center of Buoyancy(LCB) -Displacement (D) -VOLUME V m -Moment, diferenting per 1 cm -Weight, drafting per 1 cm
DRAFT NOMOGRAM TmTm DtDt VmVm 3 M t/cmP t/cm
HYDROSTATIC CURVES SHIPS FLOATING BODY FUNCTIONS CAN CALCULATING BY HYDROSTATIC CURVES. THIS CURVES IS FUNCTIONS FLOATING SHIPS BODY STABILITY AND UNDERSEA SHIPS BODY CAPITICY. ARGUMENT FOR CALCULATING IS SHIPS DRAFT FUNCTIONS FOR CALCULATING: a) DISPLACEMENT D b) VOLUME V c) FLOATING CENTER X f d) BOYAD CENTER X C Z c e METACENTER RADIUS r f) SQUERE OF WATERLINE S
HYDROSTATIC CURVES SHIPS FLOATING BODY FUNCTION CURVES DRAFT FUNCTIONS V D S Xf Zcr
COUPLE Q m C G C1C1 M=D h sin Q l st h D Vg
PLIMSOL DISC WNA W S T F TF
LIST Q Q W1W1 L1L1 WOWO LoLo
ROLLING PERIOD SHIPS STABILITY AND ROLLING PERIOD W L T= C B h
ROLLING PERIOD The rolling period of the ships dependenced from ships stability. The formula Between ship,s stability and rolling : T = c*B/sqr GM In this formula: T – rollinperiod in sec. c - constanta B – the ships beam to outside of hull. Note: the constanta c dependenced from ships displacements. There are the followings meanings: c=0.88 – when ship is empty or ballast; c= when the ship has on board amout 20 % c=0.75 – when liquids on board 10% c=0.73 – when all liquids on board amout 5% HOWEVER, for all lagers ships Lloyds Register of shipping and the 1991 HMSO Code of Practice for Ro-Ro ships use c= 0.7