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Slide 2 Principles of Ships Stability PETRAS PIKSRYS Slide 3 SHIPS STABILITY SHIPS STABILITY IS THE TENDENCY OF SHIP TO ROTARE ONE WAY OR THE OTHER WHEN FORCIBLY INCLINED Slide 4 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 Slide 5 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 Slide 6 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 Slide 7 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. Slide 8 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 Slide 9 SHIPS STABILITY CALCULATING Z g critical CURVE 8000 10000 12000 14000 16000 18000 20000 6.10 6.20 6.30 6.40 6.50 6.60 Z g critical D Slide 10 WHO CALCULATING SHIPS CARGO PLAN AND STABILITY? 1.CARGO OFFICER (ch.mate) 2.PORT CARGO OFFICER (supercargo) 3.SHIPS MASTER Slide 11 SHIPS STABILITY Slide 12 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. Slide 13 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 Slide 14 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 Slide 15 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 Slide 16 STABILITY TRIANGLE Q m C G C1C1 l st =hsin Q l st h D Vg lflf l f Slide 17 400060008000 10000 12000 14000 16000 18000 20000 0.4 0.8 1.2 1.6 2.4 2.8 10 20 30 40 50 60 70 80 90 PHANTACORENS SHIPS BADY FORM STABILITY ARMS l f lflf DISPLACEMENT ARMS l f Slide 18 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. Slide 19 METACENTRIC HEIGHT m G C h a W L a Slide 20 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. Slide 21 SHIPS STABILITY STABILITY REFERENCE POINTS G h a r C WOWO LoLo m Zc ZGZG ZmZm Slide 22 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 Slide 23 SHIPS STABILITY METACENTER m C0C0 Slide 24 SHIPS STABILITY METACENTRIC HEIGHT FORMULAS h=r-a h= z m z G h= z c - r o - z G Slide 25 METACENTRIC HEIGHT METACENTRIC HEIGHT MEENS SHIPS INITIAL STABILITY m G C h a W L r0r0 Slide 26 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 POSITIVE SHIPS STABILITY Positive ships stability when m above G h>0 C C1C1 G m h W L W1W1 L1L1 Slide 28 SHIPS STABILITY CURVE L l st Q h 57, 3 Q POSITIVE SHIPS STABILITY h>0 Slide 29 NEUTRAL SHIPS STABILITY Neutral ships stability when m and G in the same position h=0 CC1C1 G m W L Slide 30 SHIPS STABILITY NEUTRAL SHIPS STABILITY l st Q h=0 Slide 31 NEGATIVE SHIPS STABILITY Negative ships stability when m below G h