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 CARGO5. OIL POLLUTION

FUNDAMENTALS OF STABILITYSTABILITY is the tendency of vessel to rotate one way or the other when forcibly inclined.

IMPORTENT !!

Ships stability cant catch directlyStability 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 alwayspositive. 2 Zg < Zcritical

Zg critical define according specialdiagram.

h = Zm Zg Zg defined by calculating Zm define according hydrostatic curves

SHIPS STABILITY CALCULATING SHIPS STABILITY CALCULATING BY MOMENT FORMULAS. MAIN OBJECT OF CALCULATING TO DEFINE SHIPS STABILITY CRITERIAS: GM=h METACENTER HEIGHT Zg SHIPS GRAVITY HEIGHT MOMENT FORMULA: D0Z0+P1Z1+P2Z2+.+PnZn Zg = D0 + P1 +P2 + .. + Pn

SHIPS STABILITY CALCULATING

Zg critical CURVE6.60 6.506.40 6.30

Zg critical

6.20 6.108000 10000 12000 14000 16000 18000 20000

WHO CALCULATING SHIPS CARGO PLAN AND STABILITY? 1.CARGO OFFICER (ch.mate) 2.PORT CARGO OFFICER (supercargo) 3.SHIPS MASTER

SHIPS STABILITYSTABILITY

INITIAL

OVERALL

DYNAMIC

STABILITYINITIAL 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 V0=V1 V1 m L1V0 w W1C

G C1

L

INITIAL METACENTRIC FORMULAM=D lst

lst=hsinQM=D h sin Q

mlst

Qst

hD Vg

G

C1

C

SHIPS STABILITY CALCULATING Initial stability calculating by ships stability triangle Calculating formula lst= h sinQ Overall stability calculating by hydrostatic ships body formula lf Dynamic stability is the area under the static stability curve Dynamic stability also potential energy available to return the ship to the upringing

STABILITY TRIANGLEm

lst =hsin Qlf

hG

l

Qst

Vg D lf C1

C

PHANTACORENSSHIPS BADY FORM STABILITY ARMS lf lf2.8

2.41.6 1.2 0.8 0.4

80 70 60 50

90

4030 20 10

4000 6000

8000

10000

20000 12000 14000 16000 18000

DISPLACEMENT

METACENTRIC HEIGHTMetacentric 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 HEIGHTm W G

haa

L

C

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 POINTSmZm

h r Lo a

WOZG

G

Zc

C

MAIN STABILITY POINTS m metacenter G center of gravity C center of buoyancy

m

h WoW1

Q

L1

a

G CC1

LO

Q

SHIPS STABILITY

METACENTER

m

C0

SHIPS STABILITY METACENTRIC HEIGHT FORMULAS h=r-a h=zm

zG zG

h=zc - ro -

METACENTRIC HEIGHT METACENTRIC HEIGHT MEENS SHIPS INITIAL STABILITY m

h W G aC

r0

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 h>OGa

G m

G h=O mb

h0h

m GC1

L1L

W W1

C

SHIPS STABILITY CURVEPOSITIVE SHIPS STABILITYL l st

h>0

h

57, 3

Q

Q

NEUTRAL SHIPS STABILITY Neutral ships stability when m and G in the same position h=0Gm

W

LC1

C

SHIPS STABILITY NEUTRAL SHIPS STABILITYlst

h=0

Q

NEGATIVE SHIPS STABILITY Negative ships stability when m below G h