basic stability- tahir

8/3/2019 Basic Stability- TAHIR

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REFERENCES:

BR-2170 VOL-I

BR-567


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SCHEME OF PRESENTATIONSCHEME OF PRESENTATION

INTRODUCTIONINTRODUCTION

OBJECTIVEOBJECTIVE

STABILITYSTABILITY GENERAL TERMS USED IN STABILITYGENERAL TERMS USED IN STABILITY

FREE SURFACE EFFECTFREE SURFACE EFFECT

STIFF SHIPSTIFF SHIP

TENDER SHIPTENDER SHIP

SUMMARYSUMMARY


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INTRODUCTION

Knowledge regarding ships stability is

very important for every individual

serving on ship. If we will not keep ourship in stable condition, then we will not

achieve the sea going and fighting

efficiency of a ship nor ensure the safety

of men and material.


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OBJECTIVE

The objective of this subject is to enhance

the knowledge of students regarding the

ships stability and factors effecting

ships stability.


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STABILITYSTABILITY

The tendency of a ship to come in up rightThe tendency of a ship to come in up right

position, if it inclined due to external forcesposition, if it inclined due to external forces

is called stability.is called stability.

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TheThe amountamount ofof waterwater displacedisplace oror aa putput aasideside byby aa vesselvessel isis calledcalled displacementdisplacement..

TheThe weightweight ofof waterwater displaceddisplaced byby aafloatingfloating objectobject isis alwaysalways equalequal toto thethe

weightweight ofof thethe floatingfloating objectobject andand itsitsvolumevolume isis alsoalso equalequal toto thethe immersedimmersedvolumevolume ofof thethe floatingfloating objectobject..

DISPLACEMENTDISPLACEMENT


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GRAVITYGRAVITY

It is a force by which the earth attracts

every thing towards its center.

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CENTRE OF GRAVITYCENTRE OF GRAVITY

The

The pointpoint atat whichwhich thethe wholewhole weightweight ofof thetheobjectobject actingacting downwardsdownwards..

TheThe centercenter ofof gravitygravity ofof anan objectobject alwaysalways

movemove towardstowards thethe addedadded weightweight.. TheThe centercenter ofofgravitygravity isis denoteddenoted byby GG..


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5 kg 5 kg

5 kg 5 kg

5 kg

5 kg5 kg

5 kg


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BUOYANCYBUOYANCY

TheThe upup thrustthrust forceforce ofof liquidliquid actact uponupon

floatingfloating objectobject isis calledcalled buoyancybuoyancyoror

ThatThat partpart ofof thethe buoyantbuoyant volumevolume belowbelow thethe

waterwater lineline isis calledcalled buoyancybuoyancy..


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CENTER OF BUOYANCYCENTER OF BUOYANCY

TheThe pointpoint atat whichwhich thethe wholewhole upup thrustthrust

forceforce isis actingacting

OROR

TheThe centrecentre ofof underunder waterwater portionportion ofof thethe

hullhull isis calledcalled centrecentre ofof buoyancybuoyancy.. itit isis

denoteddenoted byby BB..


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RESERVE BUOYANCYRESERVE BUOYANCY

That part of the hull above the water

That part of the hull above the waterline is called reserve buoyancy.line is called reserve buoyancy.


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WATERLINE

DEPTH

OFHULL

DRA

FT

FREE

BO

ARD

RESERVE BUOYANCY

BUOYANCY

SUPPER

STRUCTURE


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BUOYANT VOLUMEBUOYANT VOLUME

TheThe buoyantbuoyant volumevolume ofof aa shipship isis thethe volumevolume

ofof thethe entireentire waterwater tighttight partpart ofof thethe hullhull..

BUOYANCY

RESERVE BUOYANCYFREE

BOARD

NON WATER TIGHTSUPER STRUCTURE

BUOYANT VOLUME

DRAUGHT

WL

BUOYANT

VOLUME

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META CENTER

The point of intersections of the oldvertical line by the new vertical line of the

buoyancy force is called meta center.

meta center M.

INITIALWATER

LINE

INCLINED

WL

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META CENTRIC HEIGHT (GM)

The distance between G and M is

called meta centric height (GM).

If a ship having large GM then the ship

having good stability and if a ship havingsmall GM then the ship having poor

stability.

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RIGHTING LEVERRIGHTING LEVER

TheThe horizontalhorizontal distancedistance betweenbetween GGandand ZZ isis calledcalled thethe rightingrighting leverlever

(GZ)(GZ)..

INITIALWATER

LINE

INCLINED

WL

RIGHTING LEVER


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TemporaryTemporary inclinationinclination ofof shipship duedue toto externalexternalforcesforces suchsuch asas windwind oror waveswaves isis calledcalled heelheel..

HEELHEEL


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EFFECTS OF HEEL

It is difficult for personnel to go out the

ship and carryout their duties properly

when the ship is heeled.Heel may restrict the effectiveness of

weapons.

The effect of heel on the operation of air

craft and helicopters.

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PermanentPermanent inclinationinclination ofof aa shipship by by offoffcentrecentre loadload withinwithin thethe shipship isis calledcalled listlist..

ListList cancan bebe correctedcorrected byby thethe followingfollowing

threethree waysways:: ByBy removingremoving offoff centercenter loadingloading..

ByBy addadd equivalentequivalent weightweight onon thethe oppositeopposite

sideside.. ByBy shiftingshifting weightweight fromfrom lowlow sideside toto highhigh

sideside..

LIST


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G G 1

M

B

B 1

W

G

M

B

W

B 1

G

M

B

W

CORRRCTION OF LIST

shifting weightfrom low side tohighside.shifting weightfrom low side tohighside.

ortowardthe centerortowardthe center

G

B

M

Removingoffcenter loadingRemovingoffcenter loading

LIST

Add equivalent weightonthe opposite side.Add equivalent weightonthe opposite side.

B 1


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DifferenceDifference betweenbetween FWDFWD andand AFTAFT draughtdraughtisis calledcalled TrimTrim.. IfIf forwardforward draughtdraught isis greatergreater

thanthan thethe aft,aft, shipship isis saidsaid toto bebe trimtrim byby headhead..

SimilarlySimilarly ifif aftaft draughtdraught isis greatergreater thanthan FWDFWD..TheThe shipship isis saidsaid toto trimtrim byby sternstern..

W L W L

-I

I

I

I

I

I

I

I

I

-

I

I

I

I

I

I

I

I

TRIMTRIM


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TheThe inclinationinclination ofof shipship duedue toto toptop centrecentreweightweight andand freefree surfacesurface effecteffect..

LollLoll cancan bebe correctedcorrected byby::

RemoveRemove thethe weightweight fromfrom heightheight inin thethe shipship..

ReduceReduce thethe areaarea ofof freefree surfacesurface liquidliquid..

AddAdd weightweight lowlow downdown inin thethe shipship..

ShiftShift weightweight fromfrom highhigh inin shipship toto lowerlower

levelslevels

LOLL


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FREEFREE--SURFACE EFFECTSSURFACE EFFECTS

IncreaseIncrease inin inclinationinclination decreasedecrease inin

rightingrighting leverlever duedue toto tankstanks notnot

completelycompletely filledfilled isis calledcalled freefree surfacesurface

effecteffect..


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G

TheThe movementmovement ofof thethe centercenter ofof gravitygravity

fromfrom GG toto GG11 hashas been been causedcaused by by thethetransfertransfer ofof aa liquidliquid acrossacross thethe tanktank..

G


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STIFF SHIPShip with large GM Metacentric height, large

GZ Righting lever will take rapid roll has good

stability, but not good for crews known as Stiff

Ship like war ships

TENDER SHIPShip with small GM Metacentric height, small

GZ Righting lever will take slow roll has poor

stability and good for crews is known as Tender

Ship.


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SUMMARYSUMMARY


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basic stability- tahir

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