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M E R C H A N T S H I P S T A B I L I T Y SEVENTHE DITION( METRIC) By H.J. PURSEY EXTRA MASTER FORMERLYL ECTURERT O THE SCHOOLO F NAVIGATION, UNIVERSITYO F SOUTHAMPTON Revised by J. WARDLE, EXTRA MASTER uring the past few years there have been ||l l/considerable changes in the approach to ship stability,s o far as it affectst he merchants eamanT. he most obvious of these is the introduction of metric units, in addition, examination requirements have been increaseda nd recommendationsfo r a standard method of presentinga nd usings tability information have been produced, which will undoubtedly be reflectedi n the variouse xaminations, seventhe dition has beend esignedt o meet all fhis I these requirements.B asici nformationc ontained in early chapters has been retainedf or the benefit of anyonew ho is not familiar with the subiect.T he remainder of the text has been re-arrangeda nd expanded,a s desirable,t o lead into new material which has been introduced,t here is also a chapter on stability information to illustrate the standard method of presentation. theory of stability has been coveredu p to the fhe I standard requiredf or a Master's Certificatea nd includesa ll that is neededb y students for Ordinary NationaDl iplomasa nds imilarc oursesT. hish asb een carefullyl inkedu p with practice,s incet he connection between the two is a common stumbling block. Particulara ttention has also been paid to matters which may be misunderstoodo, r not fully appreciated by seamen. rsBN0 -85174-72 lltl l[ililililil| 4 MERCHANT SHIP STABILITY MERCHANT SHIP STABILITY (METRTCE DTTTON) A Companion to " Merchant Ship Construction" BY H. J. PURSEYE, xtraM aster Fomrarlyl zcturer to the Schoolo f Navigation Univer sity of So uthanpton This Edition Revised by Mr. JamesW ardle.E xtra Master. GLASGOW BROVIN,S ON& FERGUSONU, tD.,N,c,urIcALP UBLISHERS 4-ro DlnNnv SrnEer Copyright in all countriess ignatoryt o the BerneC onvention All rights reserved First Edition 1945 Sixth Edition r977 Revised 1983 Reprinted 1992 Reprinted 1996 Reprinted 2001 SeventhE dition 2006 ISBN 0 85I 74 728 0 (SeventhE dition) ISBN 0 85I 74 442 7 (RevisedS ixth Edition) @2006-BROWNS, ON& FERGUSONL,T D.,G LASGOWG 4l 2SD Printed and Made in Great Britain INTRODUCTION DLIRING the past few years there have been considerablec hanges in the 4proach to ship stability, so far as it affects the merchant searnan.T he most obvious of thesei s the introduction of metic unie. In addition, the Department of Trade have already increasedt heir examinationr equirements: they have also producedr ecommendationfso r a standardm ethodo f presantinga nd using stability information,w hich will undoubtedlyb e reflectedi n the variouse xaminations. This revisede ditionh asb eend esignedto meett he above-mentionerde quirements. Tbe basic information containedi n the early chaptersh as been retained for the benefit of thosew ho are not familiar with such matters,T he remaindero f the text hasb eenr e-arrangeda nd expandeda, sd esirable,t o lead into the new materialw hich bs beeni ntroduced;w hilst a new chaptero n stability informationh asb eena ddedt o illustratet he Departmenot f Trader ecommendations. The theory ofstability hasb eenc overedu p to the standardr equiredf or a Master's C€rtificate and includes all that is needed by students for Ordinary National Diplomas and similar courses.T his has been carefully linked-up with practice, fince the connectionb etweent he two is a conrmon stumbling block. Particular dention hasb eenp aid to maftersw hich are commonlym isunderstoodo, r not fully apreciated by seamen. H. J.P . Southampto1n9, 82. CONTENTS CHAPTER I-SOME GENERAL INFORMATION PAGE The Metric System I Increaseo f pressurew ith depth 2 Efect of water in sounding pipes 2 The Law ofArchimedes 3 Floating bodies and the density ofwater 4 Shipd imensions 4 Decks Ship tonnages 4 Grain and bale measurement 5 Displacementa nd deadweight 5 Draft. 6 Freeboard 6 Loadlines 6 CHAPTER 2-AREAS AND VOLUMES Areaso fplane figues 8 Surfacea reasa nd volumes 8 Areas ofwaterplanes and other ship sections 9 Simpson'sF irst Rule l0 Simpson'sS econdR ule - l2 The' Five-EighRt ule' l3 Sharp-endewd aterplanes t3 Unsuitablen umberso f ordinates l3 Volumeso fship shapes l5 Half-intervals l5 Coefficientosf 6neness l6 Wetted surface l8 CHAPTER3 -FORCES AND MOMENTS Force t9 Moment 20 Centre of gravity Etrect ofadded weights on centre ofgravity 25 The use of momentst o find the centre of gravityof an area 27 To find the centre ofgravity ofa waterylane 28 To find the cenhe ofbuoyancy ofa ship shape - 29 The useo fintermediateo rdinates 31 Appendages Inertia and Moment ofinertia and radius ofgyration Eouilibrium 35 VI CONTENTS CTIAPTER,I-DENSITY,DEADWEIGIITANDDRAFT PAGE Efi€ct ofdensityo n draft - 37 Tonnesp €r ceNrtimetirren mersion - 39 I,oadingt o a givenl oadline - - 40 CHAPTER s-{ENIRE OF GRAVTTYO F SHIPS Cente ofcravity ofa ship-G - 42 KG 42 ShiftofG - 42 KG for any condition of loading 44 Deadweight moment 45 Real and virtual cenbes of gravity 46 Efect oftatrks on G 47 CIIAPTER HENTRES OF BUOYANCY AND FLOTATION Centreo fbuoyancy-8 - 49 Cenheo fflotation-F - 49 ShiftofB - - 50 CHAPTER 7-THE RIGIITING LEVERAND METACENTRE Equilibriumofships----53 Ther ightingl ever-{Z - 55 Tbem etacentre-M - - - - 55 Metacentrich eight-CM - - - 55 Stableu, qstablea ndu euhale quilibrium - - 55 Inngitudinatn etacentrich eight-GM, - - 56 CIIAPTER 8-TRANSVERSE STATICAL STABILITY Mom€ot of staticals tability - - 57 Relationb etweenG Mand GZ - - 57 Initialstabilityandrangeofstability---5? Calculationo fa ship'ss tability - 58 Calculationo fBiv - - 58 Th€ hcliniry Experiment - - - 60 Staticsls tabilitya t smalla ngleso fheel - - 62 GZ by the Wall-SidedF ormula - - 62 Lotl, or list - - 63 HeelduetoGbeingoutofthecente-lne----63 Lotl duet o a negativeG M - - O CHAPTER g-FREE SUFJACE EFFECT Thee ffecto ffree surfaceo fliquids - 69 Frees urfacee ffectw hent anksa ref illed or emptied - - 71 Frees urfacein dividedt anks - - 72 Frees urfacem oments - - 74 CONTENTS vll CHAPTER IO-TRANSVERSE STATICAL STABILITY IN PRACTICE PAGE Factor afecting statical stability - 75 Placingo fweights - - '17 Stiffand tenders hips - - - 77 Unstables hips - 79 Shipsi n ballast - - 80 The effecto fwinging out weights - 8l Deck cargoes - 82 Free liquid in tanks - - 83 Free surface effect in oil tankers - 84 CHAPTER I I-DYNAMICAL STABILIry Dynamical stability - - 85 Dynamical stability from a curve of statical stability - 85 Calculation ofdynamical stability - 87 CHAPTER I2-LONCITUDINAL STABILITY Longitudinal metacentric height-GM 89 Calculatioonf SMr 90 9l Changeo fdraft due lo changeo f trim 92 Displacemenot ut ofdesignedt rim 95 Moment to changet rim by one centimete 96 The effecto fshifling a weight 98 Efect ofadding weight at the centre offlotation 99 Moderate weights loaded offthe cenhe offlotation l0l Large weights loaded offthe centre offlotation 104 To obtain special trim or draft 106 Use of moments about the after perpendicular lll CHAPTERI 3-STABILITY CI'RVESA ND SCALES Hydrostaticc urves ll4 The deadweight scale ll5 Hy&ostatic particula$ 115 Curves of statical stability 116 Cross curves tt'7 Effecto fheighto fG - - 119 r(N curves t2l The MetacentricD iagram - t2l CHAPTER I,'-BILGING OF COMPAMMENTS The efect ofbilging a compamnenr- - 123 Permeability 123 Bilging an empty compartment amidships t24 Bilging an amidships comparhnent,w ilh cargo 125 Bilging an empty comparhncnt, not amidships 126 Effect ofa watertieht flat 128 Viii CONTENTS CHAPTERIH TABILITYAND THB IJOADL INE RI,,LES PACE St$ility rcquircmcob l3l lnfcnation to bc n4plicd to sbipe t32 Ttc Sbbility Informdio Boo&la ttz Thc usco f maximun dradwcightm mcnb r37 Sinplif cd stabilityi domrtion 138 CI{APIER I6_MISCELLANEOUS MATTERS Orydoclcing8 ndg onding r42 Tbc cfiooro fdcosity m stlbility t45 Thc cffcct ofdcnsity on dni of ship 145 Doriyrtion of thc Acch-wrtcrs llowanc€ t45 Rcrcrvcb uoyancy 147 Logiodid Nfhcadc t47 Bulkhcrds ubdivisioo0 d sb€cr I'E Plaerc on bullficads 1,18 CHAPIER I7_ROLLING Thc fouation of wrvoc 150 Ttc Trochoiddl tcory 150 Thc pcriodo fwavcc 151 Tbc pcriodo fa rhip l5l Syac,bmirm l5l U[rcaistcdm ling r52 Rcsistrlc€st o lolling t52 Thcc frcctso fbilp koclr t53 Cuesf or hcavym lling t53 CHAPTIR IHUMMARY Abbrwiatims t54 Fcnulac t56 Dcdnitions l6l hoblcos l& DEADWEIGIITS CALE,T {YDROSTAilCP ARTICI,'LARASN D IIYDROSTANCCI,.'RVES - S€clion at cod ofbook