ASTM F1321-2013e1 Standard Guide for Conducting a Stability Test (Lightweight Survey and Inclining Experiment) to Determine the Light Ship Displacement and Centers of Gravity of a .pdf

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1、Designation: F1321 131An American National StandardStandard Guide forConducting a Stability Test (Lightweight Survey andInclining Experiment) to Determine the Light ShipDisplacement and Centers of Gravity of a Vessel1This standard is issued under the fixed designation F1321; the number immediately f

2、ollowing the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been ap

3、proved for use by agencies of the Department of Defense.1NOTEEditorially revised the standard from reviewer comments in October 2013.INTRODUCTIONThis guide provides the marine industry with a basic understanding of the various aspects of astability test. It contains procedures for conducting a stabi

4、lity test to ensure that valid results areobtained with maximum precision at a minimal cost to owners, shipyards, and the government. Thisguide is not intended to instruct a person in the actual calculation of the light ship displacement andcenters of gravity, but rather to be a guide to the necessa

5、ry procedures to be followed to gather accuratedata for use in the calculation of the light ship characteristics.Acomplete understanding of the correctprocedures used to perform a stability test is imperative to ensure that the test is conducted properlyand so that results can be examined for accura

6、cy as the inclining experiment is conducted. It isrecommended that these procedures be used on all vessels and marine craft.1. Scope1.1 This guide covers the determination of a vessels lightship characteristics. In this standard, a vessel is a traditionalhull-formed vessel. The stability test can be

7、 considered to betwo separate tasks; the lightweight survey and the incliningexperiment. The stability test is required for most vessels upontheir completion and after major conversions. It is normallyconducted inshore in calm weather conditions and usuallyrequires the vessel be taken out of service

8、 to prepare for andconduct the stability test. The three light ship characteristicsdetermined from the stability test for conventional (symmetri-cal) ships are displacement (“displ”), longitudinal center ofgravity (“LCG”), and the vertical center of gravity (“KG”). Thetransverse center of gravity (“

9、TCG”) may also be determinedfor mobile offshore drilling units (MODUs) and other vesselswhich are asymmetrical about the centerline or whose internalarrangement or outfitting is such that an inherent list maydevelop from off-center weight. Because of their nature, otherspecial considerations not spe

10、cifically addressed in this guidemay be necessary for some MODUs. This standard is notapplicable to vessels such as a tension-leg platforms, semi-submersibles, rigid hull inflatable boats, and so on.1.2 The limitations of 1 % trim or 4 % heel and so on applyif one is using the traditional pre-define

11、d hydrostatic charac-teristics. This is due to the drastic change of waterplane area. Ifone is calculating hydrostatic characteristics at each move,such as utilizing a computer program, then the limitations arenot applicable.1.3 The values stated in inch-pound units are to be regardedas standard. No

12、 other units of measurement are included in thisstandard.1.4 This standard does not purport to address the safetyconcerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety andhealth practices and determine the applicability of regu

13、latorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:E100 Specification for ASTM Hydrometers3. Terminology3.1 Definitions:3.1.1 inclining experimentinvolves moving a series ofweights, in the transverse direction, and then measuring theresulting change in the equilibrium heel angl

14、e of the vessel. By1This guide is under the jurisdiction of ASTM Committee F25 on Ships andMarine Technology and is the direct responsibility of Subcommittee F25.01 onStructures.Current edition approved Oct. 1, 2013. Published October 2013. Originallyapproved in 1990. Last previous edition approved

15、in 2008 as F1321 92 (2008).DOI: 10.1520/F1321-13.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1using this information and applying basic naval architectureprinciples, the vessels vertical center of gravity KG is deter-mined.3.1.2 Co

16、ndition 1vessel in Condition 1 is a vessel com-plete in all respects, but without consumables, stores, cargo,crew and effects, and without any liquids on board exceptmachinery fluids, such as lubricants and hydraulics, are atoperating levels. Condition 1 is sometimes referred to as“operational light

17、 ship.”3.1.3 Condition 0vessel in Condition 0 is a vessel asinclined.3.1.4 lightweight surveythis task involves taking an auditof all items which must be added, deducted, or relocated on thevessel at the time of the stability test so that the observedcondition of the vessel can be adjusted to the li

18、ght shipcondition. The weight, longitudinal, transverse, and verticallocation of each item must be accurately determined andrecorded. Using this information, the static waterline of theship at the time of the stability test as determined frommeasuring the freeboard or verified draft marks of the ves

19、sel,the vessels hydrostatic data, and the seawater density; the lightship displacement and longitudinal center of gravity can beobtained. The transverse center of gravity may also becalculated, if necessary.3.1.5 relative density(formerly known as specificgravity)ratio of the mass of a given volume

20、of material at astated temperature to the mass of an equal volume gas freedistilled water at the same or different temperatures. Bothreferenced temperatures shall be explicitly stated.4. Significance and Use4.1 From the light ship characteristics one is able to calcu-late the stability characteristi

21、cs of the vessel for all conditionsof loading and thereby determine whether the vessel satisfiesthe applicable stability criteria.Accurate results from a stabilitytest may in some cases determine the future survival of thevessel and its crew, so the accuracy with which the test isconducted cannot be

22、 overemphasized. The condition of thevessel and the environment during the test is rarely ideal andconsequently, the stability test is infrequently conducted ex-actly as planned. If the vessel is not 100 % complete and theweather is not perfect, there ends up being water or shipyardtrash in a tank t

23、hat was supposed to be clean and dry and soforth, then the person in charge must make immediate deci-sions as to the acceptability of variances from the plan. Acomplete understanding of the principles behind the stabilitytest and a knowledge of the factors that affect the results isnecessary.5. Theo

24、ry5.1 The Metacenter(See Fig. 1). The transverse metacen-ter (“M”) is based on the hull form of a vessel and is the pointaround which the vessels center of buoyancy (“B”) swings forsmall angles of inclination (0 to 4 unless there are abruptchanges in the shape of the hull). The location of B is fixe

25、d forany draft, trim, and heel, but it shifts appreciably as heelincreases. The location of B shifts off the centerline for smallangles of inclination (“”), but its height above the molded keel(“K”) will stay essentially the same. The location of M, on theother hand, is essentially fixed over a rang

26、e of heeling anglesup to about 4, as the ship is inclined at constant displacementand trim. The height of M above K, known as “KM”, is oftenplotted versus draft as one of the vessels curves of form. As ageneral “rule of thumb,” if the difference from the design trimof the vessel is less than 1 % of

27、its length, the KM can be takendirectly from either the vessels curves of form or hydrostatictables. Because KM varies with trim, the KM must be com-puted using the trim of the ship at the time of the stability testwhen the difference from the design trim of the vessel is greaterthan 1 % of its leng

28、th. Caution should be exercised whenapplying the “rule of thumb” to ensure that excessive error, aswould result from a significant change in the waterplane areaduring heeling, is not introduced into the stability calculations.5.2 Metacentric HeightThe vertical distance between thecenter of gravity (

29、“G”) and M is called the metacentric height(“GM”). At small angles of heel, GM is equal to the initialslope of the righting arm (“GZ”) curve and is calculated usingthe relationship, GZ = GM sin . GM is a measure of vesselstability that can be calculated during an inclining experiment.As shown in Fig

30、. 1 and Fig. 2, moving a weight (“W”) acrossthe deck a distance (“x”) will cause a shift in the overall centerof gravity (GG) of the vessel equal to (W)(x)/displ andparallel to the movement of W. The vessel will heel over to anew equilibrium heel angle where the new center of buoyancy,B, will once a

31、gain be directly under the new center of gravity(G). Because the angle of inclination during the incliningexperiment is small, the shift in G can be approximated byFIG. 1 Movement of the Center of BuoyancyFIG. 2 Metacentric HeightF1321 1312GMtan and then equated to (W)(x)/displ. Rearranging thisequa

32、tion slightly results in the following equation:GM 5W!x!displ! tan !(1)Since GM and displ remain constant throughout the incliningexperiment the ratio (W)(x)/tan will be a constant. Bycarefully planning a series of weight movements, a plot oftangents is made at the corresponding moments. The ratio i

33、smeasured as the slope of the best represented straight linedrawn through the plotted points as shown in Fig. 3, wherethree angle indicating devices have been used. This line doesnot necessarily pass through the origin or any other particularpoint, for no single point is more significant than any ot

34、herpoint. A linear regression analysis is often used to fit thestraight line.5.3 Calculating the Height of the Center of Gravity Abovethe KeelKM is known for the draft and trim of the vesselduring the stability test. The metacentric height, GM,ascalculated above, is determined from the inclining exp

35、eriment.The difference between the height KM and the distance GM isthe height of the center of gravity above the keel, KG. See Fig.4.5.4 Measuring the Angle of Inclination(See Fig. 5.) Eachtime an inclining weight, W, is shifted a distance, x, the vesselwill settle to some equilibrium heel angle, .

36、To measure thisangle, , accurately, pendulums or other precise instruments areused on the vessel. When pendulums are used, the two sides ofthe triangle defined by the pendulum are measured. (“Y”) is thelength of the pendulum wire from the pivot point to the battenand (“Z”) is the distance the wire d

37、eflects from the referenceposition at the point along the pendulum length where trans-verse deflections are measured. Tangent is then calculated:tan 5 Z/Y (2)After each weight movement, plotting all of the readings foreach of the pendulums during the inclining experiment aids inthe discovery of bad

38、readings. Since (W)(x)/tan should beconstant, the plotted line should be straight. Deviations from astraight line are an indication that there were other momentsacting on the vessel during the inclining. These other momentsmust be identified, the cause corrected, and the weight move-ments repeated u

39、ntil a straight line is achieved. Figs. 6-9illustrate examples of how to detect some of these othermoments during the inclining and a recommended solution foreach case. For simplicity, only the average of the readings isshown on the inclining plots.5.5 Free SurfaceDuring the stability test, the incl

40、ining ofthe vessel should result solely from the moving of the incliningweights. It should not be inhibited or exaggerated by unknownmoments or the shifting of liquids on board. However, someliquids will be aboard the vessel in slack tanks so a discussionof “free surface” is appropriate.5.5.1 Standi

41、ng Water on DeckDecks should be free ofwater. Water trapped on deck may shift and pocket in a fashionsimilar to liquids in a tank.5.5.2 Tankage During the IncliningIf there are liquids onboard the vessel when it is inclined, whether in the bilges or inFIG. 3 A Typical Incline PlotFIG. 4 Relationship

42、 between GM, KM, and KGFIG. 5 Measuring the Angle of InclinationF1321 1313the tanks, it will shift to the low side when the vessel heels.This shift of liquids will exaggerate the heel of the vessel.Unless the exact weight and distance of liquid shifted can beprecisely calculated, the GM from Eq 1 wi

43、ll be in error. Freesurface should be minimized by emptying the tanks completelyand making sure all bilges are dry or by completely filling thetanks so that no shift of liquid is possible. The latter method isnot the optimum because air pockets are difficult to removefrom between structural members

44、of a tank, and the weight andcenter of the liquid in a full tank must be accurately determinedto adjust the light ship values accordingly. When tanks must beleft slack, it is desirable that the sides of the tanks be parallelvertical planes and the tanks be regular in shape (that is,rectangular, trap

45、ezoidal, and so forth) when viewed fromNOTE 1Recheck all tanks and voids and pump out as necessary; redoall weight movements and recheck freeboard and draft readings.FIG. 6 Excessive Free LiquidsNOTE 1Take water soundings and check lines; redo Weight Move-ments 2 and 3.FIG. 7 Vessel Touching Bottom

46、or Restrained by Mooring LinesFIG. 8 Steady Wind From Port Side Came Up After Initial ZeroPoint Taken (Plot Acceptable)NOTE 1Redo Weight Movements 1 and 5.FIG. 9 Gusty Wind From Port SideF1321 1314above, so that the free surface moment of the liquid can beaccurately determined. The free surface mome

47、nt of the liquidin a tank with parallel vertical sides can be readily calculatedby the equation:Mfs5 lb3/12Q (3)where:Mfs= free surface moment, ft-Ltonsl = length of tank, ft,b = breadth of tank, ft,Q = specific volume of liquid in tank (ft3/ton), and(See Annex A3 for liquid conversions or measure Q

48、directly with a hydrometer.)Lton = long ton of 2240 lbs.Free surface correction is independent of the height of thetank in the ship, location of the tank, and direction of heel.5.5.3 As the width of the tank increases, the value of freesurface moment increases by the third power. The distanceavailab

49、le for the liquid to shift is the predominant factor. Thisis why even the smallest amount of liquid in the bottom of awide tank or bilge is normally unacceptable and should beremoved before the inclining experiment. Insignificantamounts of liquids in V-shaped tanks or voids (for example, achain locker in the bow), where the potential shift is negligible,may remain if removal of the liquid would be difficult or wouldcause extensive delays.6. Preparations for the Stability Test6.1 General Condition of the VesselA vessel should b