1、Designation: F1321 131F1321 14 An 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 imme
2、diately following 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 ha
3、s been approved for use by agencies of the U.S. Department of Defense.1 NOTEEditorially 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 con
4、ducting a stability 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
5、 to the necessary 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 exam
6、ined for accuracy 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 light ship characteristics. In this standard, a vessel is a traditionalhull-formed vessel. The stabi
7、lity test can be considered to be two separate tasks; the lightweight survey and the incliningexperiment. The stability test is required for most vessels upon their completion and after major conversions. It is normallyconducted inshore in calm weather conditions and usually requires the vessel be t
8、aken out of service to prepare for and conductthe stability test. The three light ship characteristics determined from the stability test for conventional (symmetrical) ships aredisplacement (“displ”), longitudinal center of gravity (“LCG”), and the vertical center of gravity (“KG”). The transverse
9、center ofgravity (“TCG”) may also be determined for mobile offshore drilling units (MODUs) and other vessels which are asymmetricalabout the centerline or whose internal arrangement or outfitting is such that an inherent list may develop from off-center weight.Because of their nature, other special
10、considerations not specifically addressed in this guide may be necessary for some MODUs.This standard is not applicable 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 apply if one is using th
11、e traditional pre-defined hydrostatic characteristics.This is due to the drastic change of waterplane area. If one is calculating hydrostatic characteristics at each move, such as utilizinga computer program, then the limitations are not applicable.1.3 The values stated in inch-pound units are to be
12、 regarded as standard. No other units of measurement are included in thisstandard.1.4 This standard does not purport to address the safety concerns, if any, associated with its use. It is the responsibility of theuser of this standard to establish appropriate safety and health practices and determin
13、e the applicability of regulatory limitationsprior to use.2. Referenced Documents2.1 ASTM Standards:E100 Specification for ASTM Hydrometers1 This guide is under the jurisdiction of ASTM Committee F25 on Ships and Marine Technology and is the direct responsibility of Subcommittee F25.01 on Structures
14、.Current edition approved Oct. 1, 2013May 1, 2014. Published October 2013May 2014. Originally approved in 1990. Last previous edition approved in 20082013 asF1321 92 (2008).F1321 131. DOI: 10.1520/F1321-13.10.1520/F1321-14.This document is not an ASTM standard and is intended only to provide the use
15、r of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as
16、 published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3.1 Definitions:3.1.1 inclining experimentinvolves moving a series of weights, in the transverse direction, and
17、 then measuring the resultingchange in the equilibrium heel angle of the vessel. By using this information and applying basic naval architecture principles, thevessels vertical center of gravity KG is determined.3.1.2 Condition 1vessel in Condition 1 is a vessel complete in all respects, but without
18、 consumables, stores, cargo, crew andeffects, and without any liquids on board except machinery fluids, such as lubricants and hydraulics, are at operating levels.Condition 1 is sometimes referred to as “operational light ship.”3.1.3 Condition 0vessel in Condition 0 is a vessel as inclined.3.1.4 lig
19、htweight surveythis task involves taking an audit of all items which must be added, deducted, or relocated on thevessel at the time of the stability test so that the observed condition of the vessel can be adjusted to the light ship condition. Theweight, longitudinal, transverse, and vertical locati
20、on of each item must be accurately determined and recorded. Using thisinformation, the static waterline of the ship at the time of the stability test as determined from measuring the freeboard or verifieddraft marks of the vessel, the vessels hydrostatic data, and the seawater density; the light shi
21、p displacement and longitudinal centerof gravity can be obtained. The transverse center of gravity may also be calculated, if necessary.3.1.5 relative density(formerly known as specific gravity)ratio of the mass of a given volume of material at a statedtemperature to the mass of an equal volume gas
22、free distilled water at the same or different temperatures. Both referencedtemperatures shall be explicitly stated.4. Significance and Use4.1 From the light ship characteristics one is able to calculate the stability characteristics of the vessel for all conditions ofloading and thereby determine wh
23、ether the vessel satisfies the applicable stability criteria.Accurate results from a stability test mayin some cases determine the future survival of the vessel and its crew, so the accuracy with which the test is conducted cannot beoveremphasized. The condition of the vessel and the environment dur
24、ing the test is rarely ideal and consequently, the stability testis infrequently conducted exactly as planned. If the vessel is not 100 % complete and the weather is not perfect, there ends up beingwater or shipyard trash in a tank that was supposed to be clean and dry and so forth, then the person
25、in charge must make immediatedecisions as to the acceptability of variances from the plan. A complete understanding of the principles behind the stability testand a knowledge of the factors that affect the results is necessary.5. Theory5.1 The Metacenter(See Fig. 1). The transverse metacenter (“M”)
26、is based on the hull form of a vessel and is the point aroundwhich the vessels center of buoyancy (“B”) swings for small angles of inclination (0 to 4 unless there are abrupt changes in theshape of the hull). The location of B is fixed for any draft, trim, and heel, but it shifts appreciably as heel
27、 increases. The locationof B shifts off the centerline for small angles of inclination (“”), but its height above the molded keel (“K”) will stay essentiallythe same. The location of M, on the other hand, is essentially fixed over a range of heeling angles up to about 4, as the ship isinclined at co
28、nstant displacement and trim. The height of M above K, known as “KM”, is often plotted versus draft as one of thevessels curves of form. As a general “rule of thumb,” if the difference from the design trim of the vessel is less than 1 % of itslength, the KM can be taken directly from either the vess
29、els curves of form or hydrostatic tables. Because KM varies with trim,the KM must be computed using the trim of the ship at the time of the stability test when the difference from the design trim ofthe vessel is greater than 1 % of its length. Caution should be exercised when applying the “rule of t
30、humb” to ensure that excessiveerror, as would result from a significant change in the waterplane area during heeling, is not introduced into the stabilitycalculations.FIG. 1 Movement of the Center of BuoyancyF1321 1425.2 Metacentric HeightThe vertical distance between the center of gravity (“G”) and
31、 M is called the metacentric height(“GM”). At small angles of heel, GM is equal to the initial slope of the righting arm (“GZ”) curve and is calculated using therelationship, GZ = GM sin . GM is a measure of vessel stability that can be calculated during an inclining experiment. As shownin Fig. 1 an
32、d Fig. 2, moving a weight (“W”) across the deck a distance (“x”) will cause a shift in the overall center of gravity (GG)of the vessel equal to (W)(x)/displ and parallel to the movement of W. The vessel will heel over to a new equilibrium heel anglewhere the new center of buoyancy, B, will once agai
33、n be directly under the new center of gravity (G). Because the angle ofinclination during the inclining experiment is small, the shift in G can be approximated by GMtan and then equated to(W)(x)/displ. Rearranging this equation slightly results in the following equation:GM5 W!x!displ! tan! (1)Since
34、GM and displ remain constant throughout the inclining experiment the ratio (W)(x)/tan will be a constant. By carefullyplanning a series of weight movements, a plot of tangents is made at the corresponding moments. The ratio is measured as the slopeof the best represented straight line drawn through
35、the plotted points as shown in Fig. 3, where three angle indicating devices havebeen used. This line does not necessarily pass through the origin or any other particular point, for no single point is more significantthan any other point. A linear regression analysis is often used to fit the straight
36、 line.5.3 Calculating the Height of the Center of Gravity Above the KeelKM is known for the draft and trim of the vessel duringthe stability test. The metacentric height, GM, as calculated above, is determined from the inclining experiment. The differencebetween the height KM and the distance GM is
37、the height of the center of gravity above the keel, KG. See Fig. 4.5.4 Measuring the Angle of Inclination(See Fig. 5.) Each time an inclining weight, W, is shifted a distance, x, the vessel willsettle to some equilibrium heel angle, . To measure this angle, , accurately, pendulums or other precise i
38、nstruments are used onthe vessel. When pendulums are used, the two sides of the triangle defined by the pendulum are measured. (“Y”) is the length ofthe pendulum wire from the pivot point to the batten and (“Z”) is the distance the wire deflects from the reference position at thepoint along the pend
39、ulum length where transverse deflections are measured. Tangent is then calculated:tan 5Z/Y (2)After each weight movement, plotting all of the readings for each of the pendulums during the inclining experiment aids in thediscovery of bad readings. Since (W)(x)/tan should be constant, the plotted line
40、 should be straight. Deviations from a straightline are an indication that there were other moments acting on the vessel during the inclining. These other moments must beidentified, the cause corrected, and the weight movements repeated until a straight line is achieved. Figs. 6-9 illustrate example
41、sof how to detect some of these other moments during the inclining and a recommended solution for each case. For simplicity, onlythe average of the readings is shown on the inclining plots.5.5 Free SurfaceDuring the stability test, the inclining of the vessel should result solely from the moving of
42、the incliningweights. It should not be inhibited or exaggerated by unknown moments or the shifting of liquids on board. However, some liquidswill be aboard the vessel in slack tanks so a discussion of “free surface” is appropriate.5.5.1 Standing Water on DeckDecks should be free of water. Water trap
43、ped on deck may shift and pocket in a fashion similarto liquids in a tank.5.5.2 Tankage During the IncliningIf there are liquids on board the vessel when it is inclined, whether in the bilges or in thetanks, it will shift to the low side when the vessel heels. This shift of liquids will exaggerate t
44、he heel of the vessel. Unless the exactweight and distance of liquid shifted can be precisely calculated, the GM from Eq 1 will be in error. Free surface should beminimized by emptying the tanks completely and making sure all bilges are dry or by completely filling the tanks so that no shiftFIG. 2 M
45、etacentric HeightF1321 143of liquid is possible. The latter method is not the optimum because air pockets are difficult to remove from between structuralmembers of a tank, and the weight and center of the liquid in a full tank must be accurately determined to adjust the light shipFIG. 3 A Typical In
46、cline PlotFIG. 4 Relationship between GM,KM, and KGFIG. 5 Measuring the Angle of InclinationF1321 144values accordingly. When tanks must be left slack, it is desirable that the sides of the tanks be parallel vertical planes and the tanksbe regular in shape (that is, rectangular, trapezoidal, and so
47、forth) when viewed from above, so that the free surface moment ofthe liquid can be accurately determined. The free surface moment of the liquid in a tank with parallel vertical sides can be readilycalculated by the equation:Mfs5lb3/12Q (3)where:NOTE 1Recheck all tanks and voids and pump out as neces
48、sary; redo all weight movements and recheck freeboard and draft readings.FIG. 6 Excessive Free LiquidsNOTE 1Take water soundings and check lines; redo Weight Movements 2 and 3.FIG. 7 Vessel Touching Bottom or Restrained by Mooring LinesF1321 145where:Mfs = free surface moment, ft-Ltonsl = length of
49、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 directly with a hydrometer.)Lton = long ton of 2240 lbs.Free surface correction is independent of the height of the tank in the ship, location of the tank, and direction of heel.5.5.3 As the width of the tank increases, the value of free surface moment increases by the third power. The distance availablefor the liquid to shift is the predominant factor. This is why even the smallest amount of
