1、Designation: F1321 92 (Reapproved 2008)F1321 13 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
2、; the number immediately 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
3、.This standard has been approved for use by agencies of the Department of Defense.INTRODUCTIONThis guide provides the marine industry with a basic understanding of the various aspects of astability test. It contains procedures for conducting a stability test to ensure that valid results areobtained
4、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 necessary procedures to be followed to gather accuratedata
5、 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 accuracy as the inclining experiment is conducted. It isr
6、ecommended 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 stability test can be considered to be two separate tasks; the lightwei
7、ght 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 taken out of service to prepare for and conductthe stability test.
8、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 center ofgravity (“TCG”) may also be determined for mobile offshor
9、e 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 considerations not specifically addressed in this guide may be nec
10、essary for some MODUs.This standard is not applicable to vessels such as a TLP, semi-submersibles, RHIB, and so on.1.2 The limitations of 1 % trim or 4 % heel and so on applies if one is using the traditional pre-defined hydrostaticcharacteristics. This is due to the drastic change of waterplane are
11、a. If one is using calculating hydrostatic characteristics at eachmove, such as utilizing a computer program, then the limitations are not applicable.1.3 The values stated in inch-pound units are to be regarded as standard. No other units of measurement are included in thisstandard.1.4 This standard
12、 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 determine the applicability of regulatory limitationsprior to use.2. Referenced Documents2.1 ASTM Standards
13、: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.Current edition approved Nov. 1, 2008Oct. 1, 2013. Published December 2008October 2013. Originally
14、 approved in 1990. Last previous edition approved in 20042008as F1321 92 (2004).(2008). DOI: 10.1520/F1321-92R08.10.1520/F1321-13.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. B
15、ecauseit 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 published by ASTM is to be considered the official document.Copyright ASTM International, 10
16、0 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 known weights, normally in the transverse direction, and thenmeasuring the resulting change in the equilibrium heel angle of the vesse
17、l. By using this information and applying basic navalarchitecture principles, the vessels vertical center of gravity KG is determined.3.1.2 light shipCondition 1a vessel in the light ship condition (“Condition I1”) is a vessel complete in all respects, butwithout consumables, stores, cargo, crew and
18、 effects, and without any liquids on board except that machinery fluids, such aslubricants 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 lightweight surveythis task involv
19、es 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 location of each item must be accurat
20、ely 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 ship displacement and longitudinal
21、 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 free distilled water at the sam
22、e 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 whether the vessel satisfies the
23、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 during the test is rarely ideal an
24、d 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 in charge must make immediatede
25、cisions 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”) is based on the hull form of a
26、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 increases. The locationof B sh
27、ifts 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 constant displacement and trim. T
28、he 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 vessels curves of form or hydrostat
29、ic 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 thumb” to ensure that excessivee
30、rror, 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 1325.2 Metacentric HeightThe vertical distance between the center of gravity (“G”) and M is called the metacentric he
31、ight(“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, Fig. 2, and Fig. 4, moving a wei
32、ght (“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 heelangle where the new center of buoyancy, B, will once again be directly under th
33、e new center of gravity (G). Because the angleof inclination during the inclining experiment is small, the shift in G can be approximated by GMtan and then equated to(W)(x)/displdispl. . Rearranging this equation slightly results in the following equation:GM5 W!x!displ! tan! (1)Since GM and displ re
34、main 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 appropriatecorresponding moments. The ratio is measuredas the slope of the best represented straight line drawn through the
35、plotted points as shown in Fig. 3, where three angle indicatingdevices have been used. This line does not necessarily pass through the origin or any other particular point, for no single point ismore significant than any other point. A linear regression analysis is often used to fit the straight lin
36、e.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 the
37、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 instr
38、uments 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 pendulum
39、 length where transverse deflections are measured. Tangent is then calculated:tan 5Z/Y (2)PlottingAfter each weight movement, plotting all of the readings for each of the pendulums during the inclining experiment aidsin the discovery of bad readings. Since (W)(x)/tan should be constant, the plotted
40、line should be straight. Deviations from astraight line are an indication that there were other moments acting on the vessel during the inclining. These other moments mustbe identified, the cause corrected, and the weight movements repeated until a straight line is achieved. Figs. 6-9 illustrate exa
41、mplesof 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
42、 of 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
43、trapped 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 exaggera
44、te the 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 shiftof l
45、iquid is possible. The latter method is not the optimum because air pockets are difficult to remove from between structuralFIG. 2 Metacentric HeightF1321 133members of a tank, and the weight and center of the liquid in a full tank must be accurately determined to adjust the light shipvalues accordin
46、gly. When tanks must be left slack, it is desirable that the sides of the tanks be parallel vertical planes and the tanksFIG. 4 Relationship between GM,KM, and KGFIG. 3 A Typical Incline PlotFIG. 5 Measuring the Angle of InclinationF1321 134be regular in shape (that is, rectangular, trapezoidal, and
47、 so 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:Mfs = free surface moment, ft-Ltonsl = length of ta
48、nk, ft,NOTE 1Recheck all tanks and voids and pump out as necessary; 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 LinesF1
49、321 135b = 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 liquid
