# SAE J1238v002

SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirelyvoluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.”SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions.QUESTIONS REGARDING THIS DOCUMENT: (724) 772-8512 FAX: (724) 776-0243TO PLACE A DOCUMENT ORDER; (724) 776-4970 FAX: (724) 776-0790SAE WEB ADDRESS http://www.sae.orgCopyright 1998 Society of Automotive Engineers, Inc.All rights reserved. Printed in U.S.A.SURFACEVEHICLE400 Commonwealth Drive, Warrendale, PA 15096-0001RECOMMENDEDPRACTICESubmitted for recognition as an American National StandardJ1238REAF.JUL1998Issued 1978-10Reaffirmed 1998-07Superseding J1238 OCT78Rating Lift Cranes on Fixed Platforms Operating in the Ocean EnvironmentForeword—This Reaffirmed Document has been changed only to reflect the new SAE Technical Standards BoardFormat. References were added as Section 2. The Tables were changed to Figures due to the complexity of theformat. Equations in the Appendix were removed.1. Scope—The scope of this SAE Recommended Practice is limited to cranes mounted on a fixed platform liftingloads from a vessel alongside. The size of the vessel is assumed not to exceed that of a work boat as definedin 3.14.1.1 Purpose—The purpose of this document is to establish the design dynamic loads, the calculation procedures,and a load rating chart format for lift cranes operating in a variety of sea conditions.2. References2.1 Applicable Publications—The following publications form a part of the specification to the extent specifiedherein. 1. J. J. Meyers, C. H. Holm, and R. F. McAllister, “Handbook of Ocean and Underwater Engineering.“McGraw-Hill Book Co., 1969.2. Carley C. Ward, “Dynamic Vertical Forces on a Crane Loading (Unloading) a Floating Platform.“ CivilEngineering Laboratory Technical Memorandum TM 51-76-11 (September 1976).3. Kenneth V. Johnson, “Theoretical Overload Factor Effect of Sea State on Marine Cranes.“ OffshoreTechnology Conference, Paper No. OTC 2584 (1976).4. D. A. Davis and H. S. Zwibel, “The Motion of Floating Advanced Base Components in Shoal Water—AComparison Between Theory and Field Test Data.“ Civil Engineering Laboratory Technical NoteNH-1371.3. Definitions3.1 Significant wave height is the average of the highest one-third of the wave height population. Wave height ismeasured trough to crest.3.2 Sea state is an indicator relating the height of the waves to sea conditions in relative terms.3.3 Wave instrument reading as used on the load rating chart, indicates the value obtained from a wave buoy or awave staff that relates to the sea conditions. The wave instrument reading can be analyzed to form the ratio ofthe average wave height to the average period (H/T).SAE J1238 Reaffirmed JUL1998-2-3.4 Surge is the fore and aft ship motion along the longitudinal axis through the center of gravity.3.5 Sway is the athwart ship motion along the transverse axis through the center of gravity.3.6 Heave is the vertical ship motion along the vertical axis through the center of gravity.3.7 Roll is the angular ship motion about the longitudinal axis through the center of gravity.3.8 Pitch is the angular ship motion about the transverse axis through the center of gravity.3.9 Yaw is the angular ship motion about the vertical axis through the center of gravity.3.10 Offlead is the percent slope from the vertical in the vertical plane of the boom, that locates the position of theload with respect to the tip of the boom.3.11 Sidelead is the percent slope from the vertical normal to the vertical plane of the boom, that locates theposition of the load with respect to the tip of the boom.3.12 Dynamic rated load is the maximum load that can be lifted under specified dynamic conditions, withoutexceeding allowable strength limits.3.13 Static rated load is the maximum load that can be lifted under normal land conditions, without exceedingallowable strength limits.3.14 A typical work boat is a vessel of 180-ft length, 40-ft beam, and 1500-long-ton displacement.4. Dynamic Load—The dynamic load being addressed is imposed on the crane at the time of the load lift off fromthe moving deck of the vessel alongside. Additionally, consideration is directed to the effects of the horizontaldisplacement in the plane of the boom and normal to the plane of the boom caused by surge and sway of thevessel.After studying the motions of a workboat, it is assumed that the vertical motion follows the wave amplitude andthat horizontal motions include sway, surge, and yaw, but exclude drift.The vertical dynamic load, P (lb), that occurs when the lifted load W (lb) is directly under the boom tip is givenby the equation:(Eq. 1)where:g = Acceleration due to gravity (ft/s2)k = Vertical structural stiffness component with the load force at appropriate offlead (lb/ft)VD = Absolute value of velocity of the deck at the pick point (ft/s)VH = Absolute value of velocity of the load hook (ft/s)AD = Acceleration of the deck at pick point (ft/s2). Refer to Reference 2.1.(2) for appropriate signconvention.PW 11kgW-------- VD VH+()2 ADg-------2+1/2+=SAE J1238 Reaffirmed JUL1998-3-If the pick point is assumed to coincide with the point of maximum wave downward velocity, then AD = 0 andVH and VD are related by the sinusoidal wave equation and the constant line speed equation and Equation 1reduces to:(Eq. 2)where:WD = Dynamic rated loadPmax = Maximum equivalent static force with offlead and sidelead that produces the maximum allowableload in any crane componentandor(Eq. 3)where:m = Impact coefficient ()H = Average wave height (ft)T = Average wave period (s)The coefficient 1.058 in Equation 3 includes a 90% probability that the next wave will have a velocity less than1.577 pi H/T (see Appendix A).Implicit in Equation 2 are the dynamic effects of picking impact as well as sidelead and offlead effects. SeeFigure 1 for sidelead and offlead values. Equation 3 is to be used to calculate a series of values for mcorresponding to values of H/T, such as those listed in Figure 2.FIGURE 1—PERCENT OFFLEAD AND SIDELEAD(1)Wave InstrumentReading H/T(ft/s) 0.25 0.46 0.80 1.17 1.61Static DynamicOffLead (%)0 6 8 12 16 22SideLead (%)2 3 4 6 8 11WD Pmaxm2k2---------- Pmaxm2k m2k2----------2+ 1/2–+=m VH VD+g---------------------------=m 1.058 HT----=ft1. Alternatively, % offlead sidelead(180 ft) (% indicated)boom tip height above boat deck--------------------------------------------------------------------------------------Minimum sidelead not to be less than 2%.=SAE J1238 Reaffirmed JUL1998-4-FIGURE 2—MARINE CRANE RATING CHART FOR FIXED PLATFORM5. Calculation Procedure5.1 Calculate Pmax—For each WD that will be listed on the rating chart, each structural component of the crane isanalyzed to find the value of Pmax that could be applied to produce a maximum allowable load in a particularcomponent. Appropriate offlead and sidelead factors are found in Figure 1. The allowable load in a particularcomponent is determined by standard industry practice for land cranes contained in SAE J987 (structures) andSAE J959 (ropes).5.2 Select Pmax—For each WD to be shown on the rating chart, a Pmax, for each structural component of the craneis found, and the minimum value of Pmax is selected. This will leave one Pmax for each WD.5.3 Calculate k—For each WD to be shown on the rating chart, and with appropriate offlead as shown on Figure 1,calculate the system springrate, k effective, at the load point. The term k is a function of load line, suspensionline, A-frame, boom, and jib deflections under service load. Fewer components may be used in thedetermination of k as this will make the resulting ratings more conservative.5.4 Calculate m—Using Equation 3, calculate the required values of m.5.5 Calulate WD—Using the Pmax, k, and m values determined previously for each WD to be shown, applyEquation 2 to calculate WD.Manufacturer _________________________________________________________________________Model ____________________ Boom Length 100 ft S/N ______________________Boom Foot to Sea Level Distance 120 ft Static Conditions Dynamic ConditionsWave InstrumentReading H/T(ft/s) 0 0.25 0.46 0.80 1.17 1.61Maximum Parts ofLine to ClearSecond WaveNotappli-cable 7 6 5 4 3Radius (ft)BoomAngle(deg)StaticRating(lb)Dynamic Ratings forFour-Part Main Hoist Line7/8 6 x 25 IWRC-EIPS25 78.5 90 000 72 000 56 000 42 900 30 50030 75.6 90 000 69 000 58 700 44 400 32 10040 69.6 90 000 67 900 56 600 41 900 30 70050 63.3 82 000 56 300 46 900 34 700 25 400Radius (ft)Boomangle(deg)StaticRating(lb)Dynamic Rating forOne-Part Whip Hoist Line7/8 6 x 25 IWRC-EIPS25 80.1 22 700 18 900 16 900 16 300 13 900 11 50030 76.1 22 700 19 000 17 000 16 300 14 000 11 60040 70.3 22 700 18 900 16 900 16 200 13 900 11 50050 64.0 22 700 18 400 16 500 15 800 13 400 11 000SAE J1238 Reaffirmed JUL1998-5-5.6 Calculate the Maximum Number of Parts of Line, Nρ—Calculate the maximum number of parts of line, NP:Using Equation 4, calculate the maximum number of parts of line that will permit the load to clear the secondwave (see Appendix A).(Eq. 4)where:NP = Integer value of the right side of Equation 4 and represents the maximum parts of line required for theload to clear the second wave.VL = Hoist line speed (ft/s) when the rope is on the first layer of the drum. The coefficient 1.051 in Equation4 includes a 90% probability that the next wave will have a velocity less than 1.577 pi H/T.6. Marine Crane Rating Chart Format—A suggested format for a marine crane rating chart for fixed platforms isgiven in Figure 2. This format is suggested for use at the discretion of each manufacturer; some suggestionsand comments regarding the content of this chart follow.6.1 Each rating chart should be prepared for a fixed number of parts of load hoist line.6.2 Each rating chart should also indicate ratings for a single part whipline.6.3 The maximum parts of line that will permit the load to clear the second wave involves machinery parameterssuch as hoist capability and hoist line speed. It is advisable not to show ratings for cases in which the numberof parts of line are not adequate for the load to clear the second wave.6.4 The wave instrument reading, H/T, is a statistical description of the sea condition which is intended to beobtained from a wave recorder as described in 3.3. Note that H/T is equal to 0.62 times the significant waveheight in feet/average period in seconds.7. Special Ratings—This section describes procedures to be employed when it is necessary to obtain marinecrane ratings for particular values of ship motion (vertical height, S, and period, T), sidelead, and offlead asspecified by the user. In this case, the following procedure shall be applied:7.1 The calculation of the dynamic rated load (WD) from Equation 2 shall be based on a modified factor, m, givenby:(Eq. 5)7.2 The calculation of NP from Equation 4 shall be given by:(Eq. 6)7.3 The remainder of the calculations are performed as outlined in Section 5.PREPARED BY THE SAE CRANES AND LIFTING DEVICES TECHNICAL COMMITTEENP VL1.051 HT-------------------------=m 0.671 ST---=NP VL0.666 ST------------------------=SAE J1238 Reaffirmed JUL1998-6-APPENDIX ABASIS OF EQUATIONSA.1 In the usual practice of snatching a load from the deck of a heaving ship, the crane operator starts his hoistoperation at the trough of a wave. On multipart line lifts, the hoist speed often cannot follow the wave and liftthe load clear of the ship before the crest succeeding the trough. Because of the usual relationships betweenhoist speed and wave speed, the pickpoint will usually be while the ship is falling after the first crest. It will beassumed here that the pickpoint will be at maximum downward velocity of the ship.Ship motion induced by wave action is a function of sea state, hull shape, and the displacement of the ship.The common work boat often used around fixed platforms is usually 1500 ton displacement or less. Smallerships like this respond strongly to the sea, and it will be assumed (based on ship motion studies) that thevertical motion of the ship’s rear quarter deck equals the vertical wave motion.At the maximum velocity pickpoint (ωt = 3pi/2 from trough) the deck acceleration term in Equation 1 willdisappear and(Eq. A1)At the pickpoint, the simultaneous solution of line displacement (VHt) and wave displacement H (1 – cos ωt)/2shows:(Eq. A2)Since ωt = 3pi/2 at the instant of lift off(Eq. A3)in dimensional units of The factor q is a probability parameter. If wave probability is 90% (see Figure A1),then q is 1.577 and(Eq. A4)The impact coefficient m in Equation A3 is a function of H/T, the wave height divided by wave period; but waveheight and period are actually statistical functions of H and T, the tabulated averages for any given sea state.The term 3.808 is dimensionless, while 0.671 is not. Note that H = 0.62 times the significant wave height.The individual statistical functions of H/T are described in many References (e.g., section on Sea Motion in the“Handbook of Ocean and Underwater Engineering“ in Reference 2.1.(1)). Both are usually described asRayleigh or Weibull type skewed distributions and their interrelationship can be described on power spectraldensity plots. The statistical distribution of velocity is usually not shown. Analysis of test data, however,indicates that if the velocity probability density is considered as a normal (Gaussian) distribution symmetricalaround V, reasonable results will be obtained if the following assumptions are used:(Eq. A5)(Eq. A6)PW-----1VH VD+g-------------------- kW-----+ 1 m kW-----+==VH VD+g--------------------HpiTg---------- 1cos ωt–ωt--------------------------sin ωt– m==m 3.808g-------------- HT----0.671 HT--- 0.671 q HT----===ft.m 0.671 x 1.577 HT⁄ 1.058 HT⁄==V 1N--- Vi pi HT----≈i 1=N∑=V2()1N--- Vi2 1.20V()2≈i 1=N∑=SAE J1238 Reaffirmed JUL1998-7-where:Vi is pi Hi/Ti as obtained by the zero-up-crossing count method (see Reference 2.1.(1)). The velocityvariance σv2 is:(Eq. A7)The H/T variance σ2 and the standard deviation σ are:(Eq. A8)(Eq. A9)The number of standard deviations to give the cumulative probability P that H/T is less than q H/T may be readfrom any normal distribution table, and factor q is calculated from:(Eq. A10)where:n is the required number of standard deviations.Equation A10 may be evaluated for various values of wave velocity probabilities P as shown in Figure A1.FIGURE A1—WAVE VELOCITY PROBABILITIESSince wave velocity pi H/T is proportional to H/T, one interpretation from Figure A1 may be, th