Computer-Aided Ship Design at MarAdAlan H. Woodyard

Maritime Administration

Introduction

The preliminary design process for a ship, which involvesan iterative series of calculations based upon a data basethat describes the hull shape, is a natural for designautomation. Figure I illustrates the spiralling nature of thedesign verification from basic requirements to final designof the ship and indicates the sequential nature of thecalculations.

At the Maritime Administration, automating the designprocess started some time ago with the creation of batchprograms for each spoke in the spiral. The following fiveprograms, requiring direct access to the hull-form data base,

46

comprise the Hull Scientific Package: Bonjeans/Hydro-statics (hull characteristics of volume, centers, and areas),Floodable Length (compartment length required to preventsinking when flooded), Longitudinal Strength (bendingmoment and shear forces on the ship when loaded),Capacities (tankage volume and centers), and DamagedStability (ability to survive in a damaged condition). Otherprograms in the spiral rely on data obtained from the HullScientific Package but do not access the hull-form database.

Although these programs were computationally effi-cient, they suffered on both the input and output sides.The addition of interactive creation of input files, a

COMPUTER

digitizer, and a plotter for graphical output have since giventhe total system a new dimension. In order to betterdescribe the system's capability, a sample design will bedeveloped in the following paragraphs explaining the role ofeach program in the design spiral.

BasicRequirements

HullShape

BonjeansHydrostatics

Floodable \Lengths

Hull andMachinery Arrangements

StructureDesign

The "Design Spiral" was introduced by Professor J. H. Evens in thearticle "Basic Design Concepts" printed in the November 1959Journal of the American Society of Naval Engineers.

Figure 1. The Design Spiral

Fl LES

Total System Arrangement

Whereas a series of batch programs is computationallysatisfactory, input preparation problems arise, both real(documentation inadequate, control cards confusing) andpsychological. The addition of timesharing services permitsprograms to prepare input files and control card files forthe user in a conversational manner. In fact, since the userin our case was separated geographically from the computerservice group, he did not have the batch terminal at hisdisposal. The user did have a timesharing terminal, however,and so necessity rather than efficiency instigated theprogramming of input file creation.

The input files are stored on the timesharing system andsent to the batch system along with a control card file forexecution by the user-selected batch program. Output maybe dispatched to either system, but normally is dispatchedto the remote batch printer and plotter.

The system's attributes may be summarized as follows:1. Central Computer

Remote BatchTime Sharing

2. File OrganizationControl Card FilesInput FilesProgram FilesData Base FilesOutput Files

OUTPUT

a 0

COMPUTER

0000Batch TimeBatch Share

- -

Plotter Printer

INPUT

LIZ N

Cards D isplay

Display

DigitizerFigure 2. Computer Aided Design Environment

April 1975 47

HALF-BREADTH

3. Input SourceTime-Sharing TerminalBatch Card ReaderDigitizerGraphics Display (to be added)Tape

4. Output DeviceTime-Sharing TerminalBatch PrinterPlotterGraphics Display (to be added)Cards or Tape

This gives considerable flexibility in program control(Figure 2). The anticipated addition of a graphics displayterminal should speed up the plotted output as well as adda new dimension to the system.

Hull Definition

Now that the system has been defined we may proceedwith a sample ship design to better illustrate eachcomponent's function. Returning to the design spiral ofFigure 1, we can see that initially the basic hull-formrequirements must be obtained.

PD - 159 BREAK BULK SHIP MODIFIED HULL FORM TO CP s *595AND LCBE 262.5 FT. AFT FP MAY 1972

%A BON JEAN DATA

MAXIMUM BEAM

LOAD WATERLINE

LENGTH FOR CALCULATIONS

LENGTH BETWEEN PERPENDICULARS

a 80.00

= 532.00a 525.00

a 525.00

STATION SPACING

NO. OF STATIONS

HULL GIRDER DEPTH

FULL LOAD DRAFT. MOLDED

ASSUMED BASE LINE

STATION NO. 0.00

SEGMENT CODES

W.L.0.0000.0000.0001.0002.0003.0004.000

%A4.377

c 5.0006.0007.0008.0008.7539.00010.00011.00012.00013.00014.00015.000lb .000

1 4 4 4 1 4 4 1

AREA0.000.000.004.2510.8818.5626.6529.6834.6142.2449.4155.9760.4461.8066.8471.17

74.8677.9980.6482.8784.17QL. la

V.M. N.u. T.M. RAD.0.00 0.000 0.00 0.00Q.00 0.000 0.00 0.000.00 .757 0.00 0.002.44 2.893 2.42 3.7412*50 3.644 7.92 3.7431.78 3.991 15.32 3.7460.08 4.048 23.48 3.7472.78 4.000 26*54 3.7495.90 3.908 31.42 16.50137.82 3.709 38.69 16.50184*34 3.444 45.11 16.50233.53 3.110 50.b0 16.50270*90 2.811 53.81 16.50283.00 2.711 54.76 30.00

330.82 2.335 57.94 30.00376.19 1.998 60.28 30.00418.60' 1.700 61.99 30.00457.72 1.439 63.22 30.00493.43 1.215 64.10 30.00525.80 1.026 64.72 30.00555.10 .872 65.17 30.00CsRI-77 .752 65.50 30.00

.666 65.74 -.~~~~~~.00.0030.00

Figure 4. Bonjeans Data Calculations

COMPUTER

Figure 3. Body Plan - Input

a 25.ooo

a 21

a 48.000- 3l.000

a 15.000

x

0.00

0.00

.32.32.32.32.32

-12.37-12.37-12.37-12.37-12.3730.6030.6030.6030.6030.6030.6030.6030.6030.6030.6030.6030.60

V

0.000.000.003.713.713.713.713.712.282.282.282.282.2820.0720.0720.0720.0720.0720.0720.0720.0720.0720.0720.07?0.07

48

A hull form may be either an original creation by thenaval architect or a variation of a hull form already inexistence. The hull-form variation is the more commonmethod. In fact, a library of hull forms is kept for just suchoccasions.

In either case the original form is recorded from a bodyplan which has been "faired" or smoothed in 'all threedimensions to assure there are no bumps or unwantedknuckles in the ship. The body plan displays the ship as aseries of transverse sections or "stations." Each stationmust' be recorded by inputting sufficient offset data(half-breadth and waterline coordinates -for each station) todefine it mathematically.

Recording the offset data has been speeded upconsiderably with the addition of a digitizer which, with atouch of its stylus,- records the coordinates of the pointtouched. This eliminates the two-step process of recordingthe offset value on an input form and then punching cardsto create the input file. The digitizer places the offset valuedirectly in the input file.

However, before any input file is sent to the batchsystem it should be checked for accuracy. In the case of theoffset file this is accomplished by having the data points

plotted (Figure 3). Any station which does not have theshape intended by the original body plan may be corrected.The timesharing terminal text editor permits changes to bedone quickly.

With the hull offset data on file the user has the optionof varying the form with the Bonjeans Program to meetlength, beam, draft, displacement, or center-of-buoyancyrequirements which may differ from the parent form. If thenew requirements are not drastically different' from theonginal ship, the resulting new form will be as fair as theparent form.

Whether or not a variation is performed, the BonjeansProgram stores the final form in a data file which has valuesof station areas and moments at equally spaced waterlines.These data comprise the Bonjeans File (Figure 4). Fromthis file plotted output of the body plan, Bonjeans (stationarea as a function of waterline height), and waterlines(Figures 5-7) may be obtained.

The waterline plots are particularly helpful for hull andmachinery arrangements. The user may select a particularwaterline and have it plotted between limits of ship lengthto represent machinery space or decks for arrangementpurposes.

PD 159-Break Bulk Ship This is Sample Ship Data Processed forBonjeans/Hydrostatics with Hull Form Variation. May 1972.

LWLBEAMDEPTH

476.00 DRAFT74.00 NO. STATIC43.00 STAT. SPAC

WATE R Li N ES

Figure 5. Body Plan - Output

IL

G

a:IL

0

28.33)NS 21.,I NG 23.80

UNITS/INCH = 20

AREA AREA

Figure 6. Bonjeans Curves

April 1975

Figure 7. Waterlines

49

Programs Using the Data Base

From the Bonjeans File the user can request hydrostaticinformation which is used for determining trim andstability, displacement, and coefficients of form. As before,the user returns to the timesharing terminal, specifies therequired Bonjeans File, and lists the waterlines for whichthe hydrostatic data are needed. The headline for theresultant output is seen in Figure 8.

Other programs are accessed as indicated by the designspiral to compute floodable length (length of cargo space

required to have one compartwnt flooded and stillsurvive), capacities (volume and centers of all tanks andcargo spaces), damaged stability (stability in a damaged or

flooded condition), and longitudinal strength (shear andbending moment imposed on the ship by different loadingconditions). These programs all require Bonjeans data andso must be run after the Bonjeans Program. Thelongitudinal strength program has plotted output (Figure 9)which is scaled so that the user may insert it directly in thefinal design report.

Other Design Programs

Returning to the design spiral (Figure 1) we can now see

how the creation -of the ship form data file permits the user

to analyze the initial choice of hull shape from many

aspects. If any of these tests indicates the selection isdeficient in some manner, the user may have to return tothe original body plan and alter it accordingly. In that case

a new Bonjeans data file would need to be created and theabove process repeated. Normally, the first circle of thespiral will fix all ship proportions, and each successive circlewill only add more detail to the initial selection (e.g., newloading conditions, different options for arrangeinent, moredetailed costs).

Some interactive programs do not need to access theBonjeans File to obtain the desired information. One suchexample is the speed-power curve which relies on

user-supplied ship-form data for input. Again, a timesharingprogram asks the user the appropriate questions concerningthe ship form and asks if plotted output is desired. The user

follows the instructions provided by the program for

HYDROSTATIC CALCULATIONS

BONJEANS / HYDROSTATICS WITH HULL FORM VARIATION MAY 1972PD IS9 - BREAK BULK SHIP THIS IS SAMPLE SHIP DATA PROCESSED FORSAMPLE TITLE FOR HYDROSTATICS RUN.

MAXIMUM BEAM

HULL GIRDER DEPTH

FULL LOAD DRAFT.MOLUED

LENGTH ON LOAD WATERLINE

LENGTH FOR CALCULATIONS

a 74.00

a 43.00

a 28.33

-- 476.00

= 476.00

STATION SPACING

NO. OF STATIONS

SPEC. VOL. (FW/SW))

APPENDAGE ALLOWANCE

ASSUMED BASE LINE

LENGTH BETWEEN PERPENDICULARS = 470.00

TD - TOTAL DISPLACEMENT(LONG TONS)MD - MOLUED DISPLACEMENT (LONG TONS)KB - KEEL TO VERTICAL CENTER OF BUOYANCY (FEET)LCB - LONGITUDINAL CENTER OF BUOYANCY FROM FORWARD PERPENDICULAR (FEET)

BMT - VERTICAL CENTER OF BUOYANCY TO TRANSVERSE METACENTER (FtET)KHT - KEEL TO TRANSVERSE METACENTER (FEET)BNL - VERTICAL CENTER OF dUOYANCY TO LONGITUDINAL METACENTER (FEET)KML KEEL TO LONGITUDINAL METACENTER (FEET)

LCF LONGITUDINAL CENTER OF FLOATATION FROM FORWARD PERPENDICULAR (FEET)A P - AREA OF WATER PLANETPI - LONG TONS PER 1 INCH IMMERSION IN SALT wATERMTI - MOMENT TO TRIM I INCH (FUOT/TONS)CD12A - CHANGE IN DISPLACEMENT FOR 12 1NCHES AFT-TRIM(LONG TONS)

AIO - SECTIONAL AREA AT STATION 10AM MAXIMUM SECTIONAL AREA.CM1O - MIUSHIP COEFFICIENT AT STATION 10CM - MIDSHIP COEFFICIENT AT LARGEST SECTIONAL AREA(STATION)CB - BLOCK COLF-FICIENT (LWL)CBP BLUCK COEFF1C.1ENT(LBP)CP - LONOITUDINAL PRISMATIC COEFFICIENT(CB/CMIO)CPP LONG ITUDINAL PRISMATIC COEFFICIENT (CBP/CM10)WPC - WATERPLANE COEFFICIENTTIC - TRANSVERSE INERTIA COEFFICIENT

LMI - LONGITUDINAL MOMENT OF INERTIA(FEET4)TMI TRANSVERSE MOMENT OF INERTIA(FEET4)

LENGTH FOR CALC. IS USED FOR CD12A AND MT1. LWL IS USED IN DEFAULT.

Figure 8. Hydrostatic Calculations

50

a 23.80O

5 21

a 35.00

a .005

a 15.000

COMPUTER

sending the power data file and control card file to thebatch computer. The resultant output is seen in Figure 10.

Other steps in the design spiral are hand calculationsrelying on input from the preceding programs. They havenot been computerized at this time.

Figure 9. Bending Moment Curve

SCHEME I DEEP ORRFT

a01

C4.

0

9F4.

0

a'0a,:

!2

DISPL. 22260.DRAFT 26.00LWL 640.00BERM 62.00Cm 0.987CP 0.765P.C. 0.70SERV. ALLOW. 1.25APP. ALLOW. 0.03ROUGHNESS

PLLOW¶NCE 0.0002

10.005PEEO tI h OI --

12.00 111.00 16.00 15.00ISPEEO (KNOTSI

20.00 22.00

Figure 10. Shaf Horsepower Curve

April 1975

Where Do We Go From HereThe ship design procedure has been outlined as it relates

to the automation found within the Maritime Administra-tion. This process is not static, and improvements andadditions to the programs mentioned here are constantlyoccurring.

One such addition is that of a graphics terminal inconjunction with a dedicated minicomputer. MarAd has aPDP-11 at present, and it is being exercised in a learningprocess prior to any attempt to incorporate. it into thedesign environment. A graphics terminal is to be purchasedthis fall, and many of the plot programs will be modifiedfor display on the scope with the user having the option ofsaving or discarding what he sees.

The added dimension of the minicomputer and CRT willbring a new efficiency to the automation of ship design.Other, newer developments will undoubtedly supersedethese within the year.

Alan H. Woodyard is presently employed as Sr.Naval Architect with Continental Oil Companyin Houston, Texas. Prior to that he wasemployed for six years with MARAD as a navalarchitect with the Engineering ComputerBranch. Mr. Woodyard is a graduate ofClaremont Men's College, the University ofMichigan, and holds an MS degree in OceanEngineering from the Massachusetts Institute ofTechnology. IHe is the author of several paperson computer-aided design.

Reader Service Number 431

DIGITAL SYSTEM DESIGN AUTOMATION:LANGUAGES, SIMULATION AND DATA BASE

Edited by Melvin A. Breuer, University of Southern CaliforniaAvailable June, 1975, 430pp. (approx.), $17.95

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