stability manual

Maxsurf Stability

Windows Version 20

User Manual

Bentley Systems, Incorporated 2013

iii

License and Copyright

Maxsurf Stability Program & User Manual

2013 Bentley Systems, Incorporated

Contents

v

Contents

License and Copyright ...................................................................................................... iii Contents .............................................................................................................................. v About this Manual .............................................................................................................. 1 Chapter 1 Introduction ........................................................................................................ 3

Input Model .............................................................................................................. 3 Analysis Types ......................................................................................................... 4 Analysis Settings ...................................................................................................... 4 Environment Options ............................................................................................... 4 Stability Criteria ....................................................................................................... 5 Output....................................................................................................................... 5

Chapter 2 Quickstart ........................................................................................................... 7 Upright Hydrostatics Quickstart .............................................................................. 7 Large Angle Stability Quickstart ............................................................................. 8 Equilibrium Condition Quickstart ............................................................................ 9 Specified Condition Quickstart .............................................................................. 10 KN Values Quickstart ............................................................................................ 11 Limiting KG Quickstart ......................................................................................... 11 Floodable Length Quickstart .................................................................................. 12 Longitudinal Strength Quickstart ........................................................................... 13 Tank Calibrations Quickstart ................................................................................. 14 MARPOL Oil Outflow Quickstart ......................................................................... 15 Probabilistic Damage Quickstart ............................................................................ 15

Chapter 3 Using Maxsurf Stability ................................................................................... 16 Getting Started ....................................................................................................... 16

Installing Maxsurf Stability ......................................................................... 16 Starting Maxsurf Stability ............................................................................ 16

Maxsurf Stability Model ........................................................................................ 17 Preparing a Design in Maxsurf .................................................................... 18 Opening a New Design ................................................................................ 25 Opening an Existing Maxsurf Stability Design File .................................... 26 Effect of Zero Point change ......................................................................... 27 Updating the Maxsurf Stability Model ........................................................ 30 Maxsurf Stability Sections Forming ............................................................ 31 Checking the Maxsurf Stability model ........................................................ 34 Setting Initial Conditions ............................................................................. 38 Working with Loadcases.............................................................................. 43 Auto ballasting ............................................................................................. 56 Modelling Compartments ............................................................................ 59 Tank sections ............................................................................................... 70 Forming Compartments ............................................................................... 70 Compartment Types ..................................................................................... 77 Sounding Pipes ............................................................................................ 78 Damage Case Definition .............................................................................. 80 Cargo dropout .............................................................................................. 84 Damage Analysis and Partial Flooding ........................................................ 85 Partial Flooding Modelling and Analysis ................................................. 87 Key Points (e.g. Down Flooding Points) ..................................................... 93 Margin Line Points ...................................................................................... 95 Modulus Points and Allowable Shears and Moments ................................. 95 Floodable Length Bulkheads ....................................................................... 95 Stability Criteria ........................................................................................... 96

Contents

vi

Analysis Types ....................................................................................................... 96 Upright Hydrostatics .................................................................................... 97 Large Angle Stability ................................................................................. 100 Water on Deck Stockholm Agreementt .................................................. 106 Equilibrium Analysis ................................................................................. 115 Specified Conditions .................................................................................. 118 KN Values Analysis ................................................................................... 120 Limiting KG ............................................................................................... 123 Limiting KG for damage conditions with initially loaded tanks................ 126 Floodable Length ....................................................................................... 130 Longitudinal Strength ................................................................................ 133 Tank Calibrations ....................................................................................... 136 MARPOL Oil Outflow .............................................................................. 141 Probabilistic Damage ................................................................................. 146 Starting and Stopping Analyses ................................................................. 179 Probabilistic damage Log file .................................................................... 179 Batch Analysis ........................................................................................... 183

Analysis Settings .................................................................................................. 185 Heel ............................................................................................................ 186 Trim ........................................................................................................... 187 Draft ........................................................................................................... 189 Displacement ............................................................................................. 189 Specified Conditions .................................................................................. 190 Permeability ............................................................................................... 190 Tolerances .................................................................................................. 190

Analysis Environment Options ............................................................................ 192 Fluids Analysis Methods ........................................................................... 193 Density of Fluids ........................................................................................ 195 Hog and Sag ............................................................................................... 197 Waveform .................................................................................................. 197 Grounding .................................................................................................. 199 Stability Criteria ......................................................................................... 200 Damage ...................................................................................................... 200

Analysis Output .................................................................................................... 200 Reporting ................................................................................................... 201 Copying & Printing .................................................................................... 203 Select View from Analysis Data ................................................................ 204 Saving the Maxsurf Stability Design ......................................................... 205 Exporting ................................................................................................... 206

Chapter 4 Stability Criteria ............................................................................................. 209 Criteria Concepts .................................................................................................. 209

Criteria List Overview ............................................................................... 210 Types of criteria ......................................................................................... 212

Criteria Procedures ............................................................................................... 213 Starting the Criteria dialog ......................................................................... 213 Resizing the Criteria dialog ....................................................................... 214 Working with Criteria ................................................................................ 214 Editing Criteria .......................................................................................... 216 Working with Criteria Libraries ................................................................. 218

Criteria Results ..................................................................................................... 220 Criteria Results Table ................................................................................ 220 Report and Batch Processing ..................................................................... 222

Nomenclature ....................................................................................................... 222

Contents

vii

Definitions of GZ curve features ............................................................... 222 Glossary ..................................................................................................... 225

Chapter 5 Maxsurf Stability Reference .......................................................................... 227 Windows .............................................................................................................. 227

Assembly View and Property Sheet .......................................................... 227 View Window ............................................................................................ 227 Loadcase Window ...................................................................................... 229 Damage Window ....................................................................................... 229 Input Window ............................................................................................ 230 Results Window ......................................................................................... 231 Graph Window ........................................................................................... 235 Report Window .......................................................................................... 239

Toolbars ............................................................................................................... 242 File Toolbar................................................................................................ 242 Edit Toolbar ............................................................................................... 242 View Toolbar ............................................................................................. 242 Analysis Toolbar ........................................................................................ 243 Window Toolbar ........................................................................................ 243 Design Grid Toolbar .................................................................................. 243 Visibility Toolbar ....................................................................................... 243 Edge VIsibility Toolbar ............................................................................. 244 Render Toolbar .......................................................................................... 244 Report Toolbar ........................................................................................... 244 View (extended) Toolbar ........................................................................... 244 Design Grid Toolbar .................................................................................. 244 Extra Buttons Toolbar ................................................................................ 244

Menus ................................................................................................................... 245 File Menu ................................................................................................... 245 Edit Menu .................................................................................................. 248 View Menu ................................................................................................ 250 Case Menu ................................................................................................. 252 Analysis Menu ........................................................................................... 253 Display Menu ............................................................................................. 255 Data Menu.................................................................................................. 259 Window Menu ........................................................................................... 260 Help Menu ................................................................................................. 261

Appendix A: Calculation of Form Parameters ............................................................... 262 Definition and calculation of form parameters .................................................... 262

Measurement Reference Frames ................................................................ 262 Nomenclature ............................................................................................. 264 Coefficient parameters ............................................................................... 264 Length ........................................................................................................ 265 Beam .......................................................................................................... 266 Draft ........................................................................................................... 267 Midship and Max Area Sections ................................................................ 268 Block Coefficient ....................................................................................... 269 Section Area Coefficient ............................................................................ 269 Prismatic Coefficient ................................................................................. 269 Waterplane Area Coefficient ..................................................................... 270 LCG and LCB ............................................................................................ 270 Trim angle .................................................................................................. 271 Maximum deck inclination ........................................................................ 271 Immersion .................................................................................................. 271

Contents

viii

MTc or MTi ............................................................................................... 271 RM at 1 deg................................................................................................ 272

Potential for errors in hydrostatic calculations ..................................................... 272 Integration of wetted surface area .............................................................. 272

Appendix B: Criteria file format .................................................................................... 274 Appendix C: Criteria Help.............................................................................................. 276

Parent Calculations............................................................................................... 276 Selecting a calculation in a criterion .......................................................... 276 Angle calculators ....................................................................................... 276 GM calculators ........................................................................................... 277

Parent Heeling Arms ............................................................................................ 280 Heeling Arm Definition ............................................................................. 280 Parent Heeling Moments ........................................................................... 290

Parent Stability Criteria ........................................................................................ 292 Criteria at Equilibrium ............................................................................... 292 GZ Curve Criteria (non-heeling arm) ........................................................ 293 Heeling arm criteria (xRef) ........................................................................ 310 Heeling arm criteria ................................................................................... 311 Multiple heeling arm criteria ..................................................................... 323 Heeling arm, combined criteria .................................................................. 331 Derived heeling arm criteria ...................................................................... 335 Other combined criteria ............................................................................. 340 Specific stand alone heeling arm criteria ................................................... 341 Stand alone heeling arm criteria ................................................................ 341 Stand alone heeling arm combined criteria ................................................ 342

Appendix D: Specific Criteria ........................................................................................ 345 Dynamic stability criteria ..................................................................................... 345

Capsizing moment ..................................................................................... 345 Heeling arms for specific criteria - Note on unit conversion ............................... 347

IMO Code on Intact Stability A.749(18) amended to MSC.75(69) ........... 347 IMO HSC Code MSC.36(63) .................................................................... 349 USL code (Australia) ................................................................................. 351 ISO 12217-1:2002(E) ................................................................................ 352 ISO 12217: Small craft stability and buoyancy assessment and categorisation. ............................................................................................ 354

Appendix E: Reference Tables ....................................................................................... 356 File Extension Reference Table ........................................................................... 356 Analysis settings reference table .......................................................................... 357

Appendix F: Quality Assurance ..................................................................................... 358 Quality Assurance ................................................................................................ 358

Quality Principles ...................................................................................... 358 Structured Programming ............................................................................ 358 Verification of Algorithms ......................................................................... 358 Testing of Implementation ......................................................................... 361 Testing of Upgrades ................................................................................... 361 Beta Testing ............................................................................................... 361 Version Control .......................................................................................... 361 But we're not Perfect .................................................................................. 361

Index ............................................................................................................................... 362

About this Manual

Page 1

About this Manual

This manual describes how to use Maxsurf Stability to perform hydrostatic and stability

analyses on your Maxsurf design.

Chapter 1 Introduction

Contains a description of Maxsurf Stability functionality and its interface to Maxsurf

Chapter 2 Quickstart

Gives a quick walk through the analysis tools available in Maxsurf Stability.

Chapter 3 Using Maxsurf Stability

Explains how to use Maxsurf Stability' powerful floatation and hydrostatic analysis

routines to best advantage.

Chapter 4 Stability Criteria

Gives details of the stability criteria that may be evaluated with Maxsurf Stability.

Chapter 5 Maxsurf Stability Reference

Gives details of Maxsurf Stability' windows and each of Maxsurf Stability' menu

commands.

If you are unfamiliar with Microsoft Windows interface, please read the owner's

manual supplied with your computer. This will introduce you to commonly used terms

and the basic techniques for using any computer program.


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Maxsurf Stability is a hydrostatics, stability and longitudinal strength program

specifically designed to work with Maxsurf. Maxsurf Stability adds extra information to

the Maxsurf surface model. This includes: compartments and key points such as

downflooding points and margin line.

Maxsurf Stability analysis tools enable a wide range of hydrostatic and stability characteristics to be determined for your Maxsurf design. A number of environmental

setting options and modifiers add further analysis capabilities to Maxsurf Stability.

Maxsurf Stability is designed in a logical manner, which makes it easy to use. The

following steps are followed when performing an analysis:

Input model

Analysis type selection

Analysis settings

Environment options

Criteria specification and selection

Run analysis

Output

Maxsurf Stability operates in the same graphical environment as Maxsurf; the model can

be displayed using hull contour lines, rendering or transparent rendering. This allows

visual checking of compartments and shows the orientation of the vessel during analysis.

Input Model

Maxsurf design files may be opened directly into Maxsurf Stability, eliminating the need

for time-consuming digitising of drawings or hand typing of offsets. This direct transfer

preserves the three-dimensional accuracy of the Maxsurf model.

Tanks can be defined and calibrated for capacity, centre of gravity and free surface

moment. Tanks and compartments can be flooded for the purpose of calculating the

effects of damage.

A number of loadcases can be created. The loadcase allows static weights and tank-

fillings to be specified and calculates the corresponding weights and centres of gravity as

well as the total weight and centre of gravity of the vessel under the specified loading

condition. Loadgroups may also be created and cross referenced into loadcases.

Other input consists of: tank sounding pipes; key points, such as downflooding points,

immersion and embarkation points; margin lines and section modulus.


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Analysis Types

Maxsurf Stability contains the following analysis tools:

Upright hydrostatics

Large angle stability

Equilibrium analysis

Specified Condition analysis

KN values and cross curves of stability

Limiting KG analysis

Floodable Length analysis

Longitudinal Strength analysis

Tank Calibrations

MARPOL oil outflow

Probabilistic damage (Maxsurf Stability Ultimate only)

Although common analysis settings are used where possible, different analyses may

require different settings. For example: the upright hydrostatics analysis simply requires

a range of drafts; whereas the longitudinal strength analysis requires a detailed load

distribution. The analysis settings for each analysis type are explained in detail in the

analysis synopsis below.

Analysis Settings

The analysis settings describe the condition of the vessel to be tested. For example, a

range of drafts in the case of upright hydrostatics, or a range of heel angles for a large

angle stability analysis.

The following analysis settings are available:

Heel

Trim

Draft

Displacement

Permeability

Specified condition

The analysis settings are specified prior to running the analysis. Settings that are not

relevant to the selected analysis type are greyed out in the Analysis menu.

Environment Options

Environmental options are modifiers that may be applied to the model or its environment

that will affect the results of the all the hydrostatic analysis types.


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Depending on the analysis being performed, different environmental options may be

applied to the Maxsurf Stability:

Type of Fluid Simulation

Density (of fluids)

Wave form

Grounding

Intact and Damage condition

Stability Criteria

Maxsurf Stability has the capability to calculate compliance with a wide range of

stability criteria. These criteria are either derived from the properties of the stability

curve calculated from a Large Angle Stability analysis or from the vessels orientation and stability properties calculated from an Equilibrium analysis. Limiting KG and

Floodable length analyses also use stability criteria.

Maxsurf Stability has an extensive range of stability criteria to determine compliance

with a wide range of international stability regulations. In addition, Maxsurf Stability has

a generic set of parent criteria from which virtually any stability criterion can be

customized.

Output

Views of the hull are shown for each stage of the analysis, complete with immersed

sectional areas and actual waterlines. The centres of flotation, gravity and buoyancy are

also displayed. Heeled and trimmed hullforms and water plane shapes may be printed.

Results are stored and may be reviewed at any time, either in tabular form, or as graphs

of the various parameters across the full range of calculation. All results are accumulated

in the Report window (which can be saved, copied and printed), or output directly to a

Word document.

The criteria checks are summarised in tables listing the status (pass/fail) of each criterion

as well as the margin. The criterion settings and intermediate calculation data may also

be displayed if required.

For a brief overview of the different analysis that Maxsurf Stability has available,

continue reading Chapter 2 Quickstart.

Chapter 3 Using Stability

Page 7

Chapter 2 Quickstart

This chapter will briefly describe each analysis type and its output. For each analysis

type, a list of the required settings as well as the available environment options is given.

Maxsurf Stability contains the following analysis types

Upright Hydrostatics

Large Angle Stability

Equilibrium Condition

Specified Condition

KN Values

Limiting KG

Floodable Length

Longitudinal Strength

Tank Calibrations

MARPOL Oil Outflow

Probabilistic Damage

Each analysis has different settings that may be applied

Heel

Trim

Draft

Displacement

Specified condition

Permeability

Loadcase

Tank and compartment definition

Maxsurf Stability offers different environment options that may be applied to the

analyses

Fluid Densities

Treatment of fluids in tanks: fluid simulation or corrected VCG

Wave form

Grounding

Damage

Maxsurf Stability offers an extensive range of stability criteria that are applicable to

equilibrium, large angle stability, limiting KG and Floodable length analysis.

The Analysis types section describes each of the analysis types, settings and environment

options in more detail.

Upright Hydrostatics Quickstart

For Upright Hydrostatics, heel is fixed at zero heel, trim is fixed at a user defined value

and draft is varied in fixed steps. Displacement and centre of buoyancy and other

hydrostatic data are calculated during the analysis.


Page 8

Upright hydrostatics requirements

Range of drafts to be analysed

VCG (for calculation of some stability characteristics such as GMt and GMl only)

Trim

Upright hydrostatic options

Fluid Densities

Wave form

Damage

Compartment definition (in case of damage)

The results are tabulated and graphs of the hydrostatic data, curves of form and sectional

area at each draft are available. Bonjean Curves are also calculated.

For more detailed information please see: Upright Hydrostatics on page 97.

Large Angle Stability Quickstart

For the analysis of Large Angle Stability, displacement and centre of gravity are

specified in the loadcase. A range of heel angles are specified and Maxsurf Stability

calculates the righting lever and other hydrostatic data at each of these heel angles by

balancing the loadcase displacement against the hull buoyancy and, if the model is free-

to-trim, the centre of gravity against the centre of buoyancy such that the trimming

moment is zero.

Large angle stability requirements

Range of heel angles to be analysed

Trim (fixed or free)

Loadcase or loadgroup

Tank definition in the case of tank loads being included in the Loadcase (and/or for

the definition of damage)

Large angle stability options

Fluid Densities


Wave form

Damage


Key points

Margin line and deck edge

Analysis of stability criteria

Water on Deck (WoD) Stockholm Agreement


Page 9

The key output value is GZ (or righting lever), the horizontal distance between the

centres of gravity and buoyancy. A graph of these values at the various heel angles forms

a GZ curve. Various other information is often overlaid on the GZ curve, including

upright GM, curves for wind heeling and passenger crowding levers and the angle of the

first downflooding point. These additional data depend on which (if any) stability criteria

have been selected.

A number of other graphs may be selected from the pull-down list in the graph window.

Remember that you can access this data in tabular form by double clicking in the graph

window:

Dynamic stability curve (Area under GZ curve, integrated from upright)

Variations of other hydrostatic and form parameters may be plotted against heel

angle.

Maximum safe steady heel angle

The sectional area curve at each of the heel angles tested may also be displayed.

Note that some of these graphs have parameters that may be adjusted in the Data Format

dialog

If large angle stability criteria have been selected for analysis, these results will also be

reported in the criteria results table and they may lead to additional curves being

displayed on the GZ curve.

Downflooding angles for any key points, margin line and deck edge will also be

computed and tabulated.

For more detailed information please see: Large Angle Stability on page 100.

Equilibrium Condition Quickstart

Equilibrium Analysis uses the Loadcase, to calculate the displacement and the location

of the centre of gravity. Maxsurf Stability iterates to find the draft, heel and trim that

satisfy equilibrium and reports the equilibrium hydrostatics and a cross sectional areas

curve.

Equilibrium analysis requirements

Loadcase or loadgroup



Compartment definition and damage case (in case of damage)

Equilibrium analysis options


Page 10

Fluid Densities


Wave form

Grounding

Damage


Key points


Analysis of equilibrium criteria

Equilibrium analysis result table lists the hydrostatic properties of the model. If a wave

form has been specified there will be a number of columns; each column contains the

results for a different position of the vessel in the wave as given by the wave phase

value. The sectional area curve is also calculated, as is the freeboard to any defined key

points, margin line and deck edge. Any equilibrium criteria will also be evaluated and

their results reported.

For more detailed information please see: Equilibrium Analysis on page 115.

Specified Condition Quickstart

In the specified condition each of the three degrees of freedom, for which the hydrostatic

properties of the model are to be calculated, can be set.

Specified Condition Requirements

Specified Conditions Input Dialog

If fixed trim is specified, you may enter the trim or specify the forward and aft drafts

(these are at the perpendiculars as specified in the Frame of Reference dialog).

Specified Conditions options

Fluid Densities

Wave form

Damage

Tank and Compartment definition (in case of damage)


Page 11

The output for the specified condition consists of a curve of cross sectional areas and

hydrostatics of the vessel in the specified condition.

For more detailed information please see Specified Conditions on page 118.

KN Values Quickstart

KN values or Cross Curves of Stability are useful for assessing the stability of a vessel if

its VCG is unknown. They may be calculated for a number of displacements before the

height of the centre of gravity is known. The KN data may then be used to obtain the GZ

curve for any centre of gravity height (KG) using the following formula:

GZ = KN - KG * sin(Heel)

where GZ is the righting lever measured transversely between the Centre of Buoyancy

and the Centre of Gravity, and KG is the distance from the baseline to the vessel's

effective Vertical Centre of Gravity.

KN Values Analysis Requirements

Range of displacements to be analysed



Estimate of VCG (provides more accurate result if free-to-trim)

TCG (if required)

KN Values Analysis Options

Fluid Densities

Wave form

Damage


Output is in the form of a table of KN values and a graph of Cross Curves of Stability.

If the analysis is performed free-to-trim and an estimate of the VCG is known, this may

be specified. The computed KN results will then give a more accurate estimate of GZ for

KG close to the estimated VCG since the effects of VCG on trim have been more

accurately accounted for.

For more detailed information please see KN Values Analysis on page 120.

Limiting KG Quickstart

The Limiting KG analysis may be used to obtain the highest vertical position of the

centre of gravity (maximum KG) for which the selected stability criteria are just passed.

This may be done for a range of vessel displacements. At each of the specified

displacements, Maxsurf Stability runs several Large Angle Stability analyses at different

KGs. The selected stability criteria are evaluated; the centre of gravity is increased until

one of the criteria fails.

Limiting KG Analysis Requirements


Page 12




Stability criteria for which limiting KG is to be found

TCG (if required)

Limiting KG Analysis Options

Fluid Densities

Wave form

Damage


Laodcase (in case of initial loading of damaged tanks)

Key points (if required for criteria)

Margin line and deck edge (if required for criteria)

A graph of maximum permissible GZ plotted against vessel displacement is produced as

well as tabulated results indicating which stability criteria limited the VCG. If limiting

curves are required for each of the stability criteria individually, this may be done in the

Batch Analysis mode.

A check will be made to ensure that any selected equilibrium criteria are passed,

however at least one large angle stability criterion is required. Only relevant criteria will

be used, i.e. if a damage case is chosen, only damage criteria will be evaluated; if the

intact condition is used, only intact criteria will be evaluated. Some criteria, such as

angle of maximum GZ, are very insensitive to VCG and may prevent the analysis

converging. If the analysis is unable to converge for a certain displacement this will be

noted and the next displacement tried.

For more detailed information see Limiting KG on page 123.

Floodable Length Quickstart

This analysis mode is used to compute the maximum compartment lengths based on

user-specified equilibrium criteria. Floodable Lengths may be computed for a range of

displacements; the LCG may be specified directly or calculated from a specified initial

trim. In addition a range of permeabilities may be specified. The VCG is also required to

ensure accurate balance of the CG against the CB at high angles of trim. As well as the

standard deck edge and margin line immersion criteria (one of which must be specified)

the user can also add criteria for maximum trim angle and minimum required values of

longitudinal and transverse metacentric height.

Floodable Length Analysis Requirements


Page 13


VCG

Range of permeabilities to be analysed

Trim (free- to- trim to either initial trim or specified LCG)

Floodable length criteria to be tested

Margin line and deck edge (required for criteria)

Floodable Length Analysis Options

Fluid Densities

Wave form

The output is in the form of tabulated Floodable Lengths for each displacement and

permeability. The data is tabulated for each of the stations as defined in Maxsurf. The

data is also presented graphically.

For more detailed information please see Floodable Length on page 130.

Longitudinal Strength Quickstart

Maxsurf Stability calculates the net load from the buoyancy and weight distribution of

the model. That data is then used to calculate the bending moment and shear force on the

vessel.

Longitudinal Strength Analysis Requirements

Loadcase (including distributed loads if required)



Longitudinal Strength Analysis Options

Fluid Densities

Treatment of fluids in tanks: fluid simulation is always used for Longitudinal

Strength analysis

Wave form

Grounding

Damage

Compartment definition and damage case (in case of damage)

Allowable shear and bending moment


Page 14

The longitudinal strength graph and tables contain all information on weight and

buoyancy distribution, the shear force and bending moment on the vessel. If defined,

graphs of allowable shear and bending moment are superimposed on the graph.

For more detailed information please see Longitudinal Strength on page 133.

Tank Calibrations Quickstart

Tanks can be defined and calibrated for capacity, centre of gravity and free surface

moment (FSM). Fluid densities and tank permeabilities can be varied arbitrarily. Tank

calibrations may be calculated for a range of trim and heel angles. Maxsurf Stability uses

its fluid simulation mode to calculate the actual position of the fluids in the tanks, taking

into account the vessel trim and heel; i.e. the position of the fluid in the tank will be

computed so that the fluid surface is parallel with the external seawater surface. Tank

ullages are measured from the top of the sounding pipe to the free surface of the liquid

within the tank along the sounding pipe and in a similar manner, soundings are measured

from the bottom of the sounding pipe to the free surface.

Tank calibrations may be performed for a range of heel and trims. The results for a

single condition are shown in the results table. The condition to be viewed may be

selected from the Results toolbar; Tabulated results may be customised using the Data

Format dialog:

Tank calibration analysis requirements

Tank definitions

Sounding pipe definition (if required)

Sounding intervals for calibration levels

Trim range

Heel range

Tank calibration analysis options


Page 15

Fluid Densities

Treatment of fluids in tanks: fluid simulation always selected

Damage: Intact case always selected

What to calibrate (Analysis | Calibration options)

For each tank, a table of capacities, volumes etc. is calculated. These results are

presented in both tabular and graphical forms.

For more detailed information please see Tank Calibrations on page 136.

MARPOL Oil Outflow Quickstart

MARPOL probabilistic oil outflow calculation may be computed according to the

following MARPOL regulations:

Resolution MEPC.141(54), Regulation 12A: Oil fuel tank protection

Resolution MEPC.117(52), Regulation 23: Accidental oil outflow performance

Seltect the Reolution and tanks to be included in the analysis in the MARPOL options

(Analysis menu) dialog. Then in the MARPOL results data table, edit any values as

required; the resulting oil outflows will be calculated automatically. The Start Analysis button will send the tabulated results to the Report.

For more detailed information please see MARPOL Oil Outflow on page 141

Probabilistic Damage Quickstart

Attained index using probabilistic damage analysis may be computed.

Probabilistic damage analysis requirements

Loadcase definitions

Tank and compartmentation definition

Main probabilistic damage analysis parameters and criteria setup

Subdivision definitions

Heel angle range for GZ curve calculation

Trim

Probabilistic damage analysis options


Wave form

Key points


For more detailed information please see the Probabilistic Damage section on page 146.


Page 16

Chapter 3 Using Maxsurf Stability

This chapter describes

Getting Started

Maxsurf Stability Model

Analysis Types

Analysis Settings

Analysis Environment Options

Analysis Output

Getting Started

This section contains everything you need to do to start using Maxsurf Stability

Installing Maxsurf Stability

Starting Maxsurf Stability

Installing Maxsurf Stability

Install Maxsurf Stability by inserting the CD and running the Setup program, then follow

the instructions on screen.

Note:

Before installing any program from the Maxsurf suite for the first time,

please read the purchase letter (also referred to as installation manual).

Starting Maxsurf Stability

After installation, Maxsurf Stability should be accessible through the Start Menu. Simply

select Maxsurf Stability from the Maxsurf menu item under Programs in the Start menu.

Windows Registry

Certain preferences used by Maxsurf Stability are stored in the Windows registry. It is

possible for this data to become corrupted, or you may simply want to revert back to the

default configuration. To clear the Maxsurf Stability preferences, start the program with

the Shift key depressed. You will be asked if you wish to clear the preferences, click OK,

doing this will reset all the preferences.

The following preferences are stored in the registry:


Page 17

Colour and line thickness settings of contours and background

Fonts

Window size and location

Size of resizing dialogs (alternatively, these may be reset by holding down the shift

key when activating them)

Density of fluids

Heel angles for large angle stability, KN and Limiting KG analyses

Permeabilities for floodable length analysis

Location of files

Units for data input and results output

Convergence tolerance (Error values)

Maximum number of loadcases

Reporting preferences

Note:

The default density for the fluid labelled "Sea Water" is stored in the

windows registry. All hydrostatic calculations use this. Check the density of

seawater after resetting your preferences.

It is recommended to save your customized densities with your project

using the File | Save Densities As command.

Maxsurf Stability Model

This section describes how to open a Maxsurf model in Maxsurf Stability and provides

some important information to ensure that your model is correctly interpreted by

Maxsurf Stability.

Preparing a Design in Maxsurf

Opening a New Design

Opening an Existing Maxsurf Stability Design File

Updating the Maxsurf Stability Model

Maxsurf Stability Sections Forming

Checking the Maxsurf Stability model

After checking the Maxsurf Stability model, the next step is to check the Maxsurf

Stability settings and initial analysis conditions.

Setting Initial Conditions

Depending on the analysis performed, you may need to set up the following additional

model data:


Page 18

Working with Loadcases

Modelling Compartments

Forming Compartments

Compartment Types

Damage Case Definition

Sounding Pipes

Key Points (e.g. Down Flooding Points)

Margin Line Points

Modulus Points and Allowable Shears and Moments

Stability Criteria

Preparing a Design in Maxsurf

There are several important checks that must be carried out in Maxsurf before opening a

design in Maxsurf Stability:

Setting the Zero Point

Setting the Frame of Reference

Setting the Windage Surfaces

Skin Thickness

Outside Arrows

Trimming

Coherence of the Maxsurf surface model

Setting the Zero Point

Ensure that the zero point is correctly setup in Maxsurf. A consistent zero point and

frame of reference should be used for the model throughout the Maxsurf suite. In

Maxsurf Stability you have the option of displaying longitudinal measurements such as

LCB or LCF from the model zero point or amidships.

Setting the Frame of Reference

It is vital that the Frame of Reference is correctly setup in Maxsurf before attempting to

analyse the model in Maxsurf Stability. The Frame of reference should not be changed in

Maxsurf Stability. The frame of reference defines the fore and aft perpendiculars, the

baseline and the datum waterline; midships is automatically defined midway between the

perpendiculars. By convention, in the profile and plan views, the vessels bow is on the right.

The perpendiculars define the longitudinal positions of the vessels draft marks and cannot be coincident. The base line is the datum from which the drafts and KG are

measured.

The frame of reference cannot be changed in Maxsurf Stability. However it is possible to

specify upto nine additional locations at which the drafts should be reported. This is done

through the Data | Draft Marks dialog.

Note: Draft and Trim specification

It should be remembered that the drafts specified for an analysis are the

drafts at the perpendiculars (or amidships) and the trim specified (and

reported) is the difference between the draft at the AP and draft at the FP.


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Setting the Windage Surfaces

Windage areas and underwater projected areas definitions have been added to the

Maxsurf vessel model. These data may be defined and edited in both Maxsurf Modeler

and Maxsurf Stability via the Windage Surfaces dialog in the Data menu.

Windage Surfaces dialog (Data menu)

If no Windage groups are defined, then the older system for the calculation of windage

and lateral projected underwater area is used. That is the hydrostatic sections are

projected into the transverse plane. The outer perimeter formed by joining the upper and

lower limits of these projected sections is then used to calculate both the windage area of

the hull and the underwater projected area. The zero-trim waterline at the current

midship draft is used to determine which part of the projection is underwater and which

part is windage area. Because of these limitations, the effects of vessel trim and "holes"

in the model are not accounted for by this older method. The new method overcomes

these limitations as well as adding new features.

Windage Groups

The concept of a Windage Group has been added. This groups together model surfaces

which should be treated as a single object. There are always at least two Windage

Groups and the first one defines the surfaces that should be used to calculate the

underwater lateral projected area. Individual surfaces may be included in multiple

Windage Groups. Apart from the underwater group, Windage Groups have various

factors associated with them:

F_drag: winage drag factor; default value 1.0

F_shield: shielding factor; default value 0.0

F_user: a user-defined factor; default value 1.0

usershielddragtotal .0.1. FFFF

Windage Groups may be added and deleted with the respective buttons in the dialog. The

surfaces to be included in each group are defined in selected by double clicking in the

"Surfaces" cell in the table, in a similar manner to the selection of boundary surfaces for

Tanks and Compartments.


Page 20

Windage Group definition and Surface selection

The color of the Windage Profile outline can be changed in the Colors dialog; the

underwater profile is shown using the "Immersed Sections" color.

Color selection


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Wind direction

The Windage direction specifies the projection direction used for the surfaces: 90deg.

gives a projection in the lateral plane; 0deg. gives a direction in the longitudinal plane.

Angles between 0 and 180deg are allowed since the sign of the projection vector does

not matter.

Note that to improve performance, the projected windage contour uses a fairly coarse

surface mesh. This may result in the projected windage contour not exactly

corresponding with the surface edges, but the effect on projected area and center of area

is negligible. Due to the calculation method used for the projected conoturs, it is possible

that some visual artifacts may be present but again these have negligible effect on

projected area and center of area.

Windage projections viewed in profile at 90deg (upper) and 70deg (lower)

Display

In Maxsurf Stability, when the vessel is at the DWL, the normal windage profile view is

shown and the wind profile groups may be modified. However once a Large Angle

Stability analysis has been performed, it is possible to select the windage profile used for

any of the defined velocity profile wind heeling arms (see below for deails).

Display | Windage Profile dialog

Effect of heel

Maxsurf Stability has the option of using just the upright (zero heel) projected windage

profile or calculating the actual projection of the heeled vessel. The option is specified in

Edit | Preferences dialog. It should be noted that calculating the projected windage

profile at each heel angle can add significantly to the time required to complete the

analysis. For criteria evaluation, the underwater lateral projected area and center of area

for the upright (zero heel) vessel is always used; however the wind heeling moment will

use the actual inclined (including heel) projected windage area if this option has been

selected in the Preferences dialog.


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Upright or heeled/inclined projected windage area calculation preference

Windage profile calclated for the upright vessel and used for all heel angles

Windage profile calclated using heeled/inclined projected windage area method


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Surface Use

In Maxsurf you can choose between two types of surface use

Hull

Hull surfaces are used to define the watertight envelope of the hull.

Internal structure

Internal structure surfaces are used for all other surfaces (any surfaces which do

not make up the watertight envelope) and also surfaces which are to be used in

Maxsurf Stability to define the boundaries of tanks and compartments that have

complex shapes.

The following table describes the difference between each surface use in Maxsurf

Stability:

Included: Hull Shell Internal

Structure

Hydrostatic sections

Selection of tank/compartment

boundaries

Skin thickness applied to the surface

Verify that all surfaces that are to be used as tank/compartment boundaries are defined as

Internal Structure. If a surface is defined as internal structure, it is not included as part of

the hull shell by Maxsurf Stability, i.e. internal surfaces will be ignored in the forming of

hydrostatic sections.

Skin Thickness

If skin thickness is to be used in hydrostatic calculations, ensure that the thickness and

projection direction have been specified for the hull shell surfaces. Thickness can be

specified differently for each hull surface, resulting in more accurate hydrostatics. To

activate skin thickness in Maxsurf Stability ensure that the Include Skin Thickness option is selected when reading the file or calculating the hull sections.

Note

Tank boundaries made from internal structures surfaces do not have skin

thickness. To include skin thickness, the internal structure surface should be

placed to model the inside of the tank if the tank wall has significant

thickness.

Skin thickness for hull surfaces will be treated so that the hull sections go to

the outside of the plate whilst any tanks are trimmed to the inside of the

plate.

Outside Arrows

The surfaces outside arrows define the orientation of the surfaces. Ensure that you have used the Outside Arrows command from the Maxsurf Display menu to define which

direction points outwards (towards the seawater) for each surface. The surface direction

may be flipped by clicking on the end of the arrow.


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Trimming

Ensure that all surfaces are trimmed correctly. At any longitudinal position on the hull,

you should have completely closed transverse sections or sections with at most one

opening (e.g. the deck).

Correct Section with no opening.

Correct section with one opening: this section will be closed across the top.

Also see:

Maxsurf Stability Sections Forming on page 31

Checking the Maxsurf Stability model on page 34

Coherence of the Maxsurf surface model

Maxsurf Stability will generally have no problem correctly interpreting your design as

long as the following requirements for the Maxsurf model are observed:

Make sure that each surface touches its adjacent surfaces at its edge, preferably by

bonding the edges together

Where surfaces intersect, trim away the excess regions of the surface; e.g. the part

of the keel that is inside the hull and the part of the hull that is inside the keel

Do not have surfaces that cannot be closed in an unambiguous fashion, i.e. a

maximum of one gap in a transverse section through the hull.

Remember that the inner portions of each intersecting contour will be trimmed off

Check surface use; internal structure surfaces are ignored when forming the hull

sections in Maxsurf Stability

Note:

For groups internal structure surfaces that will be used to define tank (or

compartment boundaries) the same requirements apply.

Also see:

Checking the Maxsurf Stability model on page 34.


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Opening a New Design

File opening in Maxsurf Stability is window specific, i.e. Maxsurf Stability will

automatically look for compartment definition files when you are in a Compartment

Definition window and a loadcase in a Loadcase window.

To open a design for analysis, ensure that the design view window is active, then select

Open Design from the File menu. Choose a Maxsurf design file (.msd).

The following dialog will appear:

Calculate new Sections

Choosing Calculate Sections will calculate the specified number of sections through the

hull. These will then be used for the Hydrostatics calculations.

The meaning of (ignore existing data, if any) is explained in Opening an Existing

Maxsurf Stability Design File.

Include Plating Thickness

At this stage, any surface thickness specified in the Maxsurf Surface Properties dialog

may be included.

Use Trimmed Surfaces

If the Maxsurf model has trimmed surfaces, the Use Trimmed Surfaces item should be

ticked.

Stations

When calculating stations, you may select how many stations should be used. Reducing

the number of stations will speed up the analysis time but reduce the accuracy,

conversely increasing the number of stations will increase the analysis time but lead to

higher accuracy results; the maximum number of stations which may be used is 500.

The first option allows you to use the station grid created in Maxsurf. This is extremely

useful for hulls that have features such as keels or bow thrusters that need to be

accurately modelled and may need a locally denser station spacing to do so. It also

allows designs with significant longitudinal discontinuities in their sectional areas to

have stations specified either side of the discontinuity, avoiding any errors inherent in

the integration of evenly spaced stations. For example, if it was known that a design had

a significant discontinuity in its sectional area curve at amidships, by specifying one

station 1mm aft of amidships and one station 1mm forward of amidships this

discontinuity can be modelled very accurately.


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Surface Precision

The Surface Precision options has two functions:

Setting for calculating the hydrostatic sections

Setting used to form new compartments or tanks.

The precision at which the design was saved in Maxsurf is included in the Maxsurf

design file (.msd). Maxsurf Stability recognises this precision setting and will and set the

Surface Precision button accordingly.

Note:

Maxsurf surface trimming information may vary for different precisions.

Therefore it is recommended not to change the precision setting when

opening the Maxsurf design file in Maxsurf Stability.

The accuracy of the results depends much more on the number of sections

than the accuracy at which the sections are calculated. Reducing the

precision of the sections can greatly improve performance, usually at

relatively small impact on the accuracy of the hydrostatics.

Opening an Existing Maxsurf Stability Design File

After saving the Maxsurf design file for the first time in Maxsurf Stability, a Maxsurf Stability Design file (.hmd) is created. The Maxsurf Stability design file will consist of the hydrostatic sections and all input data such as loadcases, compartment definition, key

points, sounding pipes etc. Maxsurf Stability also allows saving of all input and output

files into individual files.

To open an existing design, there are two options:

Double click on the .hmd file from any Windows explorer window

Use the Maxsurf Stability Open command form the file menu and select the .msd

file

An existing Maxsurf Stability design consists of a number of files with different file extensions.


Page 27

When Maxsurf Stability opens a .msd file, it will look for a .hmd file with the same

name as the .msd file. For example: when opening OSV.msd, the OSV.hmd file is found.

The Calculate Sections dialog now has the option to read the sections from the file.

Ensure Read existing data and sections is selected and click OK.

Maxsurf Stability will now open the .hmd file. This contains hydrostatic sections

information and all input information from last time the .hmd file was saved, i.e.

compartment definitions, loadcases, damage cases, key points etc.

Notes:

1) When selecting Read existing data and sections (do not update geometry) the Maxsurf surface information is not recalculated. This means that changes to the

hull shape in the Maxsurf Design file, are not automatically incorporated. You will

load your existing sections, loadcases and compartment definitions etc. See:

Updating the Maxsurf Stability Model on page 30 for more information.

2) Calculate new sections (ignore existing data, if any) means that Maxsurf

Stability will recalculate the hull sections and ignore any data stored in the .hmd

file. You will have to reload your individual loadcases and compartment definition

files etc after you have selected this option and pressed OK. Do not choose this

option if you wish to keep the additional Maxsurf Stability data and you have not

yet saved them as individual files as if the model is saved in Maxsurf Stability the

.hmd file will be overwritten and any existing data lost. For more information on

file properties and extensions in Maxsurf Stability, please see: File Extension

Reference Table on page 356.

Effect of Zero Point change

The description below relates to what happens in the following situation:


Page 28

A hull model is generated in Maxsurf

Tank and load etc. data is then created in Maxsurf Stability and that data all saved

in the .hmd file (as is done when you chose Save when the drawing window is top

most).

The model is closed in Maxsurf Stability

The model is opened in Maxsurf and for some reason the location of the zero point

is changed

The model is reopened in Maxsurf Stability and the tank and load etc. data is

automatically read from the .hmd file.

Maxsurf Stability 13 behaviour

It may sometimes occur that the model zero point location is changed in Maxsurf after

tank, loadcase. Etc. data is defined in Maxsurf Stability. In previous versions of Maxsurf

Stability this could cause problems because the loadcase and tank data maintained their

position relative to the zero point, where as the key points and margin line remained in

the same position relative to the hull.

The two images from Maxsurf Stability 13 show this problem. The first image shows the

model as initially defined in Maxsurf Stability with the zero point amidships and at the

baseline. In the second image, the zero point has been moved (in Maxsurf) to the aft-

perpendicular and the DWL. Note that whilst the margin line and key points have

remained in their same locations relative to the hull, the tanks and centre of gravity (from

the loadcase) have remained in their same locations relative to the zero point.

Original location of data as entered in Maxsurf Stability before zero point change in Maxsurf.


Page 29

Effect of Zero point change in Maxsurf 13.

Maxsurf Stability 14 behaviour

To rectify this problem, when loading a .hmd file, Maxsurf Stability now detects if the

zero point has been modified in Maxsurf when the model is reopened in Maxsurf

Stability. Note that this is only possible with Maxsurf Stability models that have been

saved from the new version of Maxsurf Stability (because the new version of Maxsurf

Stability now saves the zero point independently so that it can check for changes).

Original location of data as entered in Maxsurf Stability before zero point change in Maxsurf.

Now, if the zero point has changed, Maxsurf Stability will display the following

message:

If the zero point is moved in Maxsurf, you will now be prompted.


Page 30

Selecting yes will maintain the position all the Maxsurf Stability data relative to the hull; essentially just the zero point it moved. This of course means that the numerical

values of the various data are changed:

Click yes to maintain position of tanks, loads etc relative to the hull.

Selecting no will move all data other than the margin line with the zero point. Thus the tanks and loads etc. will move relative to the hull, but their numerical values will remain

the same: The example shown is quite extreme, it is more likely that this option would be

selected if it was realised that the zero point for the tank plan were slightly different than

the zero point of the lines plan and a small correction to the zero point was required.

Click no to maintain position relative to zero point.

Updating the Maxsurf Stability Model

To update the hydrostatic sections to the latest Maxsurf Design File, select Recalculate Hull sections in the analysis menu after reloading the Maxsurf Design File with the read existing data and sections from file option selected. This function can also be used to include/exclude surface thickness or change the number of sections and to

change use/not use trimmed surfaces without reloading the Maxsurf Design File.

The Recalculate Hull Sections command recalculates Hull surfaces as well as Tank Boundary surfaces (Internal Structure surfaces in Maxsurf). Any tanks and loadcases

will also be updated with this command.


Page 31

Note:

Changes to the Maxsurf design are only recalculated after the new Maxsurf

design has been re-loaded into Maxsurf Stability. This means that if the

model is simultaneously being edited in Maxsurf and Maxsurf Stability, it is

necessary to:

1) save and close the model in Maxsurf Stability

2) save in Maxsurf

3) open in Maxsurf Stability, using Read existing data and sections to make sure the loadcase, compartment definition etc remain part of the

Maxsurf Stability design file.

4) use the Recalculate Hull Sections from the analysis menu.

Maxsurf Stability Sections Forming

Maxsurf Stability works by applying trapezoidal integration to data calculated from a

series of cross sections taken through the Maxsurf model surfaces. Maxsurf Stability will

automatically form these sections, called Maxsurf Stability sections, hydrostatic sections or just sections. Maxsurf Stability deals only with sections that are completely closed, or can be unambiguously closed. This section outlines the section

forming process used in Maxsurf Stability and may be helpful when preparing a Maxsurf

design for Maxsurf Stability. Whilst it is always preferable to give Maxsurf Stability a

completely closed model with no ambiguities, Maxsurf Stability will try to resolve any

problems with the model definition in the manner outlined in the following sections.

Note:

The golden rule is that for any longitudinal position, the section must be

made up of closed, non-intersecting (and non-self-intersecting) contours. In

practice, one opening is acceptable and this will be automatically closed

with a straight line.

Furthermore, contours cannot be contained wholly within another contour.

The same is true for groups of internal surfaces that have been selected to

define a tank boundary.

Where a section consists of an open shell (e.g. a hull surface with no deck), Maxsurf

Stability will automatically close the section with a straight line connecting the opening

ends.

Section forming process in Stability

If, however, the section is made up of two line segments, (e.g. having both a gap at the

centreline as well as an open deck), an ambiguity exists as to how the two line segments

will be connected. This is not an acceptable shape.


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Insufficient data for Stability to interpret the section

In the example above, if either the top or bottom gap had been closed in Maxsurf the

design would cease to be ambiguous.

Multiple surfaces that are trimmed correctly, bonded together or use compacted control

points will not cause any problems when opened in Maxsurf Stability. Maxsurf Stability

will form a closed section through multiple surfaces by linking the curve segments

together.


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Stability closes the outside contour and trims remnants

A section through a multihull containing a single closed contour

A section comprising two closed contours

Maxsurf Stability will link curve segments together if they are only separated by a small

amount. The user cannot change these tolerances, because there are too many

dependencies in the program.

Where surfaces intersect, Maxsurf Stability will make an attempt to remove excess

portions of the curve to form a single continuous contour. However this is not always

possible so it is much better practice to trim the model correctly manually.


Page 34

Ambiguous Sections (e.g. decks, bulwarks)

A common example of ambiguous sections is a model with multiple decks. Maxsurf

Stability will have difficulties distinguishing the intended main deck.

Avoid using "Hull" surfaces for intermediate decks

The example above has bulwarks; generally these will be treated correctly by Maxsurf

Stability and removed, but this depends on the height of the bulwark relative to the rest

of the section. To prevent ambiguities it is recommended to trim the bulwark in Maxsurf.

If the bulwarks volume is expected to influence the hydrostatic calculations, the bulwarks volume has to be properly modelled in Maxsurf by modelling both the outside and the inside of the bulwark.

Checking the Maxsurf Stability model

Before starting any analysis you should check whether Maxsurf Stability has been able

to correctly interpret your design. The following tools are available to validate the

Maxsurf Stability model.

Show Single Hull Section

Checking the Sectional Area Curve

Using Rendering to Check the Model

Note:

Sections that are not formed correctly cause the majority of problems with

Maxsurf Stability models. Therefore, checking your sections after opening

the design in Maxsurf Stability is strongly recommended. Incorrect sections

in the model will give incorrect results.

These sections should be continuous with no gaps and no unexpected lines.

In particular, look closely at intersections between surfaces to make sure

that Maxsurf Stability has interpreted the shape correctly.


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Show Single Hull Section

In the body plan view, you can step through the sections one-by-one to verify that they

have been correctly calculated. This is done by selecting Show Single Hull Section in

Body Plan view from the Display menu. You can then click in the inset box to view the

sections, the left and right arrow cursor keys will enable you to step through the sections

one-by-one. This works the same as the Maxsurf body plan window and is an extremely

powerful tool to validate your Maxsurf Stability model. For more information see the

Maxsurf manual.


Page 36

Checking the Sectional Area Curve

Another way of checking the Maxsurf Stability model is to perform a specified condition

analysis at quite deep draft and look carefully at the sectional area curve in the graph

window. If this displays any unexpected spikes or hollows Maxsurf Stability may not

have correctly interpreted the hull shape. This is not a foolproof method since it does not

necessarily highlight problems in the non-immersed part of the hull.

This Cross Sectional Area curve indicates there may be a problem with section forming from 12 m to 16 m.

Using Rendering to Check the Model

The model may also be rendered, which makes it easier to see if there are any areas of

the model which have not been properly defined. Select Render from the Display menu

whilst in the perspective view and turn on the sections:

Note:

In rare instances incorrect rendering may occur. This does not necessarily

mean that the model is incorrect. As long as the sections are formed

correctly, the model is correct.


Page 37

Further detailed checking of hull and tank/compartment sections

When checking that your model is correct, you are interested in whether the sections are

correct. To do this go to the body plan view in Maxsurf Stability and select Show Single Section:

Then to check that the tanks are OK, leave the view as it is, but turn on the visibility of

all the tanks of interest (if there are few tanks, then you can show all of them, if there are

many it may help to hide some and check a few at a time).

In the single section view, only tank sections near the current hull section are shown:


Page 38

Setting Initial Conditions

All Maxsurf Stability calculations are performed in the frame of reference of the model.

Maxsurf Stability uses the aft perpendicular and forward perpendicular together with the

baseline and the zero point for all calculations and gives the results in the units specified

in the display menu.

Note:

Before you run any analysis using Maxsurf Stability, it is important that you

set up the required initial conditions for the design.

Coordinate System

Maxsurf Stability uses the Maxsurf coordinate system:

Longitudinal +ve forward -ve aft

Transverse +ve starboard -ve port

Vertical +ve up -ve down

View window View direction


Page 39

Body plan From the stern, looking fwd

Plan From above, Port side above the centreline (this

the opposite direction to Maxsurf)

Profile From Starboard, bow to the right.

Frame of Reference and Zero Point

It is essential that a frame of reference be specified. This should be done in Maxsurf and

not in Maxsurf Stability. Draft and trim are measured on the forward and aft

perpendiculars. If these are not in the correct positions, some analysis results will be

meaningless or may even fail to complete.

See: Setting the Zero Point and Setting the Frame of Reference on page 18.

Note:

Changing the zero point in Maxsurf will not update the compartment

definition, loadcase and other input values. Changing the zero point after

you have started analysing the model in Maxsurf Stability is not

recommended.

Draft Marks

Drafts are automatically calculated at the perpendiculars and amidships, should you

require drafts to be calculated at other locations, you may specify upto nine additional

locations at which the drafts should be reported. This is done through the Data | Draft

Marks dialog. Drafts are always measured to the Baseline in the centre plane of the

vessel. Immersed depth measurements are made perpendicualar to the free-surface.

Difference between Immersed depth and Draft measurements


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User-defined Draft Marks

Note that the Trim is still defined as the difference between the drafts at the

perpendiculars and the Midship draft (used to define the range of immersions for the

Upright Hydrostatics analysis) is the mean of the drafts at the perpendiculars; i.e. neither

of these values has changed and neither are affected by the user-defined draft locations.

Drafts can only be defined when the vessel is rotated to the DWL (Display | Set vessel to

DWL).

User-defined draft locations and new toolbar button

The draft marks allow a user-defined datum to be specified. As with normal drafts

measured to the Baseline, these drafts are also measured perpendicular to the Baseline

(i.e. perpendicular to the DWL of the vessel at zero trim). (Noting that immersed depths

to underside of keel USK- are measured perpendicular to the actual (trimmed, heeled) waterplane.

Custom Draft Marks extended to provide user-defined datum


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Different types of user-defined draft measurements

Note: Draft and Trim specification

It should be remembered that the drafts specified for an analysis are the

drafts at the perpendiculars (or amidships) and the trim specified (and

reported) is the difference between the draft at the AP and draft at the FP.


Page 42

Customising Coefficients

In Maxsurf Stability you may choose between the length between perpendiculars and the

waterline length for the calculation of Block, Prismatic and Waterplane Area

Coefficients. You may also select the draft, beam and sectional area to be used for

calculation of these coefficients.

The LCB and LCF can be displayed in the Results windows relative to the specified

Zero Point, Amidships location, Aft Perpendicular, Fwd Perpendicular or from the Aft,

Middle or fwd end of the actual waterline. You can also specify whether you want the

forward (towards the bow) or the aft (towards the stern) to have a positive sign. Finally

you can chose whether you want the LCB and LCF to be displayed as a length or as a

percentage of the waterline or LPP length as specified in the Length for Coefficients.

Data | Coefficients dialog


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Setting Units

The units used may be specified using the Units command. In addition to the length and

weight (mass) units, units for force and speed (used in wind heeling and heeling due to

high-speed turn etc. criteria) and the angular units to be used for areas under GZ curves,

may also be set. The angular units for measuring heel and trim angles are always

degrees. Units may be changed at any time.

Other Initial Conditions

See:

Fluids Analysis Methods on page 193

Density on page 195

Working with Loadcases

Loadcases define the loading condition of the vessel. Static weights that make up the

vessel lightship are specified here as well as tank filling levels, expressed as either a

percentage of the full tank capacity or as a weight.

Loadcases automatically contain all the tanks defined in the Tank definition. Loadgroups

are special loadcases that contain no tanks. These may be used to define groups of fixed

weights (such as the steel weight or lightship weight) in a single location which may then

be cross-referenced into a loadcase. Any changes to the loadgroup are then automatically

incorporated into any loadcases that reference them.

A loadgroup is included in a loadcase simply by specifying the loadgroup name in the

Item Name column.


Page 44

The loadcase will normally update the column totals automatically as weights or tank

loadings are changed. The exception to this is if tanks have not yet been formed or the

vessel is still rotated from the result of an analysis. If the loadcase does not update, click

on the update Loadcase button and ensure that the hull is at the DWL by selecting Set vessel to DWL:

The individual loads can be displayed graphically:

Creating a new Loadcase File

To create a load case, switch to the loadcase view by selecting Loadcase from the

Loadcase sub-menu in the Window menu. Then select New Load Case from the File menu or press Ctrl+N. A new load spreadsheet will be displayed in the Loadcase

window. The default loadcase will contain a lightship entry and an entry for each tank

(with a default filling of 50%).


Page 45

The tabs in the bottom of the window can be used to skip through the different loadcases

in the design.

Create New Loadcases based on Template

To avoid rework, an existing loadcase may be used as a template when creating a new

loadcase. To do this,

In the loadcase window, select the Loadcase you wish to use as a template

Bring the loadcase you wish to use as a template to the front for example by clicking on the tab on the bottom

select File | New


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First, you will be asked for a new Loadcase name after which the following dialog

appears:

A new loadcase will appear in one of the blank () loadcase tabs. If there are no blank tabs left, you will either have to close an existing loadcase, or add more loadcases using

the Case | Max. Number of Loadcases command.

Note

The template is only used during the creation of the loadcase. Once a

loadcase has been created from a template loadcase, changes made in the

template are NOT automatically changed in the loadcase derived from it.

Naming and Saving a Loadcase

A loadcase can be given any name by saving it to a separate file where the loadcase

filename will be used as the loadcase name and displayed on the tab in the loadcase

window. Alternatively,

Select Edit Loadcase from the Case menu

Changing the name in the Loadcase Properties dialog.

The next time you use the File | Save Loadcas

stability manual

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