Stability Manual

(1)

Maxsurf Stability

Windows Version 20

(2)

(3)

License and Copyright

(4)

(5)

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.

(10)

(11)

Chapter 1 Introduction

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.

(12)

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.

(13)

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 vessel’s 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.

(14)

(15)

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.

(16)

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

(17)

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

(18)

Wave form

Grounding

Damage

Key points

Margin line and deck edge

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

(19)

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

Wave form

Damage

Tank and Compartment definition (in case of 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.

(20)

Stability criteria for which limiting KG is to be found

TCG (if required) Limiting KG Analysis Options

Wave form

Damage

Tank and Compartment definition (in case of 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.

(21)

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

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

(22)

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:

(23)

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

Margin line and deck edge

(24)

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.

(25)

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:

(26)

 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 vessel’s bow is on the right.

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

(27)

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

(28)

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.

(29)

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

(30)

Upright or heeled/inclined projected windage area calculation preference

(31)

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

(32)

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

(33)

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

(34)

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

(35)

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

(36)

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.

(37)

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:

(38)

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

(39)

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.

(40)

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.

(41)

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.

(42)

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 bulwark’s volume is expected to influence the hydrostatic calculations, the

bulwark’s 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.

(43)

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.

(44)

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:

(45)

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).

(46)

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

(47)

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.

(48)

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.

(49)

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.

(50)

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.

(51)

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.

(52)

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%).

(53)

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

(54)

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 Loadcase command you will be asked to confirm the loadcase file name.

Loading a Saved Loadcase

You can load a saved loadcase into your loadcase window by:

 Select an empty tab in the loadcase window that you wish to load the loadcase into

(55)

If there are no empty tabs, you should either increase the maximum number of loadcases (see below), or close an existing loadcase.

 Select File | Open Load Case

 Select the .hml file you wish to open.

Setting the Maximum Number of Loadcases

The maximum number of loadcases (up to twenty-five) that can be loaded in Maxsurf Stability at any one time is set by selecting “Max. Number of Loadcases” from the Case menu. You may then enter the maximum number of load cases you require.

You must restart Maxsurf Stability for this change to take effect. In most cases, you will only need to set this once to the maximum number of loadcases you are ever likely to use. For convenience of use, a sensible number is recommended.

Each loadcase can be selected and used for analysis. Each may be saved and loaded independently, effectively allowing you as many loadcases as you require.

Note:

When loading a design that has more loadcases than the maximum you have currently set in Maxsurf Stability, you will receive a warning and the file will not be loaded. You must increase the maximum number of allowable loadcases and restart Maxsurf Stability before you can load the design.

Closing a Loadcase

 Select the tab of the loadcase you wish to close in the Loadcase window

 Select File | Close Load Case

Adding and Deleting Loads

To add an extra load to the loadcase,

 Select Add Load from the Edit menu or press Ctrl+A.

A new load will be inserted into the table above the currently selected row. You can repeat this process for as many loads as you wish.

If you want to remove a load from the table, simply click anywhere in the row you want to remove, and choose Delete Load from the Edit menu (or highlight the complete row by clicking the grey cell to the left of the row and press the Delete key). If you wish to delete several loads simultaneously, click and drag so that all of the loading rows that you wish to delete are selected, then select Delete Load.

(56)

For each item in the list you can specify a quantity. This is used to calculate the total weight of that item. For example: if the item was “crew” with a weight per unit, you could specify the quantity and unit weight, and the total weight of crew would be automatically calculated. The weight of each item should be entered in the next column. The weight must always be positive. If for some reason you wish to have an upward (negative) load, you can do so by entering a negative quantity – this can be useful if you want to apply a pure moment to the model by applying equal magnitude, but opposite sign loads to the vessel in the loadcase.

Tab to the next column and enter the horizontal lever for the item. After you type in this number, press enter and the total LCG will be automatically re-calculated and displayed in the bottom row of the table. The CG position will also be shown and updated in the View windows if Large Angle Stability, Longitudinal Strength or Equilibrium analysis are selected.

Note:

Levers, as with all other measurements in Maxsurf Stability, are measured from the Zero Point.

Loadcase Sorting

A number of tools are available for controlling the order in which items and tanks occur in the loadcase. You may move selected items and tanks up and down in the loadcase; you may also sort selected items by name, fluid type (for tanks) etc.

Insert row | Delete row | Sort rows | Move row(s) up | Move row(s) down

Sort selected columns

After moving loads, subtotals and subsubtotals, you may have to use Analysis | Update Loadcase ( button) to update the subtotals and subsubtotals. To ensure data

(57)

Adding Blank Lines

A blank line can be added into the load case by placing a dollar ($), apostrophe (‘) or full-stop(.) character in the Item Name field.

Adding Totals or Subtotals

A subtotal can be displayed for several loads within a load case. To do this the item name field must commence with the word ‘total’ or ‘subtotal’.

Sub-subtotals

Sub-sub-totals may also be inserted. Sub-subtotals must start with the text “subsubtotal”.

Grouping Similar Tanks

Use the move items UP or Down commands in the Edit menu to adjust the row order in the loadcase.

Quantity and Unit mass for sub total rows

If a sub total includes only tanks, then the quantity and unit mass items will be included. The unit mass is the sum of all the masses of the full tanks and the quantity is the sum of the masses divided by the sum of the full tank masses. When tanks are grouped by fluid type this can be useful for calculating the total tank capacity for that fluid type.

Loadcase Colour Formatting

Different colours can be defined for fixed mass items and tanks; alternatively, tanks may be displayed in the same colour as the fluid they contain (As defined in Analysis | Fluids dialog).

(58)

Loadcase format

It is possible to select which columns are displayed in the loadcase window. Use the Display | Data Format dialog:

The Relative density and Fluid Type which allow you to override the default tank densities as defined for each tank in the Compartment Definition window. This can be useful for vessels such as product carriers which may have cargos of different types of fluids with different densities.

Moment columns (mass * lever) can be displayed if desired.

Longitudinally Distributed Loads

Distributed loads can be entered in the Loadcase window in the aft limit and forward limit cells. The aft limit and forward limit columns only appear when Longitudinal Strength analysis is selected and the distributed loads will only have an effect on the results in this analysis mode. The “Long. Arm” column defines the longitudinal position of the centre of the load; the fore and aft limits define the longitudinal extents of the load.

(59)

Evenly distributed loads. Red = green and divided in the centre.

For trapezium shaped distributed loads the centre of gravity is not midway between the boundaries, but within the middle third 1/3 of the centre.

Trapezium shaped distributed load. Red = Green divided within middle 1/3 of centre.

Note:

Since the load is distributed as a trapezium, the centre of gravity should lie within the middle third between the forward and aft limits of the load, at these extrema, the load distribution becomes triangular.

Stability Manual

Maxsurf Stability

Windows Version 20

License and Copyright

Contents

About this Manual

Chapter 1 Introduction

Input Model

Analysis Types

Analysis Settings

Stability Criteria

Output

Chapter 2 Quickstart

Large Angle Stability Quickstart

Equilibrium Condition Quickstart

Specified Condition Quickstart

KN Values Quickstart

Limiting KG Quickstart

Floodable Length Quickstart

Longitudinal Strength Quickstart

Tank Calibrations Quickstart

MARPOL Oil Outflow Quickstart

Probabilistic Damage Quickstart

Chapter 3 Using Maxsurf Stability

Getting Started

Maxsurf Stability Model