Hydromax FAQ list

How come some surfaces are not appearing in the boundary surfaces list?

In Maxsurf set the Surface Use to "Internal Structure" in case you want to use it as an tank boundary.

Tip: if you want to display your internal structure surfaces in Hydromax, you can switch on the Internal edges in the Visibility dialog from the Display menu.



I am getting different hydrostatic results for Hydromax and Maxsurf with the same draft. Why is that?

The Hydrostatic calculations in Maxsurf and Hydromax can be different due to the following reasons: 

1) Hydromax includes skin thickness where Maxsurf does not.

2) The number of sections used may be different which gives different results.

3) Some sections may not have formed correctly in Hydromax. Consult the Hydromax manual on how to check individual sections.

4) If you have used non-buoyant volumes or are analysing a damaged case, your hydrostatics will be different.


Why is my compartment not forming correctly?

See Tips & Tricks on modelling non-buoyant volumes (login required) and the Hydromax manual, section "Forming Compartments" to troubleshoot this issue.


Some of my tanks appear not to form correctly. What could be wrong?

What can be the case is that the tank is actually formed correctly, but in some situations the display of tank edges may not give a complete display of the shape of the tank. To check whether your tank is formed correctly, ensure you check the shape of your tanks by turning on the display of tank sections.

Make sure you read the Hydromax manual on modelling tanks and compartments

It is also important to understand what Hydromax does in the background when it is forming tanks.


Is skin thickness included for Internal structure surfaces?

Skin thickness applied to internal structure surfaces is not taken into account when calculating the volume of Tanks and Compartments that use internal structure surfaces as boundaries. If you want to include the effect of the tank boundary surface's skin thickness, you have to model the surface to the inside of the tank.

The thickness of hull surfaces is taken into account. Remember to check the direction of the outside arrows when applying skin thickness.


My criteria dialog does not look good anymore, how can I fix that?

Holding down the shift key while firing up the criteria dialog, will resize the dialog to its original settings. You can then resize the dialog and change the division of the individual areas as described in Resizing the criteria dialog in the Hydromax manual (best viewed in Internet Explorer).


My tank calibration results read zero or 100% full for most of the intervals

Check your sounding pipes in the sounding pipes table. When your sounding pipes are set to User Defined and you move your tanks, the sounding pipe can become located outside of your tank. This will produce incorrect tank calibration results.

You can make sure your sounding pipes are in the correct location and of the correct length by setting them back to automatic in the Sounding pipes table:


Also see the Hydromax manual:


I am getting a Criteria analysis error message when I run an analysis. What could be wrong?

The following criteria analysis errors can occur:

1: Severe wind and rolling 

Make sure your heeling range starts at -20 degrees or less. The roll back angle to windward often requires the heeling range to start at a negative angle.

2: MAX GZ in a range 



Make sure your upper limit of your heeling arm is set to > 90 degrees, and check whether your MaxGZ value does not occur at an angle <30 degrees (the lower range bound).


How can I get bonjean data?

There is no direct method of bonjean calculation in Hydromax. However it is possible to get sectional area data at selected draughts:

  1. Run an upright Hydrostatics calculation at the required draught and trim.
  2. Go to the results table.
  3. Select each draught in turn and choose "Display | Select view from Data"
  4. Then go to "Window | Graph | Curve of Areas" -- this will bring the curve of areas to the front instead of the upright hydrostatics data, and is only required the first time.
  5. Double click anywhere in the graph window to get the data table.
  6. Copy and paste the first two columns into a spreadsheet.
  7. Then close the dialog, go back to the results table, select the next draught, select "Display | Select view from Data", go back to the graph, double click, select, copy and paste the data -- repeat for each draught.

If the windows are not maximised, you'll find it easier to switch between the results table and sectional area graph.


Which version of Hydromax should I use?

There are two different versions of Hydromax, which vary in price and capabilities, allowing you to select a product that suits your needs and budget.

Hydromax Pro is a powerful intact and damage stability analysis program with an extensive range of customisable stability criteria. It includes a built in weight and balance spreadsheet, tank calibrations, damage conditions and a range of hydrostatic analyses:
          o Upright Hydrostatics,
          o Large Angle Stability (GZ curve)
          o Equilibrium and Specified condition,
          o Cross curves of stability (KN),
          o Limiting KG,
          o Floodable length, and
          o longitudinal strength.
      Several analysis modifiers may be included such as a longitudinal wave form and grounding.

Hydromax has batch processing capabilities and a number of output options. In addition a VBA/COM interface is provided so that you can generate custom macros in (for example) Microsoft Excel which will perform an analysis and extract the results.


Hydromax/S is a simplified version of Hydromax providing only intact hydrostatics and stability functions:
          o Upright Hydrostatics,
          o Large Angle Stability (GZ curve calculation) and
          o Equilibrium analysis.
      Stability criteria cannot be evaluated and grounding is not included. There is no batch analysis mode either.



Please note that Formation Design Systems offers upgrades from Hydromax/S to Hydromax Pro for the difference in the current list price. This means that if you are using Hydromax/S and wish to upgrade to Hydromax Pro, we can email you the access code for Hydromax Pro and all you will be paying is the difference between Hydromax/S and Hydromax Pro.


Also see the Hydromax webpage for more information.


Can I rename a loadcase in Hydromax?

Yes you can. When you save a loadcase you can specify the name of the loadcase. After you have saved the loadcase, you will see that the name of the loadcase appears at the top of the loadcase window as well as on the tab at the bottom of the loadcase window.



I don't seem to be able to hide my hull sections anymore, what should I do?

You have switched on the "Show Single Hull Section in Body Plan" from the Display menu. This command overrides the display sections on/off command.

The command can be switched off when you have the Body Plan window front most.


I can not edit / change the values in a criterion. What should I do?


After a longitudinal strength analysis I get a graph, but my results table is empty. How do I get the results data?

The longitudinal strength analysis values in the results table are calculated at the design sections. Make sure you have defined sections in your model in Maxsurf. Without this, the longitudinal strength table will be empty.

Note: you can also get the graph data values by double clicking on the curve and then copying and pasting the tabular data that appears into Excel. This can be done from any graph in the Maxsurf suite.


When I open my Maxsurf model in Hydromax, some sections are wrong. What should I do to fix that?

Remember that for Hydromax to work it must be able to form sections through the model. Any extra surfaces (or missing surfaces) that cause ambiguity will give Hydromax problems and may lead to Hydromax interpreting the model incorrectly.

The 4 key rules are:

  1. At any longitudinal position, you must have non-intersecting, closed contours.
  2. For a given longitudinal position, you can have a maximum of one opening and this will be closed by a straight line -- i.e. for a monohull its generally OK to leave the deck off.
  3. You cannot have a contour completely inside another contour -- this type of feature (e.g. waterjet duct) needs to be modelled with a non-buoyant volume.
  4. Surfaces which form vertical transverse planes are generally best avoided since a section at precisely the longitudinal position of the surface is undefined (it contains the whole surface not just a simple contour).


Can Hydromax be used on submarines?

Hydromax can be used to analyse submarines. However, some analyses require that the centre of buoyancy (CoB) and centre of gravity (CoG) be balanced (Equilibrium and Stability analyses plus other analyses that use these as a basis: Longitudinal strength, Cross curves and Limiting KG). For these analyses Hydromax can be used provided that the submarine is not fully submerged. These analyses require a waterplane so that the CoB/CoG balance can be performed. As soon as the waterplane area becomes very small or zero, Hydromax (and any other Hydrostatic analysis program that works on this principle) may have difficulty in converging and the trim and heel cannot be determined. Upright hydrostatics and some Specified condition analyses can be performed for the fully submerged submarine.

In order to model the submarine, any volumes that are free-flooding should be modelled as non-buoyant volumes, whilst ballast tanks should be modelled as normal tanks.


Does Hydromax have classification certification?

Classification societies do not certify software that is used for design, analysis and production of stability booklets. In a design office you can use Hydromax without certification. It is the produced stability book that gets certified. See our Launchings pages for some examples of projects that have been successfully completed using Hydromax.

Classification societies only require software that is used on-board of a ship to be certified and then only the installation that gets installed on-board of that one particular ship (with one fixed hull form and compartment definition etcetera). Hydromax is quite suitable to be used for that purpose as well. If you are interested in us doing custom development for you, please contact us.


How can I calculate the TCB in Hydromax at different angles of heel?

This cannot be done directly in Hydromax, but attached is a spreadsheet which will extract the data from a LAS analysis once completed using the Hydromax COM interface.

  • Download the Excel Spreadsheet
  • Start Hydromax and open your model
  • Run the LAS analysis
  • Click the GetResults button in the spreadsheet and it should populate the spreadsheet with data.

Have a look at the macro to get similar results from other analyses or for additional data.

Note that there are two coordinate systems -- one is fixed in the ship reference frame, the other is in a World coordinate system with longitudinal and transverse parallel to the waterline.

See Maxsurf Automation and the Version 11 newsletter for information about automation.


Can Hydromax be used on submarines?

It is possible to analyse certain hydrostatic properties of submarines using Hydromax. This is described in the Tips&Tricks section of this knowledge base which is accessible to Maxsurf users with current subscription.


I can't modify linked negative compartments?

The negative linked compartments are created by Hydromax automatically at the intersecting volumes of tanks and compartments. You do not need to worry about them at all; they are displayed for reference purposes only because in older versions users had to define these linked negative compartments manually. The linked negative compartments are used by Hydromax internally to deduct tank volumes from a compartments' volume when flooded, but again: you do not need to worry about them.


What restrictions does the demonstration version of Hydromax have?

The demonstration version of Hydromax only allows analysis on the one sample design that is opened automatically when you select the File |Open command. This model already contains a number of tanks and compartment as well as predefined damage cases, but feel free to add more and run some analyses.

Additionally, the demonstration version of Hydromax does not allow saving of reports or copying graph or table objects.


What Quality Assurance Processes are used to ensure that Hydromax produces reliable and accurate results.

Many Hydromax users ask us how we know that Hydromax produces the correct results.  The following explains how FORMSYS has verified that Hydromax gives accurate results and what steps we take to make sure that each version of the software we ship is as reliable as possible.

Quality Principles
While it is impossible to ensure that any software product is completely free of bugs, we follow a series of engineering and testing principles and procedures to ensure that Hydromax will produce results which are consistent with the level of accuracy and thoroughness a professional engineer applies to design work.  To this end we follow a development and testing path which includes use of structured programming techniques, verification of the underlying algorithms, testing of the computer implementation of those algorithms, testing of real world problems in-house and beta testing in the field at Hydromax user sites.

Structured Programming
The best defence against bugs in software is to use structured programming techniques that have been proven to improve software reliability.  Without going into the technical details of our software development methodology, we summarize by saying that we utilize structured code, object oriented design, data hiding and encapsulation and fault tolerant programming practices to enhance our software's reliability. Hydromax is a complex software system of over 400,000 lines of code and we believe our history of reliability reflects the effort we have put into using reliable coding practices.

Verification of Algorithms
When new design or analysis algorithms are introduced into Hydromax, we first carry out testing on the algorithms on Reference Designs – these are proven test cases with known analytical solutions.

Reference Designs
A folder of reference hull shapes is included with Maxsurf and Hydromax. These designs are of simple geometric shapes and can be used to validate calculations performed by Hydromax. Below is a table of results derived analytically from these shapes compared with results obtained from Maxsurf and Hydromax at different precisions.

Testing of Implementation
Once the basic algorithms have been proven correct, testing is then carried out on more complex sample problems to which a solution has already been established using a proven analysis program.  These results may either come from Naval Architecture and Marine Engineering texts such as well as from other results carried out by Formation Design Systems or other engineers using other software products such as NAPA, AutoShip etc.

Testing of Upgrades
As each new version of Hydromax is released we perform a series of tests to ensure it functions correctly.  At each release the results from these tests are compared with the results from the previous release to ensure conformance with answers which have been established as being correct.

Beta Testing
Immediately prior to the release of each new version of Hydromax, we conduct a beta test of the software.  This involves sending the software to practicing engineers and having them use it on design work in progress to determine its reliability for actual design use.  These beta testers provide us with feedback on the reliability and accuracy of the program as well as its useability and suitability for everyday work.  Once the beta test program is completed and all testers are happy with the program, we begin shipping the commercial version.

Version Control
Each new version of Hydromax displays a version number indicating the version and the date the software was first shipped.  If the version is a development, alpha test or beta test release, the version number may also include a letter and number suffix indicating the type and number of the release.  A development version is usually only for internal use and is a very early demonstration of a possible new product or feature.  It is highly experimental and not reliable. An alpha release is a first public release of a program for initial testing and comment, it is not reliable.  A beta release is a final test version of the program released for field testing prior to commercial release. It is mostly reliable but may contain some bugs.  A commercial release is a completed, debugged program reliable and ready for professional use.
For example
1.0d1        The first development release of version 1.0
1.5a2        The second alpha test release of version 1.5
1.6b2        The second beta test release of version 1.6
1.64          A commercial release of version 1.64

But we're not Perfect
We make every effort to ensure that our software will meet our users' needs and perform accurately.  However, as with all complex software systems, it is possible for errors to occur.  If you suspect a problem with Hydromax, please contact our technical support staff by email at support@formsys.com and explain what you believe the problem to be.  In the unlikely event of a problem being found, we will correct it as soon as practicable, and send you a new corrected version of the program.

To get accurate results from Hydromax, it is necessary for you to model the problem correctly and to correctly interpret the results produced. It is the users' responsibility to correctly model the structure and assume responsibility for the results.


Copyright © - Formation Design Systems Pty Ltd trading as FormSys