Advanced Hydrostatics & Stability

Compartmentation modeling, Fluid and Fixed Loads definition, Intact and Damaged Stability Analysis with Free Surface Effects, Stability Criteria Evaluation, Tank Capacity Tables, and more all within Rhino. No need to import or export your model!

Building on Orca3D’s Basic Hydrostatics & Stability calculation engine, the Advanced Stability feature starts with creating a complete compartmentation model of the vessel with tanks, watertight compartments, and non-watertight compartments. Load Cases are then defined with fixed and fluid loads, after which hydrostatics, stability, and stability criteria evaluation analyses can be run, with output to formatted reports as well as export to Excel, Word, and PDF.

As with other Orca3D functions, hull models imported from other software or created in Rhino without Orca3D can be used to create compartmentation models just as if the hull was created with Orca3D.

Because Orca3D computes the hydrostatic properties based on the surface model using three-dimensional volume integration rather than station integration, there is really no limit to the type of vessel or object that it can analyze. Orca3D is especially useful for non-ship shape models, where the traditional approach of station-based integration can be challenging.



Compartmentation begins with a model that is composed of one or more closed, solid surfaces and/or polysurfaces. The model is then subdivided into tanks and compartments using simple planes including transverse and longitudinal bulkheads and horizontal decks. For more complex shapes any Rhino geometry can be used as a subdivider, including closed objects that are completely within the hull, objects that intersect the hull, and even curves that will be extruded. 

Once compartments are created, their properties are set. This can include defining the compartment as a tank and selecting the default contents and permeability. Or it might be defining the compartment as non-watertight, as in the case of superstructure that is included in the model for wind heeling moment calculations and/or compartment area/volume studies. 

 Load Cases

Load Cases define a particular condition of the vessel for analysis. This is a combination of any fixed loads (lightship weight, cargo, crew & effects, etc.) and fluid loads in tanks. Tank loads may be specified by % full, sounding, ullage, or volume. The method for computing tank free surface may be specified as an actual shift of the fluid center of gravity due to heel and trim, or the traditional approach using a virtual rise in the center of gravity. The Orca3D Load Case editor allows you to override the default fluid contents and permeability of any individual tank as well as define the tank status as Intact, Damaged, or Frozen. 

The Load Case editor also allows you to immediately solve for the equilibrium flotation condition for any given tank loading, fixed loads, and compartment status, and has options to override the computed weight and/or center of gravity. The equilibrium flotation condition may also be specified by Sinkage, Trim, and Heel and a residual weight and its center of gravity will be computed to achieve that condition.


Using one or more Load Cases, various analyses may be run:

  • Hydrostatics – Solve for the equilibrium flotation and report all hydrostatic data.
  • Stability – Hydrostatics as above and adds righting arm data at a user-specified range of heel angles. The height above the waterplane is also reported for any Points of Interest that have been defined.
  • Stability Criteria Evaluation – Stability as above and adds the automatic evaluation of a user-selected set of stability criteria including heeling moments, downflooding, margin line and deck edge immersion, and freeboard computations.

Complete formatted reports are generated, which may be printed or exported in formats such as PDF, Word, and Excel. Additionally, data may be exported to .csv files for import into Excel for further analysis.

Points and Curves of Interest

Points of Interest (Rhino points) and Curves of Interest (Rhino curves) may be defined for use as downflooding points, margin line, or deck edge curves for Stability Criteria Analysis. The height above the waterplane of all Points of Interest is reported for each flotation condition during an analysis.

Stability Criteria and Heeling Arms/Moments

Orca3D can evaluate your vessel against stability criteria in any Loading Condition. Orca3D is delivered with some predefined sets of criteria, and it’s easy to add or edit your own using a the stability criteria definition form. The report will show Pass/Fail and document the important quantities such as angle at downflooding, righting arm at GZmax, angle of GZmax, etc.

Heeling Arms and Moments may be defined with beam winds, beam winds with rolling, moments due to lifting weights over the side, passenger crowding or offset weights, towline pull, high-speed turning, or custom quantities. Wind heeling moments can automatically use the projected area of the model or a Rhino curve, or you can specify the area and centroid.


Each analysis includes a formatted report documenting the input to the analysis and the results. The report may be printed directly or exported to PDF, Word, Excel, and other formats. In addition, analysis results may be saved directly to a .csv file for further analysis in Excel.

Reports may be customized with the use of the Report Options:

Tank Tables & Area/Volume Report

Tank Tables are easily generated at a user-specified trim and heel. Input quantities may include percentage full, volume, mass, sounding, or ullage. Sounding and ullage use sounding tubes that are automatically generated when a tank is defined, but custom sounding tubes may be defined by drawing a polyline in Rhino to represent the sounding tube.

Output can include all Tanks, all Tanks and Compartments, or just selected Tanks and Compartments, and the report is written directly to Excel or a .csv file.

An Area/Volume report is easily generated in text, .csv, or XML format. The details of each tank and compartment are included such as total area, deck area, volume, centroid, and for a tank the contents and permeability.

Updating Hull Geometry

Since the subdivision history of a model is saved as it’s being built, if it becomes necessary to modify the hull geometry after the compartmentation model is created, Orca3D can swap in the new hull geometry while maintaining the compartmentation information, if the new geometry doesn’t invalidate it.

Original Hull Geometry with Bulb

Replaced Hull Geometry without Bulb


The creation of a compartmentation model, definition of Load Cases, and execution of analyses may all be automated through scripting. To help with this process the subdivision history of a model is saved as it’s being built interactively. This history can be exported to a text file which can then be edited and re-run to make changes. Scripting also allows the system to be driven by external tools such as ModelCenter.