As a BREP solid based hydrostatic solver, MAAT Hydro only calculates the hydrostatic features of the BREP solids currently present in the model.

When the imported model doesn't contain any BREP solid, no hydrostatic data can be calculated before the user has built one or more BREP solid(s) from the imported entities.

Importing and displaying model's faces correctly is therefore not enough for calculating ship's hydrostatic features, these faces still having to be joined together in order to create the watertight BREP solid(s) which can be calculated.

MAAT Hydro's Part II and Part IV manuals, which can be dowloaded from its 'Help' tab as well as from the resource page, explain how to create BREP solids from the imported faces.

At last, a good setting of your 3D modeler's IGES export options often allows exporting directly BREP solids to MAAT Hydro, making the imported data immediately usable for hydrostatic calculations (by example, see What are Rhino's best IGES Export Settings for MAAT Hydro ? below).

MAAT Hydro can import IGES files complying with IGES 5.2 specifications, the following IGES entities being accepted:

  100: Circular Arc

  102: Composite Curve

  108: Plane (bounded)

  110: Line (segment)

  120: Surface of Revolution

  122: Tabulated Cylinder

  124: Transformation Matrix

  126: Rational B-Spline Curve

  128: Rational B-Spline Surface

  141: Boundary / Outline

  142: Curve on Parametric Surface

  143: Bounded (Parametric) Surface

  144: Trimmed (Parametric) Surface

  186: Manifold Solid B-Rep Object

  504: Edge

  508: Loop

  510: Face

  514: Shell

Moreover, the following points must also be respected:

   - Lines must be exported as NURBS (avoid Splines).

   - Faces must unconditionally be exported as trimmed NURBS.

   - If possible, convert rational NURBS to non-rational ones.

   - If possible export BREP solid(s), in order to get directly MAAT Hydro’s native objects.

The Rhino 5 IGES export options shown below provide an optimal tuning with MAAT Hydro:

 At last, it is important to mention that, as Rhino 5 allows detecting model’s leaks easily (Analysis/Edge Tools/Show Edges/Free Edges), the ‘watertight’ / closed polysurfaces needed by MAAT Hydro can be created easily before their IGES Export.

Selecting '/File/Open', in MAAT Hydro's menu bar and, then,  selecting '*.igs' in the format selector for opening Rhino's IGES export file, will allow getting the corresponding MAAT Hydro model almost immediately (see details on IGES file opening) .

Although no obvious difference appears on the model views, unadapted unit and tolerance settings can cause huge IGES exports (dozens of Mb) and, accordingly, unusually poor response times in MAAT Hydro. 

By example, a rectangular shell face can be trimmed by a simple 4 knots NURBS with the appropriate precision settings but may require thousands of knots when the modeling precision is too high*, producing huge export files and overloading MAAT Hydro for nothing.

In order to make the most compact Rhino model (IGES file size < 10-20 Mb), a special attention must therefore be paid to Rhino’s precision settings before modeling the ship (and not only before exporting it), as unnecessarily sharp Rhino tolerances may considerably increase MAAT Hydro's model size and slow down its calculations accordingly (sometimes more than 10 times), without any significant incidence on the accuracy of its hydrostatic data.

By experience, it is therefore a good habit to use millimeters for modeling a ship (a 20 m  ship will, therefore, be modeled as a 20 000 mm object).

The other most important setting concerns the absolute tolerance: 

 - A 0.001 mm tolerance is usually appropriate for modeling ship's parent hull and deck surfaces. 

- A 0.1mm tolerance is most often sufficient for trimming ship's faces (deck / superstructure intersections, compartment subdivision, etc..), as the hydrostatic calculations generally don't need a sharper geometric tolerance.

Rhino allows setting these parameters by selecting 'Options / Units / Model' in the menu bar, the following settings usually providing excellent results with MAAT Hydro:

In order to illustrate the incidence of this important Rhino setting on the amount of exported data, the following figure shows how the number of control points of NURBS x NURBS intersections grow according to the tolerance reduction:

Moreover, when exporting complex models to MAAT Hydro (i.e. parent hull, compartments, bulkheads, remarkable lines, etc...) a step by step procedure is often more efficient, starting with parent hull's export and control, and ending by the import of the subdivision elements if necessary.

At last, when the amount of imported data cannot be optimized at source  (by example, when you receive the file from a third party), MAAT Hydro also provides several tools allowing to reduce model's size by approximation (see IGES Import Options), in particular 3D browser's 'Optimize' and 'Reduce' functions. Response times can also be optimized according to model's features (see FAQ item on this topic).

As MAAT Hydro’s re-approximation functions may have a certain incidence on model's geometry, you can minimize this alteration by identifying the huge elements and only reducing them.

In this case, the best strategy consists in identifying the ‘huge’ solids first:

- Create an empty folder.

- Double click on it to make it current

- Switch to the rendered display mode and / or open the hydrostatic viewport..

- Drop / paste the ship compartments one by one in the new folder.

- Identify the ‘huge’ solids by comparing individually their display / hydrostatic calculation times after dropping them in the new folder.

When the ‘huge’ solids are identified, they can be directly ‘Reduced’ from the 3D browser or even more sharply optimized as follows:

- Explode the ‘huge’ solid (/Solid/Explode).

- Identify solid's ‘huge’ faces like you identified the ‘huge’ solids.

- Reduce the identified ‘huge’ faces (select the faces in the 3D browser and right click to select ‘Reduce’ and/or 'Optimize').

- Re-build the solid from its optimized faces (/Solid/Join).

* As shown in the figure,the amount of data produced by Rhino's surface x surface intersection highly depends on its current modeling precision and is one of the most common causes of unnecessarily heavy IGES export  files.