Hullform Design & Fairing in General Purpose CAD Tools vs. FastYacht by Proteus Engineering

In short, the main issues are:

1. What is a hull in CAD terms
2. Philosophy behind the CAD tool
3. Nature of the CAD tool
4. Functions made available by the CAD tool
5. Complementary Features of FastYacht / FastShip and general purpose CAD tools.
6. The purpose of the generic CAD tool.
7. Enhancing the role of the generic CAD tool: new possibilities.

1. What is a hull in CAD terms.
The main body of a hull is a continuous surface, exhibiting single and / or double curvature characteristics. In the case of planning hulls with chines / knuckles, the surfaces at hand may be more than one, but nevertheless intimately connected in terms of curvature and shape evolution in 3D space.
Other components of the hull are more or less varied in the nature of their surface topology. For example, yacht and transoms vary from simple flat surfaces to cylindrical shapes, to intricate 3D compositions of flat and / or arbitrarily curved shapes. The same holds for yacht decks and superstructures, and for some work boats.

2. The philosophy behind FastYacht / FastShip is to provide a specialized hull design, modeling and fairing tool. The nature of a hull does not change from the very early conceptual stages through final fairing, therefore the tool must be flexible and powerful as to be used on the same hull model through its evolution during the various phases.

3. The CAD tool must fulfill the modeling requirements: creation, modification and fairing of surfaces.
The only type of surface lending itself to be used continuously from simple sketching to final fairing is NURBS (Non-Uniform-Rational-B-Spline). Only NURBS can represent any shape, and curvature-continuous transitions between shapes. The creation of NURBS surfaces is not tightly connected to purpose and final shape, because NURBS shapes can be modified at will.

Modification of NURBS takes place via the displacement of control points (vertices) in space. This technique is called direct surface editing. User control over the displacement of vertices and the accurate monitoring of the shape undergoing transformation are fundamental in the achievement of the desired shape. Fairing equals modifying, although at a finer and generally more local level. Hence, modification and fairing tools should be the same.

4. FastYacht / FastShip functions are targeted to main hull surface management work, and to all shapes lending themselves to the use of direct surface editing (keels, bulbs, large deck and superstructure surfaces, sails, etc.).

In observance of the above considerations, the functions offered in FastYacht / FastShip have remained through the years minimum in number and of maximum power and flexibility. Furthermore, a very heavy emphasis is put on:
- support of traditional hull definition techniques within the NURBS environment (direct graphical and numerical monitoring and measurement of stations, area curve, etc.)
- support of advanced NURBS modeling techniques
- graphical and numerical shape control techniques
- measurement and comparison tools for shape control
- downstream measurement tools, like hydrostatic and stability routines
- interface to complementary CAD tools

5. Complementary Features of FastYacht / FastShip and general purpose CAD tools.
No general purpose CAD tool offers environment and functions specific to hull modeling and fairing comparable to those of FastYacht / FastShip. Many CAD programs include functions, originally developed for other purposes, which can be used to some extent in hull modeling work, but which do not provide the environment necessary for shape management and control and, most of all, fairing.

On the other hand, FastYacht / FastShip is not always the tool to be used when working with certain primitive shapes (ex. spheres), intricate compositions of many surfaces (ex. certain transoms and decks), or wire frame based models (ex. sweep portions of superstructures). Therefore, coupling FastYacht / FastShip to a generic CAD program offering the corresponding high level and topological quality environment and functions will provide a complete solution.

6. The purpose of the generic CAD tool.
The generic CAD tool is therefore used to:
- complement the hull-specific FastYacht / FastShip in modeling some parts of the vessel
- generate drawings
- address non-hull-specific parts of the product model (interiors, deck equipment, structure, piping, etc.) As the generic CAD tool is sometimes used to modify the water-bound portion of the hull (ex. the transom), further hydrostatic and stability calculations may then be required, which generic CAD tools are not equipped to do.

7. Enhancing the role of the generic CAD tool: new possibilities.
In light of the above, enhancing the role of the generic CAD tool is an important step in the improving the complementary features of specialized and generic CAD tools.

Rhino3D is probably the most commonly used generic surface / solid CAD tool in our industry. It also used for general drafting. Therefore, the decision was made to port the FastYacht / FastShip hydrostatics and stability routines to the Rhino3D environment, e.g. as a "plug-in", under the name RhinoMarine.
It should be mentioned that other software developers are also working in the same direction. For example:

- Albacore Research Ltd, Canada, have ported portions of the ShipConstructor module Hull to Rhino3D, under the name Expander ($895).

- Creative Systems Inc,  have ported portions of the GHS module Model Converter to Rhino3D, under the name GHS Interface / AttachGHSData (free, available in the Bonus Tools library of Rhino3D), and have created a "plug-in" handle for the complete GHS suite of programs (requires the GHS module COM).

- HydroComp Inc., have created a specific Export to SolidWorks routine from their PropCAD software modeling tool.
- etc.

 
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