Designing and fairing a ship's surface is one of the most important tasks in the overall cycle of ship design and construction. The organization of this process can vary significantly across different design bureaus: some give it more attention, while others less. When communicating with representatives of various companies, it is always interesting to learn how they create surfaces. Often, this is an indicator of the overall quality of the project execution.
The topic of ship surface design is vast, covering many aspects and attracting great interest. Therefore, it is difficult to cover everything in a single article—most likely, this will be a series of publications.
In this article, we will examine the tools used for surface design in shipbuilding. Unlike mechanical engineering, automotive manufacturing, and aerospace industries, shipbuilding is far less widespread. All of these industries share many similarities and employ comparable design methodologies. Thousands of mechanical engineering companies use the same software, making them a priority market for software developers. The high demand for such solutions allows for significant investment in their development.
Most solid modeling algorithms have been well known for over 30 years, so developing corresponding software today mainly involves improving user interfaces and increasing ease of use. Additionally, data exchange interfaces between different software from various manufacturers are well established, enabling seamless data transfer across different platforms.
In shipbuilding, however, the situation with software is different. The demand for specialized modeling software is significantly lower than in mechanical engineering, and shipbuilding software solutions have distinct features. The primary difference lies in the complex freeform surfaces and unique geometric constructions used exclusively in shipbuilding. Another major factor is the hull structural models, which contain numerous details adjoining the external curved surface. These models often include an enormous number of elements, creating challenges for most standard 3D modeling software designed for mechanical engineering. Additionally, shipbuilding requires specialized calculations that are not commonly used in other industries.
Thus, selecting software for shipbuilding is no easy task. One must carefully choose the optimal combination of software solutions and resolve data compatibility issues. Even large software packages like Aveva or Cadmatic do not fully cover all the needs of shipbuilders, and some modules within these packages do not entirely meet user expectations. As a result, the overall productivity of a design company heavily depends on its software toolkit. Only by skillfully combining different software solutions and leveraging their strengths can the best results be achieved.
There are numerous programs that allow ship hull surface modeling in one way or another. These include both specialized software developed specifically for this purpose and general-purpose software that provides tools for hull surface modeling. Some programs are part of large software suites and come at a high cost, while others are conditionally free or completely free.
Based on the modeling method, ship surface design software can be divided into two categories:
1. Grid-Based Surface Modeling
This approach defines the hull surface using a network of intersecting longitudinal and transverse sections. The resulting hull surface is composed of individual surface patches, whose boundaries are the grid lines. This method enables modeling of complex surface shapes but is relatively labor-intensive. The hull surface is automatically generated as an interpolation between adjacent limiting curves. A Bézier surface patch can be used as the interpolation algorithm, with the patch shape influenced by tangents along its boundaries. However, ensuring smooth transitions between surface patches is not always feasible.
A well-known example of this approach is the NAPA software. Despite its labor-intensive process, many companies still use this method due to its intuitive simplicity. It typically takes 3–4 weeks to fair a hull form for production. One advantage is that the hull can be divided into fore and aft ship, allowing two designers to work in parallel. This method is more suitable for fairing a pre-defined hull shape rather than designing one from scratch. Additionally, making local modifications to an existing hull shape can be difficult.
2. Patch-Based Surface Modeling
This method constructs the hull surface from large patches, whose shape is defined not only by boundary curves and tangents but also by control points within the patch itself. This approach provides more degrees of freedom in defining the hull shape. The resulting surface model is often referred to as a boundary representation (B-Rep), where the patches rely on key design curves.
The primary advantage of this method is that surface smoothness is maintained across large patches. However, modifying the hull shape can be less intuitive. For example, controlling a control polygon, whose vertices do not lie directly on the surface, is not as visually straightforward as modifying a waterline or frame curve. Despite these drawbacks, this method is the most convenient and widely used among designers. Most modern surface modeling programs employ this approach, but the effectiveness of the software depends on the quality and usability of its surface modification tools. The ease with which designers can adjust surface patches directly impacts both the labor required and the final quality of the hull surface.
The software used for ship surface modeling should include advanced quality control tools and capabilities for local shape modifications. Ideally, it should also support version control, enabling users to track all modifications throughout the project's lifecycle. Additionally, seamless data exchange with other programs without shape distortion is crucial. When transferring surface data between different programs, any geometric inconsistencies must be avoided.
Some companies use different modeling programs at various stages of a project. For instance, in early design stages, it may be convenient to use a quickly generated hull prototype, but such a model may not be suitable for detailed design work. Due to differences in how various programs format models, data transfer between them can be more complex than expected. Using multiple programs for ship hull modeling can also lead to fairing errors, which can be extremely difficult to detect in the detailed design stage.
On several occasions, I have witnessed temporary models mistakenly making their way into production, only to have the errors discovered on the completed ship.
Conclusion
To summarize, the correct selection of tools for ship surface design and fairing significantly impacts the technology, quality, and timeline of the entire project. Choosing the right software combination, ensuring seamless data exchange, and maintaining proper version control are all crucial factors in achieving the best possible results in ship design.
Do not miss the continuation in the next article - "Preparation of initial information."
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