Comparative Analysis of Ship Hull Surface Design Software: Free!Ship and Shape Maker

General Background and Problem Statement

Ship hull surface design is one of the key tasks in shipbuilding, directly affecting hydrodynamic performance, manufacturability, and operational characteristics of a vessel. Despite the importance of hull geometry, the automation of its generation and fairing has long remained a challenging engineering problem.

With the development of computer-aided design (CAD) systems, various approaches to hull surface modeling have been proposed, based on different mathematical representations and algorithms. Currently, a wide range of software solutions exists, differing in functionality, accuracy, and application domain.

The selection of software is typically determined by the following factors:

• prior experience within an organization;

• availability of trained specialists;

• economic considerations, including licensing costs.

The purpose of this study is to compare Free!Ship and Shape Maker in terms of their underlying mathematical models, surface modeling technologies, and functional capabilities.

Mathematical Models for Surface Representation

Subdivision Surface Representation (Free!Ship)

Free!Ship is based on a polygonal mesh representation consisting of vertices and faces, with subsequent smoothing using subdivision surface algorithms similar to the Catmull–Clark scheme.

The mesh may include elements of various topologies (triangular, quadrilateral, and pentagonal faces), as well as special features such as boundaries and crease edges. The surface geometry is defined by vertex positions and mesh topology.

This approach provides:

• flexibility in creating smooth shapes;

• intuitive control at early design stages.

However, it has several limitations:

• local modifications significantly affect the global shape;

• increased mesh density is required to localize deformations;

• lack of exact representation of analytical surfaces;

• limited control over parameterization.

Therefore, this method is primarily suitable for conceptual design stages.

Example of surface discretization in Free!Ship

Parametric NURBS Representation (Shape Maker)

Shape Maker employs a parametric surface representation based on NURBS (Non-Uniform Rational B-Splines) with topological connectivity between model elements. The surface is constructed from a set of quadrilateral patches bounded by curves.

Key characteristics include:

• rigorous mathematical parameterization;

• local control over surface complexity;

• continuity preservation between adjacent patches;

• invariance of shape under refinement (increasing control points).

Topological connectivity ensures consistent modification of the entire model when individual elements are edited, enabling progressive refinement without distortion.

Unlike mesh-based methods, this approach allows exact representation of analytical surfaces (planes, cylinders, conical sections), which is essential for engineering applications.

Example of surface discretization in Shape Maker

Visualization and Model Interaction Tools

Visualization Approach

Free!Ship uses a multi-window interface with standard orthogonal projections and a perspective view. Surface analysis modes (e.g., curvature or zebra shading) restrict editing capabilities.

Zebra pattern visualization in Free!Ship

Shape Maker provides a single-window interface with switchable views. All analysis modes (curvature plots, inflection lines, sections) remain fully interactive and allow continuous editing.

This approach improves efficiency by:

• reducing context switching;

• maximizing screen space for model visualization;

• enabling uninterrupted editing.

Zebra pattern visualization in Shape Maker

Geometry Editing Tools

In Free!Ship, editing is primarily performed at the level of individual vertices, with limited support for group operations.

Shape Maker provides advanced tools, including:

• group editing of control points;

• definition of influence regions;

• directional constraints for transformations;

• object snapping;

• precise positioning in all projections.

These features significantly enhance geometric control and reduce modeling effort.

Model Structure Organization

Free!Ship uses a layer-based system organized as a flat list, providing basic control over visibility and attributes.

Shape Maker utilizes a hierarchical structure (block tree), enabling:

• organization of complex models;

• management of nested elements;

• reuse of components;

• control over editing permissions.

Hierarchical data organization is more efficient for large-scale projects.

Surface Modeling Technology

In Free!Ship, the modeling process is based on deforming an initial mesh, often derived from a prototype. This leads to increased effort when creating complex engineering geometries and limits model reuse.

Layers in Free!Ship

Shape Maker constructs geometry from boundary curves, followed by surface generation. It also supports:

• parametric transformations;

• reuse of existing models;

• adaptation of geometry to new requirements.

This approach provides:

• reduced design effort;

• support for design variations;

• accumulation and reuse of design knowledge.

Block tree in Shape Maker

Data Exchange and Integration Capabilities

Free!Ship supports several import and export formats; however, data exchange (e.g., via IGES) involves surface approximation, which may alter the model structure.

Shape Maker is designed for integration into industrial workflows and supports:

• standard CAD formats (IGES, STEP, DXF);

• interaction with analysis tools;

• generation of production documentation.

This enables the use of models throughout all stages of design and manufacturing.

Comparative Evaluation and Application Scope

The analyzed software systems are based on fundamentally different modeling approaches:

• Free!Ship uses subdivision surfaces, offering flexibility at early design stages;

• Shape Maker uses parametric NURBS surfaces, ensuring accuracy and control.

Accordingly, their application domains differ:

• Free!Ship is suitable for conceptual modeling;

Shape Maker supports the full engineering design cycle, including production documentation.

Model in Free!Ship. Created without explicit definition of planar regions. Even cylindrical inserts are absent.

Model in Shape Maker. The model shows a subdivision of the surface into planar and cylindrical regions.

Final Remarks

The analysis shows that the choice of software depends on requirements for geometric accuracy, level of control, and integration into production workflows.

NURBS-based systems provide significant advantages for engineering applications in shipbuilding, while mesh-based approaches are more suitable for early-stage conceptual design but limited in detailed engineering development.

Therefore, Free!Ship can be considered a tool for preliminary modeling, whereas Shape Maker represents a specialized solution for professional ship hull surface design.