Software Use in Small Craft Design

Role of software in the design spiral

In small craft design, software is most valuable when it accelerates iteration without hiding the physics. The best toolchain makes it easy to:

• build a fair, editable hull model (so the geometry is not a dead end),
• extract hydrostatics/stability quickly for multiple load cases,
• estimate resistance and required power early, then refine where risk is highest,
• size structure and verify critical regions, and
• produce unambiguous drawings and build documentation.

A recurring failure mode is false precision: producing colorful plots and many significant digits that mask uncertainties in loading assumptions, sea state, appendage drag, or surface finish. The best practice is to pair each tool with an explicit fidelity level (concept, preliminary, detailed), and to use sensitivity studies (e.g., varying displacement, CG, and roughness) to ensure decisions do not depend on fragile inputs.

Hull and arrangement modeling (CAD)

Most modern small craft workflows begin with a 3D model that serves as the “single source of geometry truth”. For small craft, hull modeling is often done with NURBS surface tools, because they support fair curves and controlled continuity.

General-purpose CAD used heavily in marine work

Rhino (Rhinoceros 3D) is widely used in boat design because it is flexible for surface modeling and has a large ecosystem of marine plug-ins and workflows.¹ Designers often keep early hull surfaces “light” (few control points, clean sections) to preserve fairness and keep hydrostatics stable as the shape evolves.

Mechanical CAD platforms (e.g., Autodesk Fusion and SOLIDWORKS) are commonly used for parts, mechanisms, and manufacturing-ready models (engine beds, brackets, hardware, molds, jigs, and CNC/3D-print fixtures). They are typically less convenient than Rhino-type tools for freeform hull surfaces, but excellent for assemblies, drawings, and CAM outputs.¹⁰¹¹

Marine-focused hull modeling suites

Dedicated naval architecture suites integrate hull modeling with analysis. For example, Maxsurf positions itself as a single parametric 3D model that supports hull modeling, stability, resistance, motions, and structural work within one environment.⁴ DELFTship similarly emphasizes that it derives hydrostatic and stability calculation data directly from the hull model to maintain consistency.⁵

What “good CAD” looks like for boats

• Fairness first: control point discipline, curvature plots, and consistent section spacing.
• Parametric where it matters: principal dimensions, sheer/keel definitions, and appendage positions.
• Model “intent,” not triangles: keep the master model analytic (NURBS/solids); export meshes only as downstream artifacts.
• Unit and coordinate discipline: agree on units (mm vs in), waterline reference, and LCG/VCG sign conventions early.

Hydrostatics and stability tools

Hydrostatics is the earliest “hard gate” in the design spiral because it ties geometry to displacement, trim, freeboard, and initial stability. Stability analysis requires not just hull volume, but also the weight statement (including CG) and downflooding points.

Integrated hydrostatics inside modeling environments

Orca3D (a Rhino-based marine suite) describes its ability to compute intact hydrostatics and righting arm curves at multiple waterlines or across displacement/CG combinations—an approach aligned with how designers iterate loading cases during concept development.² For more complex assessments, Orca3D’s advanced stability workflow includes tank and compartment modeling, load cases, and report outputs to office formats.³

Practical stability software practices

• Model downflooding correctly: define openings and immersion angles; avoid “paper stability” that ignores flooding.
• Track free-surface effects: partially filled tanks can materially reduce stability in small craft.
• Use load-case libraries: lightship, typical operating, worst-case payload, and “owner-added weight” scenarios.
• Document operating limits: stability is a system property; publish loading guidance alongside results.

Resistance, powering, and performance prediction

Performance tools are used to answer three questions early: (1) does the concept meet its speed/range targets, (2) what is the propulsion system size, and (3) how sensitive is performance to weight growth and trim?

Empirical prediction tools and integrated suites

Maxsurf states that it includes resistance prediction and motions capabilities alongside hull modeling and stability, which is typical of integrated naval architecture suites meant to support preliminary performance studies before committing to expensive validation steps.⁴ Some design environments also advertise “speed vs horsepower” type tools for early feasibility checks; these are useful for screening options, but should be treated as preliminary without propulsor matching and verified drag assumptions (appendages, windage, and surface condition).

Best practice: performance is a curve, not a point

Software makes it easy to report a single “top speed,” but design decisions are usually driven by curves: resistance vs speed, power vs speed, and fuel burn vs speed. Use software to generate the curves, then test robustness:

• Weight growth: +5–15% displacement is common between concept and reality; ensure the design still works.
• CG shifts: changes in LCG can increase trim and power demand, especially for planing and semi-planing craft.
• Sea margin: calm-water predictions are not “service speed” unless margins and sea state are considered.

CFD for hydrodynamics and seakeeping

CFD becomes valuable when (a) the design is outside well-populated empirical families, (b) appendages and flow features dominate performance, or (c) you are trying to reduce risk in high-speed, high-power, or unusual hull forms.

Open-source and commercial CFD ecosystems

OpenFOAM is distributed as free and open-source CFD software by the OpenFOAM Foundation, with broad use across engineering domains—often attractive for organizations that want transparency and scripting control, but it demands strong internal CFD expertise and verification discipline.⁶

Commercial CFD tools emphasize integrated workflows, model libraries, and vendor support. Examples include Ansys Fluent for CFD and Siemens Simcenter STAR-CCM+ for multiphysics CFD workflows and industrial simulation use cases.⁷⁸

CFD “gotchas” specific to small craft

• Free-surface modeling: wave making and spray matter; choose models appropriate to the regime and validate against known cases.
• Scale effects: turbulence models and roughness assumptions can shift results; do not overfit to a single mesh or model setup.
• Trim and sinkage coupling: for planing craft, forces and attitude are coupled—ensure the solution method respects equilibrium.
• Uncertainty quantification: mesh independence, timestep sensitivity (if transient), and boundary condition sensitivity are mandatory.

In many small-craft projects, a targeted CFD campaign (a few high-value cases) is more cost-effective than attempting to replace all preliminary methods with CFD.

Structure and FEA

Structural analysis software supports two distinct tasks: (1) rule/standard-based sizing (scantlings) and (2) detailed verification of critical areas (engine beds, mast steps, chainplates, foils, hard points, and slamming-prone panels).

Finite element analysis tools

Ansys Mechanical is positioned as a structural FEA solver for broad classes of structural problems, and is representative of high-end analysis environments used when loads are complex or consequences are high.¹² SOLIDWORKS also offers integrated simulation products that can be convenient for part-level and assembly-level checks in mechanical CAD workflows.¹³

Practical FEA guidance for small craft

• FEA does not replace scantling rules: use rules/standards for baseline sizing; use FEA to evaluate exceptions and hotspots.
• Load realism dominates: slamming, rig loads, and impact are hard to model—err on conservative load cases and verify with test/experience.
• Model joints intentionally: adhesive bonds, welds, and laminate terminations often govern failures.
• Stiffness matters: excessive deflection causes “oil-canning,” seal failures, and fatigue—even if stresses are below allowables.

Production, detailing, and build support

A successful small craft design must be buildable. Production software often determines schedule and cost more than performance tools do.

Drawings, nesting, and CAM

Many builders rely on CAD drawings for cutting, templates, and CNC workflows. Mechanical CAD platforms (Fusion, SOLIDWORKS) and general CAD tools (Rhino) can produce drawings and export STEP/DXF files for fabrication, while CAM toolpaths support CNC cutting and machining.¹⁰¹¹

Shipbuilding-oriented production suites (relevant to larger “small craft”)

For larger craft approaching the top end of “small craft” length ranges, shipbuilding-oriented suites can bring value in production integration and outfitting documentation. For example, SSI’s ShipConstructor positions itself around design-to-production integration and collaboration workflows.¹⁴

Digital build packages

Treat the deliverables as a package: hull lines, structural plan, laminate schedules, machinery installation, wiring and plumbing schematics, and a bill of materials. Software helps here primarily by enforcing consistency and enabling controlled revisioning.

Data management, traceability, and interoperability

Small craft designs frequently fail in the handoff from “design model” to “build reality.” The software challenge is less about tools and more about controlled translation between them.

File formats and geometric integrity

• NURBS/solids exchange: STEP and IGES are common; validate units, tolerances, and surface continuity after import.
• Mesh exchange: STL/OBJ are common for 3D printing and some CFD/visualization; maintain separate “analysis meshes” from the master CAD.
• 2D exchange: DXF/DWG remain common for cutting patterns and drawings; define line weights, layers, and scale conventions.

Traceability practices that pay off

• Revision control: version every geometry release; tie stability and weight reports to the exact model revision used.
• Assumption registers: record what each analysis assumed (loading, sea state, roughness, openings, materials).
• Benchmark cases: keep a small set of “known” models to validate each tool after upgrades or workflow changes.

How to select a toolchain

Tool selection should be driven by the design’s risk profile and the team’s capabilities, not by feature lists. A practical selection rubric:

In many small craft projects, a balanced toolchain is: (1) surface/CAD modeler, (2) hydrostatics/stability module, (3) preliminary resistance/power estimator, and (4) optional CFD/FEA for the few questions that materially affect safety, cost, or performance.

A practical workflow example

1. Concept geometry: build a clean hull surface model (Rhino or a naval-architecture modeler).¹
2. Hydrostatics: compute displacement/trim for load cases; iterate principal dimensions; identify downflooding points.²
3. Stability with tanks/compartments: add compartmentation and tanks once the arrangement stabilizes; evaluate key criteria and document limits.³
4. Powering: generate resistance and power curves; perform sensitivity checks for weight growth and CG shifts; select propulsion concept.
5. Targeted CFD (if warranted): run high-value cases (trim, spray, appendage interactions, unusual hull forms) using OpenFOAM/Fluent/STAR-CCM+ as appropriate.⁶⁷⁸
6. Structure: baseline scantlings per your chosen framework; verify hard points with FEA where needed.¹²
7. Production package: release drawings, cut files, laminate schedules, and a controlled BOM; keep reports tied to model revisions.

The key: the “center of gravity” of software work should be early iteration and risk reduction, not late-stage plot generation.