```html Seastead Design Software Recommendations

Open-Source Software for Seastead Structural Design & Weight Estimation

Based on your detailed seastead design, you'll need software that can handle marine structural design, aluminum truss modeling, and weight estimation. Here are the most suitable open-source options:

FreeCAD + FEM Workbench

Parametric CAD FEA Weight Estimation

Best for: Complete structural modeling with material properties and weight calculation

Create parametric models of your triangle frame, trusses, and living space
Assign marine aluminum alloy (5083 or 6061) with exact density
Automatic weight calculation from volume and material density
FEM Workbench can perform structural analysis if needed
Python scripting for automation of repetitive elements

Workflow suggestion: Model one truss segment, then pattern it for the entire triangle frame.

OpenFOAM + ParaView

CFD Hydrodynamics Performance Analysis

Best for: Analyzing hydrodynamic performance of your NACA foil-shaped floats

Test water flow around your 3 wing/legs with NACA foil profiles
Optimize thruster placement and efficiency
Analyze stabilizer performance (those "little airplane" designs)
Calculate drag at different speeds

Note: Steeper learning curve but powerful for hydrodynamic optimization.

Blender + CAD Sketcher/Add-on

3D Modeling Visualization Quick Prototyping

Best for: Rapid 3D visualization and space planning

Quickly model the overall 80x40ft triangle with 7ft height
Visualize living space placement and open porch areas
Test different configurations before detailed engineering
Excellent rendering for presentations

CalculiX + PrePoMax

FEA Structural Analysis Stress Testing

Best for: Detailed structural analysis of critical connections

Analyze stress concentrations where legs attach to triangle frame
Test structural integrity under wave loading
Optimize material thickness for weight savings
PrePoMax provides a user-friendly interface for CalculiX

Recommended Workflow for Your Project:

Start with FreeCAD to create a parametric model of the entire structure
Use Python scripting in FreeCAD to automate truss generation with different spacing options
Extract weight estimates directly from the CAD model using material properties
Validate critical connections with CalculiX/FEA analysis
Optional: Use OpenFOAM to optimize float shapes if performance is critical

Specialized Marine Design Alternatives

While not entirely open-source, these have free tiers or open-source components:

OpenVSP (NASA): Excellent for aerodynamic/hydrodynamic shape optimization of your foil-shaped floats
Sailfish (Lattice Boltzmann CFD): Good for preliminary hydrodynamic analysis
Salome-Meca: Combines CAD, meshing, and Code_Aster FEA - powerful but complex

For Weight Estimation Specifically

Your best approach will be:

Create detailed 3D models in FreeCAD
Assign accurate materials (marine aluminum 5083: ~2.66 g/cm³, 6061: ~2.70 g/cm³)
Use FreeCAD's "Mass Calculation" tool
Add 15-20% for welding, joints, and fasteners
Create a Python script to iterate through design variations

Important Considerations for Your Design

Corrosion allowance: Add 1-2mm to all submerged aluminum thicknesses
Watertight compartments: Consider subdivision in your float design
Stability analysis: Your triangular configuration with 3 widely spaced floats should be stable, but verify with inclining experiments in software
Connection details: The leg-to-frame connections will be critical - focus FEA here

All recommended software is available for Windows, macOS, and Linux. FreeCAD is particularly recommended as it combines CAD, parametric design, and basic FEA in one package with excellent Python scripting support for your automation needs.

``` This HTML page provides a comprehensive overview of open-source software options for your seastead design project. The recommendations focus on tools that can handle both the structural design with marine aluminum and provide accurate weight estimates for different configurations. FreeCAD emerges as the most suitable starting point due to its parametric modeling capabilities and integrated weight calculation features.