🌊 Seastead Structural Design & Weight Estimation: Open-Source Software Stack

There is currently no single turnkey open-source application that automatically generates marine-grade truss structures, foil-shaped floats, and outputs detailed bills of materials with weight breakdowns. However, you can build a highly capable, parametric design pipeline using open-source Python/CAD libraries that run locally or on a web server.

🛠️ Recommended Open-Source Stack

Component	Tool	Role	License
Parametric CAD & Weight Calculation	CadQuery / Build123d	Generate truss, foils, living space, calculate volume/mass per part, export STEP/GLB	BSD-3 / Apache-2
GUI Alternative	FreeCAD	Visual editing, FEM analysis, Arch/Ship workbenches, BOM export	LGPL-2.1
Hydrostatics & Stability	NEMOH + Python wrappers	Small-waterplane-area hydrostatics, wave response, stability metrics	GPL-3
Data & Reporting	Pandas, Matplotlib, Jupyter	Weight tables, sensitivity analysis, design iteration tracking	BSD / PSF
Web Visualization	Three.js + gltf_viewer	Browser-based 3D preview, lightweight interaction	MIT

📐 Parametric Workflow for Weight Estimation

Define Inputs: Triangle footprint (80×40 ft), truss spacing/material thickness, foil chord/span/lift distribution, living space dimensions, rail height.
Generate Geometry: Script creates hollow extrusions for truss chords/webs, NACA foil extrusions for legs, roof/floor plates, and stabilizer mounts.
Assign Material: Marine aluminum (5083-H321 or 6061-T6). Density ≈ 2700 kg/m³ (0.0975 lb/in³).
Calculate Mass: Volume × Density × Joint Efficiency (~0.85–0.90 for welded marine structures).
Export BOM: Table with part name, material, volume, mass, estimated fabrication notes.
Iterate: Adjust parameters → re-run → compare weight/stability trade-offs.

💻 Example: CadQuery Weight Pipeline (Python)

import cadquery as cq
import pandas as pd

# === PARAMETERS ===
TRI_FRONT_BACK = 80 * 12  # inches
TRI_WIDTH = 40 * 12
TRUSS_SPACING = 24        # inches
WALL_THK = 0.25           # inches (marine 5083 plate)
FOIL_LEN = 19 * 12
FOIL_WIDTH = 3 * 12
FOIL_CHORD = 10 * 12
AL_DENSITY = 0.0975       # lb/in³
JOINT_EFF = 0.88

# Helper: hollow rectangular truss member
def truss_member(length, width, height, thk):
    outer = cq.Workplane("XY").box(width, length, height)
    inner = cq.Workplane("XY").box(width-2*thk, length-2*thk, height-2*thk)
    return outer.cut(inner)

# Generate example: single truss edge + foil leg
bottom_edge = truss_member(TRI_WIDTH, TRI_WIDTH*0.05, 84, WALL_THK).translate((0, 0, 0))
foil_leg = (cq.Workplane("XY")
            .sketch()
            .parametricCurve(lambda t: (FOIL_CHORD*(1-cq.NACA4(0, 10, 20, 0).evaluate(t)[0]), 
                                       FOIL_CHORD*cq.NACA4(0, 10, 20, 0).evaluate(t)[1]))
            .extrude(FOIL_WIDTH)
            .translate((0, 0, -FOIL_LEN/2)))

# Combine assembly
assy = cq.Assembly()
assy.add(bottom_edge, name="Truss_Edge", loc=cq.Location((0,0,0)))
assy.add(foil_leg, name="Foil_Leg", loc=cq.Location((0, -TRI_WIDTH/2, -FOIL_LEN/2)))

# Weight Calculation
parts_data = []
for obj in assassy.solids():
    vol = obj.val().Volume()
    mass = vol * AL_DENSITY * JOINT_EFF
    parts_data.append({"Part": obj.name, "Volume_in3": round(vol,1), "Mass_lb": round(mass,1)})

df = pd.DataFrame(parts_data).sort_values("Mass_lb", ascending=False)
print(df)
print(f"\nTotal Estimated Mass: {df['Mass_lb'].sum():.1f} lb")

Tip: CadQuery's Solid.Volume() returns exact geometric volume. For realistic marine fabrication, add 5–10% for weld beads, brackets, gussets, and corrosion allowance.

🌐 Web Integration Guide

Client-Side (Lightweight): Use Pyodide to run CadQuery in the browser. Users adjust sliders → Python recalculates BOM → outputs JSON table. 3D preview via .exportGLTF() + Three.js.
Server-Side (Production): Host a FastAPI backend that accepts JSON parameters, runs CadQuery, returns GLB + CSV BOM. Keeps computation fast and avoids browser memory limits.
Export Formats: STEP for CNC/fabrication, STL/GLB for web preview, CSV for spreadsheet integration.
Open-Source Viewer: https://modelviewer.dev/ or https://threejs.org/examples/#webgl_loader_gltf for interactive rotation/slicing.

⚠️ Engineering Notes & Limitations

Marine Aluminum Selection: Use 5083-H321 for welded saltwater structures. Avoid 6061 in direct immersion unless properly coated. Apply DNV-RP-C201 fatigue guidelines.
Joint Efficiency: Welded marine aluminum typically uses 0.75–0.85 efficiency factors depending on weld quality and NDT inspection level.
Hydrodynamic Stability: Weight estimation ≠ stability. Small waterplane area vessels have high roll/pitch sensitivity. Validate with NEMOH or OpenFOAM before construction.
RIM Thrusters & Stabilizers: Add 15–25% structural reinforcement around thruster mounts and elevator pivot points. Dynamic loads > static weight.

⚠️ Disclaimer: This pipeline generates geometric mass estimates only. Marine structural design requires certified naval architecture review, wave load analysis, corrosion planning, and compliance with ABYC/DNV/ISO 12215 standards.

🚀 Next Steps

Install CadQuery: pip install cadquery
Clone a starter template: CQ-Editor for interactive design
Parameterize your triangle truss, foil legs, and living space module as Python classes
Add a Pandas export → auto-generate weight tables per design iteration
Deploy via FastAPI + Three.js for browser access

With this stack, you can rapidly iterate seastead configurations, compare structural mass across foil/truss variants, and export fabrication-ready data entirely with open-source tools.