Half-Scale Seastead Prototype
Design: 1/2 linear scale, Marine Aluminum (6061-T6), Bolt-Together Kit, 50 kWh LiFePO4, 2x Yamaha HARMO RIM Thrusters
⚓ Range & Endurance Estimate
| Parameter | Value | Notes |
|---|
| Target Speed | 4 – 5 knots | ~2.0 – 2.6 m/s |
| Estimated Required Power | 4 – 6 kW (electrical) | Low Froude #, NACA 0030 foil struts reduce friction/wave drag significantly |
| Propulsion Efficiency | ~75 — 80% | RIM hub motors + ducted propeller |
| Battery Capacity | 50 kWh | LiFePO4 with BMS & thermal management |
| Expected Endurance | 8 – 12 hours | At 4 kts (~5kW) or 5 kts (~6kW) |
| Estimated Range | 32 – 50 nautical miles | Conservative, calm-to-moderate sea state |
The square-cube scaling law works in your favor: mass drops by 1/8, foil area by 1/4, and drag reduces disproportionately. At equal speed, the prototype operates at a lower power-to-weight ratio than the full-scale design, improving efficiency for a day-sailer profile.
⚖️ Weight & Buoyancy Breakdown
All values are engineering estimates based on Aluminum 6061-T6, marine fasteners, and commercial LiFePO4 pack specs.
| Component | Est. Weight (lbs) | Notes |
|---|
| Legs / Foil Struts (3×) | 1,050 – 1,200 | 9.5ft span, 5ft chord, 1.5ft max thickness, 1/4″ plate & internal ribs |
| Triangle Truss & Roof Frame | 1,600 – 1,900 | 35ft × 35ft × 17.5ft perimeter, 3.5ft high, deck subframe, solar racking |
| Seats, Net, Deck, Misc Fittings | 100 – 150 | Marine polymer net, aluminum brackets, light seating |
| 50 kWh LiFePO4 Batteries + BMS | 800 – 950 | ~16 kg / kWh cell weight + 15–20% enclosure/wiring |
| 2× Yamaha HARMO RIM Drives | 120 – 150 | Incl. mounts, cables, controllers |
| Stabilizer Assemblies (3×) | 90 – 130 | Carbon/aluminum wings, linear actuators, bearings, pivot brackets |
| 7ft RIB + Mounts | 120 – 160 | Lightweight hypalon, aluminum transom, davit fittings |
| Solar + Electrical + Plumbing | 60 – 80 | Flex/rigid panels, inverter, charge controller, wiring, small tanks |
| Total Estimated Empty Weight | ~4,050 – 4,650 lbs | |
Displacement & Payload Capacity
| Parameter | Value |
|---|
| NACA 0030 Cross-Section Area (half-scale) | ~4.9 ft² per leg |
| Submerged Draft (design 50%) | 4.75 ft per leg |
| Total Displacement Volume (3 legs) | ~70 ft³ |
| Theoretical Buoyancy (SW @ 64 lb/ft³) | ~4,450 lbs |
| Reserve for Crew & Cargo | 200 – 500 lbs (drafts to ~55 – 60%) |
The design floats very close to the intended 50% waterline at rest. Adding 3 – 4 people (~450 lbs) will increase draft. This is intentional: at speed, the aft stabilizers act as lifting foils, raising the craft back toward the 50% waterline and reducing drag. Verify trim in calm water before sea trials.
🏗️ Marine Aluminum & Off-the-Shelf Truss Options
Since you plan a no-weld, bolt-together assembly, avoid 5083-H111 (optimized for welding) and specify 6061-T6 or 6061-T651 extrusions. These machine and drill cleanly, handle cyclic loads well, and pair safely with coated stainless or aluminum fasteners.
| Suggested Parts / Systems | Notes |
|---|
| Aluminum Square/Rectangular Tube | Standard 2×2, 3×3, and 4×4 in 1/4″ or 3/16″ wall. Available from online metals distributors. Ensure mill certified and saltwater compatible. |
| CNC Aluminum Gusset Nodes | Custom-drilled to your truss angle (30°/60°/90°). Order from aluminum fabrication shops in China or US. Anodize or apply marine epoxy coating. |
| Galvanic Isolation | Use Tefgel 825, Duralac, or HDPE washers between Al and SS fasteners. Critical for saltwater. |
| Marine Truss Kits | Companies like Truss Technology, Alustage (marine-rated series), or Grip-Span offer pre-drilled modular nodes, but expect marine markup. Custom CNC nodes are usually cheaper and fit foil/truss intersections better. |
Kit Packaging: A 40″ container can neatly hold 3 legs, truss chords/diagonals, deck plates, solar rails, and stabilizer spars if nested and vacuum-cradled. Pre-drill all holes to H9 tolerance for blind-pin assembly in Anguilla.
💰 Estimated Build Cost
Excludes DIY labor, crane time, and personal tools. Assumes direct-to-fabricator pricing + container shipping.
| Category | Low | High |
|---|
| Chinese Fab & CNC (Aluminum kit, pre-drilled, coated) | $7,500 | $11,000 |
| Ocean Freight (40ft FCL to Caribbean) | $4,000 | $5,500 |
| 2× Yamaha HARMO RIM Drives + Controllers | $9,500 | $10,500 |
| 50 kWh LiFePO4 Pack + BMS + Enclosure | $3,200 | $4,200 |
| Marine Fasteners, Isolators, Sealants, Coatings | $1,200 | $1,800 |
| Stabilizers (wings, shafts, actuators, bearings) | $1,800 | $2,500 |
| 7ft RIB & Mounting Hardware | $1,200 | $1,800 |
| Solar Panels, MPPT, Inverter, Wiring | $900 | $1,300 |
| Misc (ladders, davits, cushions, netting) | $400 | $700 |
| Total Estimated Cost | ~$29,700 | ~$39,300 |
Budgeting $35k – $38k covers unexpected shipping variances, import duties, and minor fab revisions. The modular approach heavily reduces on-site labor and tooling costs.
🔧 Technical Recommendations
- Trim & Lifting Foil Tuning: Start with a conservative +2° elevator bias. Use a simple IMU/stern sensor to log heave pitch during runs. The 25% chord pivot notch balances static load well, but ensure the hinge pin is stainless (A4-80) with sealed bronze bushings.
- RIM Thruster Placement: Mounting 3ft from the foil base keeps them clear of surface chop but may increase moment arm for yaw. Keep cable routing inside the foil spine or external chafe-guarded conduit.
- Corrosion Control: Even with 6061-T6, saltwater demands annual coating inspection. Use zinc anodes on each leg >500mm above the waterline to avoid galvanic paths through the aluminum.
- Prototype Validation Steps:
- Dry assembly & bolt-torque mapping
- Float test in calm water (record % draft per leg)
- Taxi test at 2 & 3 kts (check stabilizer response)
- Cruise test at 4 & 5 kts (log kWh/nm, adjust actuator curves)
This document contains preliminary mass, hydrostatic, and cost estimates. Full Finite Element Analysis (FEA) on the 35ft/17.5ft truss intersections and Computational Fluid Dynamics (CFD) or towing tank verification of the NACA 0030 struts are strongly advised before open-water trials.
Generated for prototype planning • Anguilla Sheltered Waters Test Window • Scale 1:2
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