Half‑Scale Seastead Prototype – Design Summary

1. Scaled Dimensions (½ of full‑scale)

Item	Full‑Scale	Half‑Scale (×0.5)
Leg length (span)	19 ft	9.5 ft
Leg chord (fore‑aft)	10 ft	5 ft
Leg thickness (height)	3 ft	1.5 ft
Triangle side lengths	70 ft, 70 ft, 35 ft	35 ft, 35 ft, 17.5 ft
Triangle truss height (floor‑to‑ceiling)	7 ft	3.5 ft
Estimated roof area (solar coverage)	≈ 1 186 ft²	≈ 300 ft²

2. Estimated Range with 50 kWh Battery

Drag was estimated using a frontal area of about 22 ft² for the three foil‑shaped legs (Cd ≈ 0.2). Propulsive efficiency of the RIM drives is taken as 50 %.

Speed (kn)	Approx. Drag (lb)	Prop. Power (hp)	Electrical Power (kW)	Energy / hour (kWh)	Range (nm) for 50 kWh
4	≈ 200	≈ 2.5	≈ 3.5	≈ 3.5	≈ 45–55
5	≈ 310	≈ 5	≈ 7	≈ 7	≈ 30–40

Solar gain on a sunny day (~3 kW average) can extend these distances by roughly 30 % during daylight operation.

3. Component Weight Breakdown

Component	Qty	Unit Weight (lb)	Total Weight (lb)	Notes
Aluminium leg hull (foil‑shaped)	3	≈ 280	≈ 840	4 mm plate on extruded ribs; includes internal stiffeners
Triangle truss (3 sides, 7 ft high)	1	≈ 300	≈ 300	2 in × 2 in 6061‑T6 square tubes + diagonals
Solar‑panel array (≈ 300 ft²)	≈ 20 panels	≈ 12	≈ 240	Light‑weight flexible panels; aluminium mounting rails
Battery pack (50 kWh Li‑ion)	1	≈ 1 100	≈ 1 100	Marine‑rated modules; includes BMS
Yamaha HARMO RIM drives (1.5 ft Ø)	2	≈ 200	≈ 400	Mounted low on each side of a leg
Stabiliser “mini‑airplane” (incl. actuator)	3	≈ 40	≈ 120	Carbon‑fiber wing & elevator; pivot near leg tip
Control electronics, wiring, sensors	1	≈ 50	≈ 50	Motor controllers, IMU, GPS, simple PLC
Seats & safety net (day‑sailer fit‑out)	1	≈ 70	≈ 70	Canvas seats + rope net on aluminium frame
Payload – crew (4 × 180 lb)	4	180	720	Adult crew
Total weight (without extra cargo)			≈ 3 840 lb

4. Buoyancy & Payload Margin

Buoyancy at 50 % leg immersion (half‑scale): ≈ 5 240 lb (submerged volume ≈ 84 ft³ × 62.4 lb/ft³).
Total weight (components + crew): ≈ 3 840 lb.
Reserve buoyancy (payload capacity) ≈ 1 400 lb – equivalent to ~8 adults or the same weight in gear.

The stabiliser wings can be set to a slight positive angle of attack while underway, providing a modest lift (≈ 200 lb at 5 kn) that further reduces the load on the legs.

5. Approximate Cost Breakdown

Item	Estimated Cost (USD)	Notes
Leg hull & truss – CNC/fabrication in China	$8 000	All parts fit into one 40 ft container
Aluminium plate & extrusion (off‑the‑shelf)	$3 000	6061‑T6 sheet 4 mm, square tubes, angles
Hardware (bolts, brackets, fasteners)	$500	Stainless‑steel marine‑grade
Solar panels (≈ 300 ft² flexible)	$2 500	≈ $125 / panel; includes mounting rails
Battery 50 kWh (marine Li‑ion modules)	$10 000	10 × 5 kWh modules + BMS
Yamaha HARMO RIM drives (2 units)	$10 000	$5 000 each
Stabiliser “mini‑airplane” – carbon‑fiber parts + actuator	$2 000	Custom CNC‑cut; local assembly
Control electronics, motor controllers, sensors	$1 000	Off‑the‑shelf marine PLC, IMU, GPS
Transport / shipping (container to Anguilla)	$3 000	Includes customs & local delivery
Miscellaneous (wire, conduit, safety gear)	$500
Total (materials & fabrication)	$40 500	Assembly by owner (no labor cost); crane already assumed

Prices can vary ± 20 % depending on exact specifications and market conditions.

6. Off‑the‑Shelf Marine‑Aluminium Components

Structural tubes: 2 in × 2 in × 0.125 in wall 6061‑T6 square tube – stocked by OnlineMetals, Ryerson, Industrial Metal Sales. Use for truss chords and diagonal braces.
Aluminium angle: 2 in × 2 in × 0.125 in 6061‑T6 angle for frame joints and supports.
Plate for leg skins: 4 mm (≈ 0.125 in) 6061‑T6 sheet – suitable for welding and forming the foil shape. Available cut to size from the same suppliers.
Modular t‑slot extrusion (optional): 80/20 Inc. “Series 10” t‑slot (1 in × 1 in) – useful for quick‑connect framing of the roof rack and solar mounts.
Fasteners: Marine‑grade stainless‑steel hex bolts, washers, nyloc nuts (e.g., 3/8 in × 2 in).
Connectors: Custom‑laser‑cut aluminium brackets that match the tube geometry; can be bundled with the Chinese fabrication order.

7. Next Steps & Recommendations

Detailed structural analysis: Perform FEA on the leg foil under combined wave‑load and thrust forces. Verify that 4 mm plate + internal ribs meet a 2.5× safety factor for manned operation.
Model testing: Tow a 1‑m long geometric model in a wave tank to calibrate drag and lift coefficients for the foils and stabilisers.
Control‑system development: Write the PID/vector‑control software for the RIM drives and stabiliser actuators early – this is the “software‑in‑the‑loop” part you mentioned.
Regulatory check: Confirm compliance with local maritime regulations (life‑preserver requirements, navigation lights, etc.) for small‑vessel operation near Anguilla.
Procurement timeline: Order aluminium stock and custom parts now (≈ 8‑10 weeks to CNC and ship). Battery and drives can be ordered later once the hull is ready.

All figures are order‑of‑magnitude estimates based on the information provided. Detailed engineering, local codes, and site‑specific wave data should be incorporated before construction begins.