A first-build seastead whose structural aluminum parts all fit in one 40-ft container, shipped flat-packed from a Chinese robotic shipyard and assembled in the Caribbean.
The constraint that all structural parts fit in one 40-ft container (internal usable ~39.5 ft × 7.7 ft × 7.8 ft) dominates the design. No single piece can exceed ~39 ft, and the total volume of parts (folded/nested) must fit inside ~2,350 ft³.
I recommend an isoceles, slightly forward-tapered triangle rather than equilateral — it keeps the front cross-section narrow (lower wind/wave drag) while giving a wide stable rear, and lets the longest single piece (the side rails) be exactly the longest thing in the container.
| Parameter | Value |
|---|---|
| Side rails (left & right) | 39 ft each (max container length) |
| Back rail | 20 ft (two 10-ft segments, bolted at midpoint) |
| Front "point" cut off as a 4-ft flat | For practical doors/joinery |
| Truss height (floor-to-ceiling) | 7 ft |
| Living-area footprint | ~373 ft² (see calc below) |
| Roof solar footprint | ~373 ft² (slightly more with overhang trim) |
Triangle area: with base 20 ft and the apex 38.5 ft from the base (Pythagorean from 39-ft sides): ½ × 20 × 38.5 = 385 ft² gross; after wall thickness and the truncated nose, usable interior ≈ 373 ft².
| Parameter | Value |
|---|---|
| Leg length | 19 ft (fits in container diagonally or as 2 × 9.5-ft halves) |
| Chord | 10 ft |
| Thickness (NACA 0030 = 30% of chord) | 3 ft |
| Submerged length | 9.5 ft (50%) |
| Foil cross-section area | ≈ 0.30 × 10 × 3 × 0.685 ≈ 20.6 ft² |
| Submerged volume per leg | ≈ 20.6 × 9.5 ≈ 196 ft³ |
| Buoyancy per leg (seawater, 64 lb/ft³) | ≈ 12,500 lb |
| Total displacement (3 legs at neutral) | ≈ 37,600 lb (17,000 kg / 17 metric tons) |
Legs are built as two half-shells (port and starboard skins) with internal aluminum ribs, shipped flat. Each half-shell is ~19 ft × 5 ft × ~1.5 ft when nested. Three legs × two halves = 6 shells that stack like nested canoes in the container.
Waterplane area per leg ≈ 20.6 ft²; total waterplane ≈ 62 ft². This is "small-waterplane" territory — a 1-inch wave lifts only ~340 lb of buoyancy, so the platform mostly ignores chop, exactly as desired.
| Item | Estimated mass (lb) |
|---|---|
| Aluminum triangle truss frame (5083, ~1.5 lb/ft² of floor) | 2,200 |
| 3 × aluminum foil legs (skin + ribs) | 3,000 |
| 3 × stabilizer "airplanes" | 450 |
| Floor decking + roof panels (composite/ply) | 1,500 |
| Walls + plexiglass windows | 1,800 |
| Solar array (panels + mounts) | 1,200 |
| 6 × RIM thrusters (1.5 ft Ø) | 900 |
| Rear deck + dinghy davits | 500 |
| 14-ft RIB + HARMO outboard | 700 |
| Interior fit-out (galley, head, bunks) | 1,500 |
| 2 people + supplies | 800 |
| Subtotal (dry, occupied) | ≈ 14,550 lb |
| Total displacement at 50% submersion | 37,600 lb |
| Remaining for batteries + water + cargo | ≈ 23,000 lb |
Roof area ≈ 373 ft² ≈ 34.6 m². Modern rigid marine panels deliver ~210 W/m² of installed area (accounting for gaps and frame).
Total installed solar: ≈ 7,250 W (7.25 kW peak).
In the Caribbean (avg ~5.5 peak-sun-hours/day), that's ~40 kWh/day average, which comfortably runs a 2-person liveaboard (galley, A/C-light, electronics ~15 kWh/day) and leaves ~25 kWh/day for slow propulsion. At 1.5 kW cruise draw (split among 6 thrusters at low rpm), you get ~16 hours of solar-only motoring per day at ~2 knots, or faster bursts off battery.
Each tail-mounted stabilizer (12-ft span × 1.5-ft chord main wing, 2-ft × 0.5-ft elevator, 6-ft fuselage) generates pitching/heaving correction lift at cruise speed. At ~3 knots water speed the 18 ft² main wing per stabilizer at small angles produces only ~10–30 lb of correcting force, but at 6+ knots that rises to ~50–150 lb per stabilizer — enough to damp the small-waterplane pitch mode that small-waterplane craft are otherwise prone to. The servo-tab elevator means a tiny linear actuator (~50 W) can drive the whole wing.
| Part | Stowed footprint |
|---|---|
| 6 × foil half-shells (nested, 19 ft × 5 ft × ~9 ft stack) | ~855 ft³ |
| Truss frame (disassembled tubes & gussets, 39 ft × 2 ft × 2 ft bundle) | ~160 ft³ |
| Floor/roof/wall aluminum panels (flat stack 39 ft × 7 ft × 1 ft) | ~270 ft³ |
| 3 × stabilizer airplane kits | ~80 ft³ |
| 6 × RIM thrusters in crates | ~60 ft³ |
| Fasteners, brackets, helical mooring screws (3) | ~100 ft³ |
| Total | ~1,525 ft³ of 2,350 ft³ available (65%) |
Plexiglass windows and the RIB dinghy ship in a separate container or as deck cargo — they're not "structural" in the metalwork sense.
Three helical screws (one under each leg) drilled into the seabed, with Dyneema or chain tendons pre-tensioned so the seastead is pulled down ~6–12 inches into its excess-buoyancy reserve. With ~23,000 lb of unused buoyancy reserve, you can tension each leg with ~5,000 lb of pre-load — this kills almost all wave-induced motion in moderate conditions.
Marine-grade 5083/5086 aluminum, robot-cut and robot-welded, FOB Chinese port, batch of 10 units (good amortization of tooling and CNC programming):
| Item | Mass | $/lb (fabricated) | Cost per seastead |
|---|---|---|---|
| Triangle truss frame | 2,200 lb | $4.50 | $9,900 |
| 3 foil legs (skinned, ribbed, sealed) | 3,000 lb | $6.00 | $18,000 |
| 3 stabilizer airplanes (incl. servo tabs) | 450 lb | $8.00 | $3,600 |
| Floor/roof/wall aluminum panels | 1,500 lb | $4.00 | $6,000 |
| Davits, deck frames, ladder rungs, brackets | 500 lb | $5.00 | $2,500 |
| Fasteners, anodes, internal hardware | — | — | $2,000 |
| QA, packing, container loading | — | — | $2,000 |
| Structural total per seastead (FOB China) | ≈ $44,000 | ||
| 40-ft container shipping to Caribbean | ≈ $4,000 | ||
| Landed structural cost | ≈ $48,000 |
Non-structural items shipped/sourced separately and roughly priced:
| 7.25 kW solar array | ~$5,000 |
| 300 kWh LFP battery bank | ~$45,000 |
| 6 × RIM-drive thrusters (1.5 ft) | ~$30,000 |
| 14-ft RIB + Yamaha HARMO | ~$15,000 |
| Plexiglass windows + interior fit-out | ~$25,000 |
| Electronics, plumbing, watermaker | ~$15,000 |
| Assembly labor in Caribbean | ~$20,000 |
| Estimated all-in MVP cost | ≈ $200,000 |
| Spec | Value |
|---|---|
| Triangle shape | Isoceles, 39 ft sides, 20 ft back |
| Indoor living area | ~373 ft² |
| Ceiling | 7 ft |
| Rear outdoor decks | ~100 ft² |
| Solar capacity | ~7.25 kW (40 kWh/day avg) |
| Total displacement | ~37,600 lb (17 t) |
| Dry structural + outfit mass | ~14,500 lb |
| Payload (batteries + water + cargo) | ~23,000 lb |
| Recommended battery bank | ~300 kWh |
| Thrusters | 6 × RIM, 1.5 ft Ø |
| Stabilizers | 3 × servo-tab airplane tails |
| Mooring | 3 helical screws, tension-leg |
| Structural cost (FOB China, batch of 10) | ~$44,000 |
| Landed Caribbean structural cost | ~$48,000 |
| All-in MVP cost | ~$200,000 |