Conceptual design review notes — which rules apply, how they shape the design, and where the risks are. Prepared to support brainstorming ahead of formal naval-architecture work.
Concept: 44 ft equilateral-triangle aluminum semi-submersible platform · 3 NACA 0035 foil columns · 27,500 lb design displacement · container-shippable kit · battery/solar electric propulsion · helical-screw tension-leg mooring · Caribbean service.
One clarification up front: "ABS/ISO 12215" is not a joint thing. ISO 12215 is the ISO small-craft structural standard (used for self-certification under the EU Recreational Craft Directive). ABS publishes its own, separate rule sets. For this project you will most likely use ISO 12215 methods, the Aluminum Design Manual / Eurocode 9 for aluminum members, AWS D1.2 for welding, and offshore-rule methods for everything the small-craft rules don't cover.
We ran quick consistency checks on the stated concept. These are ±30% estimates for discussion only — your naval architect will own the real numbers.
| Item | Your figure | Rough check | Comment |
|---|---|---|---|
| Waterplane / stiffness | 1 ft immersion ≈ 1/7 of buoyancy | NACA 0035 section area ≈ 0.685 × (t/c) × c² ≈ 17 ft² per leg → ~50 ft² total waterplane → ~3,100 lb per ft of immersion | Same order as your 1/7 claim (≈3,900 lb/ft). The trailing-edge cut and appendages shift it a bit. Good news: your geometry is internally consistent. |
| Displacement volume | 27,500 lb buoyancy | ≈ 441 ft³ of sea water. Three submerged foil halves ≈ 3 × (17 ft² × 7.25 ft) ≈ 370 ft³ | Plausible with wall bottoms, walkway brackets and appendages making up the rest. |
| Battery energy | 25% of displacement = ~6,900 lb | LiFePO₄ packs at ~120–150 Wh/kg → roughly 375–470 kWh | Consistent with ~15 kWp solar + thruster hotel/transit loads. Buy packs at the destination (see §12 — shipping lithium is a paperwork trap). |
| Solar | "All over" the roof | Triangle area = (√3/4)·44² ≈ 838 ft² ≈ 78 m² → ~14–17 kWp | Design roof fixings for hurricane uplift or a stow/remove policy. |
| Structure weight (order of magnitude) | —"hope structure is enough under 27,500 lb" | Legs ~4–5 klb · walls ~4 klb · floors/ceiling/beams ~4–5 klb · walkway/rails ~2 klb → ~14–16 klb structure; + batteries 6.9, thrusters ~1.2, solar ~1.0, misc ~1.5 klb → ~25–26.5 klb total | This is the #1 risk. Payload for "humans and their stuff" may be only 1–6 klb. Start a formal weight & CG ledger on day one; target ≤ 20 klb of structure + systems. |
| Container packing (width) | Legs right, walls left | Legs are ~3.0 ft thick (0.35 × 8.5 ft). Nested pair ≈ 3.3–4.0 ft + third leg 3.0 ft = 6.3–7.0 ft. Walls 3 × 10 in = 2.5 ft + dunnage. Total ≈ 8.8–9.5 ft vs 7.7 ft interior. | Doesn't close as described. See §13 for fixes (most likely: nest all three legs alternately). Run the 3D packing study before freezing wall thickness. |
| Container payload | 62,000 lb | Typical 45' HC max gross 67.2 klb (CSC plate) − tare ~9.5–10.5 klb → ~56–58 klb payload. US road limit ≈ 44–46 klb payload. | Verify the actual plate rating; and note your real load (~10–14 klb) is far below either limit — just don't let it grow. See §13. |
Which standards "apply" depends on what category regulators, insurers and port states decide your seastead falls into. There are three plausible lenses:
| Lens | Treated as | Rules that come with it | Practical reality for you |
|---|---|---|---|
| A. Small vessel / yacht | A 13.4 m motor craft (multihull-ish) | ISO small-craft suite (12215, 12217, 12216, 15085, 9094, 13297/10133), ABYC (US, voluntary), EU RCD Category A (if sold in EU), flag-state registration, COLREGs | Most proportionate. Insurers accept it. Size (<24 m) keeps you below SOLAS/Load Line thresholds. |
| B. Offshore unit / classed structure | A mini semi-submersible platform | ABS MODU or floating-installation guides, DNV-OS-C101/C301/E301, API RP 2T/2SK, class survey during build | Most rigorous for the semi-sub behavior, stability and tension legs — but heavy process for a ~12 t one-off. Borrow its methods even if you don't class. |
| C. Floating building | Real estate on water | Local/state building codes, marina rules (poorly codified offshore) | Not credible for something that self-propels and carries people offshore. Avoid relying on this. |
Caribbean operations notes: carry COLREGS-compliant lights, AIS, radar reflector and an EPIRB; check each country's rules on home-built vessels, cruising permits and import duty (Bahamas and most EC countries are cruising-friendly, but a "platform" can confuse customs). If US-documented, expect a USCG documentation process (likely over