This is a review of fundamental feasibility issues. I focused on physics and numbers that could sink the concept (sometimes literally) before you spend money. I've grouped items by severity.
CRITICAL: Check whether the legs can actually float the load.
Let's compute the submerged buoyancy of your three legs.
Each leg: NACA 0040, chord 8.5 ft, length 14.5 ft, 50% submerged → 7.25 ft submerged length.
Cross-section area of a NACA 0040 foil ≈ 0.40 × chord² × (a shape factor ≈ 0.685 for the NACA thickness integral) → roughly:
A ≈ 0.685 × 0.40 × (8.5)² ≈ 19.8 ft²
Submerged volume per leg: 19.8 × 7.25 ≈ 143 ft³.
Three legs: ≈ 430 ft³.
Seawater weighs ~64 lb/ft³, so total buoyancy at the design waterline:
430 × 64 ≈ 27,500 lbs ✅
Good news: this matches your stated 27,500 lb rated buoyancy almost exactly. Bad news: that 27,500 lbs must include everything: the triangle structure, walkway, solar, the 25% allocated to batteries (~6,900 lbs), thrusters, the dinghy, people, water, stores, and reserve freeboard. That is a very tight budget for a 44-ft-per-side liveaboard platform. A welded aluminum triangle wall 44 ft × 7 ft × 3 sides, plus floor, plus roof with solar, will likely eat most or all of that by itself.
Action: Build a real weight budget (mass spreadsheet) line-by-line before anything else. I suspect you are 30–100% over your buoyancy. This is the single most likely reason the design "won't work."
CRITICAL: SWATH platforms have notoriously low stability margins.
You correctly note this is "SWATH-like." The danger: your center of gravity is HIGH (7-ft living box + roof solar above water) while buoyancy comes from narrow legs with small waterplane area. Restoring moment for small-waterplane craft depends heavily on the waterplane second moment of area, which you have deliberately minimized.
Putting batteries low in the legs (good instinct) helps, but with only ~143 ft³ per leg and 25% of displacement as batteries down low, you may still end up CG-high once the living box and solar are added. Compute GM (metacentric height) for both pitch and roll. If GM is negative or marginal, the platform can be unstable or violently "snap" upright. Many amateur SWATH designs capsize at the dock.
WARNING: The leg may not fit in the container the way you describe.
Leg thickness = 40% × 8.5 ft chord = 3.4 ft (matches your "3.4 ft of width"). Leg chord = 8.5 ft. You plan to stand the legs with chord vertical (leading edge down, trailing edge up). Container interior height is 8.9 ft — but usable interior height of a 45' HC is closer to 8.9 ft nominal / ~8.6–8.7 ft real interior. Your 8.5 ft chord "minus 0.5 ft of trailing edge" = 8.0 ft, which fits.
BUT: three legs end-to-end need 3 × 14.5 = 43.5 ft of length. Interior length of a 45' HC is ~44.1–44.6 ft. That works only if the legs have flat, square-cut ends and you ignore the heave plates, ladders, RIM drives, and trailing-edge conduit, which all add length/width and must ship separately (you did say bolt-on — good). Verify real interior dimensions from the actual container spec, not the nominal exterior numbers you listed.
WARNING: A 40%-thick "foil" behaves almost like a bluff body.
NACA 4-digit sections are only well-behaved up to ~20–24% thickness. At 40% thickness the flow separates massively; you will get a large turbulent wake and drag much closer to a cylinder than to a streamlined strut. The "low drag forward" benefit you're counting on is largely lost at 40% t/c. It's fine as a buoyancy column shape, but don't expect foil-like drag savings. Also, at slow seastead speeds (Reynolds and Froude regime) wave-making and appendage (heave plate) drag dominate anyway.
WARNING: Heave plates add huge drag underway.
Heave plates are excellent for damping vertical motion at anchor, but they create enormous added mass and drag when translating horizontally. With only 6 × 1.5-ft RIM thrusters, your available thrust is modest. Estimate: a 1.5-ft RIM thruster might produce on the order of 50–150 lbf each → ~300–900 lbf total. Dragging three legs + heave plates + a 44-ft platform through open water at any meaningful speed may exceed that. Do a thrust-vs-drag estimate at your target cruise speed. You may be limited to ~1–2 knots, which makes ocean passages weather-dependent and slow (fine for slow relocation, not for outrunning storms).
WARNING: Fixed-orientation thrusters give weak control authority in current/wind.
A 44-ft platform with high windage (7-ft walls all around acting as a sail) steered only by differential thrust will struggle in crosswinds and current. Yaw authority from differential thrust on closely-spaced legs is limited. Consider that your turning moment arm is roughly the triangle half-width; with low total thrust this may not overcome wind-induced yaw. Station-keeping in a breeze before the mooring screws are in could be a problem.
WARNING: Pre-tensioning a tension-leg platform requires reserve buoyancy > tension.
To keep tension legs taut by "pulling down 3 ft," the platform must have at least that much reserve buoyancy to pull against — i.e., the legs must be able to provide significantly more upward force than the static load. You said 1 ft ≈ 1/7 of buoyancy (~3,900 lb/ft). Pulling down 3 ft = ~11,700 lb of tension demand, which must come from reserve buoyancy you may not have (see Item 1). Also, helical screws hold well in vertical pull-out in good soil, but Caribbean seabeds are often coral/rock/thin sand over hardpan — screw-in anchors may not set. And tension legs that go slack-then-snap in any swell shock-load everything. Verify seabed type per site.
WARNING: Software-coordinated thrusters fighting wave motion is hard and risky.
Using two independent platforms' thrusters to "minimize walkway movement" in real seas is a genuinely difficult dynamic positioning control problem, and a safety-critical one (people on the walkway). Relative motion of two free-floating bodies in waves can be large and fast; thrusters respond slowly. A passive, articulated, telescoping/gimbaled gangway (like offshore crew-transfer gangways) is the proven approach. Don't rely on thruster coordination to keep people safe.
| Item | Concern |
|---|---|
| Conduit on trailing edge | External conduit + wires in seawater is a corrosion/fatigue/snag risk. It also worsens the wake. Consider internal routing in a dedicated dry chase even without "through hulls." |
| Ladders on submerged-zone front | The "top half out of water" is exactly the splash/wave-impact zone; ladders there get heavy wave loading and growth. Fine, but design for slam loads. |
| Walkway grating "lets a wave pass" | Good for green water, but a 3-ft walkway 1 ft above leg bottom is near the waterline — expect frequent submersion and large wave slam/uplift loads on the bolted brackets. |
| Two doors on the back wall | The back wall is also where the dinghy and two-seastead gangway attach. Watch for interference and watertightness of doors near waterline. |
| LiPo4 (LiFePO4) low in legs | Good for CG and safe chemistry, but you must guarantee the airtight compartments don't trap gas, and provide cooling. Salt water + battery compartment = single biggest fire/flood concern. Triple redundancy is smart. |
| Solar "all over" roof | 44-ft equilateral triangle roof ≈ 838 ft² → maybe ~15–20 kW peak. Generous for house loads, but propulsion energy at sea may exceed daily solar harvest if you push speed. Energy budget needed. |
None of these is necessarily fatal individually — but Items 1 and 2 (buoyancy budget and stability) are the ones most likely to mean the design as drawn cannot float its intended load right-side-up. Nail those two with real numbers before proceeding.
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