A 70-foot trimaran-style floating home that combines stability, comfort, efficiency, and livability — and explains the reasoning behind each choice.
A seastead is not just a boat and not just a platform. It must sit comfortably on the open ocean for long periods, move through the water when needed, generate its own power, and feel like home. This design achieves all of those goals by combining several proven principles into a coherent whole where each element supports the others.
What follows is an explanation of why each major design choice works, and why the combination is more than the sum of its parts.
The three buoyancy legs are attached near the three corners of a large triangle: two sides of 70 feet and a back edge of 35 feet. This spreads the support points far apart, creating a very wide base. The result is exceptional ultimate stability — the seastead simply cannot flip over under any normal ocean condition.
Think of it like a tripod: the wider the legs, the harder it is to tip. Most conventional boats of this length rely on a single hull with ballast below the waterline to resist capsizing. This design instead uses geometry, which is far more reliable and requires far less weight.
Each leg is 19 feet tall with a 10-foot chord and is immersed to 50% of its height. The waterline cross-section at the surface is narrow — just the thin leading and trailing edges of the foil cutting the surface. This is the same principle used by SWATH (Small Waterplane Area Twin Hull) vessels and small oil platforms.
Waves in the ocean carry most of their energy near the surface. A large waterplane area acts like a sail catching that energy, transferring it directly into the vessel as heaving and pitching. By minimizing the area at the waterline, the seastead largely decouples from the wave motion below. Small waves simply pass underneath with little felt effect.
If the waterline area were too small, a vessel could submarine or be dangerously slow to respond when waves do get large. This design avoids that problem. Because the legs have significant volume and are 10 feet wide (chord), when a big wave arrives the seastead rises with it — it effectively rides on top of large swells rather than punching through them. The transition from ignoring small waves to riding large ones is smooth and predictable.
A conventional semi-submersible platform has cylindrical columns that create enormous drag when moved through the water. This design uses a NACA 0030 hydrofoil profile for each leg — a smooth, tapered, aerodynamically optimized cross-section. The blunt leading edge faces forward, and the tapered trailing edge faces aft.
The result is that the seastead can be propelled through the water at reasonable speeds with relatively modest thrust. The drag coefficients of foil-shaped bodies are a fraction of those of cylinders or rectangular pontoons.
| Feature | Cylindrical Column | NACA 0030 Foil Leg |
|---|---|---|
| Drag coefficient (approx.) | ~1.0–1.2 | ~0.04–0.08 |
| Flow behavior | Turbulent wake, eddies | Smooth, attached flow |
| Propulsion energy | High | Low |
This means the seastead is not just a stationary platform — it is a vessel that can relocate, cruise to a new anchorage, or even outrun weather systems without needing enormous engines or fuel.
Traditional boats place buoyancy along their entire length. A 70-foot monohull, for example, requires a continuous hull from bow to stern — that is a lot of material, a lot of weight, and a lot of cost.
This design places buoyancy only at the three corners. The living area is a lightweight truss frame (7 feet high, floor to ceiling) bridging between the floats. The total structural weight can be far less than a conventional 70-foot boat of similar living area.
Marine construction costs scale roughly with weight — more material means more money. A lighter structure needs less material, less labor, and smaller (cheaper) floats to support it.
Less weight means less inertia to overcome when accelerating, less drag from the waterline, and less power needed from the thrusters and solar system.
The entire upper surface of the large triangle is covered in solar panels. With 70-foot sides and a 35-foot back, the roof area is substantial — on the order of 1,000+ square feet. At typical marine solar densities, this could yield 15–20 kW of peak solar capacity.
Because the structure is so light for its size, the solar-to-weight ratio is exceptionally favorable. The seastead can generate enough power for propulsion, climate control, cooking, computing, and all the needs of a modern digital-nomad lifestyle — all from sunlight alone.
The battery banks are placed at the bottom of the three legs, well below the waterline. This is strategically important for two reasons:
This is the same reason a spinning ice skater extends their arms to slow down — distributing mass outward and downward makes the system inherently stable and slow to respond to perturbations.
Near the back of each of the three legs, a small airplane-like stabilizer is mounted. Each stabilizer has:
The stabilizer is mounted on a pivot near the leading edge of its main wing. By angling the small elevator up or down, water flow creates a force on the elevator which rotates the entire stabilizer to a new angle of attack. This means a small, inexpensive actuator on the elevator can control a much larger main wing.
These stabilizers are effective because of two features of this design:
The notch into the front of the stabilizer wing only needs to go about 25% of the chord to balance the center of lift on the pivot point. This keeps the mounting simple and strong.
Six rim-drive thrusters of 1.5-foot diameter are mounted in pairs — one on each side of each leg, about 3 feet above the bottom. Rim-drive thrusters have no exposed shaft or gearbox; the motor is integrated into the shroud rim around the propeller, which spins inside it.
Having the flat sides of the thruster housings oriented fore-and-aft minimizes drag when the seastead is moving forward under power or sail.
When it is time to stay in one place, three helical mooring screws are driven into the seabed and tensioned lines are run to each of the three legs. This creates a tension-leg mooring configuration.
In a tension-leg system, the mooring lines are always taut — the seastead's buoyancy is pulling up while the lines are pulling down. This eliminates the catenary slack that causes conventional moorings to allow slow drifting and yawing. The seastead becomes nearly stationary, with minimal surge, sway, or yaw.
Stable enough to work on a laptop, take video calls, or set up a telescope without any noticeable rocking. The three-point tension system locks the seastead in place.
Having exactly three buoyancy legs means each leg naturally gets one mooring line. This is the minimum number for complete positional control (preventing surge, sway, and yaw).
The NACA 0030 foil shape of the legs is symmetric — the same profile upside down as right-side up, with significant thickness (30% of chord). This means the legs function as deep, high-aspect-ratio daggerboards.
When kite-sailed, a vessel needs lateral resistance to prevent leeway (sliding sideways downwind). Conventional sailboats use a keel or centerboard. Here, the three deeply immersed foil legs provide enormous lateral area far below the center of effort of a kite, giving strong upwind and reaching ability.
The large chord (10 feet) and depth (9.5 feet immersed) give a very high aspect ratio for each leg, which means low induced drag and efficient lift generation when the seastead is moving at an angle to the wind.
Similarly, when running from a storm, a drogue on a harness can be used for directional control. The foil legs ensure the seastead tracks straight and does not yaw dangerously in heavy following seas.
A 14-foot RIB dinghy with an electric Yamaha HARMO outboard is mounted sideways at the center of the backside of the living area, held by two supports and two ropes. When the seastead is under way, the living area acts as a wind break, shielding the dinghy from headwinds and spray.
Flanking the dinghy on the left and right are 5-foot-wide decks extending beyond the back of the triangle. These provide outdoor social and working space with a view — the natural gathering point at sunset — and convenient access to the dinghy for shore excursions.
Marine construction in China, particularly with significant CNC machining and automated composite layup, offers substantial cost savings over construction in North America, Europe, or Australia. The truss-frame living area and composite foil legs are well suited to modern automated fabrication methods.
Because the design is inherently light (see Principle 4), material costs are lower to begin with. Combined with efficient manufacturing, the total cost of a 70-foot seastead with this design can be a fraction of a conventional motor yacht of similar size.
No single feature of this design is entirely new. SWATH vessels, trimarans, tension-leg platforms, rim-drive thrusters, and kite sailing all exist independently. What makes this design work is how each choice reinforces the others:
Wide spacing enables stability without weight. Low weight enables large solar area per unit of cost. Foil-shaped legs give low drag and serve as daggerboards. Small waterline area gives a soft ride and makes the stabilizers more effective. Three legs give natural three-point mooring and three-point kite-sail lateral resistance. Batteries in the legs lower the center of gravity and the legs are already there as structure.
Every element earns its place by serving more than one purpose. That is the hallmark of a design that works.