Current design uses four 2.5-meter propellers (two per side) with differential steering. With 2 thrusters per side, the system maintains steering authority even with 50% failure. For normal operation, only one working thruster per side is required, providing effective redundancy for calm-weather maneuvering.
Using alternating sea anchors as "movable ground tackle," where the seastead winches itself toward a deployed parachute while a dinghy resets the other anchor ahead. The system acts like a lever, extracting energy from the water mass rather than the seafloor.
Speed is constrained by the power required to overcome both the seastead's hull drag and the sea anchor's drag:
Where P = 2000W, ρ = 1025 kg/m³ (seawater).
| Sea Anchor Diameter | Drag Area | Estimated Speed | Practical Assessment |
|---|---|---|---|
| 10 meters (33 ft) | 78.5 m² | ~0.7 MPH (0.6 knots) | Excessive drag; requires massive handling gear. Overkill for 16-ton vessel. |
| 5 meters (16 ft) | 19.6 m² | ~1.4 MPH (1.2 knots) | Optimal match to vessel drag (~15 m² equivalent). Best efficiency point. |
| 3 meters (10 ft) | 7.1 m² | ~1.8 MPH (1.6 knots) | Anchor may skip/skate; marginal holding for kedging. |
With true bottom anchors (assuming sufficient holding power in sand/mud), the anchor drag term drops to zero, and all power overcomes vessel resistance:
However, this requires:
Effective speed: ~0.5–0.8 MPH average, but with higher burst capability when overcoming initial inertia.
Emergency setup: 3× Yamaha HARMO electric rim-drive motors (227 lbs static thrust each) on the 14' dinghy, powered from seastead batteries.
| Configuration | Total Static Thrust | Estimated Bollard Pull | Expected Speed |
|---|---|---|---|
| 1× HARMO | 227 lbs | ~180 lbs | ~0.3 MPH (insufficient) |
| 3× HARMO | 681 lbs | ~540 lbs | ~1.0–1.5 MPH |
Limitations: Tow line catenary consumes significant thrust. Alignment is critical; any yaw angle drastically increases drag. Best used for emergency relocation to sheltered water, not long-distance travel.
Stack of 20 traction kites (6' × 2' each), total area ≈ 240 ft² (22.3 m²). Two-string control for figure-8 sweeping to maximize apparent wind.
The kite operates in reduced apparent wind (True Wind – Boat Speed). Force scales with (V_wind – V_boat)².
Figure-8 sweeping increases apparent wind speed and allows the kite to pull at favorable lift/drag ratios.
If 2.0 MPH is required (e.g., to maintain steerage in currents), and 20 kites achieves this only at an angle, you would need approximately 30–35 kites to achieve 2.0 MPH directly downwind, or accept the 30° offset navigation strategy with the existing 20-kite stack.
Power Bridging: By sharing battery banks via high-amperage cables across a rope bridge, the disabled seastead could theoretically operate its thrusters at 2× power (4000W). This increases speed from ~1.0 MPH to ~1.3 MPH (cube root scaling).
Towing by Friend: Another identical seastead (36,000 lbs) using its primary thrusters (~4 HP total) could tow at 1.5–2.0 MPH depending on tow line length and alignment. A rope bridge setup reduces yaw drift and improves efficiency by 30–40% compared to free tow.
With only one functional thruster (or two on the same side), the seastead can adopt a "crab angle" using wind pressure:
Use case: Emergency positioning toward rescue vessels or away from hazards when propulsion is compromised but wind is favorable.
| Method | Speed (MPH) | Range/Energy | Weather Limits | Complexity |
|---|---|---|---|---|
| Primary Thrusters (4) | 0.5–1.0 | Solar limited | All | Low |
| Sea Anchor Kedging | 0.7–1.4* | Unlimited (mechanical) | Calm–Moderate | High |
| Shallow Kedging | 1.0–1.5* | Unlimited | Calm only | High |
| Dinghy Tow (3 HARMO) | 1.0–1.5 | Battery limited (~2 hrs) | Calm–Moderate | Medium |
| Kite (20 units, 20mph) | 1.2–2.5 | Unlimited | Wind > 15mph | Very High |
| Wind + Single Thruster | 0.5–1.5 | Battery + Wind | Downwind only | Medium |
*Effective average speed including deployment overhead