Half-Size Seastead Prototype: Design Overview & Estimates

1. Key Dimensions (Half-Size)

ComponentFull SizeHalf Size
Triangle Sides (two sides)70 ft35 ft
Triangle Side (back)35 ft17.5 ft
Truss Height7 ft3.5 ft
Leg/Wing Length19 ft9.5 ft
Leg/Wing Chord10 ft5 ft
Leg/Wing Thickness3 ft1.5 ft
Stabilizer Wingspan10 ft5 ft
Stabilizer Chord1 ft0.5 ft
Stabilizer Body Length6 ft3 ft
Dinghy14 ft RIB7 ft inflatable

2. Weight Estimates

ComponentWeight (lb)Notes
Triangle Truss (Aluminum)1500Estimated from tube lengths and typical truss construction
3 Legs/Wings (Aluminum)1000NACA 0030 foil shape, 1/8" skin with internal frames
3 Stabilizers & Actuators75Small airplane-like structures with actuators
2 Yamaha HARMO RIM Drives140~70 lb each
Batteries (50 kWh Li-ion)1320~26.4 lb/kWh
Seats & Net904 seats and a trampoline net
Dinghy (7 ft inflatable)50
Miscellaneous200Wiring, controls, safety gear, etc.
Total Estimated Weight4375

3. Buoyancy & Load Capacity

Buoyancy at 50% Leg Submersion: 4678.56 lb
Current Weight: 4375 lb
Waterline: ~46.8% of leg height submerged (slightly below half).

Reserve Buoyancy:

Maximum Buoyancy (legs 100% submerged): 9357.12 lb
Extra Load Capacity at 80% Submersion: 3110 lb
Extra Load Capacity at 100% Submersion: 4982 lb
Note: Avoid full submersion to prevent wave overtopping. The 80% limit is recommended for safety.

4. Estimated Range (50 kWh Batteries)

Speed (knots)Power Draw (kW)Running Time (hours, 80% DoD)Range (nautical miles)
41.8321.9~87
53.4311.7~58

Assumptions: 50% overall efficiency, constant speed, no waves. Drag estimates based on NACA 0030 foil drag coefficient of 0.01.

5. Estimated Cost Breakdown

ItemEstimated Cost (USD)
Aluminum Structure (truss & legs)$22,660
Stabilizers & Actuators$3,000
2 Yamaha HARMO RIM Drives$10,000
Batteries (50 kWh)$25,000
Solar Panels (200 sq ft, ~3 kW)$6,000
Seats & Net$1,000
Dinghy (7 ft inflatable)$1,000
Miscellaneous (wiring, controls, etc.)$5,000
Shipping (40 ft container from China)$5,000
Total Estimated Cost$78,660

Note: Costs are rough estimates; actual costs may vary. Labor for assembly is assumed free.

6. Additional Notes

7. Conclusion

The half-size prototype is feasible and should be an enjoyable day sailor with a range of 60–90 nautical miles at 4–5 knots. The design leverages foil-shaped legs for low drag and stabilizers for a smooth ride. The total cost is estimated under $80,000, assuming self-assembly.