Evaluation of alternative movement methods for a 40×16 ft seastead with angled leg floats
The primary propulsion system uses 4 low-speed submersible mixers with 2.5m diameter propellers, mounted on the angled leg floats. With 2 thrusters on each side, the system has built-in redundancy for differential thrust steering.
Analysis of using 10m diameter sea anchors with 2000W of power for kedging in calm conditions.
Using drag equation for sea anchors:
Parameters:
Power (P) = 2000 W
Water density (ρ) = 1025 kg/m³
Drag coefficient (Cd) = 1.0
Area (A) = π × (5m)² = 78.54 m²
Calculated Speed:
v³ = 0.04963
v = 0.367 m/s = 0.82 MPH
This is an idealized calculation assuming perfect efficiency. Real-world performance would be lower.
| Attribute | Value |
|---|---|
| Diameter | 10 meters (33 feet) |
| Estimated Cost (each) | $1,200 - $1,800 |
| Estimated Weight (each) | 60 - 90 lbs (27 - 41 kg) |
| Total for 2 anchors | $2,400 - $3,600, 120 - 180 lbs |
Note: This method assumes calm conditions and ignores the energy required for the dinghy. The switching process would reduce average speed by 20-30%.
Analysis of traditional anchor kedging in shallow water with 2000W of power.
Using seastead drag area estimated from thruster performance:
Calculated Speed:
v³ = 0.0447
v = 0.355 m/s = 0.80 MPH (continuous)
Practical Considerations:
• Actual average speed would be 0.4-0.6 MPH due to anchor resetting time
• Requires suitable bottom conditions for anchor holding
• Labor-intensive process requiring constant attention
| Phase | Distance | Time at 0.8 MPH |
|---|---|---|
| Winching in | 1000 ft | 14.2 minutes |
| Anchor resetting | — | 8-12 minutes (estimated) |
| Total per cycle | 1000 ft | 22-26 minutes |
Using a 14ft dinghy with 3 Yamaha HARMO electric motors (227 lbs thrust each, 681 lbs total) powered from seastead batteries.
Calculated Speed:
v² = 0.0677
v = 0.26 m/s = 0.58 MPH
This assumes all three motors operating at full thrust. Actual speed would be lower due to dinghy drag and power limitations.
Practical Notes:
• Requires strong tow line and attachment points
• Dinghy should be sized appropriately (14ft is borderline)
• Power cord limits range and maneuverability
• Best used for short distances or emergency situations
Analysis of a stack of 20 kites (6ft × 2ft each) in 20 MPH Caribbean winds.
| Parameter | Value |
|---|---|
| Individual kite size | 6 ft wide × 2 ft deep |
| Individual kite area | 12 ft² = 1.115 m² |
| Total area (20 kites) | 240 ft² = 22.3 m² |
| Wind speed | 20 mph = 8.94 m/s |
| Air density | 1.225 kg/m³ |
| Kite drag coefficient | 1.0 (parachute-style) |
Maximum downwind force (stationary):
| Direction | Downwind Force Component | Estimated Speed |
|---|---|---|
| Directly downwind | Full force (1091.6 N) | 0.34 MPH |
| 30° off downwind | 945.3 N (cos(30°) × max) | 0.33 MPH |
Kites Required for 2 MPH:
To achieve 2 MPH, approximately 800+ kites of the specified size would be needed. This is impractical for most applications.
Practical Considerations:
• Requires active control (human or automated)
• Wind window management is complex
• Best for supplementary power rather than primary propulsion
• Can be effective for slow, downwind travel in windy conditions
A nearby seastead could provide towing assistance, especially with power sharing through a rope bridge connection.
Advantages:
• No additional equipment required
• Can utilize combined solar/battery capacity
• Effective for repositioning in calm conditions
Limitations:
• Requires coordination between vessels
• Slow speeds (likely 0.3-0.6 MPH)
• Risk of entanglement in rough conditions
With only one or two thrusters on the same side, the seastead can be angled relative to wind/current to achieve downwind travel with a sideways component.
Effectiveness:
• Can achieve useful directional control
• Speed depends on wind/current strength
• Best for emergency maneuvering toward safety
• Requires careful angle management
| Method | Estimated Speed | Power Required | Complexity | Best Use Case |
|---|---|---|---|---|
| Primary Thrusters (4×) | 0.5-1.0 MPH | Varies | Medium | Normal operation |
| Sea Anchor Kedging | 0.6-0.8 MPH | 2000 W | Medium | Calm conditions, no currents |
| Anchor Kedging | 0.4-0.6 MPH (avg) | 2000 W | High | Shallow water with good bottom |
| Dinghy Towing (3 motors) | 0.5-0.6 MPH | ~15 kW | Medium | Short distances, emergencies |
| Kite Power (20 kites) | 0.3-0.4 MPH | Wind power | High | Downwind travel in windy conditions |
| Another Seastead | 0.3-0.6 MPH | Shared | Low | When another vessel is available |
Recommendations:
1. Maintain the primary thruster system as the main propulsion method
2. Consider sea anchors as the most viable backup for calm conditions
3. The dinghy with multiple motors provides good emergency capability
4. Kite power is best for supplementary power rather than primary propulsion
5. Asymmetric drag steering should be practiced as an emergency technique