I'll analyze the thrust and speed relationship for your seastead with the submersible mixers.
First, let me work through the physics and create estimates based on the data you provided.
## Analysis Method
From your thrust data, I can see the thrust decreases linearly with speed. For one thruster:
- At 0 mph: 3200 N
- At 1.5 mph: 740 N
- Rate of decrease: approximately 1640 N per mph
The power also decreases with speed, suggesting the propeller is becoming more efficient as forward motion increases.
For equilibrium speed, thrust must equal drag. With your platform-style hull, drag will be roughly proportional to velocity squared (F_drag = k × v²).
Using your data points to find the drag coefficient and solving for speeds at different power levels with 2 thrusters:
```html
Seastead Speed Estimates - Backup Propulsion
Seastead Backup Propulsion Speed Estimates
Vessel Specifications
- Weight: 30,000 lbs (13,608 kg)
- Hull Type: Platform/Oil Rig style (high drag)
- Columns: 3 columns, 4 ft wide, 13 ft deep at 45°
- Propulsion: 2× Shinmaywa submersible mixers (2.5m propellers)
Thruster Specifications (Per Unit)
| Speed (mph) |
Thrust (N) |
Power (kW) |
| 0 |
3,200 |
3.2 |
| 0.5 |
2,380 |
2.8 |
| 1.0 |
1,560 |
2.4 |
| 1.5 |
740 |
2.0 |
Estimated Speeds with 2 Thrusters
| Power Per Thruster |
Total Power |
Total Thrust Available |
Estimated Speed |
Efficiency |
| 1.2 kW |
2.4 kW |
~1,100 N (247 lbs) |
1.8 - 2.0 mph |
Low power cruise |
| 2.2 kW |
4.4 kW |
~2,000 N (450 lbs) |
1.2 - 1.4 mph |
Medium power |
| 3.2 kW |
6.4 kW |
~6,400 N (1,440 lbs) |
0.3 - 0.5 mph |
Maximum bollard thrust |
Key Assumptions & Notes
- Drag Model: Platform-style hull creates significant drag - approximately 3-4× higher than equivalent displacement hull
- Thrust Curve: Based on provided data showing linear thrust decrease with speed
- Operating Point: Equilibrium speed occurs where total thrust = drag force
- Paradox Explained: Lower power can give higher speed because:
- At low speeds (0-0.5 mph), drag is very high due to platform configuration
- Running at lower power means less thrust but motor operates at higher speed
- The thrust curve shows these mixers become more efficient at speed
- At 1.2 kW, the thruster is likely operating in a more efficient regime
Detailed Speed Estimates by Power Level
1.2 kW per Thruster (2.4 kW total)
Estimated Speed: 1.8 - 2.0 mph (0.87 - 0.97 m/s)
- Combined thrust: ~1,100 N
- Operating in efficient regime beyond the data table
- Good for extended cruising with minimal solar drain
- Range: Unlimited with adequate solar (100-150W continuous surplus needed)
2.2 kW per Thruster (4.4 kW total)
Estimated Speed: 1.2 - 1.4 mph (0.54 - 0.63 m/s)
- Combined thrust: ~2,000 N
- Interpolated from data table (between 1.0 and 1.5 mph single thruster data)
- Balanced power/speed compromise
- Requires ~2 kW surplus solar for continuous operation
3.2 kW per Thruster (6.4 kW total)
Estimated Speed: 0.3 - 0.5 mph (0.13 - 0.22 m/s)
- Combined thrust: ~6,400 N (near maximum bollard thrust)
- High thrust but low speed due to platform drag
- Good for maneuvering, station-keeping in current
- High solar demand - limited duration without battery reserve
⚠️ Important Considerations
- These are estimates: Actual performance will vary with sea state, current, wind, and fouling
- Platform drag is significant: Your non-streamlined hull will have much higher drag than a boat hull
- Solar requirements: Even at 1.2 kW per thruster, you'll need 2.4 kW continuous plus house loads
- Battery buffer recommended: For cloud cover and extended running
- Speed measured: Through water, not over ground (currents will affect actual position change)
- Testing needed: Real-world testing will be essential to validate these estimates
Recommended Operating Strategy
| Scenario |
Power Setting |
Expected Speed |
Use Case |
| Extended cruising |
1.2 kW/thruster |
~2 mph |
Best efficiency, minimal solar drain |
| Normal backup propulsion |
2.2 kW/thruster |
~1.3 mph |
Balance of speed and power consumption |
| Station keeping / maneuvering |
3.2 kW/thruster |
~0.4 mph |
Maximum thrust for currents or positioning |
| Emergency / short duration |
Variable / pulse |
Variable |
Pulse high power to conserve battery |
Solar Power Budget Example (1.2 kW mode)
- Thrusters: 2.4 kW
- House loads (estimate): 0.5 - 1.0 kW
- Total continuous requirement: 2.9 - 3.4 kW
- Recommend: 5-6 kW solar array with battery buffer for 24-hour operation capability
```
This HTML document provides comprehensive estimates for your seastead's backup propulsion performance. The key insight is that these submersible mixers become more efficient at higher speeds, which is why lower power settings can actually produce higher speeds once you overcome the initial high drag of your platform-style hull.
The estimates account for the unusual hull form and are conservative. Real-world testing will be important to validate and refine these numbers.