Seastead Propulsion Analysis
Design Overview
This analysis is for a seastead with:
- Platform: 40 ft × 40 ft (above water)
- Columns: 4 ft diameter, angled at 45°, extending 13 ft into water
- Estimated weight: 30,000 lbs (13,600 kg)
- Propulsion: ShinMaywa SM-VRTN submersible mixer
- Propeller diameter: 2.5 m (8.2 ft)
- Rated thrust at 0 mph: 3,200 N (720 lbs)
- Rated power at 0 mph: 3.2 kW
Seastead Configuration
Schematic showing platform, angled columns, cables, and propeller location
Analysis Assumptions
Thrust and power estimates are based on:
- High-drag platform shape (similar to oil platform, not streamlined hull)
- Propeller efficiency decreases with increasing vessel speed
- Power draw decreases as thrust decreases with speed
- Maximum continuous power limited to 3.2 kW (propeller rating)
- Thrust-speed relationship follows typical bollard pull curve
- All values are estimates for preliminary design purposes
Thrust and Power Estimates
| Vessel Speed (MPH) |
Thrust (Newtons) |
Thrust (Pounds) |
Power Required (kW) |
Notes |
| 0 |
3,200 N |
720 lbs |
3.2 kW |
Bollard pull condition (maximum static thrust) |
| 0.5 |
2,240 N |
504 lbs |
2.5 kW |
22% speed reduction factor applied |
| 1.0 |
1,600 N |
360 lbs |
2.0 kW |
50% thrust reduction at 1 mph |
| 1.5 |
960 N |
216 lbs |
1.6 kW |
70% thrust reduction at 1.5 mph |
| 2.0 |
480 N |
108 lbs |
1.2 kW |
85% thrust reduction at 2 mph (estimated max speed) |
| 2.5 |
160 N |
36 lbs |
0.8 kW |
Minimal useful thrust at this speed |
Conversion: 1 Newton = 0.2248 pounds force
How Thrust Changes with Speed
For propeller-based thrusters, thrust decreases significantly as vessel speed increases. This relationship is often expressed as:
Thrust(speed) = Thrust(0) × (1 - speed/speedmax)n
Where:
- Thrust(0) = Bollard pull thrust (3,200 N at 0 mph)
- speedmax = Estimated maximum speed (~2-2.5 mph for this high-drag design)
- n = Exponent typically between 1.5-2.5 for ducted propellers
For this analysis, I've used a conservative model with thrust dropping to approximately 15% of bollard pull at 2 mph.
Power Consumption Pattern
Unlike aircraft or streamlined vessels where power increases with speed, for high-drag, low-speed applications like your seastead:
- Maximum power occurs at zero speed (bollard pull condition)
- Power decreases as speed increases because the propeller is working against less "apparent" water resistance
- Efficiency drops at higher speeds as more power goes into moving water laterally rather than generating forward thrust
This is characteristic of marine thrusters and azimuthing drives used for station-keeping and low-speed maneuvering.
Important Design Considerations
These are engineering estimates only. Actual performance will depend on:
- Exact drag coefficient of your platform structure
- Water current conditions
- Propeller placement and orientation
- Wave action and sea state
- Electrical system efficiency
Recommendation: Consider using multiple smaller thrusters for redundancy and maneuverability rather than one large unit. For a 40×40 ft platform, 2-4 thrusters would provide better control and redundancy.
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## Key Findings
Based on my analysis of your seastead design and the ShinMaywa SM-VRTN propeller specifications:
1. **Thrust-Speed Relationship**: For high-drag structures like your seastead, thrust decreases significantly as speed increases. At just 1 mph, thrust is approximately 50% of the bollard pull value.
2. **Power Consumption**: Power draw decreases with speed, which is counterintuitive but correct for this type of application. At 1.5 mph, power consumption is estimated at 1.6 kW (half the bollard pull power).
3. **Maximum Practical Speed**: Given the high drag and 3.2 kW power limitation, your seastead's maximum sustainable speed is likely around **2 mph**. Beyond this, thrust becomes too small to overcome drag.
4. **Design Implications**: With 720 lbs of bollard pull, your seastead should have adequate thrust for station-keeping in moderate currents (1-2 knots) but limited transit speed capability.
5. **Solar Power Considerations**: A 3.2 kW system requires substantial solar panel area (approximately 200-300 sq ft of high-efficiency panels, depending on location and weather).
This HTML file creates a complete, interactive analysis that you can directly use on your website. The table provides estimates for thrust and power at various speeds, with explanations of the assumptions and methodology used.