🚀 Seastead Speed Estimation
📋 Input Parameters:
- Seastead weight: 30,000 lbs (13,608 kg)
- Thrusters: 2x submersible mixers with 2.5m propellers
- Structure: 3 columns, 4 ft wide, angled 45° into water
- Additional drag from cables to corner points
1. Understanding the Hydrodynamics
The seastead's oil-platform-like structure creates significant drag compared to a streamlined hull. Let me break down the drag components:
1.1 Underwater Geometry Analysis
Column Dimensions:
• Column width: 4 ft = 1.22 m
• Immersion depth: 13 ft = 3.96 m at 45° angle
• Horizontal projection: 3.96 m × cos(45°) = 2.8 m
Frontal Area Estimate:
• 3 columns × 1.22 m width = 3.66 m
• At 45° angle, effective width increases by ~1.4× factor
• Estimated total frontal area: 5.1 m²
• Plus cable drag (2 cables): ~0.3 m²
Total Frontal Area: ~5.4 m²
1.2 Drag Force Calculation
Using the drag equation: Fdrag = 0.5 × ρ × V² × Cd × A
Where:
• ρ (water density) = 1025 kg/m³ (seawater)
• Cd (drag coefficient) = 1.0 (blunt cylindrical shape)
• A (frontal area) = 5.4 m²
Drag at different speeds:
• At 0.5 mph (0.22 m/s): 59 N
• At 1.0 mph (0.45 m/s): 236 N
• At 1.5 mph (0.67 m/s): 531 N
• At 2.0 mph (0.89 m/s): 944 N
• At 2.5 mph (1.12 m/s): 1,475 N
2. Thruster Performance Analysis
Based on the provided thrust vs. speed data, I can interpolate to find thrust at different power levels:
| Power (kW) |
Thrust at 0 mph (N) |
Thrust at 0.5 mph (N) |
Thrust at 1.0 mph (N) |
Thrust at 1.5 mph (N) |
| 1.2 |
~1,050 |
~780 |
~510 |
~240 |
| 2.2 |
~2,000 |
~1,500 |
~1,000 |
~500 |
| 3.2 |
3,200 |
2,380 |
1,560 |
740 |
⚠️ Important Note:
The thrust drops significantly as speed increases. This is because the propellers are designed for mixing (moving water) not for propelling a vessel through water. They are most efficient at "blocked" operation (0 speed) and lose effectiveness as they start moving water past themselves.
3. Speed Equilibrium Calculation
Speed is determined where Total Thrust = Total Drag
For 2 thrusters combined:
| Power per Thruster |
Total Thrust (2 thrusters) |
Estimated Equilibrium Speed |
Notes |
| 1.2 kW |
~2,100 N max |
~0.9 mph |
Marginal maneuverability |
| 2.2 kW |
~4,000 N max |
~1.4 mph |
Moderate speed achievable |
| 3.2 kW |
~6,400 N max |
~1.8 mph |
Best speed performance |
4. Detailed Results Summary
| 1.2 kW |
0.9 mph |
0.78 knots |
0.40 m/s |
~2,100 N |
~2,100 N |
| 2.2 kW |
1.4 mph |
1.22 knots |
0.63 m/s |
~4,000 N |
~4,000 N |
| 3.2 kW |
1.8 mph |
1.56 knots |
0.80 m/s |
~6,400 N |
~6,400 N |
5. Key Findings & Conclusions
📊 Summary of Results
At 1.2 kW per thruster: ~0.9 mph (1.4 km/h)
At 2.2 kW per thruster: ~1.4 mph (2.2 km/h)
At 3.2 kW per thritter: ~1.8 mph (2.9 km/h)
🔍 Analysis Notes:
- Low speeds expected: The platform-like structure creates high drag, limiting top speed despite significant thrust available
- Thruster efficiency matters: These mixers are optimized for water movement, not vessel propulsion - a dedicated thruster would perform better
- Power is not linear: Doubling power does NOT double speed (drag increases with V²)
- Good news: Even at low speeds, this provides adequate maneuvering for positioning and weather coping
6. Recommendations
💡 For Better Performance Consider:
- Dedicated thrusters: Use propellers designed for vessel propulsion rather than mixing
- Steering strategy: With differential thrust from 2 units, you can pivot and position precisely even at low speeds
- hull optimization: Fairing the columns or adding buoyancy to reduce draft could reduce drag significantly
- Current assisted: Use tidal or wind currents when available to extend range
Calculations based on simplified hydrodynamic model. Actual performance may vary based on sea state, currents, and exact geometry.
```