The leg has a NACA 0030 foil cross-section with an area of approximately 1.69 ft². Seawater weighs about 64 lb/ft³. Therefore, an additional foot of submersion provides an extra buoyant force of:
≈ 108 lb per additional foot of submersion
This assumes the entire cross-section is submerged uniformly along the additional foot.
Estimates are based on a 4-foot wave (height) with assumed period of 5 seconds, and the stabilizer's ability to generate lift to counteract wave-induced forces. Assumptions: stabilizer wing (10 ft span, 2 ft chord), symmetric airfoil, control aiming to reduce heave motion. The following table shows the estimated reduction per crest/trough and electrical power lost to drag per stabilizer at each speed.
| Speed (knots) | Reduction per Crest (inches) | Reduction per Trough (inches) | Total Height Reduction (inches) | Power Lost to Drag (watts) |
|---|---|---|---|---|
| 4 | 5 | 5 | 10 | ~85 |
| 5 | 6 | 6 | 12 | ~164 |
| 6 | 7 | 7 | 14 | ~282 |
| 7 | 8 | 8 | 16 | ~446 |
| 8 | 9 | 9 | 18 | ~666 |
Power values are for a single stabilizer; three stabilizers are installed. Drag calculations assume parasitic drag coefficient (Cd0) of 0.01 and induced drag from lift generation.
Estimated per-unit cost for the stabilizer (including wing, body, elevator, and small actuator):
≈ $4,000 per unit
For a batch of 20, total cost: ~$80,000. This includes materials (marine-grade aluminum), machining, assembly, and actuator. Costs may vary with design complexity and quantity.
Based on the benefits of improved comfort, reduced resonant motion, and enhanced safety in large swells, I estimate that approximately 50% of customers would opt for this optional extra. The stabilizer is particularly valuable for long-term habitation and rough-sea operations.
For a 12-second period wave in deep water, wavelength is calculated as L = gT²/(2π) ≈ 738 ft.
With a seastead length of 44 ft and wave slope s = (πH)/L ≈ 0.051, the maximum height difference between ends at the steepest part of the swell is approximately:
≈ 2.25 ft
In head-sea conditions, the stabilizers can generate forces to keep the seastead level. Estimated effectiveness:
In beam sea, effectiveness may be higher due to the symmetrical arrangement of the three legs, allowing better roll control.
To lock the stabilizer when not in use or when stationary, a simple and robust mechanism is proposed:
Estimated cost per stabilizer for the locking mechanism: ≈ $200 (including hardware and installation).
Estimates account for both drag from the stabilizers and savings due to reduced leg bobbing. Assumptions: stabilizers reduce vertical motion amplitude by ~50%, leg drag coefficient (Cd) of 0.02, and constant wave conditions (4-foot wave). Positive values indicate additional power required; negative values indicate net power savings.
| Speed (knots) | Stabilizer Drag (lb force, all 3) | Leg Drag Savings (lb force, all 3) | Net Extra Drag (lb force) | Net Extra Power (watts) |
|---|---|---|---|---|
| 4 | ~27.7 | ~34.8 | ~ -7.1 | ~ -65 (saving) |
| 5 | ~43.0 | ~34.8 | ~ 8.2 | ~ +94 |
| 6 | ~61.6 | ~34.8 | ~ 26.8 | ~ +369 |
| 7 | ~83.6 | ~34.8 | ~ 48.8 | ~ +782 |
| 8 | ~109.2 | ~34.8 | ~ 74.4 | ~ +1361 |
Net power savings at low speeds occur because reducing leg bobbing decreases drag more than the stabilizer's own drag. At higher speeds, stabilizer drag dominates, leading to net power increase.
The active stabilizers can significantly reduce wave-induced motion, with effectiveness increasing with speed. At low speeds, they may even save power due to smoother leg motion. The additional cost for a batch of 20 units is estimated at $80,000, with a locking mechanism adding $200 per unit. Approximately half of customers are expected to opt for this feature.
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