Project Parameters: 30 ft length, constant displacement volume (~10.1 m³ / 357 ft³), 4-leg configuration, operational speeds 1–2 MPH, survival speed 4 MPH buckling load.
| Shape | Material | Est. Weight (kg) |
Est. Cost (USD) |
Per Container (legs) |
Drag @ 2MPH (N) |
Power @ 2MPH (kW) |
Pressure Rating |
|---|---|---|---|---|---|---|---|
| 1. Cylinder Ø3.9 ft |
Marine Al (5083) | 620 | $9,300 | 4 | 4,420 | 31.6 | Excellent |
| 2. Cylinder Ø3.9 ft |
Duplex SS (2205) | 1,820 | $54,600 | 4 | 4,420 | 31.6 | Excellent |
| 3. Stadium 4.9×2.1 ft |
Marine Al | 680 | $12,200 | 4 | 3,100 | 22.1 | Good* |
| 4. Stadium 4.9×2.1 ft |
Duplex SS | 2,000 | $70,000 | 4 | 3,100 | 22.1 | Good* |
| 5. Ellipse 4.9×2.5 ft |
Marine Al | 650 | $13,000 | 3 | 1,325 | 9.5 | Good** |
| 6. Ellipse 4.9×2.5 ft |
Duplex SS | 1,900 | $76,000 | 3 | 1,325 | 9.5 | Good** |
| 7. Lenticular 4.5×2.8 ft |
Marine Al | 670 | $14,700 | 3 | 1,770 | 12.7 | Fair** |
| 8. Ovate 4.5×3.2 ft |
Marine Al | 640 | $13,400 | 3 | 1,550 | 11.1 | Good** |
| 9. Kamm-Tail 4.9×3.1 ft |
Marine Al | 590 | $14,800 | 2 | 884 | 6.3 | Poor† |
| 10. Thick Airfoil 4.9×3.1 ft |
Marine Al | 610 | $17,100 | 2 | 2,650 | 18.9 | Poor† |
Dimensions: 30' L × 3.9' Ø (9.14m × 1.19m)
Volume: 10.13 m³
Packing: Two stacks of two, side-by-side (1.19m × 2 = 2.38m fits in 2.35m width with 3mm clearance).
Per 40' Container: 4 legs
Optimal for shipping and fabrication. Standard marine fabrication tooling.
Dimensions: 30' L × 4.9' W × 2.1' H (1.49m × 0.64m)
Cross-Section: Rectangle (2.7' × 2.1') with semicircular ends (1.05' radius)
Packing: Can stack 4 high (0.64m × 4 = 2.56m < 2.39m? No, too tall).
Correction: Stack 2 high, 2 wide (flats touching), or 3 high if angled.
Per 40' Container: 4 legs
Good compromise between hydrodynamics and manufacturability.
Dimensions: 30' L × 4.9' major × 2.5' minor axis
Cross-Section: Continuous oval
Packing: Major axis 1.49m. Side-by-side: 2.98m (too wide).
Single row, 3 high (2.5' = 0.76m; 3 × 0.76 = 2.28m < 2.39m).
Per 40' Container: 3 legs
Moderate packing efficiency; excellent drag reduction.
Dimensions: 30' L × 4.9' chord × 3.1' thickness
Packing: Alternating flip allows nesting, but 4.9' (1.49m) width exceeds container width/2 for efficient pairing.
Must ship single file: 2 high max (3.1' = 0.94m; 2 × 0.94 = 1.88m).
Per 40' Container: 2 legs
Shipping costs double per leg. Only justified for high-speed designs.
| Shape | Material | Surface Area (m²) |
Metal Weight (kg) |
Fabrication Factor |
Total Weight (kg) |
Cost/kg (USD) |
Total Cost (USD) |
|---|---|---|---|---|---|---|---|
| Cylinder | Al 5083 | 34.2 | 453 | 1.0 (base) | 620 | $15.00 | $9,300 |
| Duplex 2205 | 34.2 | 1,067 | 1.0 | 1,820 | $30.00 | $54,600 | |
| Stadium | Al 5083 | 36.5 | 483 | 1.25 | 680 | $18.00 | $12,200 |
| Duplex 2205 | 36.5 | 1,139 | 1.35 | 2,000 | $35.00 | $70,000 | |
| Ellipse | Al 5083 | 35.0 | 464 | 1.4 | 650 | $20.00 | $13,000 |
| Duplex 2205 | 35.0 | 1,092 | 1.5 | 1,900 | $40.00 | $76,000 | |
| Lenticular | Al 5083 | 36.0 | 477 | 1.55 | 670 | $22.00 | $14,700 |
| Duplex 2205 | 36.0 | 1,123 | 1.7 | 1,950 | $46.00 | $89,700 | |
| Ovate | Al 5083 | 34.5 | 457 | 1.45 | 640 | $21.00 | $13,400 |
| Duplex 2205 | 34.5 | 1,076 | 1.6 | 1,880 | $44.00 | $82,700 | |
| Kamm-Tail | Al 5083 | 32.0 | 424 | 1.75 | 590 | $25.00 | $14,800 |
| Duplex 2205 | 32.0 | 998 | 2.0 | 1,750 | $52.00 | $91,000 | |
| Thick Airfoil | Al 5083 | 31.0 | 411 | 2.0 | 610 | $28.00 | $17,100 |
| Duplex 2205 | 31.0 | 967 | 2.3 | 1,720 | $58.00 | $99,800 |
| Shape | Frontal Area (m²) |
Cd (broadside) |
Drag @ 1 MPH (N / lbf) |
Drag @ 1.5 MPH (N / lbf) |
Drag @ 2 MPH (N / lbf) |
|---|---|---|---|---|---|
| Cylinder (Ø3.9') | 10.9 | 1.05 | 1,105 / 248 | 2,486 / 559 | 4,420 / 994 |
| Stadium (4.9'×2.1') | 9.5 | 0.75 | 775 / 174 | 1,744 / 392 | 3,100 / 697 |
| Ellipse (4.9'×2.5') | 11.2 | 0.30 | 331 / 74 | 745 / 167 | 1,325 / 298 |
| Lenticular (4.5'×2.8') | 11.5 | 0.40 | 473 / 106 | 1,064 / 239 | 1,770 / 398 |
| Ovate (4.5'×3.2') | 13.1 | 0.35 | 414 / 93 | 932 / 209 | 1,550 / 348 |
| Kamm-Tail (4.9'×3.1') | 9.1 | 0.20 | 221 / 50 | 497 / 112 | 884 / 199 |
| Thick Airfoil (63% t/c) | 9.1 | 0.60 | 663 / 149 | 1,492 / 335 | 2,650 / 596 |
Power (kW) = (Drag × Velocity × 4 legs) / 0.5 efficiency factor
| Speed | Cylinder | Stadium | Ellipse | Lenticular | Ovate | Kamm-Tail | Thick Airfoil |
|---|---|---|---|---|---|---|---|
| 1 MPH (0.45 m/s) |
4.0 kW | 2.8 kW | 1.2 kW | 1.7 kW | 1.5 kW | 0.8 kW | 2.4 kW |
| 1.5 MPH (0.67 m/s) |
13.3 kW | 9.3 kW | 4.0 kW | 5.7 kW | 5.0 kW | 2.7 kW | 8.0 kW |
| 2 MPH (0.89 m/s) |
31.6 kW | 22.1 kW | 9.4 kW | 12.6 kW | 11.1 kW | 6.3 kW | 18.9 kW |
| Shape | Pressure Response | Recommended Wall | Manufacturing Note |
|---|---|---|---|
| Cylinder | Ideal. Pure hoop tension, no bending. | 5mm Al / 4mm SS | Standard pressure vessel fabrication. |
| Stadium | Flat sections bulge outward, inducing bending at semicircle junctions. | 6mm Al / 5mm SS | Requires internal frames or corrugated sections to prevent "oil canning" of flat walls. |
| Ellipse | Variable curvature creates bending moments. Major axis experiences compression. | 6mm Al / 5mm SS | Wall must resist ovalization. Bulkheads every 2m recommended. |
| Lenticular | High bending at equator. Tends to circularize. | 8mm Al / 6mm SS | Requires external ring stiffeners or heavier wall at midsection. |
| Kamm-Tail | Sharp tail edge creates stress concentration. Complex gradient of forces. | 8mm Al / 6mm SS | Tail section requires machined solid stock or heavy reinforcement, not just plate forming. |
| Thick Airfoil | Trailing edge problematic similar to Kamm-tail. Leading edge OK. | 8mm Al / 6mm SS | Internal ribs required to maintain shape under pressure. |
Impact/buckling load at 4 MPH (1.79 m/s) lateral current: approximately 21.3 kN (4,800 lbf) per cylinder.
For non-circular sections, the flat or curved sides facing the load have higher section modulus than a cylinder, potentially resisting buckling better if the load is aligned with the major axis. However, if loaded on the minor axis (thin direction), they are weaker.
Offers 30% drag reduction vs. cylinder at only 30% cost increase. Maintains 4-leg per container shipping efficiency. Flat sides simplify internal mounting of equipment. 10 PSI pressure achievable with minor internal framing.
Total Project Cost (4 legs): ~$49,000
70% drag reduction vs. cylinder. Moderate shipping penalty (3/container). Good pressure vessel characteristics with proper wall thickness. Optimal for solar-constrained power budgets.
Total Project Cost (4 legs): ~$52,000
Power Saved @ 2 MPH: 22 kW → 3.5 kW (solar array reduction possible)
Lowest drag and weight, but shipping costs double (2/container). Only recommended if speed >2 MPH is routine or if deploying locally without container shipping. Complex fabrication requires specialized shipyard.
Warning: Poor structural efficiency for internal pressure.
At 63% thickness, this shape offers no hydrodynamic advantage over a Stadium yet costs 40% more and ships poorly. True airfoil benefits require t/c < 20%, incompatible with your buoyancy/volume constraints.
Teardrop with Truncated Tail (Modified Kamm): Consider a 3:1 length-to-width ellipse with a flat cut at the trailing 10% (Kamm effect). This provides:
Dimensions: 4.0' width × 2.5' thickness (30 ft length)
Estimated Cost (Al): $13,500 per leg
Drag @ 2 MPH: ~1,100 N (25% of cylinder)