Based on design goals from seastead.ai | Generated: 2024
Geometry per Leg: 24 ft long, 3.9 ft OD (46.8 in). Submerged: 16 ft. Wall thickness: Steel 0.25" sides / 0.5" ends; Aluminum 0.5" sides / 1.0" ends. Internal pressure: 10 psi.
External pressure at 16 ft depth: ~7 psi. Net internal pressure: ~3 psi (bursting). Hoop stress $\sigma = P \cdot r / t$.
Conclusion: Both thicknesses are conservative for 10 psi. The 10 psi stiffens the shell against local buckling (wave slap) and allows leak detection.
| Component | Duplex 2205 (lbs) | Aluminum 5083 (lbs) |
|---|---|---|
| Cylindrical Shell (Sides ~22ft x 3 legs) | ~14,500 | ~7,500 |
| Dished Ends (6 total, thicker) | ~3,500 | ~3,000 |
| Internal Stiffeners/Rings (est.) | ~1,500 | ~1,000 |
| Hatches, Penetrations, Fairings | ~1,000 | ~800 |
| Total Structural Weight (Dry) | ~20,500 lbs | ~12,300 lbs |
| Factor | Duplex 2205 | Marine Aluminum |
|---|---|---|
| Material Cost (Raw) | $8–$12/lb (~$160k–$240k) | $4–$6/lb (~$50k–$75k) |
| Fabrication Difficulty | High (Specialized welding, heat control, purge gas, NDT) | Moderate (Standard marine welding, easier forming) |
| Fabrication Cost (China) | ~$150k–$200k | ~$80k–$120k |
| Total Estimated Cost (3 Legs) | $310k – $440k | $130k – $195k |
| Life Expectancy (Coated/Cathodic) | 50–100+ years (Near zero corrosion in seawater with CP) | 30–50 years (Requires meticulous coating & anodes; pitting/crevice risk) |
| Maintenance | Very Low (Inspect anodes/coating) | Moderate (Recoat cycles, anode replacement, inspection) |
| Weight Impact on Draft | Heavier -> Deeper draft or less payload | Lighter -> More payload / shallower draft |
Geometry: 3 Cylinders, Diameter = 3.9 ft ($r = 1.95$ ft), Submerged Length = 16 ft each.
Volume per leg $V = \pi r^2 h = \pi (1.95)^2 (16) \approx 191.1 \text{ ft}^3$.
Total Displaced Volume: $3 \times 191.1 = \mathbf{573.3 \text{ ft}^3}$.
Total Buoyancy Force (Seawater, 64 lbs/ft³): $573.3 \times 64 = \mathbf{36,691 \text{ lbs}} \approx \mathbf{16.4 \text{ metric tons}}$.
| Item | Weight (lbs) |
|---|---|
| 3 Aluminum Legs (Structural) | 12,300 |
| Triangle Frame & Deck Beams (Aluminum) | 6,000 |
| Pyramid Body Structure (Aluminum) | 8,000 |
| Propulsion (4 Motors + Controllers + Spares) | 1,200 |
| Solar Panels & Mounting | 2,500 |
| Batteries (2 Days Storage - see Sec 5) | 4,500 |
| House Systems (HVAC, Watermakers, Tanks, Furnishings) | 6,000 |
| Cables, Anchors, Dinghy, Safety Gear | 3,000 |
| Biofouling Allowance (Year 1) | 1,500 |
| Total Estimated Displacement (Light Ship + Systems) | ~45,000 lbs |