This design transitions from a box-frame platform to a cylindrical pressure vessel concept. This shape offers superior hydrodynamic efficiency, reduced wind drag, and exceptional torsional rigidity compared to a rectangular frame.
The primary advantage of this design over the rectangular leg-platform is Torsional Rigidity.
When your angled legs lift unevenly (e.g., front-left up, back-right up), they apply a twisting force (torque) to the hull. A rectangular box frame resists this poorly unless heavily braced with X-bracing. A cylinder, however, is naturally the strongest shape for resisting torsion. The "skin" of the cylinder acts as a continuous shear web.
Because the legs are angled at 45 degrees and exert significant outward force countered by cables, the attachment points on the hull are critical stress concentrators.
To meet your requirement of no welding during assembly, we will use an ASME-style flange connection system adapted for marine use.
Aluminum is lighter than steel, but because this is a large diameter pressure vessel, the plate thickness must be significant to handle the 10 PSI internal pressure and wave slamming loads without buckling.
| Component | Estimated Weight | Notes |
|---|---|---|
| Hull Shell (Skin) | ~14,500 lbs | Based on 0.625" (5/8") thick plate for 12ft diameter @ 10PSI + safety factor. |
| Internal Bulkheads | ~3,000 lbs | 4 major bulkheads for leg mounts + 2 intermediate stiffeners. |
| Flanges & Bolts | ~2,500 lbs | Heavy duty connection rings and hundreds of high-tensile bolts. |
| End Caps | ~2,000 lbs | Hemispherical spun aluminum. |
| Total Hull Weight | ~22,000 lbs | Empty weight. |
Note: This is heavier than your original steel estimate because a 12ft diameter tube requires much thicker material to resist bending than a 4ft wide leg. However, this hull provides significantly more buoyancy reserve.
Fitting a 12ft diameter object into a 40ft container (which is roughly 7.7ft wide internally) requires splitting the cylinder longitudinally (like a hot dog bun) or transversely (like a salami).
Recommended Approach: Transverse Split (3 Sections)
Logistics Warning: A 12ft diameter object generally requires a Flat Rack shipping container or specialized oversize transport. It will not fit inside a standard "Dry Van" container unless the cylinder diameter is reduced to under 8 feet or split longitudinally into halves (which complicates the bolting seal significantly).
Can it be done? Yes. The cylindrical aluminum design is structurally superior for torsion and drag.
Bolted Assembly? Yes, using heavy flanges. However, factory welding is required to attach those flanges initially.
Weight? Expect the hull to weigh around 22,000 lbs. With your 8,000 lbs payload and batteries, total displacement will be ~35,000 lbs. This is well within the buoyancy capabilities of a 12ft x 50ft cylinder (which can displace over 200,000 lbs if fully submerged, or ~100,000 lbs at 50% submersion).
Critical Change: To fit in a standard container, you must either reduce the diameter to 8 feet or use Flat Rack shipping. If you stick to 12ft diameter, you are looking at specialized shipping logistics.