12ft Diameter × 50ft Length | Bolt-Together Design | Container Shippable
This design features a cylindrical aluminum body constructed from modular segments that bolt together without welding. The structure is optimized for torsional resistance from the outrigger leg configuration while fitting within 40-foot shipping containers.
The body uses a "ring-frame and panel" system similar to aircraft fuselage construction, adapted for marine use with bolted connections.
CROSS-SECTION VIEW (Looking from End)
Internal Ring Frame (every 5 feet)
↓
╔═══════════════════════════════════╗
║ ┌─────────────────────┐ ║
║ ╱│ │╲ ║
║ ╱ │ HABITABLE SPACE │ ╲ ║
║ │ │ │ │ ║
║ │ │ Floor Panel │ │ ║← 12 ft
║ │ ├─────────────────────┤ │ ║
║ ╲ │ Utilities/Storage │ ╱ ║
║ ╲│ │╱ ║
║ └─────────────────────┘ ║
╚═══════════════════════════════════╝
←─────────── 12 ft ────────────────→
SIDE VIEW (Modular Segments)
┌──────┐┌──────┐┌──────┐┌──────┐┌──────┐┌──────┐┌──────┐┌──────┐
│ END ││ 10' ││ 10' ││ 10' ││ 10' ││ END ││ ││ │
│ CAP ││ SEG ││ SEG ││ SEG ││ SEG ││ CAP ││ ││ │
│ 5' ││ #1 ││ #2 ││ #3 ││ #4 ││ 5' ││ ││ │
└──────┘└──────┘└──────┘└──────┘└──────┘└──────┘└──────┘└──────┘
←──────────────── 50 feet total ─────────────────→
Worst case: Front-left and rear-right legs experience +30% buoyancy while front-right and rear-left experience -30% buoyancy simultaneously (diagonal wave loading).
| Parameter | Value | Notes |
|---|---|---|
| Diagonal couple force | 2,700 lbs × 2 corners | Two corners up, two down |
| Effective moment arm | ~22 feet | Half diagonal distance to center |
| Applied torque | 5,400 × 22 = 118,800 ft-lbs | Rounded to 120,000 ft-lbs design |
| Safety factor | 2.5× | Design to 300,000 ft-lbs ultimate |
The bolted ring-frame connections must be designed to transfer this torsional shear. This is achieved through:
Selected for excellent corrosion resistance, weldability (if needed for repairs), and strength. All fasteners are 316 stainless steel with isolation compounds to prevent galvanic corrosion.
| Property | Value |
|---|---|
| Yield Strength | 28,000 psi |
| Ultimate Strength | 40,000 psi |
| Density | 0.096 lb/in³ |
| Modulus of Elasticity | 10.3 × 10⁶ psi |
| Component | Quantity | Unit Weight | Total Weight |
|---|---|---|---|
| Ring Frames | 10 | 280 lbs | 2,800 lbs |
| Longitudinal Stringers | 16 | 180 lbs | 2,880 lbs |
| Skin Panels | ~95 panels | ~27 lbs | 2,600 lbs |
| End Caps | 2 | 400 lbs | 800 lbs |
| Leg Mount Assemblies | 4 | 150 lbs | 600 lbs |
| Internal Floor Structure | 1 | 1,200 lbs | 1,200 lbs |
| Fasteners & Hardware | ~5,000 pcs | - | 400 lbs |
| Sealants & Gaskets | - | - | 100 lbs |
| Misc. Brackets & Plates | - | - | 400 lbs |
Approximately 5.4 metric tons | Budget estimate: 12,000 - 13,000 lbs with contingency
Internal: 39'5" L × 7'8" W × 7'9" H (usable ~39' × 7.5' × 7.5')
| Container # | Contents | Est. Weight |
|---|---|---|
| Container 1 | Ring frame segments (40 quarter-rings), hardware | ~3,200 lbs |
| Container 2 | Longitudinal stringers (all 80 sections), leg mounts | ~3,500 lbs |
| Container 3 | Skin panels (curved, nested), end cap segments | ~3,400 lbs |
| Container 4 | Floor structure, remaining panels, fasteners, sealants | ~2,700 lbs |
All components fit within 40-foot container dimensions:
Construct support cradle from lumber/steel to hold cylindrical shape during assembly. Level and secure on stable ground.
Bolt together quarter-ring segments into complete rings. Install in cradle at 5-foot spacing. Verify alignment and level.
Begin with bottom stringers, bolt through ring frame webs with splice plates at each joint. Work upward alternating sides.
Attach floor beams to ring frames. This provides critical torsional rigidity - complete before skin installation.
Position and bolt heavy mount brackets at four corners. These connect to multiple ring frames for load distribution.
Start at bottom, apply butyl tape to seams, position panels, install fasteners. Work circumferentially, then forward. Overlap seams shingle-style (aft over forward) for water shedding.
Bolt end cap segments together, seal flanged connection to main body. Apply additional sealant at all exterior seams.
Torque-check all fasteners, apply exterior sealant to all seams, install any penetrations (hatches, windows, etc.).
4-6 weeks with a crew of 4-6 people, depending on experience and weather conditions.
This design can be assembled entirely without field welding, using the following strategies:
RING FRAME BOLTED SPLICE (Top View)
═══════════════╗ ╔═══════════════
Ring Segment A ║ ║ Ring Segment B
═══════════════╣ ╠═══════════════
║ ║
┌───────╨─────╨───────┐
│ Splice Plate │
│ (both sides of web)│
│ ○ ○ ○ ○ ○ ○ │← 6 bolts min
│ ○ ○ ○ ○ ○ ○ │← per side
└─────────────────────┘
│ │
═══════════════╣ ╠═══════════════
Flange bolts ║ ║
═══════════════╝ ╚═══════════════
SKIN PANEL LAP JOINT (Section View)
┌──────────────────────────┐ ← Panel A
│ Butyl Tape Seal │
═══╪════════════════════╗ │
│ ║←bolt│
│ ╔═══════════════╬─────┘
│ ║ Panel B ║
└────╨───────────────╨──────
│ │
Sealant Stringer
(exterior)
| Component | Connection Method | Reason |
|---|---|---|
| Ring frame segments | Field welded | Continuous ring = 40% stronger in torsion |
| Stringers to rings | Bolted | Allows disassembly if needed |
| Skin panels | Bolted | Replaceable, inspectable |
| Leg mounts | Shop welded + field bolted | Pre-fab strength + field attachment |
Weight savings: ~800 lbs (fewer splice plates)
If welding is truly impossible, increase structure weight by ~15% for additional splice plates and larger bolt patterns. This would add approximately 1,500 lbs to the design.
| Item | Estimated Cost |
|---|---|
| Aluminum material (5086-H116) | $35,000 - $45,000 |
| Fabrication (CNC cutting, forming, drilling) | $25,000 - $35,000 |
| Fasteners and hardware | $5,000 - $8,000 |
| Sealants and gaskets | $2,000 - $3,000 |
| Shipping (4 containers) | $8,000 - $20,000* |
| Assembly equipment rental | $5,000 - $10,000 |
| TOTAL (structure only) | $80,000 - $120,000 |
*Shipping costs highly variable based on origin/destination
A bolt-together 12' diameter × 50' aluminum cylindrical seastead body is feasible with careful engineering.
The design handles torsional loads through redundant ring frames, continuous stringers, and an integrated floor torsion box. All connections can be bolted with proper friction-grip techniques.
Document Version: 1.0 | Date: 2025
This is a preliminary design study. Professional marine structural engineering review is required before fabrication.
Design considerations: ABS Rules for Building and Classing Mobile Offshore Units, AISC Steel Construction Manual (adapted for aluminum), Aluminum Design Manual (ADM)