Seastead Construction Guidelines • Marine Aluminum Design

Marine Aluminum 70 ft triangular platform • 3 foil legs

Recommended Construction Standards

Key guidelines to keep your design buildable and certifiable. These recommendations are based on current classification society rules for similar vessels and floating structures.

Primary Standard

ISO 12215

Small craft — Hull construction and scantlings. Applicable for vessels up to ~24m. Your ~21m triangle falls within scope.

Classification

ABS / DNV

American Bureau of Shipping Rules for Yachts or Special Service Craft. Consider DNV for offshore elements.

Material Focus

Marine Aluminum

5083-H116 or 5086-H32 recommended. Follow AWS D1.2 structural welding code.

Applicable Standards & Guidelines

ISO 12215-5:2019

Hull construction and scantlings

Primary

Defines minimum plate thicknesses, framing, and load cases for small craft. Your design should meet or exceed these for the triangular platform.

ABS Rules for High Speed Craft

or ABS Yacht Rules (2024)

Better suited for vessels with foil legs and dynamic positioning. Addresses wave loads on small waterplane area designs.

DNV-GL Rules for Yachts

+ Offshore Service Vessels

Recommended if you plan for extended offshore operation or want higher safety factors on the legs and stabilizers.

Marine Aluminum Construction

RECOMMENDED ALLOYS

5083-H116

Best for hull and legs

5086-H32

Good corrosion resistance

6061-T6

Interior truss members

KEY CONSIDERATIONS

• Minimum plate thickness: 6–8 mm for legs, 5–6 mm for truss panels
• All welds per AWS D1.2 Structural Welding Code – Aluminum
• Use 5356 or 5183 filler wire
• Apply epoxy primer + antifouling on submerged sections

Design Impacts from Standards

Triangular Truss Platform

• ISO 12215 requires calculation of deck loads (including solar panel weight) and wind loads on the large glass surfaces
• The 7-foot truss height is excellent for stiffness, but the long 70 ft spans will need substantial top and bottom chords
• Potential impact: May need additional diagonal bracing or deeper truss members to resist torsion from the three offset legs

Foil Legs (NACA 0030)

• The 10 ft chord × 3 ft width foil must be treated as a vertical column under combined bending and torsion
• Standards require fatigue analysis at the waterline transition zone (especially important with 50% submersion)
• Potential impact: The 5° bottom slope is good for lift but may require additional internal stiffeners near the base
• RIM thruster mounts must be reinforced with doubler plates (minimum 1.5× leg wall thickness)

Stabilizer Wings

• Treated as appendages under ISO 12215-6 (rudders and appendages)
• The notch into the main foil for the wing attachment must maintain 75%+ of original section modulus
• Potential impact: Actuator loads on the elevator will require local reinforcement around the pivot point

Large Glass Enclosure

ISO 12215 and ABS have specific requirements for structural windows and large openings.

Important: Large glass areas will require engineered framing. Consider laminated glass with minimum 12.7mm thickness and marine-grade aluminum frames.

RIM Drive Thrusters

Mounting Requirements

• Minimum 12mm doubler plates around thruster penetrations
• Thruster tunnels should be designed as pressure vessels if operating at depth

Recommendation: Have the Naval Architect run CFD on thruster interaction with the NACA foils.

Helical Mooring System

When converting to a tension-leg mooring:

• Follow API RP 2SK for mooring design
• Helical anchors should be sized for 150% of maximum expected uplift
• Consider adding load cells on tension legs for monitoring

Stability Consideration

Your small waterplane area design will have excellent seakeeping but lower initial stability. ISO 12215 and ABS require intact and damage stability calculations, especially with the large enclosed volume above water.

Priority Actions Before Naval Architect Review

Area	Action	Standard Reference	Priority
Triangular Truss	Perform global finite element analysis (FEA) for wave + wind loads	ISO 12215-5	High
Foil Legs	Calculate section modulus at waterline and fatigue life	ABS HSC	High
Glass Windows	Specify structural glazing with wind load calculations	ISO 12215-3	Medium
Stabilizers	Verify attachment strength with actuator loads	ISO 12215-6	Medium

These guidelines should keep your design within the realm of buildable and classifiable structures. The Naval Architect will likely recommend specific plate thicknesses and framing details based on full load calculations.