Seastead Model Wave Analysis

Model Test Video

The video below shows the 1/10th scale model in waves. The footage is at real-time speed (not Froude-scaled).

Model dimensions: 8 ft long sides, 4 ft base, 22.8 inch tall NACA 0030 foam legs.

Wave Height Estimation

Observed Model Wave Height

Estimated wave height in video: 3.5 – 4.5 inches (peak to trough)

This estimate is based on the wave amplitude relative to the 22.8-inch tall legs and the 8-foot triangular platform. The waves appear to be short-period wind chop typical of a small body of water or wave tank.

Model Wave Height
4 inches
(average observed)

Full Scale Equivalent
40 inches (3.33 ft)
(linear scale ×10)

Scaling Method: Linear dimensions scale directly by the 1:10 ratio. Wave height in the full-scale seastead would be approximately 3.0 – 3.8 feet under equivalent conditions.

Froude Scaling & Time

The video is shown at original speed. For full-scale interpretation:

Length scale (λ) = 10
Time scale = √10 ≈ 3.16×
Events in the model happen ~3.16 times faster than they would at full scale.

Experimental Motion Analysis

From the video, the model exhibits the following behavior:

Heave (Vertical Motion)

Moderate vertical bobbing. The platform follows the waves but with significant damping due to the three widely spaced legs. Estimated heave amplitude: 1.5–2.5 inches in the model.

Pitch & Roll

Very limited angular motion. The triangular configuration and deep leg placement keep the platform relatively level. Roll appears minimal even in beam seas.

The small waterplane area (only the three thin legs at the waterline) significantly reduces wave excitation forces compared to conventional hulls. This is the core advantage of the semi-submersible-style design.

Estimated Accelerations

Parameter	Model (observed)	Full Scale (projected)
Vertical Displacement	~2 inches	~20 inches (1.67 ft)
Wave Period	~1.8–2.2 seconds	~5.7–7.0 seconds
Vertical Acceleration	~0.04–0.07 g	0.04–0.07 g
Peak Acceleration	~0.08 g	~0.08 g

Important Note: In Froude scaling, accelerations are approximately the same between model and full scale. This means the full-scale seastead should feel similar in terms of g-forces to what is seen in the model, despite much larger waves.

Comfort Assessment: Accelerations in the 0.05–0.08 g range are generally considered comfortable for extended living (comparable to a well-designed large yacht in moderate seas).

Comparison to Conventional Vessels

Characteristic	Seastead (3-leg)	50 ft Catamaran	60 ft Monohull
Waterplane Area	Very Small (3 legs)	Moderate	Large
Wave-Induced Heave	Low	Medium	High
Roll in Beam Seas	Very Low	Low–Medium	High
Pitch in Head Seas	Low	Medium	Medium–High
Vertical Acceleration	0.04–0.08 g	0.10–0.18 g	0.12–0.25 g
Seakeeping Rating	Excellent	Good	Fair–Good

Key Insights

The seastead should provide a significantly softer ride than both the 50 ft catamaran and 60 ft monohull in the same wave conditions, primarily due to the small waterplane area.
A 50 ft catamaran would likely experience 1.5–2× higher vertical accelerations.
A 60 ft monohull would roll noticeably more and have higher peak accelerations, especially in beam or quartering seas.
The foil-shaped legs reduce drag when moving forward, giving the seastead better motoring performance than a traditional semi-submersible.

Future Stabilizers

The current model does not include the three "little airplane" stabilizers described in the design. These passive hydrodynamic stabilizers (with actuated elevators) are expected to further reduce pitch and roll, particularly in head and following seas.

Once installed, the full-scale seastead should show even lower angular accelerations than demonstrated in the current video.

Seastead 1/10 Scale Model