Triangle Seastead — 1/6 Scale Model Test Analysis

Wave response estimation, Froude scaling to full scale, and comparison with conventional vessels

1. Model & Scaling Parameters

ParameterModel (1/6)Full Scale (×6)
Side length of triangle10 ft (3.05 m)60 ft (18.3 m)
Column (float) diameter8 in (0.20 m)48 in = 4 ft (1.22 m)
Column length4 ft (1.22 m)24 ft (7.3 m)
Froude length scale λ6
Froude time scale √λ√6 ≈ 2.449
Froude velocity scale √λ√6 ≈ 2.449
Froude acceleration scale1 : 1 (accelerations are preserved)
Key Froude insight: Linear dimensions (wave height, displacement amplitude) scale by λ = 6. Times and periods scale by √λ ≈ 2.45. Accelerations are the same at model and full scale — what you feel on the model is what you'd feel at full scale.

2. Wave Height Estimates from Video

Using the known 8-inch (0.20 m) column diameter and 4-foot (1.22 m) column length as visual references in the footage, the waves in the test can be bracketed as follows:

Wave Regime in VideoModel Wave Height (H)Full-Scale Equivalent (×6)
Small / calm intervals~2–3 in (5–8 cm)~12–18 in (1.0–1.5 ft)
Moderate / typical chop visible~4–6 in (10–15 cm)~24–36 in (2–3 ft)
Larger gusts / steeper waves~6–9 in (15–23 cm)~36–54 in (3–4.5 ft)

The wave periods in the model appear to be roughly 1–2 seconds. Scaled to full size: Tfull = Tmodel × √6 ≈ 2.4 – 4.9 seconds. These correspond to short wind-chop sea states — roughly Beaufort 3–4 (significant wave height Hs ≈ 2–4 ft, 0.6–1.2 m).

Summary: The video predominantly shows the equivalent of 2–4 foot seas at full scale — a typical coastal or near-shore choppy day. Some moments may reach the equivalent of ~4.5 ft seas.

3. Observed Motion Characteristics

From the (slowed) video, the following qualitative observations emerge:

3.1 Heave (vertical bobbing)

The platform shows remarkably low heave response. The small waterplane area of the three slender columns means that passing waves do not pump the platform up and down as aggressively as a conventional hull. Heave amplitude appears to be well under the wave height — estimated heave RAO (Response Amplitude Operator) ≈ 0.2–0.4 in the dominant wave frequency range.

3.2 Pitch & Roll (angular tilting)

With 60 ft between columns (full scale), the platform has an enormous restoring moment baseline. Observed angular excursions appear to be on the order of 1–3 degrees. This is very mild — the horizon barely tilts. By comparison a monohull in the same seas would be rolling 10–20° or more.

3.3 Surge, Sway & Yaw (horizontal drift, rotation)

Some slow drift and yaw are visible (the model appears un-moored or lightly tethered). These low-frequency motions are not particularly relevant to comfort — they would be controlled by mooring or station-keeping in practice.

3.4 Wave Interaction with Columns

Waves pass through the open structure with relatively little interaction. There is no slamming on the underside of the deck, suggesting adequate air-gap (deck clearance above waterline). The columns slice through the crests without generating significant spray, which is a hallmark of semi-submersible-type platforms.

4. Acceleration Estimation

Accelerations are the key metric for human comfort and structural loads. Under Froude scaling, model accelerations equal full-scale accelerations.

4.1 Vertical (Heave) Acceleration

Given the observed behaviour we can estimate:

a_heave = ω² × z_amplitude

Where:

  • z_amplitude (full scale heave): estimated 0.15 – 0.45 m (0.5 – 1.5 ft) in 2–4 ft seas
  • ω (wave circular frequency): for T = 3–5 s → ω ≈ 1.3 – 2.1 rad/s
  • But the RAO is well below 1.0 (say 0.3), so the effective heave amplitude is small
a_heave ≈ (1.5 rad/s)² × 0.3 m ≈ 0.68 m/s² ≈ 0.07 g

Estimated range: 0.03 – 0.10 g vertical acceleration in 2–4 ft seas.

4.2 Angular (Pitch/Roll) Acceleration at Deck Edge

a_angular_at_edge = θ_max × ω² × R

With θ_max ≈ 2° (0.035 rad), ω ≈ 1.5 rad/s, and R (distance from center to edge) ≈ 10 m:

a_angular ≈ 0.035 × (1.5)² × 10 ≈ 0.79 m/s² ≈ 0.08 g

4.3 Combined RMS Acceleration

a_RMS (triangle seastead) ≈ 0.05 – 0.12 g in 2–4 ft seas
These are very low accelerations. The commonly cited threshold for seasickness onset is approximately 0.1–0.15 g RMS sustained over hours. The triangle seastead appears to stay below or at the lower edge of this threshold in moderate seas.

5. Comparison with Conventional Vessels

Parameter Triangle Seastead (60 ft) 50 ft Catamaran 60 ft Monohull
Waterplane area Very small (3 × circular columns ≈ 3 × 1.17 m² = 3.5 m²) Large (~30–45 m²) Large (~35–55 m²)
Heave natural period ~15–25 s (well above wave periods) ~4–7 s ~5–8 s
Heave RAO in 3–5 s waves 0.15 – 0.35 0.6 – 1.0 0.8 – 1.2
Roll natural period ~20–40 s ~3–6 s ~6–12 s
Roll/pitch in 2–4 ft seas 1–3° 3–8° 8–20°
RMS vertical accel (2–4 ft seas) 0.05 – 0.12 g 0.15 – 0.35 g 0.20 – 0.50 g
RMS vertical accel (6–8 ft seas) 0.10 – 0.25 g 0.30 – 0.60 g 0.40 – 0.80+ g
Slamming risk Very low (open underside, high air-gap) Moderate (bridgedeck slamming) Moderate–High (bow slamming)
Seasickness likelihood (2–4 ft seas, hours) Very Low Low–Moderate Moderate–High

Why Is the Seastead So Much Better?

  1. Semi-submersible principle: The small waterplane area of the slender columns decouples the platform from the sea surface. Waves exert little vertical force on the structure because there is very little area at the waterline for them to push on.
  2. Deep draft: At 24 ft (full scale) draft, the bulk of the displaced volume is deep underwater where wave orbital velocities have decayed exponentially. Short-period wind chop (T < 6 s) barely penetrates to that depth.
  3. Wide column spacing: 60 ft between supports gives enormous righting moment and very long natural periods in pitch and roll — far above the energy-containing periods of typical wind-driven seas.
  4. Transparency to waves: Unlike a hull that blocks and reflects waves, the open column structure lets wave energy pass through with minimal interaction.

6. What Would Full Scale Feel Like?

In 2–4 ft seas (typical coastal day):
Standing on the full-scale triangle seastead would feel remarkably stable — similar to standing on a large dock or floating pier. You would perceive a gentle, slow rise and fall with a period of 15+ seconds. Tilting would be barely perceptible (1–3°). Coffee would stay in your mug. Most people would not feel seasick even after many hours.
In 6–8 ft seas (rough day, small craft advisory):
The seastead would have noticeable but gentle motion — perhaps 3–5° of tilt and 1–2 feet of heave. Still far more comfortable than any conventional boat of similar size. Comparable to being on a 200+ ft ship in those conditions.
On a 50 ft catamaran in 4 ft seas:
You would experience sharp, jerky motions with periods of 3–6 seconds, accelerations 2–5× higher, and periodic slamming sounds and shudders from waves hitting the bridgedeck. Many passengers feel unwell after 2–4 hours.
On a 60 ft monohull in 4 ft seas:
Rolling 10–20° with a ~8 second period. Walking requires handholds. Accelerations at the rail can hit 0.4–0.5 g. Seasickness is common. Loose objects slide. Sleeping is disrupted.

7. Summary Acceleration Comparison Chart

Estimated RMS accelerations in moderate (2–4 ft) seas:

Triangle Seastead: ██░░░░░░░░░░░░░░░░░░ ~0.05–0.12 g
50 ft Catamaran: ██████████░░░░░░░░░░ ~0.15–0.35 g
60 ft Monohull: ██████████████░░░░░░ ~0.20–0.50 g
Seasick threshold: ─ ─ ─ ─ ─ ┤ ~0.1–0.15 g sustained

The triangle seastead delivers 3–5× lower accelerations than a catamaran and 4–8× lower than a monohull of comparable overall size. It achieves motion performance typical of vessels or platforms many times its size.

8. Caveats & Limitations

  • Video-based estimation: Without wave probes or motion sensors on the model, all values are estimated from visual references. Actual instrumented tests would refine these numbers significantly.
  • Froude scaling limitations: Viscous drag on the slender columns doesn't scale perfectly (Reynolds number mismatch). In reality, full-scale damping may differ by 10–30%, generally in a favorable direction (relatively more damping at full scale).
  • Irregular seas: The test appears to be in wind-generated chop, not regular swell. This is actually more realistic than tow-tank regular waves for estimating real-world performance.
  • No current or wind loading: The video tests wave response only. Sustained wind and current would add mean tilt and slow drift that would be handled by moorings.
  • Deck mass and CG: The model's mass distribution may not perfectly match the intended full-scale design. A higher center of gravity at full scale could increase pitch/roll slightly.
  • Long-period swell: The test environment likely did not include long-period (10–15 s) ocean swell. In such conditions, the seastead's advantage narrows somewhat because the wavelengths become comparable to the platform size, though the semi-submersible effect still helps.

9. Conclusions

The scale model test strongly supports the viability of the triangle seastead concept.

  1. The platform demonstrates excellent wave transparency — waves pass through with minimal excitation of the structure.
  2. In conditions equivalent to 2–4 foot full-scale seas, the platform remains remarkably stable with minimal heave and only 1–3° of angular motion.
  3. Estimated full-scale accelerations of 0.05–0.12 g are at or below the seasickness threshold, making this a potentially comfortable permanent living platform.
  4. Motion performance is 3–8× better than conventional boats of comparable size, and comparable to vessels or offshore platforms many times larger.
  5. The semi-submersible column-stabilized design is a proven concept in the offshore industry (used for drilling rigs and FPSOs), and this test confirms its benefits translate to the smaller seastead scale.