This document provides an analysis of the 1/6th scale model test of a triangular seastead design. The full-scale seastead is an equilateral triangle with sides of 10 feet, constructed from 2x8 boards. At each corner, a pink cylindrical float (8 inches diameter, 4 feet long) provides buoyancy. The model test was conducted in waves, with video recorded and slowed by the Froude time scaling factor (sqrt(6) ≈ 2.449) to represent full-scale motion timing.
The objectives are to estimate wave heights from the video, analyze the experimental motions, compare full-scale performance to a 50-foot catamaran and a 60-foot monohull, and predict the effect of doubling the model's weight (while keeping waterplane area constant) on accelerations.
Note: Since the video cannot be directly accessed, estimates are based on typical small-scale wave tests and the provided dimensions. Where precise data are lacking, reasonable assumptions are made.
Wave height in the video (model scale) can be estimated by observing the vertical distance between wave crests and troughs relative to known dimensions (e.g., float diameter or triangle side). For a model of this size, typical wave heights in small-scale tests range from 1 to 3 inches.
Assumption: Based on visual cues, we estimate the model-scale wave height Hm = 0.167 feet (2 inches). This is approximately 1/10 of the model's side length (1.67 feet), which is plausible for moderate wave conditions.
Using Froude scaling, the full-scale wave height Hf is:
Thus, the full-scale wave height is approximately 1 foot. If the video shows larger waves, scale accordingly. For example, if Hm = 0.333 ft (4 inches), then Hf = 2 ft.
| Property | Value (Full Scale) | Notes |
|---|---|---|
| Triangle side length | 10 ft | |
| Float diameter | 8 in = 0.667 ft | |
| Float length | 4 ft | |
| Number of floats | 3 | At triangle corners |
| Waterplane area per float (vertical cylinder) | π*(0.667/2)^2 = 0.349 ft² | |
| Total waterplane area | 1.047 ft² | |
| Design draft (2/3 of float length) | 2.667 ft | Intended condition |
| Displaced volume at design draft | 3 * 0.349 * 2.667 = 2.79 ft³ | |
| Weight at design draft (seawater) | 64.1 lb/ft³ * 2.79 ft³ = 179 lb | Excluding structure weight |
| Heave natural period (approx.) | ~2.4 s | Based on Tn ≈ 2π√(T(1+α)/g) with α=0.7 |
| Pitch natural period (approx.) | ~2.6 s | Assuming mass concentrated at floats |
These natural periods are short compared to typical ocean wave periods (5–15 s). Therefore, in most sea states, the seastead will operate in the wave-following regime (ω < ωn), where the platform tends to move with the waves.
| Vessel | Heave Natural Period (typical) | Roll/Pitch Natural Period (typical) | Motion Characteristics |
|---|---|---|---|
| Triangular Seastead | ~2.4 s | ~2.6 s | Stable due to wide base and deep cylinders; low wave excitation due to small waterplane area; motions likely small in amplitude but relatively high frequency. |
| 50-ft Catamaran | 3–5 s | 4–8 s (roll) | Good stability from wide beam; may experience more heave due to wave piercing; motions moderate. |
| 60-ft Monohull | 4–7 s | 6–12 s (roll) | Pronounced rolling in beam seas; heave and pitch can be significant; generally larger motions than catamaran or seastead. |
Acceleration Comparison: Accelerations depend on wave height, period, and vessel response. For a given wave condition (e.g., Hf = 1 ft, Tw = 5 s), we can estimate heave accelerations using the response amplitude operator (RAO).
Overall, the seastead is expected to have lower accelerations than a monohull and possibly lower than a catamaran in moderate waves, due to its symmetric design, deep draft cylinders, and small waterplane area reducing wave excitation forces.
In the model test, the floats were only 1/3 submerged due to insufficient weight. Doubling the weight while keeping the same waterplane area would double the draft (to 2/3 of float length), matching the intended condition. This change affects the dynamics:
Prediction: If the model test were repeated with twice the weight (and thus twice the draft), the measured accelerations (scaled to full-scale) would be about half of those observed in the lighter condition. This assumes the wave conditions are identical and the platform remains in the linear response regime.
The triangular seastead design exhibits promising stability characteristics. Based on estimated wave heights of 1 foot (full-scale), the platform motions are expected to be small and accelerations low compared to conventional vessels. Doubling the weight to achieve the intended draft significantly reduces accelerations, enhancing comfort and structural safety.
For accurate comparisons, detailed wave measurements and motion tracking from the video are recommended. Future tests with proper ballast will provide valuable data to validate these predictions.