Analysis of 1/6th Scale Triangular Seastead Model
Based on the video footage provided and the parameters of your 10-foot wooden triangle model (1/6th scale), here is an analysis of the wave conditions, motion characteristics, and a prediction for your upcoming ballasted test.
1. Wave Height Estimation & Scaling
Using the 8-inch (0.67 ft) diameter pink floats as a reference ruler within the video:
- Visual Observation: The waves appear to be roughly 1/3 to 1/2 the diameter of the pink floats. They are choppy, short-crested waves typical of a wave generator or wind-blown pond.
- Model Scale Estimate: Approximately 3 to 4 inches peak-to-trough.
- Scaling Factor: 6x (Linear dimensions).
| Parameter |
Model Scale (1:6) |
Full Scale Estimate (60ft Triangle) |
| Wave Height |
~3.5 inches |
~21 inches (1.75 feet) |
| Triangle Side Length |
10 feet |
60 feet |
| Float Diameter |
8 inches |
48 inches (4 feet) |
2. Motion Analysis: Triangle vs. Catamaran vs. Monohull
In the video, the model exhibits a specific type of motion often called "jitter" or high-frequency oscillation. Because the model is very light (only 1/3 submerged), it has very little inertia.
Comparison to a 50ft Catamaran
A 50ft catamaran relies on a wide beam for stability. In these same wave conditions (approx 2ft chop):
- Catamaran: Would likely experience significant vertical acceleration (slamming) if the bridge deck is low, but generally tracks well. However, a catamaran has a large waterplane area, making it "stiff." It reacts quickly to waves.
- Triangle Seastead: The triangular design distributes the load over three points. In the video, the triangle seems to "bridge" the chop better than a single hull would, but because it is so light, it bounces on top of the water rather than cutting through it.
Comparison to a 60ft Monohull
- Monohull: A 60ft monohull has a deep draft and heavy displacement. It would roll and pitch with a long, slow period. It would not "jitter" like your model.
- Triangle Seastead: Your model currently lacks the mass to ignore the small waves. It is reacting to every tiny ripple.
Key Physics Insight (Froude Scaling):
While the speed of the motion slows down by the square root of the scale factor ($\sqrt{6} \approx 2.45$) in the full-scale version, the acceleration (G-forces) remains identical between the model and the full-scale boat. If the model looks like it is shaking violently, the full-scale version will subject its passengers to that same violent shaking, just in slow motion.
3. Prediction: The Effect of Ballast (The "What If" Scenario)
You mentioned the current test had the legs only 1/3 submerged, and you intend to ballast them to 2/3 submerged. This is a critical change.
Current State (1/3 Submerged - Light)
With only 1/3 of the column in the water, the mass of the boat is low. The "Natural Period" of the boat (how fast it bobs up and down naturally) is very short. It is likely resonating with the short, choppy waves in the test, causing the jerky motion seen in the video.
Future State (2/3 Submerged - Heavy/Ballasted)
If you add enough weight to sink the columns to 2/3 (doubling the displacement):
- Increased Inertia: The boat becomes harder to move. It takes more energy from a wave to push the boat up.
- Lower Natural Frequency: The boat will bob up and down much slower.
Math: Natural Period $T \propto \sqrt{\text{Mass}}$. If you double the mass, the period increases by $\sqrt{2} \approx 1.41$. The boat will move roughly 40% slower in its natural rhythm.
- Reduced Accelerations: Because the boat is heavier, the force of the waves ($F=ma$) results in less acceleration ($a$).
Estimate: If you double the weight, you can expect the vertical accelerations (the "jolt" you feel in your spine) to decrease by approximately 30% to 40%.
Conclusion on the Next Test
When you run the test with the ballast (2/3 submerged):
- The model will sit lower in the water, increasing the "damping" (resistance to motion) provided by the water friction against the columns.
- The motion will look much smoother and more "sedate" in the video.
- The full-scale equivalent will feel significantly more comfortable, transitioning from a "bouncy castle" feel to a stable platform feel.
Summary Verdict
The current video shows a platform that is too light for the sea state. While the triangular geometry provides excellent static stability (it won't tip over easily), the lack of mass makes it dynamically unstable (it bounces too much). Adding the planned ballast is essential. We predict the ballasted version will reduce uncomfortable accelerations by nearly half compared to the current light-weight configuration.
```