```html Seastead 1/6 Scale Model – Design Notes

1/6 Scale Seastead – Design & Testing Notes

This page summarises the Froude‑scaled dimensions, weight, wave‑height targets, sensor options and measurement strategies for a 1/6‑scale model of the proposed 40 ft × 16 ft living‑area seastead.

1. Geometric Scaling (Froude‐相似)

Full‑scale values → model (scale factor λ = 1/6). All linear dimensions are divided by 6. Results are given in inches to match the request.

Full‑scale dimension	Scale factor	Model dimension (inches)	Model dimension (ft‑in)
Living‑area length = 40 ft (480 in)	1/6	480 ÷ 6 = 80 in	6 ft 8 in
Living‑area width = 16 ft (192 in)	1/6	192 ÷ 6 = 32 in	2 ft 8 in
Column length = 24 ft (288 in)	1/6	288 ÷ 6 = 48 in	4 ft 0 in
Column “width” (square cross‑section) = 4 ft (48 in)	1/6	48 ÷ 6 = 8 in	0 ft 8 in
Under‑water portion of column (half of 24 ft) = 12 ft (144 in)	1/6	144 ÷ 6 = 24 in	2 ft 0 in

All four columns keep the 45° angle of the full‑scale design – the model’s geometry is a direct miniature.

2. Target Mass (Froude‑weight scaling)

Weight scales with the volume (λ³). Using the same material density as the full‑scale structure:

Model weight = 36 000 lb × (1/6)³ = 36 000 lb ÷ 216 ≈ 166.7 lb

You can aim for ~165‑170 lb. Adjust the internal ballast (e.g., steel plates or sand) to hit this target exactly.

If you use lighter materials (e.g., foam‑core panels) you will need to add extra mass to reach the 166 lb target. The target mass is what gives you correct Froude dynamic similarity.

3. Wave‑Height Scaling

Wave height scales linearly (λ). For the three full‑scale wave heights you mentioned:

Full‑scale wave height	Model wave height (inches)	Model wave height (ft‑in)
3 ft	3 ft ÷ 6 = 6 in	0 ft 6 in
5 ft	5 ft ÷ 6 ≈ 10 in	0 ft 10 in
8 ft	8 ft ÷ 6 ≈ 16 in	1 ft 4 in

These are the target heights you should try to generate (or find on the day) at the model’s water line.

4. Cable‑Tension Measurement

4.1 Rubber (surgical) tubing

Typical latex surgical tubing has a fairly low spring constant. In laboratory tests a 5 cm long piece of 2 mm‑ID latex will start to stretch noticeably at ≈0.5–1 lb and will generally fail (rupture) somewhere between 5–10 lb depending on wall thickness. Thicker silicone tubing can go up to ~20 lb but becomes quite stiff.

Because tension scales with λ³ (the same factor as weight), a 1 lb tension in the model corresponds to:

Full‑scale tension ≈ 1 lb × 216 ≈ 216 lb

So a 5 lb max safe load in the model would map to about 1 080 lb full‑scale. For a 36 000 lb seastead the static horizontal component of each column is ~12 700 lb, far larger than 1 080 lb. Consequently, plain rubber tubing would be overloaded in the static case, and would certainly break under any realistic wave loads.

Rubber tubing can only be used as a qualitative indicator of tension changes (e.g., “tension went up by 0.2 lb”). It is not suitable for measuring the full static load.

4.2 Low‑cost waterproof digital rope‑tension loggers

You won’t find a ready‑made “rope‑tension data‑logger” on Amazon, but there are several cheap devices that can be inserted in line with a rope and can log the load.

Digital hanging scales (often sold as “digital fish scale” or “digital luggage scale”). Many are not waterproof, but you can slip them into a zip‑close waterproof bag or a small waterproof housing. Typical models:
- Etekcity 110 lb/50 kg Digital Hanging Scale – ~$20, high accuracy (±0.1 lb), backlit display, auto‑off.
- Mansoo 110 lb Digital Hanging Scale – similar price.
- “SmarterEveryDay”‑type “digital scale with USB logging” – some Chinese sellers offer a RS‑232 output, but you would need a serial‑to‑USB adapter and a data‑logging board.
Waterproof digital scales – search for “waterproof digital hanging scale”. A few models claim IPX7 (brief immersion). Example: “Brooklyn® Waterproof Digital Hanging Scale” (≈$30, 50 kg/110 lb capacity).
DIY load‑cell solution – a 50 kg load cell (≈$6) + HX711 amplifier (≈$2) + waterproof enclosure + a small Arduino or ESP32 (≈$5) gives you a custom tension logger that can write to an SD card. Total parts cost ~$20–25. You can program it to log at 10 Hz or faster.

Search terms that work well on Amazon:

“digital hanging scale waterproof”
“digital fish scale”
“load cell 50kg with HX711” (you’ll need to build it)
“tension meter rope”

If you only need a quick visual read‑out, a hanging scale placed in line will work; for continuous logging you’ll need the Arduino approach or a “Bluetooth weight scale” that can stream to a phone.

5. Acceleration & Sliding‑Plate Criteria

5.1 Froude‑scaling of acceleration

Under strict Froude similarity, acceleration (in units of g) is the same in model and full‑scale. This is because velocity scales as √λ and time scales as √λ, giving a′ = a. Therefore, the numbers you record on the 1/6 model (in g) can be directly compared to the full‑scale seastead.

5.2 When will a plate start to slide?

The threshold acceleration a_slide is given by

a_slide = μ × g

where μ is the coefficient of static friction between the plate and the surface. Typical values:

Wood on wood: μ ≈ 0.3–0.5
Metal on wood: μ ≈ 0.2–0.4
Rubber on metal: μ ≈ 0.6–0.9

Using μ ≈ 0.4 (a safe middle‑ground), the sliding threshold is about 0.4 g ≈ 13 ft/s². If your model experiences accelerations above ~0.3‑0.5 g you can expect plates to move. That same threshold applies to the full‑scale.

5.3 Other useful acceleration metrics

Peak acceleration (max g) – tells you the worst‑case jerk.
RMS acceleration – gives a measure of the overall “energy” in the motion.
Spectral content – you can FFT the accelerometer data to see dominant frequencies. Those frequencies will be the same (in Hz) as the full‑scale because time scales with √λ.
Jerks (derivative of acceleration) – useful for feeling “shock” loads.
Angular acceleration – from the gyroscope you can derive pitch‑ and roll‑rate changes.

6. Smartphone‑Based Motion Logging

6.1 Recommended Android apps

Phyphox – free, open‑source, records accelerometer, gyroscope, magnetometer, etc. You can set custom rates (up to ~100 Hz). Exports CSV. It does not embed data directly into the video stream, but you can record video with the phone’s camera while Phyphox runs in the background; later you can sync the two files.
SensorLog – similar capability, more advanced logging options, can log to a file and stream over Wi‑Fi.
AndroSensor – displays all sensor data, can log to CSV, easy UI.

6.2 Overlaying acceleration on video

No mainstream Android app currently writes sensor data directly into the video file. The typical workflow is:

Start the video recording (using the phone camera or a separate action cam).
Simultaneously start a sensor‑logging app (Phyphox, SensorLog).
After the test, import both the video and the CSV into video‑editing software (e.g., DaVinci Resolve, OpenShot, or even Windows Movie Maker).
Add a text overlay that shows the most relevant values (e.g., “Accel X: 0.12 g, Pitch: 3°”) at each time‑code. You can automate this with a small Python script if you have many runs.

Alternatively, you can use a “screen‑recording” app while the sensor values are displayed on‑screen in a separate app, then capture both the visual data and the video in one file.

6.3 What to log

At a minimum capture:

Linear acceleration (x, y, z) – to obtain heave, sway, surge.
Gyroscope (pitch, roll, yaw rate) – to derive angular motion.
Barometer (optional) – can give a rough estimate of altitude changes (heave) if you need a second source.

Set the logging rate to at least 20 Hz (the higher the better for later FFT, but watch battery & storage). Phyphox can go up to 100 Hz on most phones.

7. Visual & Additional Measurement Ideas

Water‑slosh test – a clear cup or acrylic cylinder partially filled with water (as you already plan). Record the motion with the on‑board GoPro. The slosh amplitude scales with the same geometric factor (1/6) and can be compared to full‑scale theoretical slosh models.
Wave‑height pole – a marked pole (as described) gives a direct visual measurement. If you add a small float with a magnet (reed switch) that triggers a data‑logging unit each time the water reaches a certain height, you can get a time‑series of wave heights.
Laser distance sensor – a cheap laser ranging module (e.g., VL53L0X) pointed at the water surface can log the vertical distance to the surface in real time, giving a precise heave measurement.
Pressure transducer – a waterproof pressure sensor (e.g., BMP280) placed at a known depth can record the local pressure fluctuations caused by waves. The pressure signal can be converted to wave height using the hydrostatic relation.
Strain gauges on columns – if you want to directly measure the axial load in the columns, glue a small strain gauge (≈$5) to each column and use a Wheatstone bridge + HX711 to log the strain (and thus load) in real time.
Motion‑capture (multiple cameras) – set up two or three GoPros at known positions and use open‑source software (like Tracker or OpenCV) to triangulate the 3‑D position of bright markers on the model. This gives you a clean heave/pitch/roll time‑history without attaching any electronics to the model.
RTK GPS – for centimetre‑level position tracking you could mount a small RTK GPS (e.g., u‑blox NEO‑M8P) on the model. It will log latitude, longitude and altitude at 10 Hz. This is a bit pricey (~$150) but gives absolute positioning.

8. Testing Setup in Sandy Hill Bay, Anguilla

Because the model is small enough to be handled by two people, you can either:

Tie to a mooring – use a long nylon line with a little elasticity (e.g., a bungee) to keep the model from drifting while allowing limited motion.
Have a person hold a line – a volunteer on a small boat or standing in shallow water can hold a light line attached to the model. Use a “stretchy” line (bungee) to keep the force gentle.

The location’s natural wave climate will provide the wave heights you wish to test. If the bay’s typical wave heights are lower than your targets, you can place the model in a slightly more exposed spot, or create a small “wave maker” (a weighted board you pull back and release) to generate the desired heights.

Safety first: always keep a safety line attached to the model so it cannot drift away, and be mindful of local currents and boat traffic.

9. Summary Checklist

Scale model dimensions → 80 in × 32 in living area, 48 in long × 8 in wide columns, 24 in underwater.
Target model weight → ~167 lb (ballast as needed).
Wave‑height targets → 6 in, 10 in, 16 in for 3 ft, 5 ft, 8 ft full‑scale waves.
Cable‑tension: rubber tubing only qualitative; consider a digital hanging scale or a DIY load‑cell logger.
Accelerations: record in g; sliding threshold ≈ μ × g (≈0.3–0.5 g for typical surfaces).
Smartphone apps: Phyphox (or SensorLog) for acceleration & gyroscope; record video separately and sync later.
Extra measurements: laser range, pressure sensor, strain gauges, water‑slosh cup, marked pole for wave height.
Video analysis: high‑frame‑rate camera on a tripod for motion analysis; GoPro on the model for first‑person view; combine with sensor data in post‑production.

Good luck with the test! If you need more detailed drawings, CAD files, or help with Arduino code for the load‑cell logger, just let me know.

```