Scale Model Specifications
Using Froude scaling rules (length scale = 1/6), all dimensions scale by the scale factor, while time scales by the square root of the scale factor (√(1/6) ≈ 0.408), and forces scale by the cube of the scale factor (1/6³ = 1/216).
Full Scale vs. 1/6 Scale Model
| Component |
Full Scale |
1/6 Scale Model |
| Living Area |
40 ft × 16 ft (480 in × 192 in) |
80 in × 32 in (6.67 ft × 2.67 ft) |
| Column Length |
24 ft (288 in) |
48 in (4 ft) |
| Column Diameter |
4 ft (48 in diameter) |
8 in diameter |
| Column Angle |
45° |
45° (same) |
| Column Submersion |
12 ft underwater (50%) |
24 in underwater (50%) |
| Total Weight |
36,000 lbs |
166.7 lbs (target) |
| Cable Tension |
X lbs |
X/216 lbs |
| Wave Period Scaling |
T seconds |
T × 0.408 seconds |
Important: The model weight of 166.7 lbs assumes perfect geometric and density scaling. In practice, you may need to adjust ballast to achieve proper buoyancy and metacentric height similar to the full-scale design.
Cable Tension Measurement
Surgical Tubing Approach
Standard surgical tubing (latex rubber) typically has a tension range of:
- Light duty: 5-20 lbs (22-89 N)
- Medium duty: 20-50 lbs (89-222 N)
- Heavy duty: 50-100+ lbs (222-445+ N)
At 1/6 scale, forces scale by 1/216, so:
- 20 lbs in model = 4,320 lbs full scale
- 50 lbs in model = 10,800 lbs full scale
- 100 lbs in model = 21,600 lbs full scale
Note: Surgical tubing has non-linear elasticity and hysteresis, making precise tension measurement difficult. It's best for qualitative assessment only.
Digital Tension Measurement Alternatives
Instead of surgical tubing, consider these low-cost digital options available on Amazon:
- Digital Luggage Scales (e.g., "Etekcity Digital Luggage Scale") - Typically measure 0-110 lbs, cost $10-20
- Fish Scales (e.g., "Berkley Digital Fish Scale") - Waterproof options available, measure 0-50+ lbs
- Line Tension Meters - Search for "rope tension meter" or "cable tension gauge"
- DIY with Load Cell - Use a waterproof load cell with HX711 amplifier and data logger
For logging, consider connecting to an Arduino or Raspberry Pi with waterproof housing, or use a Bluetooth-enabled scale that pairs with a phone app.
Wave Simulation
Wave Height Scaling
Wave heights scale linearly with model scale (1/6):
| Full Scale Wave Height |
1/6 Scale Model Wave Height |
| 3 ft (36 in) |
6 in |
| 5 ft (60 in) |
10 in |
| 8 ft (96 in) |
16 in |
Wave Period Scaling
Wave periods scale by √(1/6) ≈ 0.408:
- If full-scale waves have 6-second period, model waves should have 6 × 0.408 ≈ 2.45-second period
- If full-scale waves have 8-second period, model waves should have 8 × 0.408 ≈ 3.26-second period
Testing Tip: In Sandy Hill Bay, position your model in different areas to find natural wave heights close to your target 6, 10, and 16 inches. Use your marked pole to verify wave heights.
Motion Measurement & Data Collection
Android Apps for Motion Sensing
- Phyphox - Excellent for acceleration, rotation, and position data. Can export data for analysis. Free.
- Physics Toolbox Suite - Comprehensive sensors including accelerometer, gyroscope, GPS. Can log data. Free.
- Sensor Kinetics - Detailed sensor data with logging capability. Paid version offers more features.
- Accelerometer Monitor - Simple app for acceleration logging. Free.
Recommended: Phyphox is ideal for your application with its data export capabilities and comprehensive sensor access.
Video with Overlay Data
Phyphox cannot overlay sensor data on video. Alternatives:
- Record separately and combine later using video editing software (DaVinci Resolve, Adobe Premiere, or even iMovie)
- Use a specialized app like "Sensor Logger" or "Data Camera" (if available for Android)
- DIY solution: Use a Raspberry Pi with camera and accelerometer, coding a Python script to overlay data
Simplest approach: Record video with one device while logging sensor data with Phyphox on another device, then synchronize and combine in post-processing using timecodes.
Acceleration Scaling & Interpretation
Acceleration Scaling
With Froude scaling, accelerations are identical between model and full scale. What you measure on the model is exactly what would occur at full scale.
Interpreting Accelerations
For plates sliding on a table:
- Static friction coefficient (μ) typically 0.3-0.5 for most surfaces
- Sliding occurs when acceleration exceeds μ × g
- For μ = 0.4, sliding occurs at ~0.4g or ~3.9 m/s²
Other useful metrics from your model:
- RMS acceleration - Good for overall motion intensity
- Peak accelerations - For extreme events
- Power Spectral Density - Shows frequency distribution of motion
- Roll/Pitch angles - Directly indicate stability
The water glass test is an excellent qualitative measure. If water doesn't spill in the model, objects won't slide at full scale under the same wave conditions (assuming identical accelerations).
Additional Measurement Methods
Recommended Additional Measurements
- Marker Tracking - Place high-contrast markers on model corners for precise motion tracking in video analysis
- Inclinometers - Simple bubble or digital inclinometers to measure static tilt
- Waterproof Sound - Record audio to correlate wave impacts with motion
- Strain Gauges - On critical structural members to measure bending
- Displacement Sensors - Laser or ultrasonic to measure heave relative to a fixed point
- Multiple Cameras - Different angles for 3D motion reconstruction if needed
Camera Setup Recommendations
- Shore Camera: Use 60+ fps for smooth slow-motion when scaled by 0.408 (2.45x slower)
- On-board Camera: Waterproof housing is essential. Consider stabilization.
- Synchronization: Use a clapper or light flash at start to sync all video and data streams
Safety Note: The 166.7 lb model is substantial. Ensure secure handling and consider using flotation devices for test personnel in the water.