1:10.5 Scale Model Dimensions (in inches)

Based on Froude scaling, all lengths are scaled by a factor of 1/10.5. The following dimensions are for the scale model:

Triangle Frame

Side length: 80 in
Base (back width): 40 in
Height (front to back): 77.43 in
Floor to ceiling height: 8 in

Legs/Wings/Foils (each)

Length: 21.71 in
Chord (leading to trailing edge): 11.43 in
Thickness (width): 3.43 in

Stabilizers (little airplanes, each)

Wing-span: 13.71 in
Chord: 1.71 in
Body length: 6.86 in
Elevator wing-span: 2.29 in
Elevator chord: 0.57 in
Notch depth (25% of chord): 0.43 in

Deck Behind

Width of each side deck extending beyond triangle: 5.71 in

RIM Thrusters

Diameter: 1.71 in
Position (up from bottom of leg): 3.43 in

Total Target Weight

The full-scale weight was estimated from the buoyancy of the three legs. Each leg is approximated as a NACA 0030 foil with submerged volume calculated using a simplified area (0.5 * chord * thickness) and a submerged length of 9.5 ft (50% of 19 ft). This yields a total displaced volume of approximately 427.5 ft³. Using a seawater density of 64 lb/ft³, the estimated full-scale displacement weight is about 27,360 lbs.

Applying Froude scaling (weight scales with λ³ = 10.5³ ≈ 1157.6), the target weight for the scale model is approximately 23.6 lbs. This includes the structural weight and any necessary ballast to achieve the correct displacement. Adjustments may be needed based on actual construction materials and equipment.

Scale Wave Heights

Wave heights scale linearly with length (Froude scaling). For simulating full-scale waves of 3 ft, 5 ft, and 8 ft, use the following model wave heights:

3 ft → 3.43 in
5 ft → 5.71 in
8 ft → 9.14 in

Ensure the wave tank or test area can generate these heights consistently. Use a wave gauge to verify.

Android Apps for Recording Motion

Recommended apps for monitoring the scale model’s motion (acceleration, jerk, pitch, roll, heave) on Android phones:

Physics Toolbox Sensor Suite (Vieyra Software): Records accelerometer, gyroscope, magnetometer data with export to CSV. Highly configurable.
Sensor Logger: Simple data logger for multiple sensors. Export to file for analysis.
Accelerometer Timer: Basic app for acceleration vs. time.
Gyroscope: For precise pitch, roll, yaw measurement.

Securely mount the phone to the model to prevent it from moving independently. Calibrate sensors before testing.

Accelerations and Plate Sliding

Plates on a table begin to slide when the acceleration exceeds μ × g, where μ is the coefficient of friction (typically 0.2–0.4) and g = 32.2 ft/s². Thus, critical accelerations are between 0.2g and 0.4g (or ~6.4–12.9 ft/s²). Due to Froude scaling, model accelerations equal full-scale accelerations, so if the model experiences 0.3g, full-scale plates with μ < 0.3 will slide.

Other Metrics

Roll/Pitch Angles: Objects slide when the tilt angle exceeds arctan(μ). For μ=0.3, angle ~16.7°.
Heave Acceleration: Vertical accelerations can cause objects to bounce or topple.
Jerk: High rates of change in acceleration may affect stability.
Relative Motion: Displacement between model parts can indicate stress.

Glass of Water Experiment

Using a glass filled with water and rocks provides a visual indicator of motion. As the model pitches or rolls, water sloshing and tipping can be recorded on video. This helps qualitatively assess motion severity. To correlate with full scale, note that water sloshing frequency scales with √(scale factor), so adjust video playback speed accordingly.

Water Depth for Deep Water Waves

Deep water waves require the water depth to be greater than half the wavelength. For typical wind waves (period 3–6 s), wavelengths in full scale range from 30–120 ft. In the model (scale 1:10.5), wavelengths are 2.86–11.43 ft, so half-wavelengths are 1.43–5.72 ft.

As a rule of thumb, use a depth of at least 10 times the scaled wave height to avoid bottom effects. For the largest intended wave height (9.14 in), a model depth of ~7–8 ft would be ideal, corresponding to ~73–84 ft in full scale. In Sandy Hill Bay, try to find a location with a depth of at least 15–20 ft to ensure deep water conditions for the intended experiments.

Doll Height for Sense of Scale

To provide a sense of scale in videos, use dolls proportional to the model. An average adult height (~5.5 ft or 66 in) scales to 66 / 10.5 ≈ 6.29 in. Recommended doll height: 6–6.5 inches.

Additional Measurement Methods

Motion Capture: Use reflective markers and cameras to track model motion precisely in 3D.
Wave Gauges: Measure wave height and period to ensure scaling accuracy.
Load Cells: Measure mooring forces if the model is tethered.
GPS/DGPS: Track drift and position changes.
Pressure Sensors: Measure wave pressures on the legs.
Laser Scanners: Capture the model’s shape for comparison with design.

References

Froude scaling laws are standard for hydrodynamic model testing. For more details, see:

Hughes, G. (1993). Physical Oceanography and the Marine Environment. Pergamon Press.
Dean, R.G. & Dalrymple, R.A. (1991). Water Wave Mechanics for Engineers and Scientists. World Scientific.