Froude scaling rules dictate that lengths scale by 1/4, areas by 1/16, and volumes/weights by 1/64. Speed scales by the square root of the length scale ($\sqrt{4} = 2$), so the model's hull speed is half the full-scale hull speed.
| Component | Full Scale | 1:4 Scale Model |
|---|---|---|
| Triangle Sides (Left/Right) | 70 ft | 17 ft 6 in |
| Triangle Back | 35 ft | 8 ft 9 in |
| Leg Length | 19 ft | 4 ft 9 in |
| Leg Chord (Lengthwise) | 10 ft | 2 ft 6 in |
| Leg Width (Thickness) | 3 ft | 9 in |
| Stabilizer Wingspan | 12 ft | 3 ft 0 in |
| Stabilizer Chord | 1.5 ft | 4.5 in |
| Stabilizer Body | 6 ft | 1 ft 6 in |
| Elevator Span | 2 ft | 6 in |
| Elevator Chord | 6 in | 1.5 in |
| Target Weight | 36,000 lbs | 562.5 lbs (36,000 / 64) |
Wave Tipping Threshold: Because the 9-inch wide legs are spaced on an 8.75 ft (back) to 17.5 ft (sides) triangle, the roll/pitch stability is exceptionally high. To tip this vessel, a wave would need to be steep enough to physically lift two of the legs entirely out of the water, submerging the third, and pushing the Center of Gravity past the Center of Buoyancy. Given the 4.75 ft draft and wide stance, this requires wave heights exceeding 12-15 feet at short, breaking periods.
Practicality of Avoidance (999/1000 days): In the Caribbean, waves of this magnitude are virtually exclusive to hurricane-force systems or severe winter swells. With modern forecasting (NOAA, Windy, Starlink weather), you have 3-5 days of advance notice. If the drone maintains a top speed of just 3-4 knots, it can easily navigate out of the path of a slow-moving tropical system or return to Anguilla. 999 days out of 1000 is a highly practical and realistic safety margin with Starlink telemetry.
Lift Capacity: 3 stabilizers at 1:4 scale = 3 ft span x 0.375 ft chord = 1.125 sq ft each. Total foil area = 3.375 sq ft. At a lift coefficient of 0.5, 3.375 sq ft of foil generates 562.5 lbs of lift at approximately 22 knots.
Drag & Power Problem: Foiling at 22 knots requires overcoming parasitic drag from the struts, foil profile drag, and aerodynamic drag. The required thrust is roughly 80-100 lbs.
6 x Blue Robotics M200 thrusters produce a maximum combined thrust of ~54 lbs.
Recommendation: SunPower flexible monocrystalline panels (or equivalent flexible marine panels). They are encapsulated in ETFE (highly tolerant of saltwater splashes), are very lightweight (~4.4 lbs per 100W), and have high efficiency (~22-24%).
Capacity: The triangle area is roughly 135 sq ft. Assuming 85% fill factor, that's ~115 sq ft of solar. At 15 watts/sq ft, this yields approximately 1,700 Watts of solar capacity.
30% of 562.5 lbs = 168.75 lbs of LiFePO4 batteries.
At ~8 lbs per 100Wh, this equates to roughly 2.1 kWh of storage.
Hotel Load: Starlink Mini (~30W), Raspberry Pi (~5W), Cameras/Nav lights/AIS (~15W) = ~50 Watts.
Wind Impact: Into the wind, aerodynamic drag on the structure and legs will reduce speeds by ~20%. Running with the wind, speeds may increase by ~10%. The foil-shaped legs act as excellent keels to prevent sideslip when crossing the wind.
MTBF of M200: Blue Robotics does not publish a strict MTBF for continuous ocean use, but brushless DC motors in submersible housings generally have an MTBF of 3,000 to 5,000 hours in continuous operation. The primary failure points are biofouling, fishing line wrapping, and seal failures.
Redundancy Math: With 6 thrusters, you can suffer 4 failures (leaving 2 on different legs) and still maintain forward progress and steering. Assuming a 4,000-hour MTBF per thruster, the probability of suffering 4 independent failures takes well over 10,000+ hours (over 1 year of continuous 24/7 operation) before the vessel is completely disabled.
Alternative: The M200 is arguably the best choice for the price point and seaweed tolerance. Cruising speeds of 3-4 knots keep the M200 well within its efficient operating envelope.
Actuator: A waterproof sub-micro servo (e.g., Hitec HS-5086WP or similar) mounted inside the stabilizer body to control the elevator tab. You are correct—using a servo tab (elevator) to control the main wing angle means the servo only holds the small tab, while hydrodynamic forces hold the main wing. No sensor is needed on the main wing.
| Component | Cost per Unit (Est. China/Direct) | Qty | Total |
|---|---|---|---|
| Marine Aluminum (Laser cut/welded legs, triangle) | $800 | 1 | $800 |
| Blue Robotics M200 Thrusters + ESCs | $120 | 6 | $720 |
| Solar Panels (Flexible ETFE) | $400 | 1 | $400 |
| LiFePO4 Battery Cells + BMS | $350 | 1 | $350 |
| Starlink Mini | $400 | 1 | $400 |
| Electronics (Pi, Navigator, AIS, Cameras, Servos) | $450 | 1 | $450 |
| Hardware, Seals, Wiring, Flotation foam | $200 | 1 | $200 |
| Subtotal per unit | $3,320 | ||
| Total for 5 Sets | $16,600 |
| Component | Estimated Weight (lbs) |
|---|---|
| Aluminum Structure (Legs, Triangle, Struts) | 150 |
| LiFePO4 Batteries (168.75 lbs) | 169 |
| 6x M200 Thrusters + Mounts | 30 |
| Solar Panels (1,700W ~4.4lbs/100W) | 75 |
| Electronics, Wiring, Cameras, Starlink | 25 |
| Buoyancy Foam (inside top of legs/aluminum) | 20 |
| Stabilizers + Actuators | 15 |
| Total Estimated Weight | 484 lbs |
Analysis: Excellent concept. With the foil-shaped legs acting as keels, differential thrust (even from just one motor) will keep the bow pointed into the wind. The windage on the flat triangle will push the vessel backward, but the keels will ensure it tracks straight backward (or at a slight angle). It will make ground toward home if home is upwind, acting exactly like a boat in "iron" slowly feathering upwind.
Analysis: This is a brilliant and simple mechanical failsafe. A hinged flap on the bottom of the front leg (or under the triangle nose). When moving forward, hydrodynamic pressure holds it flush against the hull. If the drone stops and drifts backward, the water flow drops the flap, creating massive drag at the bow, keeping the drone pointed into the waves/wind. Recommendation: Use a simple door-hinge with a small bungee cord to pull it flush when forward motion resumes.
Analysis: Highly feasible with Starlink video, but requires practice. The "bright red rope with float" on the bow, and "V-funnel with U-catch" on the stern is a proven concept (similar to naval underway replenishment systems).
Improvement: Instead of a rigid V-funnel at the stern, use a lightweight floating catch-rope that extends out from the back corners of the triangle. The rescue drone nudges its nose between the two floating lines, sliding the target's rope into the U-catch. This is much more forgiving in choppy waves than a rigid V-hook near the waterline.
Recommendation: Raspberry Pi Compute Module 4 (CM4) on a custom carrier board (or the official IO board) with eMMC. You are absolutely right to avoid SD cards. Potting is a great idea, but you must be careful.
Daytime: Standard RPi cameras with OpenCV using color/threshold filtering will easily spot thick Sargasso mats.
Nighttime: An IR camera (like the RPi NoIR) paired with IR illuminators. Sargasso doesn't emit heat, but it creates a distinct thermal barrier and surface texture that IR reflection highlights beautifully against the dark water.
Protection: Use adhesive-lined heat-shrink tubing over all solar panel wiring joints. Even "waterproof" MC4 connectors will fail under constant wave battering. Coating the junction boxes in marine-grade RTV silicone is mandatory.
The market for small USVs is projected to be over $1 Billion by 2030, growing at ~12% CAGR.
If your parts cost ~$3,300, selling for 2x parts = $6,600 is incredibly competitive. A $6,600 USV is 1/50th the cost of a Saildrone.
Why are others so expensive?