Froude scaling rules: length ∝ λ, area ∝ λ², volume/weight ∝ λ³, speed ∝ √λ, time ∝ √λ. With λ = 1/4:
| Item | Full Scale | 1:4 Model |
|---|---|---|
| Triangle sides (L,R) | 70 ft | 17 ft 6 in |
| Triangle back | 35 ft | 8 ft 9 in |
| Frame height (not built on model) | 7 ft | 1 ft 9 in |
| Leg length | 19 ft | 4 ft 9 in |
| Leg chord | 10 ft | 2 ft 6 in |
| Leg thickness (30% of chord) | 3 ft | 9 in |
| Leg draft (50%) | 9.5 ft | 2 ft 4.5 in |
| Stabilizer wingspan | 12 ft | 3 ft |
| Stabilizer chord | 1.5 ft | 4.5 in |
| Stabilizer body | 6 ft | 1 ft 6 in |
| Elevator span / chord | 2 ft / 6 in | 6 in / 1.5 in |
| Thruster diameter | 1.5 ft | 4.5 in (M200 ≈ 3 in works) |
| Camera mast height | — | 4 ft (full-size, OK to keep) |
| Weight target | 36,000 lb | 562.5 lb (36000 / 64) |
| Hull speed scaling (e.g., full = 5 kt) | 5 kt | 2.5 kt (Froude scaled) |
For a small-waterplane trimaran of this beam (~8.75 ft model, 35 ft full), capsize risk increases sharply when:
Modern marine forecasts (NOAA WaveWatch III, ECMWF, PredictWind) reliably predict significant wave height 3–5 days out with ~85–95% accuracy. With a 2–3 kt avoidance speed and active routing, avoiding breaking 8+ ft seas 999/1000 days outside hurricane season in the Caribbean is realistic — but only if you treat the seasonal hurricane window (Jun–Nov) carefully and retrieve before storms.
Each stabilizer wing: 3 ft span × 0.375 ft chord = ~1.125 ft² per wing × 3 = 3.4 ft² total lift area. At 562 lb displacement and CL ≈ 0.8 in seawater (ρ ≈ 2.0 slug/ft³):
Required speed for full foiling: V = √(2W / ρ·S·CL) = √(2·562 / 2·3.4·0.8) ≈ 14.4 ft/s ≈ 8.5 kt.
Drag while foiling (L/D ~10 with small wings + strut drag) ≈ 56 lb → ≈ 1,500 W shaft. With ~80% prop and 90% ESC efficiency: ~2 kW electrical. On a ~4 kWh battery (see below), foiling endurance is ~2 hr → ~17 nm foiling burst. Not practical as a normal mode, but useful for short escapes from weather. Recommendation: Mount thrusters slightly below the stabilizer wing chord line so they stay wetted during partial foiling.
Available roof area (triangle 17.5 × 17.5 × 8.75 ft) ≈ ½ · 8.75 · 16.95 ≈ 74 ft² ≈ 6.9 m².
At ~200 W/m² installed (de-rated), 6.9 m² → ~1,380 W peak. Enlarging triangle 10% → 8.3 m² → ~1,650 W peak.
BR does not publish a formal MTBF for the M200, but field data from ocean autonomy projects (Saildrone-style users, OpenROV/Triton) and BR's own statements suggest:
With 6 thrusters and a "need 2 working on different legs" rule, using exponential failure approximation and λ = 1/4000 hr per unit:
Probability all combinations fail = complicated, but expected time until you can no longer find 2 on different legs ≈ 9,000–12,000 hours per drone (over a year of continuous use). That's quite good.
Alternatives: T200 (more efficient but clogs in sargassum — you're right to avoid), ePropulsion Navy/Spirit (too big), small CeFlux rim drives (expensive). M200 is the right call.
Yes — driving the elevator angle alone sets the main wing's trim equilibrium (classic servo-tab / flying-tail concept). No wing-angle sensor needed; the IMU on the hull measures the result.
Use a small solenoid-pulled spring-loaded pin:
| Item | Qty | Unit (USD) | Subtotal |
|---|---|---|---|
| Marine aluminum 2" angle (frame) | ~120 ft | $4/ft | $480 |
| Aluminum sheet/tube for legs (NACA shaped, welded) | 3 | $300 | $900 |
| Stabilizer airplanes (alu, machined pivot) | 3 | $180 | $540 |
| Blue Robotics M200 + Basic ESC | 6 | $220 | $1,320 |
| SunPower 170 W flex panels | 8 | $200 | $1,600 |
| LiFePO4 cells (4 kWh) | — | — | $1,000 |
| Starlink Mini + service kit | 1 | $600 | $600 |
| Raspberry Pi CM4 + carrier + Navigator | 1 | $300 | $300 |
| 360 cameras (Insta360 or RPi HQ + fisheye ×2) | 2 | $200 | $400 |
| AIS transmitter (e.g., em-trak B954) | 1 | $700 | $700 |
| Waterproof servos for stabilizers | 6 | $80 | $480 |
| Solenoid lock pins + hardware | 3 | $25 | $75 |
| Nav lights, wiring, MPPT, BMS, misc. | — | — | $600 |
| Potting (Sylgard 184), connectors, glands | — | — | $150 |
| Total per drone | ≈ $9,150 | ||
| With 5-unit China discount (~25%) | ≈ $6,900/unit |
| Component | Weight (lb) |
|---|---|
| Aluminum frame (2" angle, ~120 ft @ 0.7 lb/ft) | 85 |
| Three legs (welded marine alu shells) | 120 |
| Three stabilizer airplanes | 30 |
| Solar panels (8 × 3 lb) | 24 |
| Thrusters (6 × 1.2 lb) | 7 |
| Batteries (target 30%) | 168 |
| Electronics, Starlink, cameras, AIS | 15 |
| Wiring, MPPT, BMS, connectors | 20 |
| Servos, lock pins, fasteners | 10 |
| Ballast/trim allowance | 30 |
| Camera mast + 360 cam | 5 |
| Total | ≈ 514 lb |
| Target | 562 lb |
| Margin | ~48 lb ✅ |
30% × 562 lb = 168 lb of LiFePO4. LiFePO4 specific energy ≈ 90 Wh/lb (pack-level). → ≈ 15 kWh. Excellent — way more than I'd have guessed, because Froude scaling keeps weight while modern batteries are dense. Plenty of room in the legs (each leg interior ≈ 2.5 ft³).
| Item | Avg Watts |
|---|---|
| Starlink Mini (avg) | 25 |
| Raspberry Pi CM4 + sensors | 5 |
| 2 cameras (low-bitrate) | 4 |
| LED nav lights (avg, mostly night) | 3 |
| AIS transmitter (mostly RX) | 2 |
| IMU, MPPT idle, BMS | 2 |
| Total hotel load | ≈ 40 W |
Usable battery: 80% × 15 kWh = 12 kWh. Daily solar (Caribbean, ~5 peak-sun hours, 1,500 W array) ≈ 7.5 kWh/day.
Three legs, each underwater frontal area ≈ 0.375 ft × 2.4 ft = 0.9 ft² × 3 = 2.7 ft² (foil shape, Cd ≈ 0.05 streamwise). Wetted area dominates: total wetted ≈ 18 ft², Cf ≈ 0.003.
Drag(lb) ≈ ½ρV²·(Cd·Afront + Cf·Awet). Solving for V at 1,000 W shaft (≈ 80% prop = 800 W = 590 ft·lb/s):
| Heading | Day (1,200 W) | Night (300 W) |
|---|---|---|
| Downwind (light following sea, 10 kt wind) | ~3.5 kt | ~2.0 kt |
| Crosswind | ~3.0 kt | ~1.7 kt |
| Upwind (15 kt headwind, chop) | ~2.2 kt | ~1.0 kt |
24-hour average ≈ 2.0–2.5 kt, daily distance ≈ 50–60 nm.
Recommended: Raspberry Pi CM4 with 32 GB eMMC + 4 GB RAM on a Waveshare/Seeed carrier — yes, eMMC is far more reliable than SD over years of writes. Power ~3–5 W typical.
Competing boards:
Potting with Sylgard 184: Excellent idea — soft, thermally conductive (~0.27 W/m·K), reworkable with care. Leave heatsink + a small air pocket above the SoC, route a thermal pad up to a finned aluminum block protruding above the potting that bolts to the leg's wet aluminum wall. The leg wall is the ultimate heatsink → water-cooled. Pi will run cold even at full load.
Yes — daytime with the existing 360 cameras and a CNN (YOLO-class) is straightforward. Night: an inexpensive uncooled FLIR Lepton 3.5 or Boson works because sargassum mats are ~1–3 °C cooler/warmer than open water at night. Alternative: a low-cost green LED + camera (sargassum fluoresces weakly) or simply slow down at night and rely on open-prop M200's ability to chop through small clumps.
Yes — definitely add adhesive-lined dual-wall heat-shrink over MC4 connector joints, then a wrap of self-amalgamating rubber tape, then a final layer of UV-resistant heat shrink. Junction boxes should be filled with marine dielectric grease (Super Lube or Boeshield). This is the #1 failure mode of marine PV — well worth the 30 min/panel.
Self-rescue via differential thrust / stabilizer drag (Part 1): Excellent. The legs are daggerboards, so beam-reach drift toward upwind home is genuinely viable — this is basically a primitive sailboat.
Auto-deploying drogue (Part 2): Great idea. Use a hinged flat plate under the front leg, weighted slightly. Forward motion lifts it; reverse/drift drops it. Simple, passive, brilliant. Make sure it can't foul the front 360 camera's view.
Rope-and-float capture (Part 3): Solid concept. Suggested improvements:
Market size: the global USV market is ~$1B today, projected $4–6B by 2030. Persistent solar/wave class is ~10–15% of that. Realistic addressable slice for a low-cost entrant: $50–200M/yr.
| USV | Type | Speed | Endurance | Weight | Price | Open? | Self-righting? |
|---|---|---|---|---|---|---|---|
| Saildrone Explorer | Wind + solar | 2–5 kt avg, 8 kt max | 12 months | ~1,500 lb | Not sold; ~$2.5M build, leased $2.5k/day | No (closed) | Yes |
| Liquid Robotics Wave Glider SV3 | Wave + solar | 1–2 kt avg | 12+ months | ~350 lb (sub) + 200 lb (float) | $250–500k | Limited (APIs) | Yes |
| AutoNaut | Wave + solar | 2–4 kt | 3–6 months | ~660 lb | ~$300k | Some openness | Yes |
| Ocius Bluebottle | Sail + solar + wave | 3–5 kt | Months | ~600 kg | ~$500k+ | No | Yes |
| Your USV | Solar (active stab) | 2–3 kt avg, 5+ kt burst | Indefinite in good wx | 562 lb | ~$14k (2× BOM) | Fully open | No |
You'd be 15–35× cheaper than the cheapest competitor. This is a totally different market segment — disposable / fleet-deployable USVs. Lose one? Buy another. That changes the economics of ocean observation entirely. The main caveat: no self-righting means a single bad weather event ends a mission. Mitigations: