Under Froude scaling (gravity-driven wave physics), lengths scale with the ratio λ = 1/4, areas with λ², volumes/weights with λ³, speeds with √λ, and times with √λ.
| Quantity | Full Scale | 1:4 Model |
|---|---|---|
| Triangle side length | 70 ft | 17 ft 6 in |
| Triangle back width | 35 ft | 8 ft 9 in |
| Frame height (truss/body) | 7 ft | 1 ft 9 in |
| Leg length | 19 ft | 4 ft 9 in |
| Leg chord (NACA 0030) | 10 ft | 2 ft 6 in |
| Leg width (thickness) | 3 ft | 9 in |
| RIM thruster diameter | 1.5 ft | 4.5 in |
| Stabilizer wingspan | 12 ft | 3 ft |
| Stabilizer chord | 1.5 ft | 4.5 in |
| Stabilizer body length | 6 ft | 1 ft 6 in |
| Elevator span | 2 ft | 6 in |
| Elevator chord | 6 in | 1.5 in |
| Rear deck width | 5 ft | 1 ft 3 in |
| Weight | 36,000 lb | 562.5 lb |
| Speed (if full scale = 6 kn) | 6 kn | 3 kn (= 6/√4) |
| Wave period matching | T | T/2 |
For a small-waterplane trimaran like this, capsize isn't dominated by static stability alone — it's about wave steepness and wavelength relative to beam. The key thresholds:
Non-breaking swells of 6–10 ft at 10+ second period would be benign for the full scale. The 1:4 model sees equivalent conditions at ~1.5–2.5 ft at 5 sec period. Breaking seas above ~3–4 ft for the model, or ~12–15 ft for full scale, are the real tip-over risk.
Yes, in the tropical Caribbean outside hurricane season (Dec–May especially). NOAA/ECMWF forecasts reliably give 3–5 day warnings of significant swell events. With a cruise speed of 3 kn the model covers ~70 nmi/day — enough to outrun or dodge most systems if you stay within ~200 nmi of shore and monitor forecasts. The 1/1000 risk is rogue waves or unforecast squalls.
Your scaling insight is correct and important:
| Parameter | Scales as | 1:4 model vs full (relative) |
|---|---|---|
| Weight | λ³ | 1/64 |
| Solar power | λ² | 1/16 |
| Power/Weight | 1/λ | 4× better |
| Stabilizer area/weight | 1/λ | 4× better |
| Thrust/weight (same prop tech) | varies | typically 3–5× better |
So the model at "over-speed" (going faster than Froude scale) will see relatively larger waves than scaled, meaning successful sea trials on the model constitute a genuinely conservative stress test.
Each stabilizer wing: 3 ft span × 4.5 in chord = 1.125 ft². Three of them = 3.375 ft² total wing area.
That's achievable but the wings are undersized for efficient full foiling. Partial lift (reducing leg wetted area by 50%) is much easier and would cut drag significantly at 4–6 kn.
With ~3 kWh usable battery (see §9) and foiling drag perhaps 25–40 W at 6 kn, you could foil 50–80 nmi on a full battery — but realistically you'd partial-foil at 4–5 kn for hundreds of watts less drag than hullborne, extending range 30–50% over non-foiling operation on solar alone.
Recommendation: Yes — mount thrusters below the stabilizer wings so they stay immersed during partial foiling.
3" OD × 1/8" wall 6061-T6 round tubing. Moment of inertia I ≈ 0.326 in⁴; section modulus S ≈ 0.217 in³.
Yield ≈ 35,000 psi; use allowable bending stress ~20,000 psi (safety factor 1.75).
Netting tension: 40 lb per rope at 6" spacing is plenty for a taut net. Use 3mm Dyneema or polyester; pre-tension ~20 lb each leg. Panels won't sag.
Triangle area (17.5 × 17.5 × 8.75 ft triangle, isoceles): area = ½ × base × height. Height from apex to 8.75 ft base: √(17.5² − 4.375²) = 16.95 ft. Area ≈ ½ × 8.75 × 16.95 = 74.2 ft².
Each BougeRV 200W panel = 52.95" × 30.91" = 11.36 ft².
Geometric fit with edge losses in a triangle: expect ~70–75% packing efficiency.
Extending triangle sides from 17.5 ft to 19 ft would cleanly fit 6 panels = 1,200 W.
Blue Robotics does not publish an official ocean-duty MTBF. Community and BR data suggest:
Alternatives: Blue Robotics T500 (more expensive, beefier), Seabotix BTD150 (older, reliable), or the new Blue Trail Engineering Cougar magnetically-coupled thrusters (no shaft seal — much better for long ocean duty). True small RIM drives (Copenhagen Subsea, ECA) exist but start at $3–8k each. For an Anguilla patrol drone, Cougar thrusters may be the best reliability/cost balance if budget allows (~$1,500 each).
Yes — if the wing pivots freely on its balance axis and the tail (elevator) is deflected, the wing will seek the angle of attack where aerodynamic moments balance. No wing-angle sensor needed — you command tail angle and the wing follows through hydrodynamic feedback. This is exactly how trim tabs on aircraft work.
| Function | Actuator | Approx Cost |
|---|---|---|
| Elevator trim (small, underwater) | Waterproof digital servo — Savöx SW-1210SG or Blue Robotics waterproof servo ($85–$150) | $100–150 |
| Wing lock (full freedom → heave plate) | Small linear actuator w/ latch, or bistable solenoid pin lock | $60–120 |
Total per stabilizer: ~$200; three stabilizers: ~$600.
Split across 3 legs: ~56 lb per leg. With leg internal volume (19 ft × ~¾ × ~¼ ft usable cavity ≈ 3 ft³ each) that's easily accommodated.
| Item | Power (avg) |
|---|---|
| Starlink Mini | 25 W |
| Raspberry Pi CM4 + SSD | 6 W |
| 2 Cameras (IP, low-power) | 4 W |
| Nav lights (LED, avg incl. duty cycle) | 3 W |
| AIS Class B transmitter | 2 W avg (bursts 5W) |
| Sensors, GPS, IMU, radio | 3 W |
| Misc regulation losses | 5 W |
| Total hotel load | ~48 W continuous |
Caribbean daily harvest (1000W peak): ~5.5 kWh over ~6 equivalent sun hours + partial shoulder hours (~12 h useful light).
Three legs × (10 ft × 3 ft) underwater portion is wrong for model — model leg: 2.5 ft chord × 0.75 ft thick × 2.375 ft submerged. Wetted area per leg ≈ 2 × (2.5 × 2.375) = 11.9 ft², but only frontal drag matters:
Frontal area (3 legs) = 3 × (0.75 × 2.375) = 5.34 ft². NACA 0030 at 0° has Cd ≈ 0.012 based on chord area, or about 0.08 on frontal area. Plus appendage drag.
| Condition | Into wind (15 kn) | Across wind | Downwind |
|---|---|---|---|
| Day (~410 W to motors) | ~3.0 kn | ~3.8 kn | ~4.2 kn |
| Night (~250 W to motors) | ~2.3 kn | ~3.0 kn | ~3.4 kn |
| 24-h average | ~2.6 kn | ~3.4 kn | ~3.8 kn |
Daily progress: 60–90 nmi/day depending on heading to wind.
| Component | Weight (lb) |
|---|---|
| Aluminum triangle frame (3" × 1/8" tube, ~70 ft perimeter + cross members ≈ 100 ft × 1.4 lb/ft) | 140 |
| 3 aluminum legs (NACA 0030 foil, 4.75 ft, welded sheet, ~35 lb each) | 105 |
| 3 stabilizer airplanes (aluminum, ~10 lb each) | 30 |
| 5 solar panels | 40 |
| Netting + hardware | 8 |
| 6 T200 thrusters + wiring | 15 |
| Batteries (LiFePO4) | 169 |
| Electronics (Pi, Starlink, cameras, AIS, MPPT, BMS, sensors) | 20 |
| Actuators (6 servos + 3 locks) | 6 |
| Enclosure skin, glazing (polycarbonate) | 20 |
| Fasteners, sealant, misc | 10 |
| Subtotal | ~563 lb |
Right on budget. Frame tube weight is the biggest variable — if it creeps up, switch some cross members to 2" × 1/16" wall.
(1) Upwind testing + single-motor differential steering: Excellent. The legs acting as deep keels give strong directional stability when pushed downwind — genuinely sailboat-like.
(2) Auto-deploying drag plate on backward motion: Clever and passive. Suggestion: a hinged plate forward-center between the front leg and back, spring-biased down but hydrodynamically lifted when water flows bow-to-stern. Even simpler: a sea-anchor in a spring-loaded compartment that releases on an accelerometer trigger.
(3) Rope-and-float rescue by another drone: The concept is solid. Improvements:
Recommendation: Raspberry Pi CM4 on a simple carrier with eMMC. Proven Linux, huge community, CM4 is industrial-grade and runs from eMMC (no SD corruption risk). 4 GB RAM / 32 GB eMMC version is plenty.
Potting: Yes, Sylgard 184 is a great choice. It's soft enough to allow rework (can be cut out), thermally conductive enough for 6 W dissipation through a heat spreader to the heat sink. Keep the USB/Ethernet/HDMI ports clear via a plastic shroud you pour around.
Alternatives worth considering:
My pick: CM4 for reliability + a separate Jetson Orin Nano only if the Pi's vision performance isn't enough. Keep both potted; the Jetson's heatsink extends above pot compound, as you described.
Camera on a ~3 ft pole (above salt spray zone), pointing forward and slightly down. Daytime detection is easy with standard CV — sargassum has a very distinct golden-brown color signature. Night:
| Item | Per-unit cost |
|---|---|
| Marine aluminum (frame + legs + stabilizers, China custom CNC/welded) | $2,500 |
| 5 × BougeRV 200W solar panels | $1,200 |
| 6 × Blue Robotics T200 thrusters ($200 ea) | $1,200 |
| LiFePO4 battery pack (9 kWh) | $1,800 |
| Starlink Mini + service activation | $600 |
| Raspberry Pi CM4 + carrier + potting + SSD | $200 |
| 6 servos + 3 lock actuators | $600 |
| Cameras (2× 360, 1 front) | $400 |
| AIS transponder + GPS + IMU + sensors | $500 |
| MPPT controllers + BMS + wiring | $400 |
| Nav lights, mounts, fasteners, misc | $300 |
| Polycarbonate glazing + sealant | $300 |
| Netting, rope, hooks | $100 |
| Rescue system (float, rope, V-capture) | $100 |
| Total parts (per unit) | ~$10,200 |
Selling at 2× parts = ~$20,000. At volume of 20+ units, parts cost could drop to $7,500; sell price $15,000.
Market size: Global USV market ~$1.2B (2024), growing 12%/yr to ~$2.5B by 2030. Low-cost persistent solar segment is perhaps 5–10% = $60–200M addressable, growing fast.
| USV | Speed | Endurance | Weight | Price | Open Platform? | Self-Right? |
|---|---|---|---|---|---|---|
| Saildrone Explorer | 3 kn cruise (wind+solar) | 12 months | ~750 kg / 1,650 lb | Not sold — leased at ~$2,500/day | No, proprietary | Yes |
| Liquid Robotics Wave Glider | 1.5 kn avg | 12+ months | ~300 lb surface + sub | ~$250,000 | Limited SDK | Yes (low profile) |
| Ocean Aero Triton | 5 kn sail, 2 kn solar | 3 months | ~1,400 lb | ~$500,000+ | No | Yes |
| AutoNaut | 1.5–3 kn (wave-prop) | months | ~300 lb | ~$150,000+ | Limited | Yes |
| Your drone (model) | 3–4 kn cruise, 6+ kn burst | Weeks of solar-only, indefinite theoretical | 562 lb | ~$20,000 | Yes, fully open | No (but cheap enough to lose a few) |
Your competitive position: You lose on self-righting and maturity, but you beat competitors 10–25× on price, offer full open-platform customization, and have comparable speed/endurance. At $20k, you compete in a market where the next-cheapest capable persistent solar USV is Saildrone at ~$1M-equivalent lifetime lease. This is a serious market opening — the "disposable sensor platform" or "dozens of cheap eyes" buyer has almost no options today.
Self-righting is a real concern, but your tip-over threshold is decent, and at $20k a customer can deploy 5 for the cost of one AutoNaut. The rescue-drone concept strongly mitigates the non-self-righting issue.
Absolutely plausible. A larger version (say 1:2 scale, 4,500 lb, 10-kW solar) could autonomously deliver 500 lb payloads between full-scale seasteads at 4–5 kn, crossing 50 nmi in a day. The same technology stack — Starlink, Pi-based autonomy, T-series thrusters, solar, self-rescue — scales linearly. Food and Amazon delivery between a Caribbean seastead community is a very natural endpoint for this platform family.
Summary: The 1:4 model at 562 lb, ~$20k parts cost, with 9 kWh battery and 1 kW solar, is a genuinely feasible persistent ocean USV that hits a sweet spot no commercial competitor currently occupies. The scaling math works out favorably — the model is actually harder to kill than the full scale, making it an excellent testbed. Build one, put it out past the Anguilla reef, and see what you learn.