Froude-scaled model dimensions, weight budget, power analysis, and build recommendations for a Caribbean solar drone.
Scaling factor k = 1/4. Linear dimensions ÷ 4. Areas ÷ 16. Volumes / Weights ÷ 64. Speeds divide by √4 = 2 for true dynamic similitude, though the model can be driven faster than scale speed.
| Item | Full Scale | 1:4 Scale Model |
|---|---|---|
| Target Displacement | 36,000 lbs | 562.5 lbs |
| Tri. sides (left/right) | 70 ft | 17 ft 6 in |
| Tri. back width | 35 ft | 8 ft 9 in |
| Tri. frame height (floor to ceiling) | 7 ft | 1 ft 9 in |
| Leg / float total length | 19 ft | 4 ft 9 in |
| Leg chord (fore-aft) | 10 ft | 2 ft 6 in |
| Leg max thickness (NACA 30%) | 3 ft | 9 in |
| Leg submerged (1/2 length) | 9 ft 6 in | 2 ft 4.5 in |
| Thruster diameter (RIM drive concept) | 1 ft 6 in | 4.5 in |
| Thruster height from bottom | 3 ft | 9 in |
| Back deck width (each side) | 5 ft | 1 ft 3 in |
| Stabilizer wingspan | 12 ft | 3 ft 0 in |
| Stabilizer chord | 1 ft 6 in | 4.5 in |
| Stabilizer body length | 6 ft | 1 ft 6 in |
| Stabilizer elevator span | 2 ft | 6 in |
| Stabilizer elevator chord | 6 in | 1.5 in |
| Camera mast height | 4 ft | 1 ft 0 in |
| Camera mast diameter | 1 in | 0.25 in |
| Recovery bow rope (est.) | 4 ft | 1 ft 0 in |
Below is a realistic allocation for a 562.5 lb model built from thin-wall marine aluminum and lightweight flexible solar.
| Component | Est. Weight (lbs) | Notes |
|---|---|---|
| Aluminum triangle frame (angle extrusion + cross braces) | 45 | Use thin-wall 2" angle or 1.5" angle to keep it light. |
| 3 x Leg shells (NACA 0030, watertight) | 60 | 1/8" 5052 aluminum welded, internal ribs. Trim to save weight. |
| 3 x Stabilizers & hardware | 20 | Small aluminum frames and hinges. |
| Flexible solar panels | 90 | ~65 sq ft of semi-flexible ETFE panels. |
| Batteries (LiFePO₄) | 169 | 30% of total displacement budget; see §3. |
| Thrusters (6 × M200) + ESCs | 20 | ~3 lbs each incl. cabling. |
| Electronics (Pi, Starlink, AIS, cameras, GPS) | 12 | Starlink Mini is ~2.5 lbs alone. |
| Wiring, connectors, conduit | 25 | Marine tinned wire, IP68 connectors, fuse blocks. |
| Actuators, locking pins, servos | 15 | 3 elevator servos + locking hardware. |
| Hardware, fasteners, deck lines | 20 | All stainless or marine aluminum. |
| Mast, LED nav lights, misc. | 8 | |
| Subtotal | 484 | |
| Contingency / margin | 78.5 | For resin, coatings, extra brackets, absorbs errors. |
| Grand Total | 562.5 |
Verdict: The weight budget is tight but achievable. You must build the legs as thin-wall watertight shells and keep the frame minimal. If you find the frame is coming in heavy, switch from 2" angle to 1" or 1.5" angle with gusseted joints.
169 lbs ≈ 77 kg of LiFePO₄ battery.
Pack-level LiFePO₄ energy density is typically 40–50 Wh/lb (88–110 Wh/kg) when including BMS, casing, and wiring.
At this scale, 169 lbs of battery fits comfortably inside the dry upper halves of the three foil-shaped legs if you build custom flat or curved packs that follow the inner contour.
The full-scale triangle area is ½ × 35 ft × 67.8 ft ≈ 1,186 sq ft. At 1:4, that area becomes 74.1 sq ft. Allowing for framing, you can use roughly 65 sq ft of active panel.
Use semi-flexible ETFE monocrystalline laminate with SunPower / Maxeon or similar 22%+ efficient cells on a thin aluminum or fiberglass backsheet. Do not use heavy rigid glass panels—they will blow your weight budget on the first wave hit.
With 65 sq ft of quality cells (~15 W/sq ft practical average in tropical marine conditions):
If you enlarge the triangle slightly from the exact Froude dimensions, you can push toward 1,100+ W. At this weight, more solar is always better.
| System | Power (W) |
|---|---|
| Starlink Mini (varies with activity) | 30 |
| Raspberry Pi CM4 + carrier board | 7 |
| Navigator / autopilot / PWM board | 2 |
| 2 × small IP cameras | 6 |
| AIS transponder (avg) | 5 |
| LED navigation lights | 3 |
| Misc sensors, antennas, idle ESC draw | 5 |
| Base / Hotel Load | ~58 W |
Using a 58 W hotel load and your battery/solar constraints:
| Condition | Total Power Available | Motor Power (est.) |
|---|---|---|
| Peak Day (clear, overhead sun) | 950 W | ~800 W |
| Average Day (mix of clouds) | 450 W | ~390 W |
| Night (running on battery, 80% DoD budget) | 470 W avg over 12 hrs | ~400 W (slow and steady) |
| Night (conservative / long endurance) | 260 W avg over 20 hrs | ~200 W |
Your model is essentially a small SWATH. Drag is dominated by skin friction and pressure drag on the three submerged foil sections. The estimated speeds below assume clean aluminum fairing and minimal biofouling.
| Motor Power | Calm / Downwind | Into 15 kt Trade Wind | Across Wind |
|---|---|---|---|
| 200 W (night conservative) | 2.5–3.0 kn | 2.0–2.5 kn | 2.5–3.0 kn (some leeway) |
| 400 W (avg day/night) | 3.5–4.5 kn | 3.0–3.8 kn | 3.5–4.2 kn |
| 800 W (sprint, midday) | 5.0–6.0 kn | 4.2–5.2 kn | 5.0–5.5 kn |
Note: Because the scale model uses real ocean waves (not scaled waves), wave-making drag does not decrease the way Froude predicts. The legs see real chop, so the upper-end speeds are optimistic in seas >2 ft and assume the active stabilizers are working.
With an 8 ft 9 in beam and a very low center of gravity (batteries in the keel-like legs), this design is formidably stable in roll. However, it is not self-righting.
With Starlink weather routing and a sprint speed of 5+ knots, you can outrun or avoid most organized weather if a human is watching. But mechanical issues (seaweed, battery drain, one thruster down) can strand it.
Realistic expectation: With active weather routing and a upwind-of-home operating box, you can probably avoid dangerous breakers 95–98% of deployed days. To reach 99.9%, you need either self-righting, a much larger beam, or active station-keeping inside a protected lagoon. For Anguilla, patrolling the immediate EEZ on fair-weather days is very practical.
The three stabilizers give a combined wing area of roughly 3.4 sq ft (3 × 3 ft × 4.5 in). Could they lift part or all of the 562.5 lb model?
Conclusion: Full hydrofoiling is not practical with only 3.4 sq ft of wing. However, at 4–6 knots the stabilizers can carry 100–150 lbs of hull weight, which unloads the legs, reduces wetted drag, and makes the vessel ride flatter. Sprinting on a full battery with 800 W into the motors might yield:
If you want real foiling, you would need dedicated hydrofoils roughly double that area and ideally a fourth steering stabilizer. Thrusters should stay low (just above the leg bottom) where the waterline stays during modest lift; if the legs come fully out of the water, propulsors re-enter aerated flow and lose thrust.
Order custom-cut SunPower Maxeon Gen III cells (or equivalent shingled monocrystalline) laminated in ETFE + fiberglass backsheet to fit your triangle geometry. Alternatively, source semi-flexible "marine" 100 W panels from a Chinese OEM (e.g., Shenzhen-based flexible solar shops on Alibaba/1688), trim the corners, and wire in series-parallel.
Why: Maxeon cells have excellent low-light performance and no front-side busbars, so occasional salt film hurts performance less. ETFE sheds salt better than PET and survives flexing.
You are correct that the Blue Robotics M200 is one of the best choices for weed tolerance because the open frame sheds Sargasso better than the enclosed T200.
Recommendation: Stock spare shaft seals (Prop Shaft Seal Kits) and 1–2 spare thrusters. Perform an R&R seal service every 6 months if the drone is in the water continuously.
For a servo-tab, the actuator only needs to move the small elevator, not the whole wing. A standard waterproof hobby servo is sufficient. Because this is a USV and must survive salt, use a metal-gear servo with some form of conformal coating or a true marine servo:
Concept: Spring-loaded stainless pin engages a hole in the stabilizer root when the wing aligns with the leg (zero angle). The pin is held retracted by a small servo or solenoid. When you want to lock, command the wing to neutral; the spring pushes the pin into the hole. To unlock, the actuator retracts the pin against the spring.
Parts list (per stabilizer):
Per-stabilizer cost: ~$30–$50. Total for 3: <$150.
Tip: Design the geometry so the spring naturally drives the pin into the hole when aligned. Use a small limit switch or hall sensor to confirm "locked" state if your autopilot needs to know.
Recommended board: Raspberry Pi Compute Module 4 (CM4) with 32 GB eMMC and a compact carrier board (e.g., Waveshare CM4-NANO-A or CM4-IO-BASE) instead of a full-size Pi 5. The eMMC eliminates SD-card salt-corrosion failures.
Is potting good? Yes, provided you use a soft (low-modulus) silicone like Sylgard 184 and avoid trapping air. Use a vacuum chamber if possible. It makes the electronics almost impervious to salt spray and condensation.
The following assumes you are ordering raw materials and fabricated components from Guangdong/Zhejiang suppliers, shipping to Anguilla, and assembling locally. Aluminum fab and custom solar are the biggest line items.
| Line Item | Qty for 5 sets | Est. Cost |
|---|---|---|
| Aluminum fabrication (triangle frame + 3 legs + 3 stabilizers; laser + brake + weld) | 5 sets | $8,500 |
| Custom ETFE flexible solar laminates (~900 W per unit) | 5 sets | $2,500 |
| LiFePO₄ batteries (custom flat packs, ~7 kWh each) | 5 sets | $3,500 |
| Blue Robotics M200 thrusters | 30 units | $9,000 |
| BasicESC / comparable BLDC ESCs | 30 units | $1,500 |
| Electronics (CM4 carriers, cameras, AIS, GPS, LEDs, connectors) | 5 sets | $2,500 |
| Starlink Mini terminals | 5 | $3,000 |
| Actuators, servos, locking hardware | 15 each | $800 |
| Wiring, conduit, heat-shrink, hardware | Bulk | $800 |
| Shipping + customs to Anguilla (~5%–15% duty) | — | $2,500 |
| Total for 5 Raw Kits | ~$35,600 | |
| Per-unit parts cost | ~$7,100 | |
| Sell price at 2× parts | ~$14,200 |
This is a rough estimate. Aluminum weldments and custom battery builds have large price variance. If you buy in true volume (20+), per-unit costs drop closer to $5,000.
Anguilla sits in the Sargasso drift. For daytime avoidance, a wide-angle USB camera + Google Coral TPU or Raspberry Pi AI HAT running an edge model (YOLO or MobileNet) is absolutely viable. Train a small model to detect weed mats vs. clean water.
Night: Thermal / IR contrast over open ocean at night is poor for floating weed. Best strategy is to slow down or drift at night, using current/wind forecasts to estimate drift corridors. Avoid active transects through known weed lines after dark. If you have radar, it will not see Sargasso.
Your instinct is correct. Even "waterproof" MC4 junctions are not designed to be submerged or hit by waves repeatedly.
Verdict: Excellent and elegant. Keeping the vessel pointed upwind and letting the daggerboard-like legs drive it upwind while desalinating with one thruster is a sound survival mode. The active stabilizers can indeed induce differential drag to yaw the vessel if thrusters fail.
Verdict: A hinged "_Float-Back_ plate" that drops when ground speed reverses is a classic passive safety device. It forces the bow into the wind like a sea anchor.
Improvement: Make the plate out of thin G10/FR4 or aluminum and mount it on a stainless torsion spring so it is normally floating just below the surface. If the boat begins drifting backward, the spring geometry and the reversed flow snap it down. Add a weak-link (nylon bolt) so if it deploys in surf, it tears away rather than ripping the bow apart.
Verdict: It makes sense, but needs refinement.
Market size: Niche but growing. The "low-cost solar USV" segment is probably a $50M–$100M annual market globally, fragmented across dozens of small countries and research institutes.
| Platform | Propulsion | Size / Weight | Speed | Endurance | Est. Price | User Code? |
|---|---|---|---|---|---|---|
| Saildrone Explorer | Wind + Solar | ~22 ft / ~2,400 lbs | 2–8 kn | Up to 12 mo | $250k–$400k | API / Payload SDK |
| Liquid Robotics Wave Glider | Wave + Solar | ~2.1 m / ~90 kg | 1–3 kn | Up to 1 yr | $300k+ | Limited / proprietary |
| AutoNaut | Wave foil + Solar | 5 m / ~150–200 kg | 2–5 kn | Months | £150k–£200k | Payload friendly |
If you sell at 2× parts (~$14k), you are 20× cheaper than the alternatives. For Anguilla, a low-cost, locally serviceable, aluminum solar drone is very competitive. However, you are trading:
Bottom line: Perfect for developing-nation governments, research labs, and prosumers who want a hackable platform. Less competitive for commercial oil/gas or military users who require 99.9% uptime guarantees.
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