Seastead 1:4 Scale Model Design Report

1. Froude Scaling and Model Dimensions

Using Froude scaling rules for a 1:4 linear scale model, all dimensions are reduced by a factor of 4. The target model dimensions are:

Component	Full Scale (ft)	Model Scale (ft)	Model Scale (inches)
Triangle Side Length	70	17.5	17 ft 6 in
Triangle Base (Back Width)	35	8.75	8 ft 9 in
Frame Height (Floor to Ceiling)	7	1.75	1 ft 9 in
Leg Length	19	4.75	4 ft 9 in
Leg Chord	10	2.5	2 ft 6 in
Leg Thickness (Width)	3	0.75	9 in

Target Model Weight

Weight scaling follows the cube of length (Froude scaling): W_model = W_full × (1/4)³ = W_full / 64. Assuming a full-scale displacement of approximately 150,000 lbs (estimated for a loaded seastead), the target model weight is:

Target Model Weight ≈ 2,344 lbs

Note: This is a rough estimate. Actual weight will depend on materials and equipment chosen. The weight can be adjusted by using lighter materials (e.g., carbon fiber for non-structural parts, high-efficiency batteries) to meet performance goals.

2. Wave Stability and Operational Safety

The model is designed to be tested in real ocean waves that are 4 times higher than the waves a full-scale seastead would typically experience (due to Froude scaling). This acts as stress testing for control algorithms.

Wave Conditions That Could Cause Capsize

• The design relies on three foil legs for buoyancy and stability, with active stabilizers (small airplane-like fins) for control. Capsize is most likely if:
  • Wave height exceeds the righting moment provided by the foil legs and stabilizers.
  • For the model, wave heights above ~2–3 ft (0.6–0.9 m) could begin to pose a risk, especially if combined with strong winds.
  • The high solar array creates windage, so extreme winds can exacerbate instability.
• For the full-scale, this translates to waves above 8–12 ft (2.4–3.7 m), which are typical storm conditions.

Practicality of Avoiding Extreme Waves

With modern weather forecasting (e.g., NOAA, Windy.com) and the drone's speed (see Section 6 for speed estimates), it is highly practical to avoid storm conditions. In the Caribbean:

• Typical significant wave height is under 6 ft (1.8 m) for >99% of the year.
• Storm events (waves >10 ft) are rare and predictable 3–7 days in advance.
• The drone can be remotely commanded to seek shelter or return to port when conditions deteriorate.

Based on historical data, it is reasonable to operate safely 999 days out of 1000 by avoiding storm periods. The risk of capsizing is extremely low under normal conditions, especially with active stabilizers and careful route planning.

3. Cost Estimate for 5 Sets (Parts from China)

The following is an estimate for parts that need to be purchased (excluding items you already have: trolling motors, solar panels, charge controllers, inverters, computers, Starlink, rope). Costs are based on bulk manufacturing in China and are approximate.

Component	Estimated Cost per Set (USD)	Notes
Aluminum Frame (3" Square Tubing, Truss Structure)	$800	Includes cutting, welding, corrosion coating.
Leg Foils (NACA 0030, 3 Sets)	$1,500	CNC milled foam core with fiberglass or carbon skin.
RIM Drives (6 × 1.5 ft Diameter)	$1,800	Includes motors and controllers.
Stabilizers (3 Sets, with Actuators)	$600	Small airplane-like fins with micro actuators.
Batteries (LiFePO4, ~30 kWh)	$2,000	Weight ~450 lbs; costs vary with supplier.
Electronics (Raspberry Pi CM4, AIS, Cameras, Lights)	$500	Includes encasement and basic sensors.
Miscellaneous (Fasteners, Wiring, Sensors)	$300
Total per Set	$7,500
Total for 5 Sets	$37,500

Note: Shipping, duties, and taxes are not included. Assembly labor is not included (your boys work for free). Prices may vary with supplier and material choices.

4. Solar Panel Coverage and Wattage

The triangle roof area is used for flexible solar panels (2 ft × 4 ft each, covering 8 ft²). The original 1:4 scale model triangle has:

• Base: 8.75 ft, Height: 16.94 ft, Area: ~74.12 ft².
• A maximum of 9 panels can be fitted without cutting (9 × 8 ft² = 72 ft², covering 97% of area).

If a small increase in triangle size is acceptable, we can fit 12 panels by increasing the base to 10 ft and sides to 20 ft (area ~96.8 ft²). This is a 14% increase in base length but improves solar coverage.

Solar Wattage

Typical flexible panels output ~120 W each in ideal conditions. Accounting for ~80% efficiency (shading, angle, temperature), net output per panel is ~96 W.

Configuration	Number of Panels	Gross Wattage	Net Wattage (80%)
Original 1:4 Scale	9	1,080 W	864 W
Enlarged Triangle (Optional)	12	1,440 W	1,152 W

We recommend the enlarged triangle if additional solar is needed for higher speed or longer endurance.

5. Battery Sizing

Assuming 30% of the model weight is allocated to batteries. Based on the target weight of 2,344 lbs:

• Battery weight = 0.30 × 2,344 lbs = 703 lbs.
• Using LiFePO4 batteries at ~12 lbs/kWh, total capacity = 703 / 12 ≈ 58.6 kWh.
• Usable capacity (avoiding last 20%) = 58.6 × 0.8 ≈ 46.9 kWh.

If a lighter battery is used (e.g., lithium polymer at 8 lbs/kWh), capacity could be higher, but safety and cycle life favor LiFePO4.

6. Power Consumption, Motor Watts, and Speed Estimates

Base Load (Hotel Load)

Component	Power (W)
Raspberry Pi CM4 (with accessories)	10
Starlink Mini	75
Cameras (2 × 360°)	10
LED Navigation Lights	5
AIS Transmitter	10
Total Base Load	110

Available Motor Power

Assuming 2 trolling motors (each rated 500W, total 1,000W max), and solar output of 864 W net (from 9 panels), we have:

• Daytime: Solar power 864 W minus base load 110 W = 754 W available for motors (throttled to 1,000W max if solar allows). However, to avoid over-discharging batteries during the day, we assume all surplus solar goes to motors. Motor power: 864 W (but limited by motor rating to 1,000W). Propeller efficiency ~50%, so thrust power: ~500 W.
• Nighttime: Battery provides base load and motors. To conserve battery, we limit motor power to 500W (total), giving thrust power ~250 W. This allows long endurance.

Estimated Speed (Into/Across/Down Wind)

Using simplified drag calculations (water drag from foil legs, air drag from superstructure) and the formula: v = (P_thrust / (0.5 × ρ_water × Cd_water × A_water + 0.5 × ρ_air × Cd_air × A_air))^(1/3). Assumptions:

• Water drag area (legs): 0.522 m², Cd = 0.1 (aligned).
• Air drag area (triangle front): 0.711 m², Cd = 1.0.
• Across wind: water drag area doubles, Cd = 0.2.

Condition	Thrust Power (W)	Into Wind (m/s)	Across Wind (m/s)	Down Wind (m/s)
Day	500	2.64 (5.1 kt)	1.67 (3.2 kt)	2.66 (5.2 kt)
Night	250	2.10 (4.1 kt)	1.32 (2.6 kt)	2.11 (4.1 kt)

Note: 1 m/s ≈ 1.944 knots. These are rough estimates; actual speeds will vary with sea state, currents, and exact drag coefficients.

7. Salt Spray Protection Recommendations

Salt spray can degrade cameras, solar panels, and Starlink. Recommendations:

• Cameras: Use marine-grade enclosures with IP67 or higher rating. Apply hydrophobic coating to lens. Consider a small wiper or freshwater spray system.
• Solar Panels: Flexible panels are naturally curved, reducing salt accumulation. Clean periodically with freshwater. Apply anti-corrosion spray to connections.
• Starlink: The dish has internal heating to prevent ice, but salt spray can coat the feed. Wipe with a damp cloth occasionally. Consider a protective radome (if available) or a simple plastic cover when not in use.
• General: Design all enclosures with drainage holes. Use marine-grade stainless steel or plastic fasteners. Apply dielectric grease to electrical connections.

8. Electronics and Potting

Raspberry Pi Recommendation

The Raspberry Pi Compute Module 4 (CM4) eMMC is recommended for its reliability:

• No SD card to fail.
• Wide temperature range (-40°C to 85°C for industrial grade).
• Integrated Wi-Fi and Bluetooth (for local debugging).
• Compatible with many I/O boards.

For extreme reliability, the industrial-grade CM4 (CM4I) is preferred.

Alternative Low-Power Options

• Orange Pi 5/Orange Pi 5B: Similar performance but less community support. May have higher power consumption.
• BeagleBone AI-64: More powerful, but higher power draw. Good for AI workloads.
• NVIDIA Jetson Nano: For AI/ML tasks, but higher power and cost.

For your use case, the CM4 strikes a balance between power, reliability, and ecosystem support.

Potting in Resin

Potting the electronics in thermally conductive epoxy (e.g., DP-460 or similar) is an excellent idea:

• Prevents salt water intrusion.
• Provides mechanical protection.
• Thermally conductive resin helps dissipate heat from the CPU.

Tips:

• Leave a heat sink protruding above the resin. The leg hulls are water-cooled, so embed the assembly in a metal tube within the leg for direct thermal contact.
• Ensure all connectors are sealed before potting.
• Use a potting compound with low viscosity to avoid air bubbles.

9. Rescue Drone Concept

The proposed rescue method uses a bright red rope with a float, cameras for guidance, and a V-shaped funnel to catch the rope. This is a sound concept for the following reasons:

• Simple and robust: No complex mechanisms to fail.
• Low cost: Uses standard rope and floats.
• 360° cameras provide situational awareness.

Potential improvements:

• Active gripping: Add a small motorized hook or claw that can close around the rope once engaged.
• Buoyancy aid: In case the disabled drone is upside down, the rescue drone could deploy a lift bag to right it (if feasible).
• Communication: Use automated beacons on disabled drones to aid localization.
• AI guidance: Implement computer vision to autonomously align and hook the rope, reducing operator load.

10. Market Analysis

Potential Markets

• Maritime patrol: Illegal, unreported, and unregulated (IUU) fishing surveillance.
• Ocean research: Water quality monitoring, marine mammal tracking.
• Environmental monitoring: Oil spill detection, plastic debris tracking.
• Border control and coastal surveillance.
• Communication relays and maritime internet of things (IoT).

Market Size Estimate

Global demand for USVs is growing. For small (<30 ft) USVs, estimates suggest a market of $1–2 billion by 2030, with hundreds of units annually for government and research applications. In the Caribbean alone, with many small island nations, there is a need for dozens of patrol USVs.

11. Competitive USVs

Below are two leading competing USVs that your drone would compete against:

1. Saildrone Explorer

• Speed: 5–10 knots (2.6–5.1 m/s)
• Endurance: Up to 12 months
• Range: Thousands of miles (solar-powered)
• Weight: ~1,300 lbs (600 kg)
• Cost: ~$100,000–$150,000
• Open for Custom Code: Yes, with open API
• Self-Righting: Yes (wind-powered, sail)

2. Liquid Robotics Wave Glider

• Speed: 1–2 knots (0.5–1.0 m/s)
• Endurance: Months to years (wave-powered)
• Range: Thousands of miles
• Weight: ~300 lbs (140 kg)
• Cost: ~$50,000–$80,000
• Open for Custom Code: Yes, with standard interfaces
• Self-Righting: Yes (inherently stable)

Competitive Positioning

Your drone, with an estimated parts cost of $7,500 and selling for twice that ($15,000), is significantly cheaper than competitors. It offers higher speed (up to 5 knots) and active propulsion, making it more maneuverable. However, it lacks self-righting capability, which is a risk for sales. To mitigate, emphasize modular design, ease of recovery, and the rescue system.

12. Future Possibilities

As seasteads become more common, there could be demand for autonomous delivery drones to serve them. Your platform, scaled up or down, could be adapted for:

• Food and package delivery to seasteads.
• Emergency medical supply transport.
• Mobile charging stations for electric boats.

The current 1:4 scale model is an excellent testbed for control algorithms and systems that could later be scaled to full-size delivery drones.