Based on your description of a seastead with a 40x16 ft living area, 36,000 lbs weight, and propulsion via submersible mixers (up to 2,880 lbs thrust at 12.8 kW max), I've analyzed the feasibility of adding small windmills for electricity generation. This focuses on units producing 1,000 watts in 20 mph winds, suitable for a Caribbean marine environment. Assumptions include marine-grade turbines with feathering/folding blades, sourced from China. All calculations are approximate and based on standard wind turbine formulas (e.g., power output equation: P = 0.5 * ρ * A * v³ * Cp, with air density ρ ≈ 1.225 kg/m³ and efficiency Cp ≈ 0.4).
A wind turbine producing 1,000 watts at 20 mph (8.94 m/s) would typically have a peak (rated) power output higher than this, as turbines are designed to reach maximum efficiency at higher wind speeds. Based on typical small wind turbine curves, the peak rating would likely be around 1,500–2,000 watts, achieved at wind speeds of 25–30 mph (11–13 m/s). This assumes a cut-in speed of about 7–10 mph and a furling/cut-out speed of 40–50 mph to prevent damage.
For 1,000 watts at 20 mph, the rotor (blade) diameter would be approximately 8–10 feet (2.4–3 meters). This is derived from the swept area needed to capture sufficient wind energy: roughly 5–7 m² of swept area, leading to a diameter calculation of about 2.7–3 meters. Smaller diameters are common for marine turbines to reduce drag and improve durability in high winds.
The force exerted by the wind on the turbine (which translates to drag or "push" on the seastead) can be estimated using the momentum theory. At 1,000 watts output in 20 mph winds, the axial force (thrust) on the rotor is approximately 150–250 pounds (670–1,100 N). This is a rough calculation: Force ≈ (2P / v), where P is power and v is wind speed, yielding about 225 lbs at peak efficiency. In practice:
Overall, for your 0.5–1 mph speed, this drag is manageable given your 2,880 lbs total thrust capacity, but it could increase power consumption slightly when heading upwind.
Yes, marine wind turbines with feathering (adjusting blade pitch to reduce lift) or folding blades are available. These features allow the turbine to "idle" in strong winds or when not needed, minimizing drag to near-zero (similar to a bare mast). Examples include models from brands like Rutland or Chinese equivalents (e.g., from suppliers on Alibaba). Feathering is automatic via centrifugal governors or manual/electronic controls, making them suitable for your setup to avoid excess drag during upwind movement or storms.
Marine-grade wind turbines on yachts typically last 5–10 years with regular maintenance, but the salty ocean environment accelerates wear on bearings, seals, and electronics due to corrosion. Expect more frequent issues like blade erosion or generator failures in humid, salty conditions. With proper sealing (e.g., IP67-rated components) and annual inspections, you could achieve 7–8 years of reliable service. They're not as maintenance-free as solar panels, but not drastically worse than other marine equipment like pumps or winches.
Sourcing marine-grade, feathering/folding wind turbines rated for ~1,000 watts at 20 mph from China (e.g., via Alibaba or manufacturers like IstaBreeze or similar), the cost per unit would be approximately $800–1,500, including shipping and basic mounting hardware. For 4 units: $3,200–6,000 total. This assumes bulk purchase; prices could drop to $600–1,000 per unit for direct factory orders.
Each turbine (including rotor, generator, and basic mount) would weigh about 50–80 pounds (23–36 kg). For 4 units: 200–320 pounds total. This is lightweight enough not to significantly impact your 36,000 lbs seastead stability, especially mounted on the 4-foot-wide columns.
Wind turbines can produce noticeable noise, typically 40–60 dB at 10–20 feet away in 20 mph winds (similar to a conversation or light traffic). With your rubber isolation between columns and the main cabin, vibration transmission would be minimized, keeping interior noise low (under 40 dB, like a quiet room). However, aerodynamic whooshing from blades could still be audible outside or in strong winds. Overall, it's tolerable for most users, especially if mounted away from sleeping areas, but sensitive individuals might find it annoying during gusts.
Is 4 of this size reasonable?
Yes, 4 turbines (one per column) make sense for redundancy and balanced power generation (up to 4,000 watts total at 20 mph). They complement your solar setup well in the windy Caribbean, providing backup during cloudy periods or at night. The added drag is minor compared to your thrust capacity, and feathering reduces issues.
Should we go even larger?
Not necessarily—larger turbines (e.g., 15–20 ft diameter for 2,000–3,000 watts at 20 mph) would add more weight (100+ lbs each), drag (300–500 lbs force), and cost ($2,000+ each), potentially complicating stability on your 50x74 ft float base. Stick to this size unless you need significantly more power.
Should we just have 1 in case it is cloudy for too long for our solar?
One would provide basic backup (~1,000 watts), but for a 36,000 lbs seastead with 12.8 kW propulsion draw, 4 offers better reliability and distribution. If budget/space is tight, start with 2 for balance.
Do windmills break so much faster than everything else?
They do require more maintenance than solar panels (e.g., bearing lubrication every 6–12 months), but they're comparable to your submersible mixers in durability. In a marine environment, expect similar failure rates to other moving parts—annoying but manageable with spares. Overall, I recommend proceeding with 4: the benefits (diversified energy, wind assistance downwind) outweigh the cons for your design.