Weather & Navigation Analysis: Caribbean Seastead

Based on your design specifications (40x16 ft living area, 45-degree column supports, ~30,000 lbs displacement) and your proposed location (Anguilla and the Lesser Antilles), here is an analysis of the weather challenges and mobility constraints for your seastead.

Design Note

Your design resembles a semi-submersible platform (like a mini oil rig). This is excellent for stability in swells but presents a high profile to the wind. The 2.5m propellers provide significant thrust, but your "hull" creates immense drag compared to a streamlined ship.

1. The "1 MPH" Reality Check: Storm Avoidance

Your calculation of moving 75 miles in 3 days is mathematically correct (24 miles/day), but operationally, this speed creates specific vulnerabilities regarding storm avoidance.

The Math of Evasion

System Speed: A tropical wave or developing storm typically moves at 10–15 MPH (often accelerating to 20+ MPH as it develops). A major hurricane can have a forward speed of 15-25 MPH.
Size of Systems: A tropical storm or hurricane is not a point; it is a massive field. The "danger zone" (where sea states become dangerous for a small seastead) can extend 200–300 miles from the center.
Evasion Failure: If a storm is 500 miles away and moving toward you at 15 MPH, you have roughly 33 hours before it arrives. In that time, moving at 1 MPH, you will travel only ~33 miles. You cannot outrun the storm, and you cannot move far enough to exit the wide radius of dangerous seas.

Conclusion: You cannot practice "active storm avoidance" (running away) with a 1 MPH vessel. Your strategy must be "Positional Avoidance"—being in the safest geographic location before the season starts, or moving slowly to a "safe harbor" (lee of an island) days before a threat develops.

2. Wave Heights: The "15 Foot" Assumption

You asked if you should expect waves over 15 feet outside of hurricane season. The answer is yes, absolutely.

North Atlantic Swells (November - March)

While you may avoid hurricanes (June-Nov), the winter months bring the "North Swell" season. Powerful low-pressure systems far in the North Atlantic generate long-period swells that travel thousands of miles south into the Caribbean.

Frequency: These swells arrive every 3–5 days during peak winter.
Height: It is common to have 10–15 foot swells in the open Caribbean waters during winter, with occasional sets reaching 18–22 feet.
Effect on Seastead: Because your seastead is small (40ft length), you will experience significant vertical motion. However, the period (time between waves) of these swells is long (12-18 seconds). Your platform should handle this well, acting like a buoy, but the motion will be noticeable.

Wind Waves vs. Swells

Outside of hurricanes, the Trade Winds blow consistently from the East at 15-25 knots. This generates "wind chop" or local waves of 4–8 feet on top of any underlying swells. These are short and steep. Because your columns are fixed at 45 degrees and have high drag, these short, steep waves may cause vibration and "slamming" if the structure isn't tightly tensioned.

3. The "Lee Side" Strategy

Your plan to stay on the downwind (lee) side of the Lesser Antilles is your most effective safety measure.

How the Islands Help

Islands like Anguilla, St. Martin, St. Kitts, and the Virgin Islands act as giant breakwaters.

Wind Shadow: The wind drops significantly within 5–10 miles of the lee shore.
Wave Shadow: The islands block the full force of the Atlantic swells. While swells do refract (bend) around the corners of islands, the wave energy on the Caribbean side (west side) is typically 30-50% of that on the Atlantic side (east side).

Warning - The "Corner Effect": While the center of the lee side is calm, the corners of islands (where the Atlantic meets the Caribbean) are dangerous. Swells wrap around these corners, creating confused, crossing seas. Do not anchor or drift near the northernmost or southernmost tips of islands during winter swells.

4. Currents and Propulsion

The Caribbean Current flows generally West to Northwest.

Speed: It averages 0.5 to 2 knots.
Your Propulsion: At 1 MPH (~0.87 knots), you are slower than the current in some passages.
The Eddy Strategy: This is your smartest move. By using eddies (reverse currents that form behind islands), you can "hitchhike" and effectively double your speed relative to the ground without extra power.
Risk: If you drift into the main Caribbean Current without power, you will be swept helplessly. You must ensure your solar/battery bank can provide 24/7 maneuvering capability, as you lack the speed to "push through" a strong current.

5. Summary of Recommendations

Weather Windows

Do not rely on a 3-day window to move away from a storm. Use weather windows to move between islands only when you have 5–7 days of calm forecast.

Safe Haven Strategy

Instead of trying to roam the open sea, adopt a "Island Hopping" doctrine. Stay within 10 miles of the lee coast of the islands. If a storm approaches, move close to shore (with proper permits/anchors) where the island blocks the wave energy.

Structural Stress

Your cable system will face "snap loads" in steep Caribbean wind waves. Ensure the cables are tensioned to prevent slack-snap cycles. The 15-foot swells will likely not stress the cables as much as the 6-foot short-period chop caused by local trade winds.