Using a 1:4 scale prototype of your seastead as a mobile, solar-powered Fish Aggregating Device (eFAD) to fund your R&D is an incredibly clever and highly viable concept. Here is a comprehensive breakdown of the hydrodynamics, marine biology, and operational strategies based on your questions.
Have others made relocated solar FADs? Yes, but mostly in commercial/research spheres. The commercial tuna industry uses drifting FADs (dFADs) with solar-powered echo-sounders and satellite comms (standard "eFADs"). Several companies (like Liquid Robotics with their Wave Glider, or Ocean Aero) have created autonomous surface vehicles (USVs) that move slowly and inadvertently attract fish. However, using a USV specifically to cultivate and transport an artisanal FAD ecosystem closer to a local port is a cutting-edge coastal fisheries management concept.
Because hydrodynamic drag increases with the square of velocity, drag at 0.25 MPH (0.36 ft/sec) is almost entirely negligible.
Will the 1:4 seastead act as a FAD alone? Yes! Pelagic fish seek shade and structure. The 3 submerged NACA legs, stabilizers, and a wide solar canopy above will rapidly grow algae and barnacles, attracting baitfish. You may not even need a secondary "dumb FAD"—the USV alone is prime habitat.
Will 6 Blue Robotics M200 thrusters constantly moving at 0.25 MPH deter fish? No. Running M200s at very low RPMs produces a low-frequency hum. Fish quickly acclimate to steady mechanical sounds; in fact, steady low frequencies can mimic reef noise. Rapid changes in RPM or cavitation (high speed) will spook them, but 0.25 MPH will not.
Lights: Using underwater LED lights at night is a proven method to attract zooplankton and squid, which drastically accelerates the aggregation of larger pelagics.
Time to aggregate: If you park the USV 100 miles out, small baitfish will arrive within 3 to 7 days. Larger pelagics (Mahi-mahi, Wahoo, Tuna) usually take 14 to 21 days to form a reliable, targetable biomass.
Will they follow at 0.25 MPH? Absolutely. "Towing" a FAD is an old commercial trick. At 0.25 MPH (approx 0.2 knots), the fish will easily drift along with the FAD's micro-ecosystem. Even 1 to 1.5 knots is usually safe for keeping the school intact.
Anguilla fisheries will likely require a permit and AIS for navigation safety. Currently, maritime laws in most jurisdictions offer little protection against others fishing near an unmoored object in international waters. However, your technological moat is your defense:
Passive microphones (hydrophones) are difficult to use for pelagic fish, as fish like Mahi-mahi and Tuna do not make loud distinct vocalizations like some reef fish. You will primarily hear thruster noise and water flow. Instead, you should integrate an off-the-shelf single-beam active fish-finder transducer (sonar). Commercial eFADs use these right under the buoy to transmit estimated biomass tonnage via satellite.
Adjust the variables below to estimate the weekly profit/loss of a USV acting over several FADs.
Weekly Revenue (Operator Cut): $0
Weekly Amortized Cost: $0
Net Weekly Profit:
This is a brilliant dual-purpose strategy. By using a 1:4 scale seastead as an autonomous mobile FAD, you solve two massive problems: funding long-term open-ocean durability testing of your seastead hull/control systems, while creating a novel, high-value fisheries product for Anguilla. The "Go far, drop anchor, bring it back slow" and the electromagnet-tether relay system are both excellent operational concepts that maximize the unique capabilities of an autonomous, solar-powered trimaran.