This is a fascinating and highly multifaceted project. Combining seastead prototype testing with a commercially viable Smart eFAD (electronic Fish Aggregating Device) is a brilliant way to fund R&D while providing real value to the local Anguillian community. 

Here are the answers to your questions, followed by the interactive HTML calculator.

### eFADs & Towing Physics
**Have others made solar/thruster FADs?** 
Yes, but mostly for industrial purse-seine tuna fishing (companies like Zunibal and Satlink). These are usually passive satellite buoys with solar panels. *Actively propelled* FADs relocating under their own power are very rare and mostly experimental. Your concept of a USV towing a dumb FAD, or acting as the FAD itself, is novel for artisanal fishing.

**Force to tow a traditional FAD at 0.25 MPH?**
A traditional artisanal FAD has a lot of net, rope, and drag in the water. At 0.25 MPH (0.22 knots), water drag is exponentially lower than at higher speeds, but the wetted area is huge. Estimate: **15 to 30 lbs of continuous thrust**. 

**Force for an "easy tow" FAD?**
If you design a FAD specifically for low drag (horizontal slats instead of vertical netting, streamlined floats, minimal rope exposure), you could reduce this to **5 to 10 lbs of thrust**. Your Blue Robotics M200 thrusters (which put out about 2-3 lbs of thrust each) would easily handle this at low RPM.

**Can 0.25 MPH maintain control using eddy currents?**
0.25 MPH is very slow. Ocean currents around Anguilla regularly run 0.5 to 1.5 knots. You cannot fight the current at 0.25 MPH. However, if you "surf" the currents—using predictive ocean current models (like Copernicus or OSCAR data)—you can maneuver your way back toward the island. You won't hold a strict position, but you can keep it from drifting out to the open Atlantic and loop it back toward Island Harbor.

### Fish Behavior & Attraction
**Will the 1:4 scale seastead act as a FAD by itself?**
Yes. Fish aggregate under three things: **Shade, Structure, and Turbulence**. Your 1:4 scale model (roughly 17.5 ft wide, 5 ft legs) provides a large shadow. The 3 legs and 3 stabilizers provide physical structure. The small turbulence from the thrusters mimics a school of baitfish breathing. It will absolutely attract fish.

**Will moving at 0.25 MPH still attract fish?**
Yes. In fact, a very slow drift is often *better* than a stationary FAD because it creates a constant subtle wake and covers more water, increasing the chance of pelagic fish encountering it. 

**How long to aggregate fish, and will they stay if it moves?**
- **Baitfish & small pelagics (jacks, ballyhoo):** Hours.
- **Dolphinfish (Mahi) & Tuna:** 2 to 4 days for a solid biomass. 
If you start moving at 0.25 MPH, Mahi and Wahoo will absolutely follow the structure. They follow drifting debris for months across the ocean. Just don't exceed 1 MPH or they will fall behind.

**Will fish follow into shallow water / the drop-off?**
This is where your idea is incredibly smart. Pelagic fish (Mahi, Tuna, Wahoo) are highly sensitive to water temperature and depth. If you drag the FAD from 1000ft water into 100ft water over a flat bottom, the fish will scatter. *However*, the drop-off 5-6 miles NE of Island Harbor is a sheer cliff. The fish will follow the FAD right along that drop-off because the upwelling and depth remain comfortable for them. You can bring them right to the fishermen's doorstep.

**Underwater lights?**
100% yes. Underwater green/white LED lights at night are a massive force multiplier. They attract phytoplankton, which attracts baitfish, which attracts the predators. 

**Acoustic detection (Microphones)?**
Fish absolutely make noise. Snapping shrimp, grunts, and tuna clicks are loud. However, you need **hydrophones** (underwater microphones), not air microphones. With a basic hydrophone and a Raspberry Pi running an AI audio model, you can detect fish presence, and even classify species by their sounds.

### FAD Rules of Thumb
- **Spacing:** 10 to 15 miles apart minimum. Any closer, and you split the same school of fish rather than attracting new ones.
- **Mass:** A typical artisanal FAD (ropes, net, floats) is 100–200 lbs in the water.
- **Biomass:** A mature FAD can hold 1,000 to 10,000 lbs of fish at any given time.
- **Catch:** A good visit by an artisanal fisherman yields 50–200 lbs of high-value pelagics (Mahi, Tuna, Wahoo).
- **Revisits:** Usually every 2 to 4 days. If left alone for a week or two, the biomass peaks. If fished too hard (every day), the FAD gets "spooked" and fish leave.

### Legal & Defensive Strategies
In Anguilla, the Fisheries Department regulates FADs. Usually, the person who registers the FAD has "priority rights" to fish it, but it's hard to police. Using AIS is standard, and the government will likely mandate it. 

Your idea of running away at high speed if another boat approaches is legally gray but practically hilarious and effective. A USV is legally a "vessel," and you are allowed to navigate it. Just be careful not to violate maritime right-of-way rules if a boat gets close.

***

### Economic Calculator
Here is the interactive web calculator for your eFAD economics. You can save this as an `.html` file and open it in any browser.

```html
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Smart eFAD Economics Calculator</title>
    <style>
        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            background-color: #f4f7f6;
            color: #333;
            margin: 0;
            padding: 20px;
            display: flex;
            flex-direction: column;
            align-items: center;
        }
        .calculator {
            background: #fff;
            padding: 30px;
            border-radius: 10px;
            box-shadow: 0 4px 15px rgba(0,0,0,0.1);
            max-width: 600px;
            width: 100%;
        }
        h1 {
            color: #2c3e50;
            text-align: center;
            margin-bottom: 5px;
        }
        h2 {
            color: #2980b9;
            font-size: 1.2em;
            text-align: center;
            margin-top: 0;
            font-weight: normal;
        }
        .input-group {
            margin-bottom: 15px;
        }
        label {
            display: block;
            margin-bottom: 5px;
            font-weight: 600;
            color: #34495e;
        }
        input[type="number"] {
            width: 100%;
            padding: 10px;
            border: 1px solid #bdc3c7;
            border-radius: 5px;
            font-size: 16px;
            box-sizing: border-box;
        }
        .result {
            margin-top: 30px;
            padding: 20px;
            background: #e8f4f8;
            border-left: 5px solid #2980b9;
            border-radius: 5px;
        }
        .result h3 {
            margin: 0 0 10px 0;
            color: #2c3e50;
        }
        .profit-number {
            font-size: 2em;
            font-weight: bold;
            color: #27ae60;
        }
        .loss-number {
            font-size: 2em;
            font-weight: bold;
            color: #e74c3c;
        }
        .breakdown {
            margin-top: 15px;
            font-size: 0.9em;
            color: #555;
            line-height: 1.5;
        }
    </style>
</head>
<body>

<div class="calculator">
    <h1>eFAD Economics Calculator</h1>
    <h2>Anguilla Smart FAD Business Model</h2>

    <div class="input-group">
        <label for="costUsv">1. Cost of USV ($)</label>
        <input type="number" id="costUsv" value="12000" min="0" step="100">
    </div>

    <div class="input-group">
        <label for="costFad">2. Cost of Dumb FADs ($)</label>
        <input type="number" id="costFad" value="500" min="0" step="50">
    </div>

    <div class="input-group">
        <label for="fadsPerUsv">3. Dumb FADs per USV</label>
        <input type="number" id="fadsPerUsv" value="6" min="1" step="1">
    </div>

    <div class="input-group">
        <label for="lifeUsv">4. Months till unrecoverable loss of USV</label>
        <input type="number" id="lifeUsv" value="12" min="1" step="1">
    </div>

    <div class="input-group">
        <label for="lifeFad">5. Months till unrecoverable loss of dumb FADs</label>
        <input type="number" id="lifeFad" value="8" min="1" step="1">
    </div>

    <div class="input-group">
        <label for="daysBetween">6. Days between FAD visits</label>
        <input type="number" id="daysBetween" value="3" min="1" step="1">
    </div>

    <div class="input-group">
        <label for="lbsPerVisit">7. Lbs of fish caught per FAD visit</label>
        <input type="number" id="lbsPerVisit" value="80" min="0" step="5">
    </div>

    <div class="input-group">
        <label for="pricePerLb">8. Price of fish ($/lbs)</label>
        <input type="number" id="pricePerLb" value="7" min="0" step="0.5">
    </div>

    <div class="input-group">
        <label for="operatorShare">9. % of fish sales $ going to USV operator</label>
        <input type="number" id="operatorShare" value="30" min="0" max="100" step="1">
    </div>

    <div class="result">
        <h3>Weekly Profit / Loss</h3>
        <div id="weeklyProfit" class="profit-number">$0.00</div>
        
        <div class="breakdown">
            <div><strong>Weekly Gross Revenue:</strong> $<span id="weeklyRev">0</span></div>
            <div><strong>Weekly USV Depreciation:</strong> $<span id="weeklyDepUsv">0</span></div>
            <div><strong>Weekly FAD Depreciation:</strong> $<span id="weeklyDepFad">0</span></div>
            <div style="margin-top:10px; font-size:0.85em; color:#777;">
                *Assumes 4.33 weeks per month. Depreciation represents the cost of capital spread over expected asset life.
            </div>
        </div>
    </div>
</div>

<script>
    const inputs = document.querySelectorAll('input[type="number"]');
    const weeklyProfitEl = document.getElementById('weeklyProfit');
    const weeklyRevEl = document.getElementById('weeklyRev');
    const weeklyDepUsvEl = document.getElementById('weeklyDepUsv');
    const weeklyDepFadEl = document.getElementById('weeklyDepFad');

    function calculate() {
        // Get values
        const costUsv = parseFloat(document.getElementById('costUsv').value) || 0;
        const costFad = parseFloat(document.getElementById('costFad').value) || 0;
        const fadsPerUsv = parseFloat(document.getElementById('fadsPerUsv').value) || 0;
        const lifeUsv = parseFloat(document.getElementById('lifeUsv').value) || 1;
        const lifeFad = parseFloat(document.getElementById('lifeFad').value) || 1;
        const daysBetween = parseFloat(document.getElementById('daysBetween').value) || 1;
        const lbsPerVisit = parseFloat(document.getElementById('lbsPerVisit').value) || 0;
        const pricePerLb = parseFloat(document.getElementById('pricePerLb').value) || 0;
        const operatorShare = (parseFloat(document.getElementById('operatorShare').value) || 0) / 100;

        // Calculations
        const visitsPerWeekPerFad = 7 / daysBetween;
        const totalVisitsPerWeek = visitsPerWeekPerFad * fadsPerUsv;
        const totalLbsPerWeek = totalVisitsPerWeek * lbsPerVisit;
        
        const weeklyGrossRevenue = totalLbsPerWeek * pricePerLb;
        const weeklyOperatorRevenue = weeklyGrossRevenue * operatorShare;

        // Depreciation (Weekly = Monthly Cost / 4.33)
        const weeksPerMonth = 4.33;
        const weeklyDepUsv = (costUsv / lifeUsv) / weeksPerMonth;
        const weeklyDepFad = (costFad * fadsPerUsv / lifeFad) / weeksPerMonth;

        const totalWeeklyCost = weeklyDepUsv + weeklyDepFad;
        const weeklyProfit = weeklyOperatorRevenue - totalWeeklyCost;

        // Display Updates
        weeklyRevEl.textContent = weeklyOperatorRevenue.toFixed(2);
        weeklyDepUsvEl.textContent = weeklyDepUsv.toFixed(2);
        weeklyDepFadEl.textContent = weeklyDepFad.toFixed(2);

        if (weeklyProfit >= 0) {
            weeklyProfitEl.textContent = '$' + weeklyProfit.toFixed(2);
            weeklyProfitEl.className = 'profit-number';
        } else {
            weeklyProfitEl.textContent = '-$' + Math.abs(weeklyProfit).toFixed(2);
            weeklyProfitEl.className = 'loss-number';
        }
    }

    // Add event listeners to all inputs
    inputs.forEach(input => {
        input.addEventListener('input', calculate);
    });

    // Initial calculation
    calculate();
</script>

</body>
</html>
```