Your seastead’s wide, stable SWATH-like hull form, enclosed truss living area, and RIM-drive maneuverability already remove many of the classic risk factors that make sailing yachts dangerous when a crew member goes overboard. But eliminating the weather deck and the sailing duties only solves half the problem. Detection and recovery speed remain the deciding variables in survival.
Falling overboard is one of the top causes of boating fatality. In U.S. waters alone, roughly 100–150 recreational boaters die each year after falling overboard, representing roughly one-quarter of all boating deaths. Globally the number is certainly in the mid-to-high hundreds annually, although reporting is patchy outside developed boating nations.
Your estimate that a MOB event on a family yacht carries a ~50% fatality risk is in the right ballpark for open-water, cold-water, or night-time incidents without immediate detection. Once the victim is out of sight, conning a conventional hull back to the datum can take five to fifteen minutes—an eternity in cold water. A rapid-stop, self-launching retrieval system changes the survival calculus entirely.
The concept is simple: turn the phones already in pockets into continuous marine safety beacons. A base station on the seastead maintains a low-energy radio link to each phone. When the link breaks, an alarm fires. When submersion is suspected, the boat stops and backs up.
A BLE-enabled door sensor on exterior hatches can enforce a last line of defense: if the door opens and no authorized phone is within BLE RSSI range, the base station issues an immediate verbal warning through the PA and logs the event.
Your intuition is correct. BLE should be the primary radio:
The verdict: A pure BLE beacon mode is a modest battery tax. Adding continuous high-rate accelerometer polling is heavy. The right approach is to let the phone’s motion co-processor (Apple M-series motion chip, Android sensor hub) do the work.
| Mode | Approx. Battery Impact | Will It Last the Day? |
|---|---|---|
| BLE beacon (1/s, connectionless) | ~5–12% extra | Yes, easily. |
| BLE + connected GATT heartbeat | ~10–20% extra | Yes, for most modern phones. |
| BLE + Wi-Fi fallback active | ~25–45% extra | Marginal; charge at mid-day. |
| High-rate accelerometer (50–100 Hz) | ~30–60% extra | No; drains in hours. |
| Wake-on-motion (hardware interrupt only) | ~3–8% extra | Yes. |
Recommendation: Keep the default energy mode to BLE beacon + wake-on-motion. Expose the high-rate zero-G stream as an "offshore night watch" toggle that the user enables only when performing high-risk deck work.
bluetooth-central, location if you want GPS assist), and keep the paired Bluetooth accessory simulated or real. A persistent BLE connection or location callback effectively keeps the app alive.Several commercial systems have touched this space. None combine exactly your proposed open-source stack + auto-maneuver logic, but they prove the concept:
| Product / Category | How It Works | Limitation vs. Your Plan |
|---|---|---|
| OLAS (Exposure Marine) | Bluetooth tags + mobile app/base station. Alarm on disconnect or out-of-range. | App-reliant, consumer-grade integration; no boat-auto-stop logic. |
| Raymarine LifeTag | Legacy wrist-fob RF system; alarm on link loss. | Discontinued; proprietary; no phone leverage. |
| AIS MOB Beacons (Ocean Signal, Kannad) |
Dedicated DSC/AIS transmitter in a wearable. Triggers vessel AIS/DSC alarms. | Expensive per-person hardware (~$250–$400); no automated boat maneuvering; relies on crew noticing alarm. |
| Apple Watch / Garmin Fall Detection | Wearable accelerometer detects hard falls; can call emergency services. | Marine-tailored integration poor; requires cellular; not linked to vessel helm. |
| CrewWatcher / standalone apps | Various app+tag combinations. | Closed source; subscription/cloud dependent; limited vessel automation. |
The gap in the market is exactly where you are aiming: an open-source, phone-native protocol paired to a locally-run base station that can issue nav commands (stop/reverse/track) rather than merely sounding a horn.
Yes. The barrier to "Hello World" on a phone has collapsed. A prototype that passes BLE heartbeats from a Flutter or React-Native app to a Python server and plays an alarm when the link drops is a weekend project with AI assistance, not a six-month embedded ordeal.
flutter_blue_plus package, or React Native with react-native-ble-plx.bleak library scanning for manufacturer advertisements.asyncio UDP/TCP listener.The hard part is not the scaffold; it is the edge cases. AI can generate 90% of the code, but you must physically test:
Plan for a month of real-world tuning after the AI-generated MVP compiles.
Absolutely. This is the best part of the concept:
Before your seastead is even welded, this software stack could be deployed on cruising sailboats and powerboats as a real-world proving ground. It would be a genuine contribution to marine safety.
| Risk | Mitigation |
|---|---|
| False alarms from packet loss | Use a sliding window (e.g., require >60% packet loss over 5 s, or use exponential backoff). Maintain a "alert" vs "maneuver" severity ladder. |
| Phone battery dies | If the base sees a graceful OS-level disconnect vs an abrupt RF void, it can treat them differently. But a dead phone looks like a dead phone. Pair with a watchword policy: the app warns the user at 30% battery to charge; if a user exits the app intentionally, they must confirm a PIN to avoid a Silent Sentinel from triggering. |
| RF shadowing inside the truss | Place a single BLE/USB bridge in the center of the triangle. If the structure is mostly composite/glass with metal nodes, test RSSI at the extremities. Add a second receiver on the aft cross-beam if needed. |
| Submerged phone destruction | The phone only needs to survive long enough to send the zero-G alert (if enabled) and for the base to notice RF loss. After that, the phone can fail; the rescue logic is on the base station. |
| Solo sailor asleep below | The door sensor fixes this: hatch opens + no phone in pocket = immediate audible warning to the occupant. |
| App store rejection / background limits | Build the iOS version using legitimate background modes. On Android, use a foreground service with a persistent notification. Publish as open-source APK so users sideload if needed. |
| Return-to-datum precision | Record GPS at 1 Hz but also dead-reckon with IMU during the stop maneuver. RIM drives should allow holonomic-like translation to hold position on the datum. |
| Legal liability of an auto-maneuvering boat | Open-source license must disclaim warranty. Design the default marine mode to "alarm + stop" rather than "autonomous reverse" unless the user explicitly arms the maneuver logic. |
Your seastead’s geometry already makes falling overboard less likely. Your RIM drives already make recovery faster. The missing link is simply detection speed. A phone-based sentinel app, paired with a local base station, is not a fantasy—it is a low-cost software project that is entirely feasible with AI-assisted development tools today. It could be tested on existing yachts this season, refined in the open-source community, and ready to bolt onto your seastead’s navigation computer when the hull touches water.
Recommended next step: Spawn a public GitHub organization, name it something evocative (SentinelMOB, OpenSeaguard, DatumWatch), and task Claude/Cursor with generating a Flutter + Python MVP. In a few tens of hours you will have a working alarm. The rest is marine RF testing and tuning.