Seastead Convoy Mode: Systems Architecture & Implementation Guide

Overview: Convoy mode enables a fleet of identical seasteads to maintain a dynamic, grid-relative formation while transiting or station-keeping. The system relies on moving-base RTK GPS for centimeter-level relative positioning, distributed 5 GHz directional mesh networking, multi-node camera parallax for shared situational awareness, and a hybrid human/AI watch protocol. All nodes run identical containerized software for redundancy and rapid deployment.

• Moving Base RTK GPS: One designated node (rotating or fixed) acts as the RTCM base station. All others operate as RTK rovers. Relative accuracy: ±2 cm horizontally, ±4 cm vertically.
• Hardware: Dual-frequency L1/L2 GNSS receivers (e.g., u-blox F9P, Septentrio mosaic), surveyed mounting points on the rigid truss, low-LNA coaxial routing.
• Synchronization: PPS (1 Pulse Per Second) + NMEA/RTCM stream distributed over mesh. GPS time used as single source of truth for all sensors and control loops.
• Grid Alignment: Each node is assigned a local coordinate in the convoy grid (e.g., X/Y in meters relative to convoy origin). The origin drifts with the lead node or is set by mission command.

• Actuation: 6 RIM drive thrusters (2 per leg), 3 foil stabilizers with electro-hydraulic elevators.
• Controller: Model Predictive Control (MPC) or gain-scheduled PID with disturbance feedforward (wind, current, wave drift).
• Thrust Allocation: 6×2 allocation matrix handling surge, sway, yaw, and damping. Automatically redistributes thrust if a thruster fails.
• Hydrodynamics: NACA legs provide natural damping at low speeds; stabilizers adjust angle of attack for pitch/roll trim during transit.
• Convoy Behavior: Nodes maintain setpoints relative to neighbors using spring-damper virtual forces. Avoidance: repulsive fields trigger smooth lateral offsets within grid bounds.

• Camera Layout: 4 wide-angle + 2 telephoto per node, time-synced via PTP (IEEE 1588) or GPS-disciplined NTP with hardware timestamping.
• Parallax Tracking: Multi-node stereo vision + AI object detection (YOLOv8/v9 or equivalent). Baseline of 40–80m (grid spacing) enables ranging out to 2–5 NM depending on lens and pixel density.
• Track Fusion: Kalman or particle filters merge detections across nodes into a single shared track database. Tracks published via DDS/MQTT with unique IDs, position, velocity, heading, and confidence score.
• Data Sources: Cameras, AIS receivers, VHF traffic alerts, optional X-band/Solid-state radar. Fusion engine weights AIS (high certainty) vs visual (needs validation).

For convoy operations, a hybrid mesh combining directional 5 GHz Wi-Fi and low-bandwidth fallback provides optimal cost, reliability, and latency.

4.1 Hardware Recommendation

4.2 Expected Performance (5 GHz Directional)

• Range: 1.5 – 3 nautical miles reliable over water (line-of-sight, antenna height ≥ 5m above waterline). Range degrades in rain, fog, or high sea spray.
• Real-world Data Rate: 100 – 300 Mbps TCP (802.11ac/ax). Sufficient for telemetry, compressed video, voice, and database sync.
• Latency: 1 – 12 ms per hop. Mesh routing adds minimal overhead with proper AP/client topology.
• Cost Efficiency: Commodity enterprise CPEs are significantly cheaper than marine sat-comms or licensed RF systems. Open-source firmware keeps ongoing licensing at $0.

4.3 Software & Routing Stack

• Firmware: OpenWRT (stable releases) for full routing control.
• Mesh Protocol: B.A.T.M.A.N.-Adv (Layer 2) or OLSRd (Layer 3). B.A.T.M.A.N. handles dynamic link drops better in marine conditions.
• Network Segmentation (VLANs):
  • VLAN 10: Control & RTK (highest priority, QoS marked EF)
  • VLAN 20: Telemetry & Track DB (MQTT/DDS)
  • VLAN 30: Video & Camera Sync
  • VLAN 40: User/Watch Station UI & Starlink Backhaul
• Backup: LoRa mesh broadcasts heartbeat, position, and critical alerts when 5 GHz fades. Range: 3–8 NM, bandwidth: 50 kbps.

• Human-AI Hybrid: Each node has designated watch stations. AI handles routine monitoring; humans confirm anomalies, handle edge cases, and make final maneuvering decisions when required.
• Check-In Protocol: Every 10–15 minutes, watch personnel press a physical/software "I'm attentive" button. Failure to check in triggers local alert, then mesh-wide escalation, then automated safe-hold mode.
• Status Broadcasting: On-watch state, fatigue tracking (optional), and shift handover logs broadcast via LoRa/VLAN 10. Ensures no gaps in coverage.
• Alert Routing: Tiered system:
  1. Local UI + audible alarm
  2. Mesh-wide broadcast to all convoy nodes
  3. Starlink/AIS/VHF external alert to authorities or nearby vessels

• RTK Loss: Degrades to single-point GPS + IMU + visual odometry. Thrust controllers switch to position-hold drift compensation. RTK reacquires automatically when signal returns.
• Comms Loss: Node holds last valid grid position, reduces speed to 2 knots, broadcasts acoustic/VHF distress, switches to local autonomy. If comms restore >5 min, resumes grid.
• Thruster Failure: Reallocation matrix compensates. If >2 thrusters on one leg fail, node requests grid offset and reduces convoy speed.
• Collision Avoidance: Dynamic repulsive fields + AIS priority. If object enters 0.5 NM, node automatically yields right-of-way per COLREGs and notifies convoy lead.
• Weather/Sea State: Grid spacing auto-adjusts based on wave height. In heavy seas, convoy may transition to "drift chain" mode (reduced formation integrity, increased safety margin).

┌─────────────────┐     ┌───────────────────┐     ┌──────────────────┐
│  GNSS + PPS Sync│────▶│ RTK Positioning   │────▶│ Trajectory Gen   │
└─────────────────┘     └───────────────────┘     └────────┬─────────┘
                                                          │
┌─────────────────┐     ┌───────────────────┐     ┌────────▼─────────┐
│ AI Vision + PTP │────▶│ Parallax Tracking │────▶│ Track Fusion DB  │
└─────────────────┘     └───────────────────┘     └────────┬─────────┘
                                                          │
┌─────────────────┐     ┌───────────────────┐     ┌────────▼─────────┐
│ Watch Station UI│────▶│ Human Check-In    │────▶│ Alert & Escalation│
└─────────────────┘     └───────────────────┘     └────────┬─────────┘
                                                          │
┌─────────────────┐     ┌───────────────────┐     ┌────────▼─────────┐
│ MPC Controller  │◀────│ Thruster Allocation│◀────│ Convoy Coord.    │
└─────────────────┘     └───────────────────┘     └──────────────────┘
    

• Core Framework: ROS 2 (Humble/Iron) for real-time control, DDS for inter-process communication.
• Networking: OpenWRT (mesh), MQTT/DDS (telemetry), SQLite/PostgreSQL (local tracks), FastAPI/Django (web UI).
• Monitoring: Prometheus + Grafana for system health, vessel performance, and mesh telemetry.
• Deployment: Docker containers on ruggedized x86_64 or ARM SBCs. OTA updates via Starlink when convoy is idle.

1. Phase 1 (Single Node): Mount GNSS + RTK baseline, calibrate thruster allocation, test MPC station-keeping, deploy LoRa + 5 GHz point-to-point.
2. Phase 2 (2-Node Convoy): Implement moving-base RTK, basic virtual spring-damper formation control, MQTT telemetry sync, watch check-in prototype.
3. Phase 3 (3+ Nodes): Parallax tracking pipeline, track fusion DB, AI anomaly detection, automated alert routing, full mesh B.A.T.M.A.N. deployment.
4. Phase 4 (Production Convoy): Redundant hardware hardening, COLREGs compliance, degraded-mode validation, long-range transit testing, human-machine handover drills.

Design Tip for Production: Marine environments demand IP68/NEMA 6X enclosures, stainless/corrosion-resistant fasteners, sealed RF connectors, and conformal-coated PCBs. All directional antennas should be mounted on the upper truss rail with vibration-damping grommets to prevent micro-fractures from wave-induced hull stress.