```html Seastead Convoy Mode Concept

Seastead "Convoy Mode" Concept

This document fleshes out a practical convoy mode for a fleet of seasteads that hold fixed positions relative to each other while underway or while drifting slowly together. It focuses on:

Short answer: For local convoy networking, a hybrid system makes the most sense:
  1. Primary local data links: 5 GHz directional Wi-Fi bridges between nearest neighbors
  2. Backup/omni local link: marine Wi-Fi or 2.4/5 GHz omni for low-rate control and discovery
  3. Longer-range backup: Starlink internet as fallback path between members
  4. Navigation basis: moving-base RTK GNSS + IMU + heading sensors + local relative ranging if possible
  5. Control basis: distributed autopilot with convoy manager and collision / separation safety rules

1. What "Convoy Mode" Should Do

A good convoy mode should provide these functions:

  1. Maintain formation: each seastead holds a target offset from a convoy reference frame.
  2. Allow joining: a new seastead approaches from outside, is assigned a slot, and smoothly enters formation.
  3. Allow leaving: a seastead exits without causing instability or confusion.
  4. Share sensors: AIS, cameras, radar if fitted, alerts, weather, obstacle tracks, status, and watchstanding information.
  5. Degrade safely: if communications or navigation become unreliable, each unit falls back to safe independent mode.
  6. Reduce watch burden: the fleet acts as a cooperative observation network.

2. Formation Model

2.1 Grid Layout

Your idea of a grid is sensible. The simplest model is a 2D rectangular or staggered lattice:

For seasteads of your rough size, a practical spacing might be something like:

Final spacing depends on:

Important: even with very precise RTK positioning, spacing should be determined by control error in waves and gusts, not just by GPS precision. RTK can tell you position to centimeters, but your structure may still move several feet or more dynamically.

2.2 Convoy Reference Frame

Each seastead should know its desired pose in a shared convoy coordinate system:

A convoy can be controlled in one of two ways:

  1. Leader-follower: one designated lead defines convoy motion; others hold offsets.
  2. Virtual leader / consensus: no single leader required; fleet agrees on reference using distributed logic.

For early versions, leader-follower is much simpler. A convoy master can be elected automatically, with backup masters ready.

3. Joining and Leaving the Convoy

3.1 Joining Sequence

  1. New seastead requests admission over Starlink or local radio/Wi-Fi.
  2. Convoy software assigns a candidate slot.
  3. New unit approaches from outside the convoy perimeter.
  4. At a pre-entry point, software verifies:
  5. When inside a specified activation radius, convoy mode arms.
  6. Autopilot transitions from self-navigation to formation keeping.
  7. Slot status changes to occupied.

3.2 Recommended Join Logic

Use several concentric zones rather than a single threshold:

This is safer than "within half a grid spacing and then switch on."

3.3 Leaving Sequence

  1. Member requests departure.
  2. Convoy manager checks neighboring slots and traffic.
  3. Departure corridor is assigned.
  4. Neighbors slightly expand spacing if needed.
  5. Leaving member transitions to independent navigation mode.
  6. Slot marked free and optionally offered to next joining unit.

4. Communications Network Architecture

4.1 Best Practical Architecture: Hybrid

Do not rely on only one network. Use at least three layers:

Layer Purpose Suggested Tech
Primary local high-rate Convoy telemetry, sensor sharing, video snapshots, software sync 5 GHz directional Wi-Fi point-to-point / point-to-multipoint
Secondary local low/medium-rate Discovery, control backup, short messages, health beacons Omni Wi-Fi and/or sub-GHz / LTE-style private link
Wide-area fallback If local mesh breaks, route via internet Starlink VPN / WireGuard tunnels

4.2 Why 5 GHz Wi-Fi Makes Sense

Yes, 5 GHz Wi-Fi 5/6 can make sense because it is:

But on the ocean:

4.3 Practical Hardware Choices

Commercial outdoor bridge gear from vendors like these is commonly used:

For a cost-sensitive prototype, Ubiquiti or MikroTik are probably the easiest starting point.

4.4 Directional Antenna Layout

Your idea of 4 directional antennas is reasonable if the convoy uses a grid and each seastead mainly talks to near neighbors.

A practical arrangement:

This supports a nearest-neighbor mesh and reduces interference compared to all-omni links.

4.5 Expected Range and Data Rate

Approximate numbers for 5 GHz outdoor directional Wi-Fi under good conditions:

Link Type Typical Distance Realistic Throughput Notes
Short directional link 300 ft to 0.5 mile 100 to 500+ Mbps Very easy if line of sight is clear
Moderate directional link 0.5 to 2 miles 50 to 300 Mbps Still practical with decent gear
Longer directional link 2 to 5+ miles 10 to 200 Mbps Depends strongly on antenna gain, alignment, channel width, weather

For convoy spacing on the order of a few hundred feet, this is far more than enough. Convoy control and telemetry only need very low bandwidth, usually well under 1 Mbps per vessel unless you are sharing a lot of video.

4.6 Approximate Cost

Very rough 2026-ish price ranges per seastead for local networking:

Component Low-Cost Range Higher-End Range
Outdoor directional radio/antenna unit $80 to $250 each $300 to $900 each
4 directional units $320 to $1,000 $1,200 to $3,600
1 omni backup AP/link $100 to $300 $300 to $800
Managed PoE switch + router/firewall $150 to $500 $600 to $2,000
Marine mounting, enclosure, lightning/surge, cabling $300 to $1,000 $1,000 to $3,000

A practical low-cost prototype local network per seastead could likely be done for roughly: $1,000 to $3,000 in hardware, or more if you want robust marine-grade installation.

Recommendation: Start with 4 directional 5 GHz radios plus 1 omni backup radio, all powered by PoE, with a small industrial router running a VPN and mesh/routing software.

4.7 Software / Networking Stack

Recommended network/software stack:

For simplicity:

This gives:

5. Navigation and Relative Positioning

5.1 Moving Base RTK GNSS

Yes, moving-base RTK GNSS is a strong choice. It can provide:

Each seastead should ideally have:

5.2 Recommended Additional Relative Sensors

RTK is good, but for close spacing and robust operation, add at least one local relative measurement source:

A very good low-cost enhancement is UWB ranging to neighbors. This can provide direct distance checks that help catch GNSS dropouts or spoofing issues.

6. Shared Situational Awareness

6.1 Sensor Sharing

Each seastead can publish:

6.2 Cooperative Object Tracking

Your parallax idea is good. If several seasteads have:

Then a central or distributed tracker can triangulate non-AIS contacts. This is useful for:

Needed for this to work well:

Camera-only ranging over long water distances is possible but can be noisy. It works much better if fused with AIS, radar, and repeated observations over time.

6.3 Watchstanding Model

A convoy watch system could include:

Practical status levels:

Status Meaning
On Watch Human actively monitoring and acknowledging prompts
AI/Auto Watch Only No confirmed human watch on that vessel
Watch Degraded Some sensors or acknowledgments missing
Watch Critical Convoy-wide minimum watch requirements not met

7. Autopilot and Control Requirements

7.1 Each Seastead Needs Independent Control

Each vessel should always remain capable of safe operation by itself. Convoy mode should be an overlay, not a dependency.

Each unit should have:

7.2 Convoy Controller Functions

The convoy controller computes:

7.3 Control Law Considerations

Because your platform likely has relatively small waterplane area and possibly unusual motion characteristics, convoy mode should account for:

A practical control stack might be:

  1. State estimator fusing RTK GNSS, IMU, heading, thruster feedback
  2. Outer-loop position controller
  3. Inner-loop heading and surge/sway controller
  4. Thruster allocator for the 6 rim-drive thrusters

8. Safety Logic

8.1 Minimum Safety Features

8.2 Failure Cases to Design For

Failure Required Response
Loss of local Wi-Fi Continue briefly on predicted state, then widen spacing or exit convoy
Loss of RTK fix Fall back to GNSS + IMU + local ranging, increase buffer distance
Thruster failure Mark vessel degraded, reassign nearby slots, possibly move failed unit to perimeter
Power failure Broadcast distress/degraded status, neighbors create exclusion zone
Unexpected traffic crossing convoy Convoy expands, parts, or turns under coordinated rule set
Human override Immediate release from slot and notify neighbors

8.3 Emergency Modes

Suggested emergency convoy modes:

9. Data Model and Messages

At minimum, every seastead should publish these messages once or several times per second:

MQTT topics could work well for this, such as:

10. Recommended Hardware Stack Per Seastead

10.1 Communications

10.2 Navigation and Sensing

10.3 Compute

Keeping control and mission compute separated is a good safety practice.

11. Software Architecture Recommendation

11.1 Minimum Viable Software

  1. Local vessel autopilot
  2. Convoy manager
  3. Shared telemetry bus
  4. Track fusion service
  5. Watchstanding dashboard
  6. Join/leave planner

11.2 Suggested Stack

Function Suggested Tooling
OS Linux
Secure networking WireGuard
Dynamic routing Babel or OSPF
Telemetry bus MQTT
Robotics middleware ROS 2 if needed
Database/logging PostgreSQL + time-series logging
Dashboard Web app on local LAN

12. Recommended Development Path

Do this in stages:

  1. Simulation first: model convoy geometry, link behavior, and control logic.
  2. Single-vessel autonomy: prove independent station keeping.
  3. Two-vessel tests: validate moving-base RTK, local Wi-Fi links, and relative control.
  4. Three-to-five-vessel trial: prove join/leave and shared tracking.
  5. Larger convoy: test dynamic routing and watch system.

13. My Recommendation Summary

Best Practical Recommendation

14. Rough Prototype Budget Per Seastead

Item Approx. Cost
4 directional Wi-Fi radios $320 to $1,000
1 omni backup radio $100 to $300
Router + PoE switch + cables + mounts $300 to $1,500
RTK GNSS + heading setup $800 to $4,000+
IMU and integration $100 to $1,000+
Cameras and synchronization $300 to $3,000+

So a basic but credible local convoy electronics package might start around $2,000 to $6,000 per seastead if done cost-consciously, not counting more advanced radar, compute redundancy, or marine-hardening upgrades.

15. Final Notes

The convoy idea is feasible, especially if convoy spacing is generous and the first versions are conservative. The most important design principles are:

If you want, I can next produce any of these in HTML too:

```