What we did, what it cost us in time, what went wrong, and enough detail that you could do it yourself. Including the bits where we got it wrong first.
October 2026 · written up in full
Marine radar and sonar imagery are proprietary. Not encrypted — just undocumented, and nobody publishes the formats. We captured both off our own instruments and worked out what the bytes meant.
The radar turned out to be run-length compressed, which is why it looked far too small on the wire to be a picture. The fishfinder turned out to be announcing its own frequency setting in plain readable English, seventy-one times a second, in a field nobody was ever supposed to look at.
Both now draw on a Raspberry Pi, on a screen no manufacturer sold us. There is still no open-source sonar display for Signal K or OpenCPN anywhere — so as far as we know this is the only one.
Running on the boat, write-ups in progress
LiFePO4 house and nav banks, a JK BMS on the boat's own screen, cell balancing, and the storage voltages that decide how long your cells last.
BotFather, API tokens, connecting it to the boat, and the real limits — including the one that catches everybody out.
A Pi, a CAN hat, a stacking header, a barometer and temperature probes watching the Fischer Panda. How it's built, what it does, and how to build your own.
Ollama and Qwen running locally with no internet, Claude Code as the teacher, and every manual aboard loaded in so it can troubleshoot and find part numbers.
Getting a Raymarine Quantum onto a Raspberry Pi — including the routing fault that made it look broken for an hour.
How routing actually works, GRIBs and polars explained, where to get them free, and turning your boat into a weather station other sailors can see.
On the list, not built yet
Publishing these before they exist, so you can hold us to them.
Boats offshore sharing live observations with each other. Not a forecast — what the wind is actually doing, forty miles upwind, right now. The pieces already exist; nobody has put them together for cruisers.
Driving a sonar transducer with our own hardware and putting the echo on our own screen. Owning the whole chain from the ping to the pixel, with nothing proprietary in the middle.
Getting the analogue gauges onto a digital platform. Oil pressure, temperature, RPM and hours logged and trended instead of glanced at. Home built, naturally.
Count every pump cycle and watch the trend. A bilge running a bit more often each week is a leak announcing itself months before you would otherwise notice. Cheap to build, and possibly the highest value sensor on the boat.
Install, plumbing, power draw and the monitoring to go with it.
Rebedding, rebuilding and replacing. Unglamorous, necessary, and the thing that decides whether your bunk stays dry.
Exodus