Pi parts worth having
on a boat.

Where to buy

The shops worth knowing

What's actually running on Exodus

Not a wish list — these are fitted

How these are wired up →

Getting a Pi onto the boat's network

The hat is the whole job

A Raspberry Pi has no marine interfaces at all. It cannot hear NMEA 2000, it cannot hear NMEA 0183, and it has no sensible way to run off 12 or 24 volts. A hat fixes all three, and which one you choose decides what the rest of the project looks like.

MacArthur HAT

From OpenMarine — the people behind OpenPlotter — and the most complete board of its kind. It takes both NMEA 0183 and NMEA 2000, which is the thing most boats actually need, because most boats are a mixture of the two.

Those opto-isolated inputs are worth the money on their own. Opto-isolation means the incoming signal is passed across a tiny internal light beam rather than a wire — so there is no electrical connection between the boat's instrument wiring and your Pi. A ground loop or a voltage spike on the 0183 line cannot follow it home.

It stacks with other hats, so you can put an AIS receiver board on top of it. Pi 3, 4 and 5, with OpenPlotter.

shop.openmarine.net · documentation

PiCAN-M

From Copperhill / SK Pang. Also does NMEA 0183 and NMEA 2000, also powers the Pi from the bus. Fewer ports than the MacArthur, longer established. Worth pricing against it.

A plain CAN hat

What's on Exodus. An MCP2515 board gets you onto NMEA 2000 and nothing else — no 0183, no SeaTalk, no power management. It is cheap and it works, and if your boat is entirely N2K it's all you need.

If we were buying today knowing what the boat turned into, we'd buy the MacArthur.

What's a multiplexer?

The word that keeps turning up

A multiplexer takes several data streams and combines them into one. That's the entire idea, and on a boat it exists because of a limitation in NMEA 0183.

Why boats need one

NMEA 0183 is point to point. One talker, one listener, one pair of wires. There is no bus, no addressing, no way for three devices to share a cable — if two talkers transmit on the same pair at once, the sentences interleave and both are ruined.

So a boat with a GPS, a depth sounder, a wind instrument and an AIS has four separate talkers, and a chart plotter with one input. The arithmetic doesn't work.

What it does about it

A multiplexer has several inputs and one output. It listens to all of them at once, buffers what arrives, and sends the sentences out of the single output one after another in good order. Nothing collides, nothing is lost, and the plotter sees one tidy stream.

Most will also do a few things beyond merging:

• Baud rate conversion — standard 0183 runs at 4800, AIS runs at 38400. A multiplexer can take both.
• Filtering — drop sentences you don't want so a slow output isn't wasted on them.
• Priority — if two devices both send position, decide which one wins.
• Protocol conversion — 0183 in, NMEA 2000 or WiFi or USB out. This is the one most people actually buy it for.

And where it went

NMEA 2000 is a bus, so it doesn't have this problem. Every device shares one backbone and the protocol handles who talks when. On an all-N2K boat there is nothing to multiplex.

What you still need is the bridge: the thing that lets an old 0183 instrument join a modern N2K boat, or lets either of them reach a tablet over WiFi.

The PredictWind DataHub

How we use it, and what it becomes offshore

The DataHub is a small box that is three things at once: a router, an NMEA 2000 gateway, and a weather terminal. On Exodus it is the centre of the whole network — everything aboard sits behind it.

What's in it

Two separate radios is the detail that matters. One box is simultaneously a client on somebody else's network and the access point for yours. That's what lets it sit between the outside world and the boat instead of beside it.

How it's used right now

Every device aboard — the Pi, the laptop, the phones, the tablets, the sensors — joins the DataHub's network. The DataHub joins whatever internet is available. Nothing aboard talks directly to the outside.

That one arrangement buys a lot:

• One place where the boat meets the internet. The firewall is at the edge, not on nine separate devices with nine different settings.
• Changing connection changes nothing aboard. Marina WiFi, phone hotspot, Starlink — the boat's own network keeps the same addresses and nothing has to be reconfigured. Devices don't even notice.
• Connection failover. It can move between upstream connections rather than dropping everything.
• Instrument data on every screen. Because it's on the N2K bus and broadcasting WiFi, any phone or tablet aboard can see the boat's data without touching an MFD.
• Remote access to the boat through PredictWind's own service, without opening anything up yourself.

What it's really for: offshore

Everything above is convenience. The reason it's fitted is what happens once the marina WiFi is a hundred miles astern.

Offshore, bandwidth stops being free. Whether it's satellite data or a metered Starlink plan, every megabyte is a decision. And the default behaviour of a boat full of modern devices is appalling — phones syncing photos, laptops downloading updates, apps checking in. Untended, a crew of two can burn an offshore data allowance in an afternoon without opening a browser.

The DataHub sits in front of all of it. It filters the rubbish and fetches what you actually asked for. You tell it which forecast models you want, at what resolution, over what area, how often — and it goes and gets exactly that, compressed, and nothing else.

That is the difference between a weather routing workflow that is usable at sea and one that isn't. Not the forecast quality — the discipline about what crosses the link.

The Starlink side

PredictWind build the DataHub to work with Starlink, and the Pro version is specified as Starlink LTE-ready. As we move offshore the plan is for Starlink to become the upstream connection, with the DataHub still sitting between it and the boat, still deciding what goes out and what comes in.

And that's where the security lives. The boat's own network stays private behind the DataHub. Starlink faces the internet; the DataHub faces Starlink; everything aboard faces only the DataHub. One edge, one place to get right.

Other things it does

• Over the Horizon AIS — AIS targets out to around 300 NM, pulled down rather than received, which is well beyond what your own antenna will ever see.
• AI polars — it watches how the boat actually performs and builds a polar from real sailing instead of the optimistic one from the brochure. For routing, a true polar is worth more than a better forecast.
• Anchor alert — drag alarm using its own GPS.
• Logging — 4 GB of boat data, kept aboard.

Weather and routing → How the networks fit together

Worth knowing before you buy

Four things that cost us time

A hat covers the pins it sits on. If you plan more than one board, buy a stacking header at the same time. It's a couple of dollars and it saves taking the whole thing apart later.

1-Wire needs a pull-up resistor. 4.7 kΩ between data and 3.3 V. Without it you get nothing and no error message explaining why. Some probe modules include it; bare probes don't.

Wire colours are not standard. On the DS18B20 probes we use, red is power, yellow is data and blue is ground. Other suppliers use black and white for the same jobs. Check before connecting — guessing can cook the sensor.

Check the voltage. The Pi's GPIO is 3.3 volt and not tolerant of 5. Plenty of modules are sold for Arduino at 5 volts. Read the board before you wire it to a Pi.

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