VNC — your whole boat, from anywhere

What VNC actually is

Virtual Network Computing

VNC shares a screen. That's it. One computer sends pictures of its display down a wire, and sends back the keystrokes and mouse movements that come the other way.

It is deliberately dumb, and the dumbness is the point. The remote end doesn't need to understand what program you're running, what operating system it is, or what the data means. It only has to draw pixels and forward a click.

How it works, in three steps

A server runs on the boat computer. It watches the screen. When a region changes, it encodes just that rectangle and sends it.
A viewer runs on your phone or laptop. It draws those rectangles as they arrive, building up a copy of the remote screen.
Input goes back the other way. Tap the screen on your phone and the viewer sends "pointer at x,y, button down". The server injects it as if a real mouse had done it.

Because only changed rectangles get sent, a mostly-static screen — a dashboard, a settings page, a chart — uses almost no bandwidth. That matters enormously on a boat, and it's why this works over a connection that would never carry video.

VNC vs a web dashboard. A web page can only show you what somebody built a web page for. VNC shows you everything — the desktop, the terminal, a settings dialog, a manufacturer's configuration tool that only exists as a Windows program. If you can see it when you're standing there, you can see it when you're not.

What that buys you on a boat

The reason it's worth setting up

The boat sits in a marina for weeks at a time while you're at work, or visiting family, or anywhere that isn't the boat. VNC turns that from a blind spot into something you can actually look at.

Change a setting without being there

Say the Victron gear needs a tweak — a charge current limit, a relay setting, something in the GX device's menus. Normally that means standing in front of it.

With VNC you open the boat computer's screen on your phone, open the Victron page in the browser that's already running there, and change the setting. The boat computer is on the boat's own network, so it can reach things your phone never could. You're not reaching into the Victron gear from outside — you're using the boat's own computer to do it, exactly as if you'd walked up to it.

Anything on the screen

Signal K's admin pages — restart a plugin that's sulking
The chart plotter software, to check an anchor alarm
A terminal, to read a log that's telling you why something stopped
The BMS page, the power grid page, the weather page
A camera feed, if you have one
The desktop itself, to see what state you left everything in

And diagnosis, which is the real one

Something stops working. Instead of guessing, or driving four hours, you look. You read the actual error. You restart the actual service. Nine times out of ten the problem is something you can fix in two minutes from a phone, and you only know that because you could see it.

Doing it safely

The part that matters more than the rest of this page

Never put VNC straight onto the internet

Do not forward a VNC port through your router. Not with a strong password. Not on a non-standard port. Not "just while I'm away".

Exposed VNC servers are scanned for continuously and automatically, by people who are not looking for your boat specifically and do not care what it is. The protocol's own password scheme is old and weak, many servers cap the password length, and plenty of setups end up with no encryption on the session at all.

An exposed screen-sharing service is not "someone might see my battery voltage". It is a keyboard and mouse on a computer that is wired into your boat's systems.

The right way: a private network, not an open door

The approach that works, and the one we use, is to put no ports on the internet at all and instead join your own devices to a private encrypted network that only your devices can see.

A mesh VPN does this. Your phone and your boat computer each sign in to your own account, each gets a private address that exists only inside your own network, and they talk directly to each other over an encrypted link. To the rest of the internet there is nothing there at all — no open port, nothing to scan, nothing to find.

Tailscale is the easy one, and it's free for personal use. WireGuard underneath it if you'd rather build it yourself.

The checklist

Do	Don't
Reach the boat over a private mesh VPN	Forward port 5900 (or any VNC port) on your router
Bind the VNC server to the local network only	Leave it listening on every interface
Use a long, unique password you use nowhere else	Reuse a password, or leave the default
Keep the VPN account behind two-factor authentication	Rely on the VNC password as your only defence
Keep the boat computer updated	Run an ancient image because it works
Know which devices are on your VPN, and remove old ones	Leave a phone you sold still able to reach the boat

Why you won't find our addresses on this site. None of the network details for this boat are published anywhere — no addresses, no hostnames, no port numbers, no device names. The techniques are worth sharing. The specifics of one particular boat are not, and anyone writing up their own setup should think the same way.

What it's like to actually use

The honest version

A desktop designed for a 24-inch monitor, viewed on a phone, is fiddly. You will be pinching and zooming. Precise clicking takes a moment. It is a tool for getting a job done, not a pleasure.

A few things make it much better:

Build pages for the phone. Most of what we actually want to see day to day is a web page served off the boat computer, so it opens properly on a phone browser without VNC at all. VNC is the fallback for the things that have no web page.
Big fonts on the boat computer. A desktop set up to be readable across a cabin is also readable on a phone.
Learn your viewer's toolbar. Every mobile VNC app hides its keyboard, modifier keys and scroll modes behind a drawer or a gesture. Find it before you need it at two in the morning.
Expect to wait. Over a slow link the screen redraws in pieces. It is not broken, it is working exactly as designed.

Bandwidth

Reading a dashboard uses very little — the screen barely changes, so almost nothing is sent. Dragging a window around a desktop with a photo wallpaper is the opposite. If you're on metered satellite data, set a plain background, keep the resolution modest, and don't scroll things you don't need to.

What we reach with it → The AI side Tools we use

Your whole boat,from anywhere.