Signal K · Remote bridge monitoring

Your bridge,
ashore.

A Signal K plugin that records your boat's bridge data — position, speed, heading, wind, depth — into an on-board history, and serves it to a live dashboard you can open from anywhere. Read-only. Your data never leaves the vessel.

Join the founding crew → See what it records

Read-only Data stays aboard Apache-2.0 RPi → Cerbo GX

BridgeTwin Bridge LIVE —

SOG / Speed over ground

8.4kn

navigation.speedOverGround

Speed over ground

Read straight from Signal K in metres per second — the SI unit the standard mandates — and shown in knots, because that is what a bridge reads.

The conversion happens on the way out, never on the way in: what we store is what the sensor said. Change your mind about units in five years and the record still answers.

m/s storedkn displayed60 s snapshot

State

Underway

SINCE 09:12 · 4h 51m

DERIVED · VOYAGE DETECTOR

Underway, moored, or lying at anchor

Nobody presses a button. The state falls out of the data: a voyage opens on sustained movement and closes on sustained stillness, and a five-minute shuffle onto a fuel dock does not end your passage.

The rule is pinned by a golden-fixture test against ten days of real vessel data — so a new release cannot quietly rewrite last season.

No manual entryDockings folded inGolden-fixture pinned

HDG

247°

navigation.headingTrue

Heading — where her bow points

Stored in radians, as Signal K requires, and served back in degrees. Heading is not course: this is the direction she is pointing, which in a cross-current is not the direction she is going.

Both are recorded, every minute, so the difference is there in the log when you want to know what the sea was doing to you.

radians storeddegrees showntrue, not magnetic

COG

251°

navigation.courseOverGroundTrue

Course over ground — where she actually went

The track made good over the seabed, after the current and the leeway have had their say. Four degrees off the heading in this snapshot — that gap is the set and drift, written down without anyone having to work it out.

A season of these, minute by minute, is a picture of how your boat behaves that no memory can give you.

vs. headingset & driftminute cadence

Wind

16kn

TWS 16.2 AWA 042°

GUST 21.4 kn · 6H

environment.wind.*

True wind, apparent wind, and the gust that mattered

Speed in m/s, angle in radians — both true and apparent, both kept. The apparent wind is what the rig feels; the true wind is what the weather was doing. Only one of them tells you whether the forecast lied.

The rolling trend keeps the peak, so the gust that put the rail under is still in the record long after the anemometer has forgotten it.

TWS · TWAAWS · AWAgust retained

Position

43°32.81′N 007°01.24′E LAST FIX 14:07:22 UTC

navigation.position

Where she is — and who gets to know

Latitude and longitude, stored on the boat, timestamped in epoch milliseconds UTC because a boat that crosses a time zone at 03:00 should not lose an hour of its own history.

Your position is the one piece of data that can genuinely hurt you if it leaks. So it is never uploaded to be kept: it stays aboard, and the relay only passes your own request through to your own boat.

lat / lonepoch ms UTCstays aboard

SOURCE: SIGNAL K · VESSEL · READ-ONLY · SNAPSHOT EVERY 60s

Zero runtime deps

DEPENDENCIES

Nothing to compile. Nothing to break.

BridgeTwin ships with zero runtime dependencies and no native modules — it is plain JavaScript. That is the whole reason it installs cleanly on a Raspberry Pi, a Cerbo GX or an old laptop without a build toolchain in sight.

The claim is verified on every release: we pack the tarball, install it into an empty directory with --ignore-scripts --omit=dev, and assert the dependency count is zero.

0 runtime deps0 native modulesPure JS101 files · 1.3 MB

RPi → Victron Cerbo GX

HARDWARE

If it runs Signal K, it runs BridgeTwin.

Every release is built and installed on ten platforms before it ships: Linux x64 and arm64, macOS, Windows — each on Node 20 and 22 — plus an armv7 emulator that matches a Victron Cerbo GX running Venus OS Large.

The build runs Signal K's own plugin CI, so the server itself checks the package layout, the entry point, the schema and the start/stop lifecycle. Not our word for it.

Raspberry PiCerbo GX · Venus OSLinux · macOS · Windows10/10 green

Node 20 · signalk-server 2.18

COMPATIBILITY FLOOR

Written for the boat you already have.

The floor is Node 20 and signalk-server 2.18 — deliberately low, because the boats that need this most are the ones nobody has updated in two seasons.

The code targets ES2022 and uses no Node 22-only API. The CI matrix builds against both 20 and 22 on every commit, so the floor cannot quietly rise under you.

Node ≥ 20signalk-server ≥ 2.18ES2022No forced upgrades

Open source plugin · Apache-2.0

LICENCE

Read it before you trust it.

The plugin and the dashboard are Apache-2.0. The thing that runs on your boat, touches your data and talks to your instruments is the part you can read, fork and keep — with or without us. It stays free and unlimited whether you ever pay us a euro or not. (The repository opens with the first public release.)

The relay is not open source, and that is the honest deal. What a subscription buys is not code — it is the hosted pipe that reaches a boat sitting behind a satellite link with no fixed address, and keeps reaching her while you are ashore. That half is ours, it is closed, and it is the only half you pay for.

The read-only promise is not a slogan: the build fails if a single write path appears in the source. Every release greps itself for handleMessage, registerPutHandler and nmea2000out, and stops at the first hit.

Plugin: Apache-2.0Relay: hostedAuditableWrite paths: 0

Hosted in the EU

JURISDICTION

The relay is a door, not a warehouse.

Remote viewing runs through a relay in the EU. It passes a request through to your boat and passes the answer back — it does not keep your track. There is no copy of your season sitting on someone else's disk.

Which means: nothing to subpoena, nothing to leak, nothing to sell. If you turn remote viewing off, the relay has nothing left to forget.

EU jurisdictionPass-throughNo history storedGDPR-shaped

What it records

Four instruments, one quiet log.

Everything runs on the boat and writes to plain files. The dashboard is built into the plugin — open it on the bridge, or from a beach a thousand miles away.

01 / TELEMETRY

Live bridge data

Position, speed over ground, heading and course, true & apparent wind, depth and barometer — read at the source, with trend sparklines.

SOG · HDG · COG · WIND · BARO · DEPTH ↗ Open the instrument

01 / TELEMETRY

Live bridge data

BridgeTwin reads straight from Signal K at the source — position, SOG, heading and course, true & apparent wind, depth and barometer — and keeps a rolling trend for each.

Every value is stored in SI units and served read-only. A fresh snapshot lands every 60 seconds.

SOG · speed

8.4kn

Heading

247°

Depth

18.2m

Wind · apparent

16kn

Wind · true speed, live gust 21 kn

24 kn 16 8 −3 h now

02 / LOGBOOK

History, on board

Every path snapshotted to NDJSON with hourly and daily rollups. Nothing is uploaded to keep it — the record lives on the vessel.

NDJSON · HOURLY / DAILY ROLLUPS ↗ Open the logbook

02 / LOGBOOK

History, on board

Every recorded path is snapshotted to plain NDJSON on the vessel, with hourly and daily rollups on top — so a season of history reads back fast.

Nothing is uploaded to keep it. Query it through the read-only REST API, or export it whole. The record is yours, on your hardware.

Streaming · tail -f snapshots.ndjson▌

UTCSOGHDGWindDepth

Jul 11 · Underway 312 rows

14:128.42471618.2

14:068.22491718.6

14:008.52471619.1

13:548.12441819.4

13:487.92511519.8

13:428.32461920.3

13:368.62391720.9

13:308.02421421.4

13:247.72501321.8

13:188.22481622.1

13:128.82451822.7

13:069.02432023.4

13:008.52471924.0

12:547.92521724.6

12:487.42541525.1

Jul 10 · Moored · Antibes 96 rows

21:000.0—74.2

20:000.1—94.1

19:000.0—114.0

18:000.2—124.1

17:000.0—134.2

16:000.0—144.3

Jul 09 · Passage · Nice → Antibes 38 rows

16:409.12182112.6

16:009.42212328.3

15:208.82241951.0

14:408.42281862.4

14:007.02311644.8

Jul 08 · Moored · Nice 96 rows

23:000.0—55.8

22:000.0—65.9

Jul 07 · Passage · Monaco → Nice 24 rows

18:207.92641233.1

17:408.52611458.7

03 / VOYAGES

Passages, detected

Voyages open on sustained movement and close on stillness — short dockings folded in. Distance, duration and a minute-cadence track for each.

GOLDEN-FIXTURE PINNED · 10 DAYS REAL DATA ↗ Open the track

03 / VOYAGES

Passages, detected

A voyage opens on sustained movement and closes on sustained stillness — short docking manoeuvres folded into the passage they belong to.

Each keeps distance, duration and a minute-cadence track. The detector is pinned by a golden-fixture test against ten days of real vessel data, so a port never rewrites the record.

Antibes → Calvi · underway

Distance

0.0 nm

Elapsed

0h 00m

SOG

7.1 kn

04 / CHART

Traffic & track

Your position and AIS targets on a self-hosted vector chart — no third-party map keys, no leaking where your boat is.

AIS · SELF-HOSTED PMTILES ↗ Open the chart

04 / CHART

Traffic & track

Your own position and nearby AIS targets on a self-hosted vector chart — no third-party map keys, no leaking where your boat is.

Tiles come from our own storage, and a region pack downloads to the boat for offline use. Not for navigation.

AIS · 6 targets in range Click a target · click the water to resume the sweep

Setup · about five minutes

Install it yourself. No one touches your boat.

From the Signal K AppStore to watching your bridge from ashore — without handing anyone a password, a network, or a device.

Install from the AppStore

One click in Signal K. Pure JS, so it installs clean.

↗ Watch it install

STEP 01 / 05

Install from the AppStore

Open Signal K's AppStore, search BridgeTwin, press Install. That is the whole step — no SSH, no npm, no build tools.

It installs clean because there is nothing to compile: zero runtime dependencies, no native modules. The installs that go wrong on a boat are the ones that need a C compiler at 2 a.m. in a marina with 3G.

One click0 dependenciesNo compiler

Signal K · AppStore

bridgetwin▌

BridgeTwinYour bridge, ashore · 0.0.1 · Apache-2.0

→ fetching signalk-bridgetwin@0.0.1 → resolving dependencies … 0 found → native modules to build … none ✓ installed in 4.2 s — restart required

signalk-autopilot4.2.0

Installed

signalk-derived-data2.1.0

Installed

Restart the server

A minute or two — we tell you straight.

~1–2 MIN ↗ See the boot log

STEP 02 / 05

Restart the server

Signal K needs a restart to pick up a new plugin. It takes a minute or two, and during it your instruments are unaffected — the plotter, the autopilot and the AIS never depended on this box.

We say "one to two minutes" rather than "instantly", because a Cerbo GX is not a laptop and pretending otherwise is how trust gets lost on day one.

~1–2 minInstruments unaffectedEnabled by default

Server · restart

$sudo systemctl restart signalk

[ ok ]stopping signalk-server …

[ ok ]plugins: 7 loaded

[ ok ]BridgeTwin 0.0.1 — read-only, recording

[ ok ]14 paths → snapshots.ndjson

[ ok ]server ready on :3000 · 1m 47s

Open the dashboard

It's already running, locally, on the boat.

↗ Look inside

STEP 03 / 05

Open the dashboard

The dashboard is part of the plugin — it is already running on the boat's own network, at the boat's own address. No account, no cloud, no internet.

Four screens: the bridge, the logbook, your voyages, and the chart with AIS. This is the free half of BridgeTwin, and it stays free forever.

Local-firstNo accountWorks offlineFree forever

Dashboard · Bridge

BridgeLogVoyagesChart

SOG8.4

HDG247

WIND16

DEPTH18.2

Antibes → Calvi34.2 nm · 4h 51m

Nice → Antibes11.8 nm · 1h 32m

Monaco → Nice9.4 nm · 1h 12m

http://boat.local:3000/signalk-bridgetwin/

Claim from your phone

Scan the code to link remote viewing.

RFC 8628 ↗ See the pairing

STEP 04 / 05

Claim from your phone

The boat shows a short code. You type it into bridgetwin.app from your phone, on any network. That is the entire pairing — the boat is never asked for a password, and it never accepts an inbound connection.

It is the same flow a TV uses to sign you in: RFC 8628 device authorisation. The code is short-lived, single-use, and useless to anyone who isn't standing at the helm.

RFC 8628Short-lived codeNo inbound ports

Device pairing · RFC 8628

On the boat's screen

BT-7K4M-92XQ

expires in 9:58

bridgetwin.app/claim

BT-7K4M-92XQ▌

✓ claimed — now approve it on board

Approve on board

One tap on the boat's screen. Live ashore.

TWO-SIDED ↗ See the approval

STEP 05 / 05

Approve on board

Typing the code isn't enough. Somebody has to tap Approve on the boat's own screen — which means remote viewing can only ever be granted by a person who is physically aboard.

Every paired account stays listed on that screen, and any of them can be cut from either end. When a boat changes hands, the new crew can see exactly who is still watching.

Physical presenceRead-only grantRevoke from either end

Approval · on the boat

Remote viewing request

Accountburak@tjock.fan

DeviceiPhone · Safari

AccessRead-only

Deny Approve

✓ Remote viewing live

Security posture

Nobody gets into your boat.
Us included.

No deltas emitted No PUT requests Auditable source EU jurisdiction

It never writes to your boat

No deltas, no PUT requests, no commands. The REST API is read-only and the source is open — grep it and see for yourself.

↗ Run the guards

01 / READ-ONLY

It never writes to your boat

A plugin that can write to Signal K can move a rudder. BridgeTwin cannot: it emits no deltas, issues no PUT requests, registers no handlers. The REST API exposes GET routes and nothing else.

This isn't a promise, it's a build gate. Every release greps its own source for the three ways a plugin can write to a vessel — and the build fails on a single hit.

0 deltas0 PUTGET-only routesEnforced in CI

CI · read-only guards

$grep -rn "handleMessage" plugin/src

0 matches

$grep -rn "registerPutHandler" plugin/src

0 matches

$grep -rn "nmea2000out" plugin/src

0 matches

$grep -rn "router.(post|put|delete)" plugin/src

0 matches

✓ read-only guards passed — build continues

Your data stays aboard

History is stored on the vessel in plain NDJSON. The relay passes a request through to the boat; it doesn't keep your track.

↗ Follow the request

02 / DATA PATH

Your data stays aboard

Your season lives on the boat, in plain NDJSON files you can copy off with a USB stick. When you look from ashore, the relay passes the request through and hands the answer back.

It keeps nothing. No track, no positions, no history — so there is no second copy of where your boat has been, sitting on somebody else's disk.

NDJSON on boardRelay: pass-through0 bytes retained

Request path

BOATNDJSON + rollupskeeps everything

RELAY · EUpass-throughkept: 0 bytes

YOUphone · ashoreread-only view

No remote access to the vessel

Not for anyone — us included. You grant support visibility when you want it, and you cut it the moment you don't.

↗ See the switch

03 / ACCESS

No remote access to the vessel

There is no support tunnel, no remote shell, no back door — not for us either. If you want help with a fault, you turn support visibility on, and it shows us exactly what you already see: a read-only view.

You cut it in one tap. When it's off, the only person who can look at your boat is you.

No shellNo back doorTime-limitedOne-tap cut

Support access

Support visibility

OFF · nobody but you can see this boat

BridgeTwin staffno access
Remote shellnever
Write commandsnever
Your own viewalways

Pairing cuts both ways

Unpair from the portal, or reset remote viewing on the boat. A paired account stays visible on the local screen — for when a boat changes hands.

↗ Cut a pairing

04 / PAIRING

Pairing cuts both ways

Every account that can watch this boat is listed on the boat's own screen — and can be cut from there, without a login, without us.

That matters the day a boat changes hands, or a captain leaves. The new crew walks up to the helm, reads the list, and ends what shouldn't be there.

Listed on boardCut from either endSurvives a handover

Paired accounts · 3

On the boat's screen

burak@tjock.faniPhone · since Mar

chief@lady-jade.euiPad · since May

owner@…Mac · since Jun

bridgetwin.app portal

burak@tjock.faniPhone · since Mar

chief@lady-jade.euiPad · since May

owner@…Mac · since Jun

Cut it on one side — it's gone on the other.

Opaque, revocable tokens

Boat tokens are hashed and rotated write-then-switch, revoked in one tap. Every pairing is approved on the boat itself.

↗ Rotate a token

05 / TOKENS

Opaque, revocable tokens

A boat's token is stored as a hash, never in the clear — a stolen database gives an attacker nothing to replay.

Rotation is write-then-switch: the new token is written and proven before the old one dies, so a rotation cannot strand a boat mid-season. Revocation kills it instantly, from the helm or the portal.

Hashed at restWrite-then-switchInstant revoke

Boat token · lifecycle

Stored assha256:9f2a…c41d

Approvedon the boat

Scoperead-only

issue rotate revoke

active

Pricing

Free on the boat. Pay only to look from ashore.

The plugin and the local dashboard are free, forever, and work with no internet at all. A subscription is only for watching remotely.

Aboard

Free/ forever

The plugin, the recorder and the built-in dashboard — running on the vessel.

Full local dashboard
Works with no internet
Read-only REST API
Yours to keep

Install it — it's live

ABOARD · FREE FOREVER

The half that runs on the boat costs nothing.

The plugin, the recorder, the logbook, the voyages, the chart, the REST API — all of it, on the vessel, free forever and working with the internet unplugged.

This is not a trial that expires. If you never pay us a cent, the boat still keeps its own history, and you can carry it off on a USB stick the day you sell her.

No accountNo expiryNo internetApache-2.0

Internet · disconnected

✕No internet · 4 days

SOG8.4

Depth18.2

Wind16

Rows today312

Recording continues · dashboard live · nothing needed from ashore

Founding Crew FIRST 25

€69/ year · locked

Everything in Remote, at a price that never rises — for the first 25 boats.

Watch your bridge from ashore
Multi-user, multi-boat
GPX / CSV export
Read-only share link
Price fixed for life

Join the founding crew →

FOUNDING CREW · FIRST 25 BOATS

€69 a year. For as long as you keep the boat.

The first twenty-five boats get everything in Remote at €69 a year, locked for life. When the price rises — and it will — yours doesn't.

What we want in return is honest: tell us what breaks. You are the crew that finds the fault on a Cerbo in a marina with no signal, and tells us before the hundredth boat hits it.

Price locked for lifeDirect line to usPre-release

Founding crew · first 25 boats

6/ 25 claimed

€69 · locked for life

Remote

€99/ year

Remote viewing for one boat. Or €12/month — pause any time she's laid up, back in one tap.

Everything in Aboard
Live view from anywhere
Multi-user & sharing
Off-season anchor watch

Tell me when it lands

REMOTE · PAY BY THE SEASON

Pay for the months you sail.

€99 a year, or €12 a month with a pause button. A boat that sails seven months and sits under a cover for five shouldn't be billed for twelve.

Paused doesn't mean gone: the boat, the history and the pairings all wait exactly where you left them. One tap brings the view back — and while you're paying, the off-season anchor watch is watching her for you.

€99 / year€12 / monthPause any timeAnchor watch

Season · 12 months

Billed this year€84

7 months × €12 = €84 — a full year would be €99

Aboard is free and unlimited. Pay by the season you sail — pause any month she's laid up; your boat and history wait, back in one tap.

Come aboard
before the rest.

The plugin is on npm today — install it and the boat's own dashboard runs, free, forever. What is still in build is the relay: the half that lets you watch her from ashore. Leave an address and you'll hear from us exactly once, the day it opens. No newsletter, no drip, no third party.

v0.0.1 live on npm · the on-board half works today · remote viewing is in build

Your bridge,ashore.

Four instruments, one quiet log.

Live bridge data

History, on board

Passages, detected

Traffic & track

Install it yourself. No one touches your boat.

Install from the AppStore

Restart the server

Open the dashboard

Claim from your phone

Approve on board

Nobody gets into your boat.Us included.

It never writes to your boat

Your data stays aboard

No remote access to the vessel

Pairing cuts both ways

Opaque, revocable tokens

Free on the boat. Pay only to look from ashore.

Come aboardbefore the rest.

Your bridge,
ashore.

Nobody gets into your boat.
Us included.

Come aboard
before the rest.