hoekens-anchor-alarm

A simple web UI anchor alarm for SignalK, built for setting from your phone, tablet or computer. Handy for setting the anchor alarm from the helm, or a quick check from bed when the wind picks up at 2am.

This started life as a fork of the venerable signalk-anchoralarm-plugin by Scott Bender, but has since grown its own personality (and a fair bit of new code). The goal is a focused web UI with my own style and a few opinionated features, like automatically cancelling the alarm when your engines fire up. If you'd rather drive everything from an external app or API, the original plugin might be a better fit for you.

Features

👀 Watch zones that aren't just circles

The classic circle is still here (now resizable by dragging a handle on the rim), but you can also switch to a sector (radius plus a draggable arc, handy when your safe swing is only astern), or a free-form polygon with draggable vertices. Drag an edge midpoint to add a point, drag a vertex onto its neighbor to remove it. Self-intersection is prevented for you, so you can't tie your watch zone in a knot.

⚓ Physically accurate boat icons

Give it your beam, LOA, and GPS antenna position and the boat icon is drawn to your boat's true size, rotating around the antenna location. At high zoom this is genuinely useful: pre-pick your spot on satellite imagery, line your bow up over the anchor icon, and drop. The alarm triggers on your GPS antenna position leaving the zone, so set your offset and it all lines up.

📐 Scope calculator

When the anchor's up, a panel shows what your scope would be at 3:1, 4:1, 5:1, and 7:1, based on current depth, your bow height above water, and estimated tidal rise. Install signalk-tides for the tide data. It'll also flag rows in red if the required rode exceeds the chain you actually have aboard (set totalAnchorChainLength in the config).

🔧 Engine override

I always forget to switch the alarm off before motoring away, so now I don't have to. If you've got engine data in SignalK (propulsion.*.rpm or propulsion.*.state), starting your engines silences an active alarm. It only kicks in when you're already outside the zone (motoring away or firing up the motor to reposition while dragging), so it just quiets the alarm you already know about. Anchor watch keeps running, and as long as you're inside the circle nothing changes.

🛰️ Tracks & fleet

Historical tracks are color-coded (green for fresh, fading to red as they age) via the @signalk/tracks-plugin. Other AIS vessels show up too, with their own tracks and accurately-typed icons. Click a vessel for a detailed popup: name, MMSI, length, beam, distance, bearing, SOG, and COG.

🕰️ Past anchorages

If your server has a history provider plugin (e.g. signalk-questdb), the plugin logs every anchoring session (drop and raise times, anchor position, watch zone) and a clock button appears on the map. It opens a list of past anchorages; pick one and its full vessel track is reconstructed from the server's recorded position history and drawn on the map. The same mechanism rebuilds the live scribble track when the tracks plugin can't supply it (not installed, or errored) — recorded position history survives where the in-memory track doesn't. Without a history provider everything behaves as before.

📊 Heads-up panels

Compact HUD panels for wind (with a wind barb on the map), depth, tide state (plus the next two tides), and anchor status. They show and hide themselves based on what data is actually available, so you're never staring at a panel full of dashes.

⚙️ In-map settings

Logged-in users can tweak the UI without leaving for the plugin config page. A gear button opens a settings dialog (panel toggles, basemap, default zone shape, fleet radius, connection type) and most changes apply live.

🔄 TimeZero anchor sync

Optionally keep your anchor watch in sync with TimeZero (TZ Professional / TZ iBoat) instances on the same network. Drop, reshape, or raise the anchor here and it appears in TimeZero; do it in TimeZero and it flows back into Signal K. Enable "Sync Anchor with TimeZero (LAN)" in the plugin config.

TimeZero pairs peers in one of two ways:

• On a Furuno NavNet (172.31.x.x) network it syncs without an account — just enable the option.

• On an ordinary LAN (⚠️ experimental) it only pairs with peers advertising the same My TIMEZERO user ID, which requires your TimeZero instances to be signed in to a My TIMEZERO account. Set "My TIMEZERO User ID" to the ID they use and they should sync here too. It is a GUID (e.g. d5ff170c-4a28-47e0-b54f-1f98bda46c1c), not your email address. TimeZero broadcasts it in the clear on UDP port 33000, so you can read it from a signed-in TimeZero machine's own beacon — field 5 of the semicolon-separated TZ Sync message:

  tcpdump -i any -A udp port 33000

  This path is derived from TimeZero's own pairing logic but has not yet been confirmed against a signed-in TimeZero, so treat it as experimental and please report what you find.

Because TimeZero's anchor watch is always a circle, only circular watch zones are synced.

Usage

This plugin is meant to be used through the web interface on a phone or computer. Point your browser at:

http://[signalk-server-ip-address]:[port-number]/hoekens-anchor-alarm/

The way I use it: anchor the boat first, then once I'm settled I open the webapp and set the alarm. This is where high-resolution tracks earn their keep; you can usually see exactly where you dropped the hook. Set your radius a touch bigger than feels necessary to avoid false alarms in the night.

It's also handy to use a circle zone to choose your spot first: position the zone where you want to anchor, then drive your boat icon until the bow sits right over the anchor icon, and let go. Since v1.3 the icons are physically accurate at high zoom, so you can get surprisingly precise, just make sure you've set your GPS antenna offset!

If you have engine data in SignalK, enable the engine check and the watch will end on its own when you motor off (see Engine override above).

[!NOTE] You can view the app without logging in (read-only). Editing controls (dropping/raising the anchor, resizing zones, settings) appear once you log into your SignalK server.

Embedding

If you want to drop the anchor alarm into another app or a dashboard (Grafana, a Node-RED dashboard, an MFD page, a custom SignalK webapp, an <iframe>), two query-string parameters let you trim the UI down to just the map. Add them to the webapp URL:

http://[signalk-server-ip-address]:[port-number]/hoekens-anchor-alarm/?embedded=true&showAnchorControls=false

| Parameter | Values | Default | Effect | | -------------------- | ---------------- | ------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------- | | embedded | true / false | false | When true, hides the tide, wind, scope, and info panels, along with the settings (gear) control, leaving a clean map. false or omitted changes nothing. | | showAnchorControls | true / false | true | When false, hides the top anchor toolbar (shape picker, radius, drop/raise). When true, shows it. |

The two are independent, so mix and match to taste:

• ?embedded=true — clean map that still keeps the anchor toolbar for setting the alarm from within the host app.
• ?embedded=true&showAnchorControls=false — a bare map with no controls at all, for a read-only status tile.
• ?showAnchorControls=false — the full HUD panels but no anchor toolbar.

Values are compared case-insensitively; anything other than true is treated as false. These parameters only affect what the webapp renders — the map, watch zone, boat, and fleet still update live, and none of your saved plugin settings are changed.

[!TIP] These pair well with the existing ?mode=night / ?mode=day parameter (used by B&G/Navico MFDs), which forces the dark or light theme instead of following the device preference.

API

Besides the web UI, the plugin exposes an HTTP API (drop/raise the anchor, set the watch zone, manage settings and the boat icon) and publishes anchor state on the Signal K tree (navigation.anchor.* and the notifications.navigation.anchor alarm). If you want to drive the anchor watch from another app, a dashboard, or a script, see docs/API.md. The machine-readable OpenAPI spec is also browsable in the Signal K admin UI under Documentation → OpenAPI.

Watch Zone Shapes

| Circle | Sector | Polygon | | :------------------------------------------------------------------------: | :------------------------------------------------------------------------: | :---------------------------------------------------------------------------: | | | | |

Recommendations

This app pairs well with some other software:

• signalk-questdb (or any v2 History API provider): enables the past-anchorages browser and makes the live scribble track survive server restarts.
• @signalk/tracks-plugin: currently used for the historical tracks. I recommend a resolution of 1000ms and 86400 points, which gives you high-resolution data for the last 24 hours. Note: support for the tracks plugin will be dropped in a future release — use a history provider instead (signalk-questdb recommended).
• signalk-tides: feeds the scope calculator and tide panel.
• signalk-autostate: just by using the anchor app, the plugin can tell the difference between moored and anchored. Great for automating things like an anchor light.
• Node-RED + Pushbullet: for push notifications to your phone. Really great for when you're off the boat, and handy on the boat too.
• Tailscale: makes accessing SignalK remotely dead simple. Free, and a five-minute setup.

Contributing

Issues and PRs are welcome; this is an open source project and I'm happy to have company. See DEVELOPMENT.md for getting set up, and CHANGELOG.md for the full history of what's changed.

Attribution

Anchor icons created by Freepik - Flaticon