Y2K's Anchor Alarm

A fork of Zach Hoeken's excellent anchor alarm plugin — with extra wind and AIS proximity alarms.

A Signal K plugin and webapp that monitors your anchored position and alerts you when something changes — your boat drifting, the wind shifting, or another vessel getting too close.

Originally built by Scott Bender (sbender9/signalk-anchoralarm-plugin) and then rewritten and extended by Zach Hoeken (hoeken/hoekens-anchor-alarm) with a modern web UI, engine override, scope calculator, historical tracks, and physically accurate boat icons.

This Y2K fork adds three new configurable alarms to the UI.

Features

Anchor Alarm (original)

• Watch zones — circle, sector, or polygon shape around the anchor
• Anchor drag detection — triggers when your GPS position exits the zone
• Engine override — auto-silences the alarm when engines are running
• No-position watchdog — alerts if GPS data stops
• Scope calculator — recommend chain length based on depth + tide + bow height
• Historical tracks — shows tracks of nearby vessels (requires @signalk/tracks-plugin)
• AIS overlay — view other vessels on the map
• Physically accurate boat icon — sized and rotated using LOA, beam, and GPS antenna position

Wind Alarms ✨ (Y2K addition)

• Wind Speed — triggers when apparent wind exceeds a configurable threshold (knots)
• Wind Shift — triggers when wind direction shifts cumulatively beyond a configurable number of degrees from the direction recorded at anchor drop
• Reset Wind Ref — press to acknowledge a wind shift and record the new wind direction as the reference
• Visual feedback — the InfoPanel shows current wind direction, reference direction, and cumulative delta ∆

AIS Proximity Alarm ✨ (Y2K addition)

• Triggers when another vessel enters a configurable radius (meters) around your GPS position
• Shows the nearest vessel name and distance in the InfoPanel
• Filters out your own vessel by MMSI and context

UI Enhancements ✨ (Y2K addition)

• Touch-friendly controls — large +/- buttons for adjusting thresholds, no fiddly number inputs
• Toggle from the map view — enable/disable alarms directly from the webapp, no need to visit the admin config page
• Alarm panel — positioned top-right, shows all three alarm toggles with current values
• Auto-reset on raise — raising anchor disables all alarms and clears notifications
• Disabled when not anchored — alarm toggles are greyed out until anchor is dropped
• Instant save — threshold changes are saved server-side immediately on each +/- click

Installation

Via npm link (recommended for development)

cd ~/.signalk
npm install https://github.com/spidgrou/y2k-anchor-alarm

Manual

git clone https://github.com/spidgrou/y2k-anchor-alarm.git
cd y2k-anchor-alarm
npm install
npm run build:ui
ln -s $(pwd) ~/.signalk/node_modules/y2k-anchor-alarm
cd ~/.signalk
npm install ./y2k-anchor-alarm

Then restart Signal K Server and enable the plugin from the admin UI.

Configuration

Via admin UI (Signal K → Plugin Config → Y2K's Anchor Alarm)

| Setting | Default | Description | |---|---|---| | Enable Wind Alarms | false | Master toggle for wind speed & direction monitoring | | Enable Wind Shift Alarm | true | Separate toggle for direction shift alarm | | Wind Speed Threshold | 30 kts | Triggers when wind exceeds this speed | | Wind Direction Shift Threshold | 90° | Triggers when wind shifts this much from the anchor-drop reference | | Wind Alarm Severity | alarm | Notification level (alert, warn, alarm, emergency) | | Wind Alarm Interval | 60 s | Cooldown between repeat wind alarms | | Enable AIS Proximity | false | Enables proximity detection | | AIS Proximity Radius | 200 m | Trigger when a vessel enters this radius | | AIS Proximity Severity | alarm | Notification level | | AIS Proximity Interval | 60 s | Cooldown between repeat proximity alarms |

Via webapp UI

From the anchor alarm web interface:

1. Alarm panel (top-right corner) — toggle each alarm on/off
2. + / - buttons — adjust thresholds with large touch-friendly controls
3. Reset Wind Ref (InfoPanel, bottom-right) — acknowledges a wind shift and records current wind as new reference
4. Values are saved instantly — no need to toggle off/on after changing a threshold

Notifications

The plugin writes Signal K notifications that you can route to dashboards, MQTT, or Telegram:

| Path | Example message | |---|---| | notifications.navigation.anchor | Anchor Dragging (45m) | | notifications.environment.wind.speed | Wind 35 kts exceeds 30 kts | | notifications.environment.wind.directionChange | Wind shifted +45° (ref 180°) | | notifications.environment.ais.proximity | CATALYST at 89m |

Requirements

• Node.js >= 20.19
• Signal K Server >= 2.26
• For historical tracks: @signalk/tracks-plugin
• For scope calculator: signalk-tides, signalk-derived-data

Credits

• Scott Bender — original signalk-anchoralarm-plugin
• Zach Hoeken — complete rewrite with custom Leaflet UI, engine check, scope calculator, boat icons, tracks integration. Check out his work at hoeken/hoekens-anchor-alarm.
• Y2K Sailing — wind alarms, AIS proximity alarm, touch-friendly controls, alarm panel

Built for Y2K, a Beneteau Oceanis 50 sailing the South Pacific. If this plugin helps you, buy Zach a coffee — he did the heavy lifting.