AIS Sonar

My boat

Position from

Heading from

My MMSI (AIS ID)

Manual heading

045°

Manual speed (kn)

AIS traffic

AIS source

Advanced: relay address

Relay address

Leave empty when this page is opened from your Worker. Live AIS comes from aisstream.io through the relay; open the Worker's HTTPS address in Chrome so GPS and compass work.

Filters

Use filtersHide vessels you don't need to see. A hidden vessel still reappears, in red, if it's on a close approach; the guard zone and beacon alarms ignore filters Hide stationary vesselsAt anchor, moored or under 0.5 kn Hide small Class B boatsLeisure-grade transponders: yachts, small fishing and work boats

Minimum length

Vessels that don't report their size are always shown.

Minimum speed

Show these types

Alarms

Close approach

A ship turns red, and the alert above the tabs appears, when it will pass closer than

within the next

Wider limits warn earlier but flag more ships in busy water. In a crowded harbour try 0.2–0.3 nm; offshore or at night, 1–2 nm and 30–60 min.

Alarm history

Close approaches, guard zone, beacons, anchor watch, and times the alarms were paused because the screen was off. Kept on this phone (last 60).

Display & sound

Map layers

CoastlineLand and shoreline behind the scope, from OpenStreetMap via OpenFreeMap. Downloads only the area on screen. With demo traffic, an invented coastline is shown instead.

Offline map

Save the coastline around you so it shows with no internet. Areas you have already viewed are kept too.

Map data © OpenStreetMap contributors, tiles © OpenMapTiles, served by OpenFreeMap. Not for navigation: coastlines can be off by tens of metres; always keep a proper lookout and use official charts.

Reading the scope

Hull shape shows vessel type; size comes from its AIS length and beam.
Line from the bow points along its heading and grows with speed. No line means stopped.
Positions are estimated between reports from speed, course, turn rate and speed changes. A dashed ring shows how far off the estimate may be; hollow squares mark the last reported positions: up to three for a moving vessel, showing its recent track.
Anchor button (top left of the scope) sets an anchor watch: pick a radius, tap Place on sonar, then tap where the anchor lies. Leaving the circle sounds a siren, vibrates and flashes the screen; losing the position warns too.
Shaded land and the shoreline come from OpenStreetMap (Settings → Map layers). Not for navigation.
Notes at the top of the scope say what the picture rests on: where your own position and speed come from (manual, weak GPS holding the last good speed, no fix), and how much AIS is being heard here. An empty scope only means no AIS was received; if nothing has been heard for 10 minutes it says so in red.
Fast vessels are heard early. Whatever range is on screen, the app receives vessels out to your close-approach time at 30 kn (10 nm for 20 min, up to 30 nm). Those beyond the area you've opened stay hidden unless they're on a close approach.
Emergency beacons (AIS-SART, man overboard, EPIRB-AIS) show as a circled cross with red ripples and raise an alarm with a sound and vibration. In test mode they are grey and silent.
Ticker above the scope: AIS safety messages scroll in red first; tap one to read it and Dismiss it. Dismissed messages and weather or sea data from AIS stations then scroll together. Tap any item for details.
Aids to navigation (buoys, beacons, lights, platforms) show chart-style symbols: cardinal marks with their two cones, a square for port-hand, a triangle for starboard-hand, dashed when virtual, yellow when off position. A mast is an AIS shore station. Tap one for its details.
Rim triangles mark every contact's bearing, brighter when closer. Hollow means beyond range.
Red contacts will pass closer than your close-approach limit (Settings → Alarms; 0.5 nm within 20 minutes by default).
Guard zone (the dashed-ring button under the anchor, top left): a dashed yellow ring; any vessel inside it sounds an alarm (also right after you turn it on or resize it), whatever its course.
Waterfall plots bearing over the last minute. Tap a trace to select that ship.
Double-tap a ship, its rim triangle or its waterfall trace to open its details.
Pinch or use − / + to change range. Your heading is the bar on the rim.