What an Anchor Watch Actually Is
An anchor watch is not a thing you wear. It is a duty — the job of making sure the boat is still where you anchored her. For as long as boats have anchored, somebody has kept it: a crew member awake through the night, taking bearings on a light ashore, watching the sounder for a change in depth, listening to the chain, and waking the skipper if anything moved.
It is also the hardest watch to keep, because nothing happens for hours and then everything happens in ninety seconds. Chartplotter makers borrowed the name for the feature that does it electronically, which is why you will find the same job called an anchor watch on a B&G display, an anchor alarm on a Garmin, and both on the App Store. They are the same idea: something that knows where the anchor is and tells you when the boat stops agreeing.
A Person or a GPS?
Honestly, they are good at different halves of the job — and the half a phone does well is the half that costs you sleep.
| The job | A person on watch | A GPS anchor watch |
|---|---|---|
| Stays alert all night | For a while. Concentration goes long before the night does. | Continuously, at the same accuracy at 04:00 as at 22:00. |
| Measures movement | By eye, against a shoreline that is dark and may be unlit. | By position, against the point where the anchor actually went down. |
| Wakes a sleeping crew | Only if the watchkeeper is awake to shout. | Sound and haptics on the phone and on your wrist. |
| Reads the weather | Yes — this is what a person is genuinely better at. | No. It watches one thing: whether you moved. |
| Notices the boat next door dragging | Yes. | No, unless their boat reaches yours. |
| Cost of a night | Somebody's sleep, every night. | Nothing. It is free. |
So the useful framing is not app versus watchkeeper. In settled conditions the app is the watch, and everyone sleeps. When it is blowing and the anchorage is filling up, it becomes one instrument among several and somebody should still be awake. The longer version of that argument is in keeping an anchor watch by GPS.
Setting the Watch
- Set the anchor first. A watch on a badly set anchor just tells you sooner. The full method is in our guide to anchoring a boat.
- Mark the anchor, not the boat. This is the mistake that produces both false alarms and late ones. You are lying a boat length plus your rode away from where the anchor actually is, and the circle has to be centred on the anchor.
- Set the radius from the rode you paid out — roughly the rode on the bottom plus your length, with a few metres for surge. The scope calculator turns your depth and chain into the number.
- Leave it running and go to bed. The watch runs with the screen locked; on Apple Watch the alert arrives by sound and haptic, which is what actually wakes people.
What it does not do
It watches one thing: whether your boat has left the circle you set. It does not read the forecast, it will not notice the boat upwind dragging down on you until they arrive, and it cannot tell a dragging anchor from a wind shift that swung you wide — only that you moved. Set the circle carefully and it is an excellent watchkeeper. Set it to a radius that ignores everything, and it is a torch with a flat battery.
Anchor Watch Questions
What is an anchor watch?
Is an anchor watch the same as an anchor alarm?
How do you set up an anchor watch on a phone?
Is there a free anchor watch app?
Can an app really replace a human anchor watch?
Read next
Keeping an Anchor Watch by GPS
Where a phone beats a watchkeeper, and the nights it does not.
GuideHow to Anchor a Boat
Spot, scope, lay, set, watch — with a pass/fail test at every step.
SafetyNight Anchoring Safety Tips
What changes after dark — the light, the watch, the bearings and the gear.
ProductAll Features
Drag alerts, safe radius, anchor points, night mode, Apple Watch and iPad.
