SeaMemo
Anchor alarm: wakes you when the anchor drags
SeaMemo's anchor alarm remembers where your anchor is and sounds as soon as the boat leaves the alarm circle. Choose the radius directly (50 metres recommended) or let the app calculate it from chain length, water depth and boat length. It works without internet. The feature is new and still marked as beta.
How the anchor alarm works
- Set the anchor. Only start the watch once the anchor holds.
- Choose the radius from the presets or let the app calculate it from chain length, water depth and boat length.
- Start the anchor watch. Your current position becomes the anchor position.
- Test the alarm. The test alarm sounds after five seconds, so you can check you hear it in silent mode.
- Sleep. If the boat leaves the circle you get an anchor dragging alarm with the distance to the anchor.
Choosing the right radius
A boat swings around its anchor. The circle it describes depends on the chain you let out and the water depth, plus the length of the boat. Set the alarm radius too small and every wind shift wakes you. Set it too large and you only notice dragging when things get tight.
That is why SeaMemo can do the maths: chain length and water depth (plus 1.5 metres of freeboard) give the horizontal distance to the anchor, and the boat length is added on top. An example: 40 metres of chain, 8 metres of depth and a 12 metre yacht give a radius of 51 metres (the app rounds up).
How to size the chain and set the anchor is covered in our guide to anchoring a boat.
Making sure the alarm really wakes you
An anchor alarm that stays silent is worse than none. The app guides you through the settings you need:
- Location set to Always, otherwise there is no alarm when the screen is locked.
- Allow notifications and on iPhone turn on critical alerts so the alarm rings in silent mode.
- On Android: remove SeaMemo from battery optimisation and allow Do not disturb access.
- Keep the phone on the charger. The anchor watch needs GPS all the time.
Important: the anchor alarm is an aid and does not replace your own checks on board. Check position and anchor immediately whenever it sounds, and don't rely on a single device in critical situations.
Beta: your feedback counts
The anchor alarm is new. When you end a watch the app briefly asks whether everything worked: false alarm, no alarm despite drifting, GPS too inaccurate or alarm not heard. This feedback goes straight into the next versions. If you head into an unfamiliar bay with a charter yacht, check anchor and chain in the charter check first.
Get SeaMemo for free
Logbook, travel journal and crew in one app. For iPhone and Android, works offline at sea.
Frequently asked questions
Does the anchor alarm work without internet?
Yes. It only needs GPS. Keep the phone on the charger though, because the anchor alarm uses location continuously.
Will the alarm wake me in silent mode?
On iPhone only if you allow critical alerts for SeaMemo. If your iPhone doesn't offer that, the alarm only sounds when the phone isn't on silent and no focus mode is active. On Android, remove SeaMemo from battery optimisation and allow Do not disturb access.
How large should the alarm radius be?
As a starting point the app recommends 50 metres, tighter in strong wind or when space is limited. It gets more precise with the calculation from chain length, water depth plus 1.5 metres of freeboard and boat length.
Can I rely on the anchor alarm?
Not on its own. It is an aid and does not replace your own checks on board. GPS can be inaccurate and phones can switch off. When the alarm sounds, check position and anchor immediately.