There are so many anchor alarm apps available on Apple Store and Google Play Store that it becomes very tedious to compare them all. Here is a comprehensive feature comparison that you might find helpful.
Anchor alarm apps are a rather useful addition to increase the safety at anchor. Essentially, they raise an audio alarm when the vessel leaves a certain perimeter and thus raise your attention that the anchor may be slipping and your vessel be dragging.
Of course, using such an anchor alarm does not mean you can neglect any of the other essential tasks and drills when anchoring, such as finding an appropriate anchorage to begin with, fit for any predicted changes in weather, making sure the anchor is properly set, and paying out enough chain / rode so as to reduce the anchor load to the minimal value and thus minimise the risk of dragging or worse from the start. For the latter, there is another app that can help you in working out the minimally required anchor chain length and the associated anchor load. It is described elsewhere on my home page: AnchorChainCalculator, and is available for Apple and Android. I sometimes dubb it as a preventive anchor alarm… 🙂 A free online version of this calculator will hopefully also become available at some point.
Assuming you have done all that, it is time to set the anchor alarm, i.e., to define an allowed perimeter within which the vessel must stay at anchor and finally arm the alarm. These apps come in a large variety, with many different features, and so it is quite confusing which app to use. For me, living at the hook, the following features of an anchor alarm app are important:
- I like to know the history of the vessel’s positions at anchor. This allows me to judge whether an alarm raised is because of a wind shift stronger than expected (the vessel is still on the same arc around the anchor position, just more on the edge of it than I had anticipated), or something more serious has happened (the vessel is rapidly moving away from the last partial arc that it had created on the map). For this reason, some kind of map needs to be available to the anchor alarm, but it may all be deep blue background for all I care… 😉
- As I never set the alarm when we are dropping the anchor – I am kind of busy with other things then 😉 – I need to set the alarm when the vessel is already at anchor. If the app can only set an alarm as a circle around the vessel’s current position, this is obviously no good then. It does not improve things much when I can move this circle away from the vessel and onto the anchor position, as it is usually hard to tell on the tiny anchor alarm’s map in which direction one is moving the circle. Moreover, it is usually done by dragging with one’s fingers, which is not very precise at all.
- Much better are anchor alarms that use the bearing of the current anchor position and a distance (which should be chain length plus the distance from the bow roller to where your phone is on the vessel) for defining the allowed perimeter. Being able to augment that by using only a partial arc rather than a full circle can be very useful in a tight spot. Alternatively, I also quite like to define the allowed perimeter for the vessel by drawing a shape with my finger on the anchor alarm’s map. In particular, when some vessel position history is already visible, it is then easy to draw a tight perimeter for the allowed vessel position.
- Anchor alarm apps have to share the phone resources with many other apps on the phone, and this can mean that they stopp functioning correctly without one becoming aware of it, they temporarily loose GPS signal, or may even be terminated for good by one’s mobile, because the operating system on the mobile decides it needs the resources for some other app. Some are not functioning when sent to the background and another app is on top. This is a fundamental problem and cannot be resolved in full. But at least, the anchor alarm should warn you when the battery level is low, the sound level is low, the GPS signal is weak or even non existent.
- It is also nice to be able to set a tolerance level against false alarms.
- Although it is a cool feature to be able to see the alarm on a 2nd remote device when ashore and away from the vessel, one has to be aware that should something happen, most likely one will not be back in time to prevent a disaster. I have not used such a feature yet, but I can imagine that being able to check that the anchor is still holding will ease this nagging feeling that something might have happened whilst you are trying to enjoy a nice dinner ashore.
And finally, I do test the app a couple of times whether it is reliable in different circumstances. Also, when the app is in the background and some other app is on the screen. A good way of periodically retesting the app is to keep the alarm on when leaving the anchorage. If the alarm does not go off, something is very fishy! It goes without saying that my phone or tablet is plugged into a power supply for the entire length of the anchor watch. GPS does drain the batteries of any phone or tablet rather quickly. If you need a louder sound for the alarm – why not use a BT connected external loudspeaker right next to your bed? (Also plugged into power, of course.)
Apple devices have a rather uniform GPS performance, but for Android the market is much less clear. Very cheap devices may also use very cheap GPS receivers, which will make the anchor alarm app perform less precise, and with more false alarms most likely.
With all this in mind I have looked at all the anchor alarm apps that I could find in Apple Store and Google Play Store and pulled together their feature lists, so that I can compare them. I guess a disclaimer is in order here: I do not claim that all information is 100% correct and accurate, and it will certainly evolve further over time. It is a best effort approach to help the community at making a better informed decision which anchor alarms to use. Please do let me know should you find any information inaccurate or even wrong. I am also not going to make a recommendation that this or that app is the best, but in the comparison chart I have highlighted the features of above which I believe are important. It is then up to you and the budget you want to invest, which app to use. Personally, as a vessel is easily worth a couple of 10 thousand dollars, or even a couple of 100 thousand dollars, and your life may depend on it, I believe this money is well spent.
Comparison chart in English is found here. (Beware, not all content is translated to English.)
The Mac OS / Numbers spreadsheet is found here.
Any comments or feedback / corrections / omissions is highly appreciated.
For the German speaking community: Der Deutsche Segler-Verband e.V. (DSV) veranstaltet am 14. September 2021 online einen Nautischer Abend: Anker-Apps, bei dem ich als Vortragender zu diesem Thema und auch dem Vergleich zu Ankeralarmen in der an Bord fest installierten Elektronik sprechen werde. Bei Interesse bitte anmelden!