Phone anchor alarms

[noelex]

our old garmin gps had an anchor alarm feature that worked great, the furono we have now doesn't and the one on the raymarine plotter isn't much use on deck!
I have tried most of the android ones and never go a full nights sleep without it going of at some point even when the swing is set to 150~200m with 20m of chain out, I think the gps goes to sleep despite all the settings being as recommended by the app developers (tried it on 3 phones and 2 tablets - all Samsung), I just put more chain down and trust to a good anchor.

Paul, you are certainly not alone in having an anchor alarm that works poorly. Having to set such a large alarm radius means the alarm is all but useless. Setting a good anchor alarm is surprisingly difficult. The hardware needs to be suitable and installed correctly. Importantly, the centre of alarm radius has to coincide with the anchor position.

In many ways it is not dissimilar to problems of anchoring itself. If you have the right equipment and technique everything is easy and reliable.

The important message is that it is possible to to set a reliable alarm that will wake you up if your anchor moves more than very short distance. We do this every time we anchor and that is most days of the year. The only false positives we ever have are when forgetting to turn the alarm off when leaving (pretty stupid, but it does show the buzzer and the rest of the system is working).

The only other times the alarm goes off are on the occasions when we deliberately set an anchor alarm that is designed to wake us with a wind shift (this is not really a false positive, as the alarm is alerting us just as it has been set to do).

So it is worth persisting to sort out the problems with your anchor alarm. While an anchor alarm is only a secondary system (the primary system is good anchoring gear) it is nevertheless an important safety device. If you anchor frequently the alarm should be working well in my view. In our case it has proved its worth on at least a couple of occasions.

 

[Neeves]

Paul, you are certainly not alone in having an anchor alarm that works poorly. Having to set such a large alarm radius means the alarm is all but useless. Setting a good anchor alarm is surprisingly difficult. The hardware needs to be suitable and installed correctly. Importantly, the centre of alarm radius has to coincide with the anchor position.

In many ways it is not dissimilar to problems of anchoring itself. If you have the right equipment and technique everything is easy and reliable.

The important message is that it is possible to to set a reliable alarm that will wake you up if your anchor moves more than very short distance. We do this every time we anchor and that is most days of the year. The only false positives we ever have are when forgetting to turn the alarm off when leaving (pretty stupid, but it does show the buzzer and the rest of the system is working).

The only other times the alarm goes off are on the occasions when we deliberately set an anchor alarm that is designed to wake us with a wind shift (this is not really a false positive, as the alarm is alerting us just as it has been set to do).

So it is worth persisting to sort out the problems with your anchor alarm. While an anchor alarm is only a secondary system (the primary system is good anchoring gear) it is nevertheless an important safety device. If you anchor frequently the alarm should be working well in my view. In our case it has proved its worth on at least a couple of occasions.

It is reassuring to read that your use of an anchoring app has proved it worth. We would find that with the phone 'downstairs' (or in our case, below the boom) the GPS reception is compromised (ignoring any compromisation caused by geography or topography) - I vaguely recall you use an external aerial of some description. Are my recollections correct - and if so - what do you use.

Jonathan

 

[Neeves]

So it is worth persisting to sort out the problems with your anchor alarm. While an anchor alarm is only a secondary system (the primary system is good anchoring gear) it is nevertheless an important safety device. If you anchor frequently the alarm should be working well in my view. In our case it has proved its worth on at least a couple of occasions.

There seems to be a contradiction here.

If your anchor alarm has proven its worth then.....

you must have dragged

if the anchor alarm is only a secondary system and the primary system is 'good anchoring gear' - then if you dragged....

your anchoring gear is not good.

Maybe a need to review.

Jonathan

And I remain interested as to whether you have some form of aerial to support your phone with its anchor app.

Thanks

 

[Solent sailer]

Paul, you are certainly not alone in having an anchor alarm that works poorly. Having to set such a large alarm radius means the alarm is all but useless. Setting a good anchor alarm is surprisingly difficult. The hardware needs to be suitable and installed correctly. Importantly, the centre of alarm radius has to coincide with the anchor position.

In many ways it is not dissimilar to problems of anchoring itself. If you have the right equipment and technique everything is easy and reliable.

The important message is that it is possible to to set a reliable alarm that will wake you up if your anchor moves more than very short distance. We do this every time we anchor and that is most days of the year. The only false positives we ever have are when forgetting to turn the alarm off when leaving (pretty stupid, but it does show the buzzer and the rest of the system is working).

The only other times the alarm goes off are on the occasions when we deliberately set an anchor alarm that is designed to wake us with a wind shift (this is not really a false positive, as the alarm is alerting us just as it has been set to do).

So it is worth persisting to sort out the problems with your anchor alarm. While an anchor alarm is only a secondary system (the primary system is good anchoring gear) it is nevertheless an important safety device. If you anchor frequently the alarm should be working well in my view. In our case it has proved its worth on at least a couple of occasions.

I agree with what you are saying, I am well aware of the need to set the center of the swing over the anchor, most app allow you to make adjustments which is good.
As i said we had a garmin gps with an excellent anchor alarm option and i installed a remote sounder so we would never miss it. Raymarine MFD has an anchor alarm option but no way to install remote sounder (i have spoken to Raymarine about this).

This leaves me with the phone apps, even if i managed to get the alarm set with the center of the 15m of chain wrong there is no way it should trigger a 200m radius alarm!
We have a metal boat (i get a decent fix with it on the chart table during the day) but i have tried leaving the phone on deck overnight. That just wakes up the Neighbours and means i have to go outside to re-set it.
I have contacted some of the alarm app developers and tried there suggestions with no luck.

They look like a great product, that said i don't see that it is possible for me to be setting it wrong, my suspicion is the phone gps is going into a low power mode that the software developers have been unable to disable, may be a compatibility issue with my phone but i have tried 3 phones and two tablets and i sleep better with no alarm and a more generous scope of chain!

 

[sailaboutvic]

We seen to set our different to some here ,
I drop the pin about 30 second the anchor drop and forget , once the anchor set I then drop it in astern and compair where I an within the circle to the amount of chain we dropped , if we within a few meters of the circle I know the anchor set almost where we dropped it , ether way I then extend the circle to give me what every distance I want big margin if we have the room so no false alarm or very tight if there boats around us .
We now on our third day in a blow and so far we had no false alarm.

The only problem I found with this particular alarm is if the screens goes into sleep mode two hour later it lose it GPS and the alarm goes off and the only way I can stop this is to keep the pad plugged into the 12v system.

 

[RupertW]

There seems to be a contradiction here.

If your anchor alarm has proven its worth then.....

you must have dragged

if the anchor alarm is only a secondary system and the primary system is 'good anchoring gear' - then if you dragged....

your anchoring gear is not good.

Maybe a need to review.

Jonathan

And I remain interested as to whether you have some form of aerial to support your phone with its anchor app.

Thanks

Mine has proved it’s worth dozens of times over and I have never dragged. It’s worth is keeping me under the duvet if I wake up feeling something has changed. And I don’t have to get up disturbing my partner but can just we have have swung around a bit or whatever.

It has woken me up with false alarms showing some big movement occasionally but this happens more rarely now as the software improves and doesn’t take one random outlying reading.

 

[noelex]

We have a metal boat (i get a decent fix with it on the chart table during the day) but i have tried leaving the phone on deck overnight. That just wakes up the Neighbours and means i have to go outside to re-set it.
I have contacted some of the alarm app developers and tried there suggestions with no luck.

We have used numerous anchor alarms over the years. Currently we use a Vesper WatchMate Vision, which has been the best so far. It allows for an external GPS, which is important. This reduces multi-path distortion and allows all the available satellites to be acquired with the best signal possible. For an anchor alarm that does not produce false positives even with a tight alarm radius, an accurate and consistent GPS fix is needed.

The second advantage of the Vesper is that if you have heading information on the NMEA bus, the boat position is displaced to show the position of the bow roller not the GPS aerial. As far as I am aware, it is the only unit that allows this. The advantage is as the boat swings at anchor the bow moves over a much shorter arc than the stern, which is where the GPS aerial is commonly located. The net result is there is less variation in the distance between the anchor and the fix location, allowing a tighter alarm radius to be set. It is only in a few situations where a tight anchor alarm radius is essential, but it is helpful to have this option available.

Finally, as the unit only displays AIS and anchor alarm information, there is little chance of software conflicts, automatic updates, sleep modes or battery issues that can occasionally disable non marine devices such as tablets, phones etc.

The drawback of the Vesper is the cost, although it is also an AIS transponder.

Open CPN is an alternative less expensive option. The anchor alarm lacks the option of using the bow position, but it otherwise has an excellent anchor alarm. It needs to teamed with the right hardware (computer and screen) that have low power consumption and a stable operating system.

The alternative of tablet and phone apps are very easy, inexpensive and much better than nothing, especially teamed up with an external aerial, but if you anchor frequently there are better choices, albeit at a cost.

 

[noelex]

if we within a few meters of the circle I know the anchor set almost where we dropped it.

This is not necessarily correct. It only indicates the GPS aerial has moved the same distance as the rode length. The centre of the alarm can still have significant position error.

If I understand your technique correctly and the GPS aerial is not at the bow you are introducing this error. It will not have any consequence unless the wind shifts direction but a better anchor alarm can be set so this is not an issue.

 

[sailaboutvic]

The error is removed by adding the difference between where the bow is and where i am standing.

So far touch wood this as word fine and the difference between the outer circle and where the boat is after we swing , is within nothing to talk about .

I found this a much better way then pointing the phone to where I think the anchor is ,
Its fine to set in this way if you given your self plenty of room but in a very tight anchorage it wasn't the first time the alarm when off for no reason doing it like that.
We been in this blow for over 50 hours now and we swinging , 360 and back around its not gone off yet .
Our offset is 10 mts

 

[noelex]

The error is removed by adding the difference between where the bow is and where i am standing.
So far touch wood this as word fine and the difference between the outer circle and where the boat is after we swing , is within nothing to talk about .
I found this a much better way then pointing the phone to where I think the anchor is ,
Its fine to set in this way if you given your self plenty of room but in a very tight anchorage it wasn't the first time the alarm when off for no reason doing it like that.
We been in this blow for over 50 hours now and we swinging , 360 and back around its not gone off yet .
Our offset is 10 mts

Sorry, Vic, I don’t really understand your method for displacing the GPS position to indicate correctly the anchor position. It sounds like you have thought about the problem and have a system in place. Importantly, your alarm is working well and that is what matters.

However, perhaps the following comments may help someone.

You need both a distance and a direction to offset the position.

Surprisingly, if the anchor alarm is set in the correct position, the alarm radius will always have to be greater than the rode length by at least the distance between the bow and the GPS aerial. This applies even if you had a theoretically perfect GPS unit with zero error.

An example may clarify. Let us assume that a typical distance between the GPS aerial that is used for the anchor alarm and the bow roller is 10m, and 50m of rode is deployed. If the rode is stretched out, the GPS aerial will be 50m from where the GPS aerial was when the anchor dropped, but the GPS aerial will actually be 50+10=60m from the anchor. So if the alarm centred correctly, over the anchor, the minimum alarm radius even assuming a theoretical perfectly accurate GPS and no allowance for error in his example would be 60m. In practice a larger alarm radius would be needed.

So, if your GPS is some distance from the bow, the successful setting of an alarm radius very close to the rode length strongly suggests the centre of the alarm radius has not been correctly set.

( I am assuming the maximum distance from the anchor is the same as the rode length, which is mathematically incorrect, but close enough at most scopes)

 

[sailaboutvic]

No problem I always happy to be correct if I'm wrong , how else do we learn .
I been setting the alarm this way for some years now , thr first anchor alarm where really hit and miss but the latest once I found much better .
We happen to be on a very tight circle , not because anchorages is full but after the first morning after the first blow I woke to find a yacht close to me , I assumed he drag and called out to him to warn him , he shouted something back but I couldn't hear cos of the wind next I heard him putting up chain I thought he was going to move , he must had pulled 20 mts then when back down below , I found this worrying thinking he could have much chain left out .
Some hours later he pulled more chain up as he was now close to another boat as we swing around a bit , I was thinking of moving now ,at the same time the wind picked up as a thunderstorm came over us a shift in the wind sent us all 360 around and now he was a very long way from us all ,
I can't imagine how much chain he must of laid in 5 Mts of water ,
Good bit is the wind is forecaster to stay like this over night and by mid day to morrow dropping to a 5 .

 

[Neeves]

It does not matter how much you spend on a phone and the anchor app or the navigational device and its soft ware if the GPS signal is degraded or distorted. This may happen because of the geography of your location as satellites fall below the horizon or because some nefarious organisation decides its a good wheeze. You need to have a back-up, which will involve some form of technology available pre, say 1990, transits, compass at the foot of your bed etc. Your navigation should be sufficiently good that if the GPS system does 'fail' you know where you are and how to get to wherever you were aiming for.

The comment that we rely too much on electronics was prescient and should not be ignored.

http://www.mysailing.com.au/cruisin...s renewed Mariner Warning on GPS interference

Jonathan