Ais alarms repeatedly in big seas

[endlessbull]

Hello,

Love opencpn. I run the latest version on my android phone. I'm sailing offshore regularly and use the ais alarm. The problem is that the same target will constantly generate alarms to the point that you turn the volume off. Neither silence alarm button nor acknowledge will stop the alarms.

I suspect that with big seas the cpa and time limits get satisfied, then not, then satisfied, then not....for quite a long time because the speed and direction of both vessels change due to the seas.

You need to be able to shut off the alarm target by target. Or set a limit to how often a single target can generate an alarm...

It is vital to.have this alarm offshore when short handed. I send my alarm to a bluetooth speaker to be sure it gets attention.

Thoughts
Bill

[ChrisJHC]

Can’t you change the CPA distance alarm to a really small value to reduce the number of times it is set off?

And then, once the vessel has passed, return it to its usual value?

[endlessbull]

Originally Posted by ChrisJHC

Can’t you change the CPA distance alarm to a really small value to reduce the number of times it is set off?

And then, once the vessel has passed, return it to its usual value?

Well that is a better answer than just turning the volume down until the target passes which is my current approach. Both are unsatisfactory in high traffic areas like the Mediterranean where I am now. Here you can ften have multiple ships to worry about at the same time and new ones entering your "danger zone".

Hopefully one of programmers can find an easy solution that will work.

[BillKny]

This is a common problem. And not just in big seas, but while sailing with shifting winds causing frequent heading changes.

All the recreational AIS systems I know of use a stupid simple algorithm for the alarm. They simply sort all targets by CPA and then alarm if any vessel has a CPA less than the alarm value. Like the OP we have found this issue to severely limit the usefulness of the AIS CPA alarm.

It would be so much better to keep track of the alarm status BY TARGET so a flag for alarm acknowledgment could be set by target

Do any of the newer/fancier systems have a better approach?

[rwidman]

How can a phone receive AIS signals?

If AIS is important to you, why not install a "real" AIS transceiver and antenna? They are just a few hundred dollars.

[Joh.Ghurt]

Originally Posted by rwidman

How can a phone receive AIS signals?

If you have a NMEA to TCP (or Wifi) gateway, you have your AIS-data on any device, including phones. Some AIS-boxes or Chart-plotter have this functionality included, otherwise you'll just have to add a cheap gateway to your net. This is a great thing to have on board.

[KimSails]

Originally Posted by Joh.Ghurt

If you have a NMEA to TCP (or Wifi) gateway, you have your AIS-data on any device, including phones. Some AIS-boxes or Chart-plotter have this functionality included, otherwise you'll just have to add a cheap gateway to your net. This is a great thing to have on board.

Exactly. That’s what I have - my Vesper 8000 unit creates a WiFi access point. I can connect a phone, tablet, or computer to it. Vesper provides a proprietary WatchMate phone app, but I generally check AIS targets on iNavX, which pulls in the data through WiFi using a TCP/IP connection for NMEA data.

[boat driver]

Originally Posted by endlessbull

Hello,

Love opencpn. I run the latest version on my android phone. I'm sailing offshore regularly and use the ais alarm. The problem is that the same target will constantly generate alarms to the point that you turn the volume off. Neither silence alarm button nor acknowledge will stop the alarms.

I suspect that with big seas the cpa and time limits get satisfied, then not, then satisfied, then not....for quite a long time because the speed and direction of both vessels change due to the seas.

You need to be able to shut off the alarm target by target. Or set a limit to how often a single target can generate an alarm...

It is vital to.have this alarm offshore when short handed. I send my alarm to a bluetooth speaker to be sure it gets attention.

Thoughts
Bill

The issue is combination of your cpa limits and heading.
First, where is the gps info arriving from? cpa limits set? heading source?
then reduce the cpa limits and dampen your heading values, the issue is the heading swings of the boat on seas/wind make the target a "new" warning, then when heading swings other way it becomes a "passed" target, then swings back to a "new" target and alarm.

[Dsanduril]

Our 10-year-old Vesper Watchmate 850 has a by-target mute function. Once you receive and mute alarms for a target they stay silent until the target is lost and re-acquired. Seems like basic functionality to me, we use it all the time. Alarm goes off, we review the CPA situation and usually mute the alarm. This is pretty standard/basic alarm control philosophy.

I don't use alarms in OpenCPN (because they work so well on the Vesper I've never seen the need), so I don't know if the feature exists. Frequently do use O to display the real-time CPA solution once I get an alarm.

[requiem]

Should this be moved to the OpenCPN forum?

Disabling tracking for a target can come back to bite you should either change course. E.g. the first two times it's a false alarm, the third time it's for real.

I would be surprised if the CPA calculations are based on heading rather than course, as that increases error from yawing. If OpenCPN uses course, then the calculation would likely be based on whichever moving average is used to determine course. Being able to smooth that out might help things. Remember, a traditional hand plot might use 3 or 6 minute intervals to determine course.

I see there's an option to calculate SOG and COG based on position changes, and you can specify the time interval. Hopefully someone else can indicate why this shouldn't be used, but if you're swinging about quite a bit in heavy seas my impression is it might help.

If the problem is other ships yawing about then I don't see an easy option, but I would expect larger ships to be more stable. In heavy traffic I'd likely disable alert popups as I'd want to be watching the screen myself and not relying on alarms to alert me. Otherwise it's like being the guy who crashed his on-autopilot Tesla whilst playing video games.

[cr180]

Originally Posted by endlessbull

Hello,

It is vital to.have this alarm offshore when short handed. I send my alarm to a bluetooth speaker to be sure it gets attention.

Thoughts
Bill

We stand watch when offshore, so the helm is always manned. We use AIS at night or in low visibility conditions, but actually track the targets on the screen visually. Agree the audible alarm function is a nuisance that distracts from its usefulness, so we do not use or rely on it. Not the response you were looking for, sorry. Can’t comment on a single handed scenario.

[wingssail]

Originally Posted by endlessbull

Hello,

Love opencpn. I run the latest version on my android phone. I'm sailing offshore regularly and use the ais alarm. The problem is that the same target will constantly generate alarms to the point that you turn the volume off. Neither silence alarm button nor acknowledge will stop the alarms.

I suspect that with big seas the cpa and time limits get satisfied, then not, then satisfied, then not....for quite a long time because the speed and direction of both vessels change due to the seas.

You need to be able to shut off the alarm target by target. Or set a limit to how often a single target can generate an alarm...

It is vital to.have this alarm offshore when short handed. I send my alarm to a bluetooth speaker to be sure it gets attention.

Thoughts
Bill

This problem has been raised previously (originally by myself in Flyspray 807, May 2012) and by others since then.

This year a solution had been implemented as reported below by Bobcat:

Admin
Dave commented on 20.03.2021 02:23
OK, I have implemented a solution in OCPN github master branch.

Solution logic:

1. An AIS Target Alert dialog will remain on-screen for a minimum of one minute (60 secs), even if the alert condition is transient and quickly disappears due to relative motion changes.

This should allow enough time to get to the screen, and react with the "Acknowldege" button.

2. Exception to (1):

a. if a Target Alert Dialog is displayed, but the target is no longer alerted (i.e. the Alert Dialog is in its 1 minute hold time)

and

b. if at the same time another AIS target becomes alerted, due to CPA/tCPA incursion...

Then, the first target Alert is cancelled, and the second, more critical, Target Alert is shown.

I think this solves the O.P critical point.

I am marking this Task Finished.

This was March 2021 so it's probably going to be in the next release. I haven't checked with the 5.2.4 because I haven't been out in rough weather near any AIS targets.

But if you think OpenCPN has this issue, try using the ais alarm function on a Standard Horizon Matrix radio, they are so impossible the only solution is to turn off the radio, how does that work for you when you are in a real impending collision situation. I've talked to Standard Horizon about it for years, they are total A**hats about it, just don't understand. I don't think anybody at Standard Horizon has ever been on a sailboat. They must do all their development and testing in a lab far from the sea.

[wingssail]

Originally Posted by Dsanduril

Our 10-year-old Vesper Watchmate 850 has a by-target mute function. Once you receive and mute alarms for a target they stay silent until the target is lost and re-acquired. Seems like basic functionality to me, we use it all the time. Alarm goes off, we review the CPA situation and usually mute the alarm. This is pretty standard/basic alarm control philosophy.

I don't use alarms in OpenCPN (because they work so well on the Vesper I've never seen the need), so I don't know if the feature exists. Frequently do use O to display the real-time CPA solution once I get an alarm.

I suggested (but they didn't implement this) that columns be added to the AIS target list for number of recent alarms(alerts), and how long ago was the most recent for each target AND ability to "acknowledge" any target on that list for a duration set in "settings".

Also, when doing an AIS Target Query, show the alert count, the time since last alert, and allow acknowledgement on that dialog even if the alert is not present at that moment.

The solution implemented (described in Flyspray 807) is pretty good and simple to implement so I think it's OK.

[sailingchiro]

Having alarms that alarm too often is no longer a safety device but a nuisance in my opinion. I shut my alarm off after the initial alarm.

Having too many alarms can be a huge distraction and safety issue. Distractions in the cockpit of a sailboat or airplane can be the downfall of a pilot/sailor.

In aviation, I shut off alarms to absolutely necessary items versus having a alarm for every time a gnat sneezes.

Always remember, fly the damn plane or sail the damn boat. Don't get lost with little distractions. Alarms are just alarms and they can be down right alarming in the wrong atmosphere.

[Dsanduril]

Avoiding alarm fatigue is a core concept in many system designs. It impacts everything from industrial control systems to medical systems at nurse's stations. It even happens at the cooking stations at McDonald's. Too many alarms, or alarms going in and out cause users to ignore alarms (boy cries wolf) or to set unrealistic limits for those alarms to avoid their generation.

It's a difficult task, when we surf down a wave at 12 knots for 30 seconds, and then drop out and do 5 knots for the next minute, what is the system supposed to do for CPA calculations? Because of that I accept the alarms, but fully expect an ACK function that allows me to say "thanks, I'm now aware of that ship, it's on me now, please go back to paying attention to other things I might have missed."

At sea we have a very broad alarm definition and the AIS frequently lets us know when the single ship within range is still over the horizon. Once we're alerted the alarm gets muted, it is then our responsibility. If conditions change (our speed, their course...) I don't expect a new alarm, others may feel different about that. We manage it by making sure we pay attention to the plot (pretty much identical to radar target tracking, but with more info).

When we came into SF Bay in the fog earlier this year the alarm was going off every 10 minutes, but once that vessel was added to our tracking I didn't need it any more, even though they were making lots of course and speed changes coming through the VTS, picking up a pilot, and transiting to/from the channel.

I'll have to give 5.x.x a try once the next release is out and see how the implementation works in the real world.