AIS Class B targets

[bcn]

We got a nicely crowded solent - courtesy of em-trak, thanks.

Pavel can play now a bit more I hope....


Hubert

if somebody else wants the file for playing, please drop me a mail at info@o-charts.org

[markpierce]

Information overload ... the law of diminishing returns ... it's just a mess of boats out there.

A sharp, visual lookout is the primary tool to avoid collision.

[markpierce]

And then there are the electronically undetectables:

[bcn]

Nobody is discussing that - issue here was how to optimize the information in order to detect the important things. How to deal with a situation like the one from the data set? Can we get a filtering that is intelligent enough to help?

And nobody here doubts neither about to have a sharp lookout (not just on the screen or perhaps the iPad....)

Hubert

[markpierce]

Yikes, a ship! Won't be crossing to the starboard side of the channel just now.

[Littlechay]

I think a nice feature to have on the AIS filter settings is the ability to save the settings as a profile. Once you have the settings set up and working how you want for a particular type of situation you could save it as a profile, e.g. at anchor, harbour, coastal, open ocean.

With saved profiles it would be easy to switch back and forth as your needs change.

This is what you can do with the Vesper Watchmate AIS units and it works very well.

Chris

[Beachcomber_]

My problem in the Adriatic is not so much the Class B clutter but the alarms they produce. The alarms from Class A are invaluable to me because of the heavy population in the area of fast ferries and my netbook running OCPN is below on the chart table. To have to go below to cancel the constant Class B alarms from those tacking yachts is so much a pain that I am now forced to inhibit all alarms. This has only happened in the last two years when Class B transponders have boomed where I sail.

Having something like anchored ship alarm suppression for Class B would be great. Or if that is too radical - to inhibit anything based on its class - perhaps on speed? Anything under 10 knots is unlikely to be a vessel likely to kill me. I understand the Watchmate has such a speed parameter for inhibiting alarms.

[bcn]

Originally Posted by Beachcomber_

Having something like anchored ship alarm suppression for Class B would be great. Or if that is too radical - to inhibit anything based on its class - perhaps on speed? Anything under 10 knots is unlikely to be a vessel likely to kill me. I understand the Watchmate has such a speed parameter for inhibiting alarms.

(RTFM) Something like this :

[Beachcomber_]

Originally Posted by bcn

(RTFM) Something like this :

Thanks for that ... but I interpret that function as "hide" the target. Presumably also all attributes including alarm generation - however, I still want to see it.

Or have I misinterpreted?

[bcn]

It's not the elegant solution, no - profiles with more option would improve the issue, yes.

[Beachcomber_]

Originally Posted by bcn

It's not the elegant solution, no - profiles with more option would improve the issue, yes.

So, from that I understand that my interpretation was not in error, there is no way to suppress alarms from non-threatening Class B target reports when within the CPA and TCPA alarm parameters without cancelling their entire display, and that to ask me to RTFM was not necessarily helpful.

The fact remains that I now inhibit all alarms because I get too many spurious ones from the many other yachts crowding the Adriatic with Class B transmissions, despite having had one very near miss from a 33 knot ferry driven by a cowboy ignoring all colregs (having had to call him on channel 16), and not an untypical situation.

[s/v Jedi]

You get spurious alarms? Can you define that? Are those alarms that are in error because of faulty equipment or is it because yachts change course after the alarm to correct the situation? Or do they keep changing course erratically?

I never saw an AIS receiver that gave me spurious alarms...

[Beachcomber_]

Originally Posted by s/v Jedi

You get spurious alarms? Can you define that? Are those alarms that are in error because of faulty equipment or is it because yachts change course after the alarm to correct the situation? Or do they keep changing course erratically?
I never saw an AIS receiver that gave me spurious alarms...

Spurious was possibly a misnomer, my apologies. They fitted the alarm parameters that were set for Class A vessels, that can be very fast-closing, by being relatively close and were persistent and repetitive after resetting because they altered course towards me randomly - probably short-tacking or not well-steered to a course.

This is not a one-off occurrence, for me the past two years in the Adriatic has needed the alarms permanently disabled due to the proliferation of Class B targets milling around.

[denverd0n]

Originally Posted by MarkJ

And when theres 300 boats coming towards you then I bet your eyes are peeled and when you see a wall of steel a thousand times bigger than one of those yachts you will notice its a ship.

Exactly. If you are using AIS as a substitute for keeping your eyes peeled then this might be a problem, and you might need a way to filter out some of the targets. But then, if you are using AIS that way, you are just an accident waiting to happen anyway, so what difference does it make?

Not only that, but the idea that you need to filter out Class B targets implies that, somehow, a collision with a Class B target is something you don't have to worry about. Excuse me, but colliding with a Class B target can ruin your day just as quickly as colliding with a Class A target. What's more, because of its size, you are more likely to actually see the Class A target from farther off.

No, the very concept of there being some need to filter out Class B targets is just completely flawed, right from the start.

[bcn]

denverd0n,

perhaps not filter them out - but what about alarm settings CPA < 1nm for Class A and CPA < .25 nm for Class B (and if you like speed and TCPA as additional or complementary parameters)?

Harbor, Approach, Coastal or Offshore might be scenarios for different settings.

Just an idea....