AIS Class B targets

[s/v Jedi]

Originally Posted by Robin3

Here in our marina we get AIS alarms as soon as we switch on[…]

Originally Posted by transmitterdan

But there are no doubt algorithms that could be proposed that would make AIS much better in crowded areas. Intelligent filtering is going to be required if AIS is to help avoid collisions in places where they are most likely.

A good first step is to disable alarms for stationary targets. This does require you to use your eyeballs to see if you're not sailing into one such stationary object, which is not obvious according to previous threads

[Littlechay]

This is a super interesting debate.

To me the Solent is a bad example. When it is so busy with races, the visibility is good enough to race, so vessel operators should be navigating 90% the traditional way with their heads outside and their eyes up off the screens. In other words it is not a situation where you would, or should, be using AIS as prime tool (turn off the alarms and look outside). When the fog comes down then obviously radar, and AIS etc. come into play but presumably by that time racing will have been called off and boats will be heading for port on more predictable courses.

Harbours are always a challenge, even here in little old Stanley, if I turn on my AIS with alarms enabled I get plenty of alarms, at least two for every ship entering: the first as they make the turn into the outer harbour when their projected track hits me even though there is a peninsula with an airport on it in the way; the second when they enter Stanley Harbour proper and make their turn to dock. On a busy day the alarm sounds continuously until I switch it off after 5 minutes due to fishing boats and cruise ships heading directly toward me at quite close range with 0CPA.

Personally as long as visibility is good I never have AIS alarms enabled, in harbour, but as soon as I am out of harbour traffic I turn them on. At sea I open everything up, max range, no filters etc.. as anything in the ocean is quite likely big and traveling fast so I want to know about ASAP especially when there is no traffic about and none expected.

I also only transmit when I am clear of harbour. With modern ships on single operator watchkeeping and not necessarily with a listening watch on CH 16 AIS and DSC are our best tools for getting noticed.

[Robin3]

Originally Posted by Littlechay

This is a super interesting debate.

To me the Solent is a bad example. When it is so busy with races, the visibility is good enough to race, so vessel operators should be navigating 90% the traditional way with their heads outside and their eyes up off the screens. In other words it is not a situation where you would, or should, be using AIS as prime tool (turn off the alarms and look outside). When the fog comes down then obviously radar, and AIS etc. come into play but presumably by that time racing will have been called off and boats will be heading for port on more predictable courses.

Harbours are always a challenge, even here in little old Stanley, if I turn on my AIS with alarms enabled I get plenty of alarms, at least two for every ship entering: the first as they make the turn into the outer harbour when their projected track hits me even though there is a peninsula with an airport on it in the way; the second when they enter Stanley Harbour proper and make their turn to dock. On a busy day the alarm sounds continuously until I switch it off after 5 minutes due to fishing boats and cruise ships heading directly toward me at quite close range with 0CPA.

Personally as long as visibility is good I never have AIS alarms enabled, in harbour, but as soon as I am out of harbour traffic I turn them on. At sea I open everything up, max range, no filters etc.. as anything in the ocean is quite likely big and traveling fast so I want to know about ASAP especially when there is no traffic about and none expected.

I also only transmit when I am clear of harbour. With modern ships on single operator watchkeeping and not necessarily with a listening watch on CH 16 AIS and DSC are our best tools for getting noticed.

Commonsense at last! Except that fog never stops Solent racing once started and it can appear or vanish in minutes with the turn of a tide . THe real culprits here are the berks that are transmitting 24/7, some because the charter companies set them up to do that ( Scumsail I think mostly in the Solent)but many because the people on board or in the charter offices know no Better or are too stupid to understand the implications of creating an electronic smokescreen that one day may backfire on them because others will simply switch off totally in despair when there are too many trees to see the woods, (dumb c**t school of crying wolf safety)

[roundm]

Hubert

I went down the boat to do some maintenance this morning, and thought I'd see what was out and about today. As it's mid march many boats are still to be launched (parking is a challenge as the boatyard is full of boats!).

I now have a file created from my boat. This is the AIS output from a Standard Horizon GX2100 connected to a an aerial mounted about 12m above the waterline (normal position on top of the mast) fed into my onboard laptop. I.e it is a single antenna and I've not left my mooring inside Portsmouth harbour. The aerial is nothing special and I have hills and land between me and some of the targets.

and before anyone starts harping on about Sunsail, Britania or any other commercial organisation, there are 12 sunsail yachts in this, but I can predict where they are going to so they are not a problem (they broadcast their routes before they race, so anyone listening can work out what they are up to if they are worried) and the main racing season has not started - the private racers are more of a problem as they often get given their courses before taking to the water (so no way for anyone to predict where they are going) and some seem to think the colregs including a right of way for racing craft - the cry of "don't you know
I'm racing" has been heard many times.

The 2 files have 135 and 139 targets shown in them. The larger file has data collected over about an hour, the other is a shorter time period. As there is a limit to some attachment sizes, I've added them by adding pdf to the extension (is there a better way to do this ?) just loose that and unzip them and Opencpn should play them.

my onboard display is a 19inch, 1400x900 monitor - so I shouldn't be short of real estate to display it on

This is early in the season and will get much worse over the next month or so, but already I think you can see the problem we face. I'm out sailing tomorrow, so will create another file whilst I'm underway and post that as well.

and as an added comment, I met with someone from the Southampton VTS a few days ago, and whilst they log all AIS transmissions and keep them incase of an incident for a month, they disable display of Class B transmitters on their working screens as they generate too much clutter! If that is the case for people who stare at the screens to navigate large vessels, then those of us who glance at the chartplotter only every few minutes have a bigger problem.

Anyway I hope this is helpful, I'll post the other log tomorrow

Regards and good sailing

Mark

[rgleason]

See Hakan's questions:
http://www.cruisersforum.com/forums/...ml#post1657576

Maybe his track buddies request should become a Tracker Item under AIS?

He asks what the difference between
Default Tracking and Always Track is...
Perhaps "Always track" shows no matter what distance away.