AIS, yes again. The good and the bad.

[Sans Bateau]

The 'Shipping lanes near-misses' thread was running its full course last week whilst I was away in Cherbourg. A trip that was meant to be a coast hop East finishing up in Honfleur, but alas three days of NE F8 gales kept us tied up in Cherbourg.

I have read parts of the thread and get the gist of the discussion, but have decided to start a new thread, particularly about AIS.

Over winter I installed a new Garmin plotter with a Comar AIS receiver. The plan was to have plotter. radar and AIS all in one place, at the helm, where it is best placed.

The trip to Cherbourg was the first useful test of the new system, so as soon as we started to encounter ships in the West bound lane I set about testing the new AIS, comparing its calculations with my own (best guess?). For several ships, I started out making a visual assessment, then backing up my thoughts with a radar plot, all that I would have previously had available. Then moving the cursor over the 'ship' on the screen, bringing up the information, including closest approach.

To begin with there was nothing startling, no potential close encounters. However the AIS readings were proving to be far more accurate than my best guess, I confirmed the distance off using the radar in every case whilst I gained confidence in the new device.

It was not until later when I got into the East Bound shipping that two incidents convinced me of the value of the AIS. The first of these two encounters was a ship that previously I would have been sweating over, doing a 360, spilling sails or changing course. However the AIS was telling me the closest approach would be about a mile, I cautiously stood on, watching and monitoring the situation. True enough, confirmed by the radar, the ship passed a good mile off. What was interesting is that the ship had altered course by a mere 2 deg about 10 minutes before he passed, had he seen me and done that? The second incident was a ship I could not even see at first, it was to far away. I started to monitor an AIS signal from a vessel an hour away, doing 9.8knts! It would pass an uncomfortable 200 meters clear. Standing on, after about 45 mins a vessel became visible, but only just. Later I could see it was one of those small coastal tankers, like a barge, that when laden sits very low in the water. It was clear that in this case I was going to to have to take action to increase the 200mtr approach, he may have been happy with 200mtrs, but I wanted more. With that I turned 30deg to Stbd and the distance soon grew to 300, 350 then 500 mtrs, we're clear to his stearn.

The first of these encounters would have previously had me unnecessarily taking action, the second incident I had to take action anyway, but hell I did have an hours notice!

Previously I had on the boat a NASA AIS screen, which was far less useful than the information that I now have.

That was the good bit about AIS.

Heading back to Chichester yesterday, after a night in Beaulieu, as we approached Horse Sand Fort, I could see the Normandy heading up past Bembridge, I switched on my AIS, but not for long. I wanted to see how fast she was going and how soon she would pass in front, a curiosity enquiry. If my AIS was to be believed, I was about to be in collision with any number of vessels from just about every angle!!

In my opinion, the large number of leisure boats that are fitting AIS transponders will devalue the worth of AIS as a tool to safe navigation. When we arrived in Cherbourg last Sat night, the marina was the home of a RORC race, around 6 boats on berths were still transmitting AIS!! How long before, in the Solent, tugs, ferries and other commercial traffic get fed up with a constant barrage of AIS targets? Is the AIS class B transmitter going to be the new 'radio check' nuisance?

 

[Blue5]

In my opinion, the large number of leisure boats that are fitting AIS transponders will devalue the worth of AIS as a tool to safe navigation. When we arrived in Cherbourg last Sat night, the marina was the home of a RORC race, around 6 boats on berths were still transmitting AIS!! How long before, in the Solent, tugs, ferries and other commercial traffic get fed up with a constant barrage of AIS targets? Is the AIS class B transmitter going to be the new 'radio check' nuisance?

I have an AIS transceiver, not ashamed to admit it and would offer the following comment.

As I see it any device that will enhance safety has to be a benefit but I take your point.

In the RTIR on Saturday the plotter screen was just a massive blob of AIS returns. Now on my unit the default setting is "on" so when I turn the batteries on I have to disable the transmit signal, no big deal but given the unit is under the nav seat a certain amount of faffing about. The AIS does not need to be actively transmitting in a gin clear day in the solent but if I am on passage Cross Channel it goes on.

I am not sure what procedures other manufaturers follow but on my unit if the default was "off" and had to manually selected to "on" I think a lot of the problems would be solved.

Just my 02p worth

 

[timbartlett]

if the default was "off" and had to manually selected to "on" I think a lot of the problems would be solved.

Just my 02p worth

I don't quite understand the "problem". In dense traffic, you see a lot of blobs. Surely that is the same with radar as well as by eye?

Why would you wish to make yourself "invisible" by turning off your AIS tranmitter? And why would you wish to make yourself "blind" by turning off your AIS receiver?

The problem is that this is still a relatively young technology (compared with radar and eyeball), and we haven't got used to it yet. As we do, I suspect we may find that our ideas about how to use it change -- just as the shipping world is gradually getting used to the idea that the AIS display needs to be a big screen at the front of the bridge, rather than three lines of alphanumeric data tucked away at the back. I think we will start to decide that overlaying everything on the chart is a mistake, and that it is better to have separate screens (or at least separate "windows") for separate jobs.

My guess (only a guess) is that in ten years time, we will all be wondering what the fuss was about, as we look at our 24-inch multi-function displays , in which the AIS, chart, and radar are displayed in three separate "windows", with overlaying as an available (but little-used) option.

 

[Danny Jo]

In my opinion, the large number of leisure boats that are fitting AIS transponders will devalue the worth of AIS as a tool to safe navigation. When we arrived in Cherbourg last Sat night, the marina was the home of a RORC race, around 6 boats on berths were still transmitting AIS!! How long before, in the Solent, tugs, ferries and other commercial traffic get fed up with a constant barrage of AIS targets? Is the AIS class B transmitter going to be the new 'radio check' nuisance?

I share this concern, but am resigned to the inevitable.

It would be nice to have a simple toggle to switch off the alarm function on my plotter before entering a harbour or marina, to prevent the deluge of "dangerous target" alarms that is irritating, if not dangerously distracting. I did install a separate switch for the NASA AIS receiver, but cannot use it with the current configuration by which the NASA AIS receiver also relays GPS data to the plotter.

But this nuisance element is greatly offset by the value of AIS data from shipping on courses crossing mine. Like Galadriel, I have found that AIS tells me about the minor course changes being taken to avoid me by ships that might otherwise have caused me periods of anxiety lasting 20 minutes or so.

 

[AIDY]

Galadriel... not on the subject.... but i heard you call in with solent last saturday mid morning... was expecting you to start your travels to scotland. but no cherb.. or have i got my wires crossed somewhere

 

[huzar30]

GPS, AIS, chartplotters (or a laptop in my case) - examples of technology that have made our lives safer. In addition, they have taken a lot of the stress out of the situation. As you say, you look at a target by eye and start worrying. You look at it on the AIS and think - I'm clear. Alternatively, you realise you aren't clear, and, as you say, you can do something about it in good time.

As to alarms - the sets need some way of having them switched off, or having some way of altering the CPA alarm setting. A 1 mile CPA mid channel is not quite the same as a 1 mile CPA coming through the forts.

 

[lw395]

I don't quite understand the "problem". In dense traffic, you see a lot of blobs. Surely that is the same with radar as well as by eye?

Why would you wish to make yourself "invisible" by turning off your AIS tranmitter? And why would you wish to make yourself "blind" by turning off your AIS receiver?

.

The problem is that sailing in congested waters, a yacht really only wants to see vessels of say 50 tons or more (plus a few special cases) not the rest of the racing fleet.
When you have too many transponders in too small a space, not only is the information hard to understand visually, but also older units may only be able to deal with a sensible number of contacts. As the commercial ships were the first to be required to have AIS, they will often have the oldest units.
There is also only a finite number of time slots for transponders, so there is a limit to the number of ships the system can handle.
I'm out of touch with the technology, but I worked on some hardware for class B some years ago. I don't think it was envisaged that the majority of yachts would fit transmitters.
I'm sure the software has evolved since then.

On a yacht, it would be OK to not display info from other yachts, or maybe only those within a very small radius.
However if you are expecting ships to monitor the tracks of all the yachts you might be disappointed.
There could be a danger of switching in filters for good reasons, then failing to switch them out again, or having some complex scheme where people lose track of exactly what is being displayed.

 

[Sans Bateau]

Galadriel... not on the subject.... but i heard you call in with solent last saturday mid morning... was expecting you to start your travels to scotland. but no cherb.. or have i got my wires crossed somewhere

No, you are right, the Scotland trip had to be cancelled for this year, I did a post.

 

[AIDY]

No, you are right, the Scotland trip had to be cancelled for this year, I did a post.

sorry behind times.... but thanks for reminding me to take note of my cg66 number

 

[Sans Bateau]

sorry behind times.... but thanks for reminding me to take note of my cg66 number

Yes, they did ask a lot of questions, didnt they?

 

[timbartlett]

Please forgive the terse tone -- it's for the sake of brevity, not to start an argument.

a yacht really only wants to see vessels of say 50 tons or more (plus a few special cases) not the rest of the racing fleet.

Who says? I might be really interested in my fellow competitors! And who would set the size limit?

When you have too many transponders in too small a space, not only is the information hard to understand visually

Don't these problems apply to radar and eyeball too? And can't you solve them by changing range, electronically sorting the information, or using other methods of collision avoidance at the same time?

There is also only a finite number of time slots for transponders, so there is a limit to the number of ships the system can handle.

Several thousand, isn't it? And if the system does overload, don't AIS B targets drop out first? And isn't it the weakest (generally most distant) that drop out?

I don't think it was envisaged that the majority of yachts would fit transmitters. I'm sure the software has evolved since then.

Unless it is made compulsory (as the USA is considering) I don't think the majority will -- and as you say, the technology is evolving.

On a yacht, it would be OK to not display info from other yachts..., However if you are expecting ships to monitor the tracks of all the yachts you might be disappointed....There could be a danger of switching in filters for good reasons, then failing to switch them out again,

I wouldn't ask (or expect) anyone to monitor all vessels, any more than they do by eye or by radar -- only those that pose a threat. And surely AIS gives us the opportunity (even if it is not universally achieved yet) to have a bridge/cockpit/wheelhouse display that highlights the most dangerous targets, rather as ARPA does?
This is not the same as filtering out whole categories of vessel. If watchkeepers are able to "filter out" class B targets, I doubt it will be long before we see the first case in which a watchkeeper is penalised for failing to keep a proper lookout by AIS (as one of the "all available means appropriate in the circumstances")

 

[Ubergeekian]

I wouldn't ask (or expect) anyone to monitor all vessels, any more than they do by eye or by radar -- only those that pose a threat.

The problem that other posters seem to be highlighting is that in crowded waters, many, many boats might potentially appear as threats. That yachts which has just tacked towards you two miles away, for example, and will (although the AIS can't know it) tack away again in five minutes. How does one go about eliminating that - and three hundred others - but not the hydrofoil ferry just behind it which won't be tacking away. Only things which are likely to collide within a given time?

Or maybe AIS simply isn't the tool to use, just as pilotage tends to depend a lot more on "what can you see right now?" and a lot less on "what's the plan on the chart?"

 

[lw395]

Fair comment Tim,
I think it can be summarised as when there is a lot of data, you need to start prioritising it, and that means discarding some.
You will want to know how that has been done. What seems a logical way to filter to one person, may not suit another.
I didn't think the capacity was for over 1000 vessels in range, but as I said I have not read the

We may one day think back fondly to being able to easily see all the ships without the clutter of yachts.

Imagine being in the early stages of a Fastnet, with a ship following you out the Needles. Loads of yachts with changing courses up the beat will constantly alter the CPA list.

 

[jonjo]

I am the biggest AIS fan on this forum but have only switched mine on twice inside the Solent during the past 3 years. When the Solent is crowded by definition the weather will be good and everyone should be using sub 1nm eyeball pilotage. I don't under stand why the YBW.com chatter keeps drifting back to these irrelevant fringe discussions about AIS info overload inside the Solent where everyone including big ships are twisting and turning making any AIS predictions over 1.5nm void.

The only time I needed AIS inside the Solent was on an August evening, 30 minutes after sunset, the air was filled with a warm front drizzle and vis about 2 miles max. I doubt there were more than 10 leisure boats out in the Eastern Solent.

My brain was discharged because I was 35 hours out of Cameret and sailing solo, 2 miles east of Cowes and heading for Portsmouth I looked through the drizzle and thought one of forts had a strange shape, next I wondered why the fort was showing a green and red light. Soon after I realized I was going head to head with a low tanker 0.5 mile away. In this case even if every leisure boat had a AIS transponder I would have picked out the tanker.

The Solent is surprisingly empty 99% of the time.

 

[Sans Bateau]

The problem that other posters seem to be highlighting is that in crowded waters, many, many boats might potentially appear as threats. That yachts which has just tacked towards you two miles away, for example, and will (although the AIS can't know it) tack away again in five minutes. How does one go about eliminating that - and three hundred others - but not the hydrofoil ferry just behind it which won't be tacking away. Only things which are likely to collide within a given time?

Or maybe AIS simply isn't the tool to use, just as pilotage tends to depend a lot more on "what can you see right now?" and a lot less on "what's the plan on the chart?"

That is exactly the point! In the example I highlighted, return to Chichester, I turned off the AIS because of the 'clutter'. I could see the Normandy clearly, so your second para rings true. But what is the point in a system where you cant separate the real dangers? On my system I could have reduced the range, but that would apply to all vessels. I'm happy to have 1 minute warning of a yacht at 7 knts, but want considerably more for a VLCS.

If the AIS receivers could allow the user to choose A or B or both, that would be a good solution.

 

[lw395]

I am the biggest AIS fan on this forum but have only switched mine on twice inside the Solent during the past 3 years. When the Solent is crowded by definition the weather will be good and everyone should be using sub 1nm eyeball pilotage. I don't under stand why the YBW.com chatter keeps drifting back to these irrelevant fringe discussions about AIS info overload inside the Solent where everyone including big ships are twisting and turning making any AIS predictions over 1.5nm void.

The only time I needed AIS inside the Solent was on an August evening, 30 minutes after sunset, the air was filled with a warm front drizzle and vis about 2 miles max. I doubt there were more than 10 leisure boats out in the Eastern Solent.
....


The Solent is surprisingly empty 99% of the time.

It is handy for those medium sized ships when you are wondering if they are going N of the Ryde Bank, or if a vessel coming out of Soton might go out the Needles instead of the Forts. It can save you getting boxed in by the exclusion zone with a little earlier warning.
Also 'seeing' those container ships before you round Gurnard can help you plan ahead.
Not going to help you avoid anything you couldn't avoid anyway, but can help you avoid it in a more convenient way.
Also, there is some mileage in using these toys often, so that when you need them you are in practice and familiar with everything.
Perhaps the more real issue is that the ships are receiving cluttered info. which will undermine the use of AIS?
I would think 37 Sunsail targets would soon get irritating!

 

[timbartlett]

Perhaps the more real issue is that the ships are receiving cluttered info. which will undermine the use of AIS?

The idea of ships being able to arbitrarily decide to delete all small craft by pressing a button fills me with horror. Even more does the thought that it would probably be buried in some menu system so that one watchkeeper wouldn't know that the guy who was on before him had done it!
But I think the problem boils down to the displays.
Ships do not piss about with 7-inch radar screens or chart plotters, far less to they try to overlay the radar onto the chart on a 7-inch screen. They have BIG screens (well, a growing proportion of them do) And if you imagine three or four 23-inch screens, one for radar, one for the chart, and one for AIS, I don't see "clutter" as such a serious problem. I'm not pretending that they are there yet ... but I think it's the general direction they are heading.

 

[jonjo]

The idea of ships being able to arbitrarily decide to delete all small craft by pressing a button fills me with horror...

How about a 20 second auto release feature?

 

[Sans Bateau]

It's a fair point you make TB, and crossing the channel, if one feels happier letting other ships who may or may not be keeping a proper watch know your out there, then an AIS transponder has a value. Personally I prefer to be relying on me doing the monitoring and being prepared to take the action, where necessary.

However it was not my intention for the thread to take the course it has, its more about the value of AIS in shipping channels. The point about the transponders, for me anyway, is why oh why does one need to be transmitting AIS from a small boat in superb vis in the Solent or on a berth in Cherbourg.

My AIS is off until the next trip outside the Solent.

 

[timbartlett]

However it was not my intention for the thread to take the course it has,

I know the feeling!

why oh why does one need to be transmitting AIS from a small boat in superb vis in the Solent or on a berth in Cherbourg.

Agreed!