AIS, yes again. The good and the bad.

[timbartlett]

Can I repeat my earlier question?

Don't see why not!

Oh, you mean you wanted an answer!

(i) S-Band. The anti-AIS lobby argues that ships may not have their AIS data displayed on screen. It also possible -- particularly in rough weather/heavy rain that they may not be looking at X-band radar, because S-band is vastly superior under such conditions. Most RTEs only use X-band. Unfortunately, although dual band RTE's do exist, they are quite new and very expensive.
Please note that although RTE's are not 100% effective, don't show up on some radars, and can be deleted altogether by cranking up the sea clutter control, I do not regard this as a reason to go round telling people that RTEs (or radar) are useless.

(ii) I think you'll find that shipfinder sites only show out of date data. If you are concerned that they will think "Oh look, Twister Ken's boat is in XXX today, so it's OK to break into his house in YYY," my personal feeling is that it is too much aggro, and they would be more likely to go for easier tricks, such as knocking at the door and seeing whether anyone answers.

 

[lw395]

I'm not part of any 'anti AIS' lobby, but I will admit to being anti 'buy lots of safety toys and leave all the thinking to the little boxes'

I suspect those of us who care enough to read these posts are not the people I'm worried about.
AIS is great, but I do worry that some people expect it to work miracles for them.

I wonder what YM theory teaches about it?

Mind how you go.

 

[jonjo]

Re criminals tracking your movements on AIS via the internet. I assume you need to be picked up by a shore station and at a 2W transmission power I wonder how often your class-B AIS squawk is going to be received onshore?

It would help if tinpot Goverment departments did not sell registration details to commercial concerns. The last case we heard about involved a payment of about £150 for SSR data, no doubt the deal was overseen by some new age civil servant called a commercial development manager on £90k p/a

 

[Danny Jo]

Can I repeat my earlier question?

Is there a hole in a strategy that combines an active RTE with receive-only AIS? In a manner of speaking, yes, because most if not all of the existing active RTEs (Sea-Me etc.) do not have a system for confirming that they are doing what they purport to do. What happens when a critical transistor fails? How does the user know it has developed a fault?

 

[AntarcticPilot]

Is there a hole in a strategy that combines an active RTE with receive-only AIS? In a manner of speaking, yes, because most if not all of the existing active RTEs (Sea-Me etc.) do not have a system for confirming that they are doing what they purport to do. What happens when a critical transistor fails? How does the user know it has developed a fault?

The Sea-Me certainly indicates when it is transmitting; as it only transmits on receiving a pulse, this confirms that the electronics chain is working from the masthead unit to the control box and that the control box is putting out a signal that is being pushed back up the mast. It is quite hard to envisage a fault that would allow reception of a radar signal, processing of same and generation of the outgoing pulse and THEN fail - the receive and transmit antenna are the same thing, so if there is a chain from the antenna to the electronics, the same route must exist in reverse.

 

[Genoa]

The Sea-Me certainly indicates when it is transmitting; as it only transmits on receiving a pulse, this confirms that the electronics chain is working from the masthead unit to the control box and that the control box is putting out a signal that is being pushed back up the mast..

Echomax the same - it tells you it is transmitting in response to a radar paint.
(Twster Ken - I think this is a perfect set up, most of the time)

Just a point, What I have on my onboard laptop (15" screen) is a chartplotter on the right and a panel on the left showing all the AIS targets. The target is highlighted if it has a CPA of <.5nm I think you can do the same on the chart as well. As TB said, this is common, so you have your filter/priority AND you can see the big picture. I tend to agree with the comment, its all about screen size and display. I am sure some software geek will allow you to paint class B a different colour to class A, but all Priority1 go red.

 

[lw395]

The Sea-Me certainly indicates when it is transmitting; as it only transmits on receiving a pulse, this confirms that the electronics chain is working from the masthead unit to the control box and that the control box is putting out a signal that is being pushed back up the mast. It is quite hard to envisage a fault that would allow reception of a radar signal, processing of same and generation of the outgoing pulse and THEN fail - the receive and transmit antenna are the same thing, so if there is a chain from the antenna to the electronics, the same route must exist in reverse.

A blown output transistor?
One of the most highly stressed parts of most transceivers?

However most marine electronics dies of water and corrosion, so there is a lot of sense in what you say.
Presumably Seeme owners ask friends with radar for a 'radio check' now and then?

 

[AntarcticPilot]

A blown output transistor?
One of the most highly stressed parts of most transceivers?

However most marine electronics dies of water and corrosion, so there is a lot of sense in what you say.
Presumably Seeme owners ask friends with radar for a 'radio check' now and then?

I would assume that the little flashing LED may well be AFTER the output transistor - as you say, this is probably the most likely bit of electronics to fail. And a very simple circuit with a diode would drive the LED from the RF output, I think - I am no electronics engineer, but have worked with electronics gurus implementing specialized radar systems; I did the software. It would seem common-sense to operate a warning light AFTER the output stage. But I don't know, so am merely guessing.

 

[lw395]

I would assume that the little flashing LED may well be AFTER the output transistor - as you say, this is probably the most likely bit of electronics to fail. And a very simple circuit with a diode would drive the LED from the RF output, I think - I am no electronics engineer, but have worked with electronics gurus implementing specialized radar systems; I did the software. It would seem common-sense to operate a warning light AFTER the output stage. But I don't know, so am merely guessing.

It's a cheap (by my military standards!) consumer peice of kit.
Is the LED going to be driven off the baseband signal (virtually no cost) or a built in test coupler, RF detector and separate baseband circuit ( significant parts and design cost, plus the signal loss of the coupler)

But it can be self defeating to worry about failure modes too much, things don't work as you expect when they are broken!
If I was going to be trusting one of these things, I would want to have seen it working or done a check with a radar. I'm sure they are very reliable, but I have seen enough non working stuff on boats to want things tested from time to time.

Possibly it's because I (and my friends ) don't tend to own new boats?

 

[Otter]

Is there an anti-AIS lobby? Is anyone anti-AIS?

My beef is with class B signals, it means when I cross the busiest shipping port in the UK (Harwich) I have to turn off the CPA and TCPA alarm because someone is tacking about, some 5 miles away and constantly setting off the alarm. I don't need to see class B signals on my plotter and I don't want to peer at a screen trying to work out which is which. Instead I want to use good pilotage skills to see the dangers with my own eyes and have AIS as a fantastic backup to spot the things I've missed. The increasing use of class B signals substantially degrades the efficacy of that backup.

And in fog I only want the absolute essentials on that screen. Sure If I get T-Boned by a Bavaria I may loose my yacht, but I can take to the liferaft. If I get T-Boned by a ship then I'm dead. So show me the targets to really worry about and don't clutter the screen with lots of £400 gizmos.

And for those who liken this attitude with a desire to get rid of radar reflectors - well AIS was designed as a huge leap forward to complement 70 year old radar technology. The biggest drawback of radar is trying to interpret what you see on the screen. And guess what, by allowing class B transmissions we will soon get to the point of having a cluttered screen, just like a radar screen, instead of the simple clear "These are the ships, avoid them" information that AIS is so brilliant at providing.

More information is not always better, just tell me the things I need to know.

 

[timbartlett]

... including my argument AGAINST AIS !

Is there an anti-AIS lobby? Is anyone anti-AIS?

Well you are quite openly against Class B AIS, and as this is a boating forum rather than a shipping forum, that (in my book) means you are anti-AIS

My beef is with class B signals

It doesn't matter whether you are in Harwich or the Solent, or the Straits of Hormuz: the argument that AIS is no good because it makes busy places look busy doesn't really hold water.

Harwich would look a lot less busy if you wore a blindfold, for instance, but I don't think anyone would seriously argue that not being able to see made life safer. Nor, I think, would many people endorse the view that lights on bicycles should be banned because it would make life easier for lorry drivers. Yet somehow, a lot of people seem to be seduced by exactly those arguments when applied to AIS.

I don't need to see class B signals on my plotter

But to extrapolate from that (not unreasonable) sentiment to one that effectively says no-one wants to see small craft is quite a big jump.

And in fog I only want the absolute essentials on that screen.

Are there really so many pleasure craft tacking in or out of Harwich in thick fog that your screen becomes hopelessly cluttered? You surprise me.

And for those who liken this attitude with a desire to get rid of radar reflectors

Actually, I don't. Radar reflectors never have worked, never can work, and never will work -- despite the mass of smoke and mirror arguments that claim otherwise. That is one reason I am so keen on AIS: it might, at long last, be the beginning of the end for a "technology" that is about as scientific and as effective as lucky rabbits' feet (feet that obviously didn't bring much luck to their original owners!)

Here's something that may surprise you...
... my argument against AIS
How many UK yachts have been involved in collisions with commercial vessels in open water in (say) the past ten years?
How many lives have been lost as a result?
For motor boats, I am pretty certain the answer to both questions is zero.
For sailing boats, off the top of my head, I can only think of four collisions (Tuila, Whispa, Wahkuna, and Ouzo) and seven deaths. There may be more, but I'm pretty confident that the only fatal ones were Tuila and Ouzo. Of course seven deaths is seven too many. But it does rather strike me that something that costs an average of less than one life per year is possibly not a major hazard.

 

[MOTORBÅD]

And for those who liken this attitude with a desire to get rid of radar reflectors

Sorry if my sarcasm clouded my point. Post 56.
I am pro AIS, even class B.
I am pro radars and radarreflectors

My point was: Nobody complains about all the radar echoes even on a small splitscreen.
Why is it that the same people are against seing the same targets on the AIS screen.
After all the ships and boats are for real out there. Why dont you want to know where they are exactly, and what they are going to do to you?

 

[lw395]

Sorry if my sarcasm clouded my point. Post 56.
I am pro AIS, even class B.
I am pro radars and radarreflectors

My point was: Nobody complains about all the radar echoes even on a small splitscreen.
Why is it that the same people are against seing the same targets on the AIS screen.
After all the ships and boats are for real out there. Why dont you want to know where they are exactly, and what they are going to do to you?

I do wonder why it's so hard to communicate that yachts keeping clear of other yachts is totally different from yachts keeping clear of ships.
Beacuse of the way yachts handle, you never need to take avoiding action until you are within a few hundred yards.
Because ships are rather different, you want to consider what they are doing very much further away.
That is why there is a potential danger in filling your AIS system with a lot of class B information, to the detriment of your ability to display and understand the actions of class A ships.

It's like wanting to cross the road and being bombarded with information about pedestrians 30ft up the pavement who are heading straight at you! If you cannot look only in the right direction, and can only 'process' 10, 20 or whatever encounters at one time, you will wish to see only the cars and trucks...

AIS is quite different from RADAR, RADAR will display however many contacts it 'sees'. AIS data is processed digitally and you never see the raw data. That's fine, but to get the most out of it, you have to understand what the processing, filtering and prioritisation of data is. If you are displaying the closest 10 CPA's and they are all yachts within 2M, are you masking a ship at 4M? Giving you info about ships at 3-10M was what AIS excelled at originally.

As for the thoughts about safety records, remember AIS is not wholly, directly a safety system, it is partly an enforcement system for TSS's, which is indirectly safety perhaps. The utility that yachts get from it is partly a by product rather than the primary aim.

Tim's figures do put a reality check on things, but what about fishing boats? Wilhemina J is remembered in a pub near me, but it's probably before the 10 year window.

 

[jonjo]

How many UK yachts have been involved in collisions with commercial vessels in open water in (say) the past ten years?
How many lives have been lost as a result?
For sailing boats, off the top of my head, I can only think of four collisions (Tuila, Whispa, Wahkuna, and Ouzo) and seven deaths.

I do not know what motivates others to fit an AIS receiver but as far as I am concerned it is primarily used for anxiety avoidance rather than a collision avoidance.

 

[lw395]

I do not know what motivates others to fit an AIS receiver but as far as I am concerned it is primarily used for anxiety avoidance rather than a collision avoidance.

That's very true, it is good for demonstrating to SWMBO that we have a grip on the situation!

 

[Otter]

It's like wanting to cross the road and being bombarded with information about pedestrians 30ft up the pavement who are heading straight at you! If you cannot look only in the right direction, and can only 'process' 10, 20 or whatever encounters at one time, you will wish to see only the cars and trucks...

I wish I could express myself as cogently and succinctly as that. Thank you, that is my point in a much better nutshell. I shall now steal that analogy and claim it was my idea.

Motorbad, apologies from me as well if I gave the impression that I didn't want others to see class B; I merely wish to filter them out myself so that I can see the real stuff to avoid and unfortunately only ships have the ability to filter out class B.

And Tim, it has got to the point where your misunderstandings and misinterpretations appear deliberate. I don't know why you do that, maybe its a desire to fire off a reply without thinking things through, maybe you have a need to be right, or maybe you just love arguments. Whatever the reason is, this thread is fast disappearing up someones fundament and I think I know who the arse is.

 

[timbartlett]

I do wonder why it's so hard to communicate that yachts keeping clear of other yachts is totally different from yachts keeping clear of ships.

I don't think it is particularly hard to communicate that: in fact I would think it's probably something that (on this forum) is pretty much self evident.

But the flip side is that because ships are rather different, they need to consider what you are doing very much further away. My experience is that ships can (and do) give way to yachts so long as they know about us well in advance.

That is why there is a potential danger in deleting yourself from their AIS displays.

It's like walking along a country road at night, and and saying "I will wear black at and make sure to switch my torch off because I don't want to worry the driver of the truck that is hurtling towards me."

RADAR will display however many contacts it 'sees'.

In the kind of overcrowded situation in which AIS becomes cluttered, radar also becomes cluttered -- more so, if anything, because it shows up buoys, piles, waves, seagulls and all sorts. Contacts merge together, contacts expand due to side lobe echoes and reflections, contacts get lost in sea clutter, or deleted because the sea clutter control has been turned up too high.

I'm a great fan of radar, but on a crowded Solent Saturday, I sincerely hope that the watchkeeper of the car carrier is looking out of the bridge windows, not at his radar.

Tim's figures do put a reality check on things, but what about fishing boats? Wilhemina J is remembered in a pub near me, but it's probably before the 10 year window.

Haven't done the research for fishing boats, I'm afraid, but I suspect the fact that Wilhemina J is remembered more than Tuila suggests that fatal fishing boat collisions are relatively rare. Or maybe it's that fishing is such a bloody dangerous way of earning a living that a fisherman dying isn't news unless it's really spectacular.

 

[Danny Jo]

The Sea-Me certainly indicates when it is transmitting; as it only transmits on receiving a pulse, this confirms that the electronics chain is working from the masthead unit to the control box and that the control box is putting out a signal that is being pushed back up the mast. It is quite hard to envisage a fault that would allow reception of a radar signal, processing of same and generation of the outgoing pulse and THEN fail - the receive and transmit antenna are the same thing, so if there is a chain from the antenna to the electronics, the same route must exist in reverse.

I would assume that the little flashing LED may well be AFTER the output transistor - as you say, this is probably the most likely bit of electronics to fail. And a very simple circuit with a diode would drive the LED from the RF output, I think - I am no electronics engineer, but have worked with electronics gurus implementing specialized radar systems; I did the software. It would seem common-sense to operate a warning light AFTER the output stage. But I don't know, so am merely guessing.

I have noted the association between radar transmitters in the vicinity and the flashing red light, and made the assumption that each flash is triggered by the receipt of a sweep from a radar set.

I checked the Sea-Me user guide dated 2005 and found this:
"Note that the red LED is triggered by the rise in current consumption which occurs when the antenna unit transmits – if the red LED flashes a transmission must have occurred."

This moderately reassuring statement is followed later by:
"When you have fitted your Sea-me it will be natural that you may ask a fellow sailor with a radar to look at you with your Sea-me switched on and switched off. When doing this you should be aware that, if he can see you with Sea-me switched off, he may not detect any difference when you switch Sea-me on. This is because his radar is already “painting” you on his screen. Most small boat radars use 4 step grey scaling on their screens and it takes experience to be able to detect a difference between adjacent steps. Perhaps a better way to give yourself confidence that Sea-me is working[my emphasis] is to have your fellow sailor monitor the ratio of paints to scans as he moves away from you. If he starts with Sea-me switched off and records the ratio until it falls to say 4 in 10 and then you switch Sea-me on he should see the ratio rise. Bearing in mind that we need to have a ratio of at least 50% for ARPA acquisition (see below) this improvement in return consistency is one of the key objectives of Sea-me. You should be aware that a small boat radar with a typical output of only 2kw is unlikely to trigger Sea-me at ranges of greater than about 4nm. This is not an issue because 4nm gives plenty of time for a small vessel to take avoiding action if necessary. The radars on big ships, our main concern, have outputs of at least 10kw, and quite likely 25kw, and these will trigger Sea-me at much greater ranges, theoretically at least 20nm given adequate heights."

A bit like radio check, then. Knowing that it was working the last time you checked it is history. Is it working now? No, no, please don't rush out and do another radio check.

 

[smartcom]

If I can join in late in this lively discussion, here are some thoughts and comments. As background, I did the AIS review for PBO, and my company also supplies software components to some of the big ship ECDIS systems out there.

First, I would personally always go for an AIS transmitter on my boat, as it is a lot easier for a yacht to see a ship than vice versa. Yes, there is a risk that they may not see my AIS transmissions because they just have the MKD display, or their display settings are set to filter out my vessels' info, but on the other hand this won't always be the case.

Regarding the MKD displays, these were allowed in the AIS specification as the assumption was that all systems would show ther AIS targets on their radar/ECDIS systems, but unfortunately that has not been the cas. However for a while now all new radar systems for SOLAS vessels are required to be able to display AIS targets, so this will change - quicker than many might imagine, now that ECDIS is being made mandatory on SOLAS vessels and so many will be upgrading their systems over the next few years.

Clutter can be a real problem, not because of the AIS system failing, but because of too many targets. But the problem here is not the transmissions themselves, but their display. Initially leisure systems supporting AIS display took the approach of "its cool to shw all these boats from this new toy" (being a bit flippant) but as the density increases it is important to have more intelligent display filters, e.g. just show targets where the CPA or TCPA or distance to the vessel is within certain parameters, or highlight those that show a significant risk of collision. This is really a user interface design issue.

Another way in which big ship systems reduce clutter is by being able to link AIS and radar targets, so a vessel only shows up once on the display.

Small displays are an issue, as it is difficult to show a lot of information clearly. This is really down to the user, making a trade-off between usefulness of the equipment against spacve and money.

Tim

 

[Gunfleet]

24 in display

Hi Tim,
I'm a bit worried about this display. It's 1/13th the length of my boat!

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.