AIS Transponder use

[DAKA]

Overheard on the VHF last week

Bigship, Bigship, this is raggie, raggie over

Bigship my AIS tells me that at your current course and speed you will cross my bow with 50 m to spare.

Raggie this is Bigship, can you alter course

Bigship this is raggie, That would mean me tacking, you will have to alter course

Raggie this is bigship, alright .

Now that got me thinking, if the Raggies have the power to shift the tankers out the way perhaps I should have one for when the ships are on my Port side

Also useful as you can leave it on in the Solent and all your mates can find the party

Whos got one and do you find it useful ?

 

[PaulGooch]

I have an AIS receiver, useful, but not the be all and end all that some claim it to be. Certainly no substitute for radar. AIS only tells you what the other ship transmits and i've seen ships at anchor with the AIS turned off, so it shouldn't be implicitly relied upon.

That said, it's not an expensive toy and it does have it's uses. A few weeks ago we spotted a vessel approaching from astern, in the distance. It looked as if it was heading directly for us, but at distance they often seem to do that, as you know. I took the radar off of standby and using target tracking and MARPA could see he was on a direct collision course with us. I got his details from the AIS and saw it was a rather large commercial vessel travelling at speed (turned out to be a big, fast cat). The AIS also gave me the vessel name, which was comforting to have as i sat watching his approach, mic in hand. Just as i was about to call him on the VHF, he changed course, guess the new radar reflector works too

Saturday, as we approached Harwich harbour, one of the Stenna ferries was also coming in. We were on a parallel course to his port side and we would both have to turn 90° to port a bit further ahead, he to enter the Stour and dock at Harwich, us to enter the Stour and cross to Shotley, at some point i needed to cross over. Checking the AIS i could see his speed and knew that we would be safe to continue and pass him, with enough time/room to cross the Stour before he made his turn.

Although you can see the big ships on radar, AIS instantly shows you which way they are heading. You can easily identify the ships, their speed, course, name, MMSI, length, beam, draft, destination etc.

I see it as a useful addon, in addition to radar. For anyone who doesn't have radar, for whatever reason, it's better than nothing.

As for your mates and the party....... for that you'll need the more expensive transponder version, that broadcasts your details. A better solution for this job is to use the DSC functions of you VHF set. Put all of your mates MMSI numbers into a group in the DSC directory and send them your position, if the have the NMEA out and NMEA in connected to their plotters, you position pops up on their plotters

 

[kcrane]

for that you'll need the more expensive transponder version, that broadcasts your details.

I've just had AIS added to the V48, having had it a few years ago on the sail boat. More use to be fair on a sail boat, much easier to get out of the way at 30knts than 6knts (though also quicker to get into trouble).

A big change appears to be the number of smaller boats fitted with transponders. It means I have had to turn off the alarms for CPA and TCPA as there are so many small boats sharing the Solent and rivers, it goes off every few minutes, whereas a few years ago I could leave it watching for big boats while I dozed peacefully in the cockpit (only kidding).

Could the small boats turn it off when they are in and around busy areas?

 

[PaulGooch]

I've just had AIS added to the V48, having had it a few years ago on the sail boat. More use to be fair on a sail boat, much easier to get out of the way at 30knts than 6knts (though also quicker to get into trouble).

A big change appears to be the number of smaller boats fitted with transponders. It means I have had to turn off the alarms for CPA and TCPA as there are so many small boats sharing the Solent and rivers, it goes off every few minutes, whereas a few years ago I could leave it watching for big boats while I dozed peacefully in the cockpit (only kidding).

Could the small boats turn it off when they are in and around busy areas?

I agree with that, i'm based at Shotley on the East coast and the alarms are a waste of time anywhere near base. At some times i can have 20 to 30 large commercial vessels close by when i'm close to home. There seem to be an increasing number of leisure craft fitting transponders, mostly raggies. The alarms did seem like a good idea when i fitted the system a year ago, ideal for a warning of big ships when fishing at anchor. I don't use the alarms now, for the reasons you give, but still find AIS a useful aid for the sake of around £250

 

[aquapower]

Have used AIS quite a lot and its very good and worth having, you can also track your boats movements using www.marinetraffic.com
was recently about to leave Lymington yacht haven and looked on the screen and could see a IOW ferry , looked like it was leaving in front of me but it was heading in the opposite direction to the vector on my screen as these ferrys go in both directions, not a problem but something to watch out for.

 

[fireball]

Have used AIS quite a lot and its very good and worth having, you can also track your boats movements using www.marinetraffic.com
was recently about to leave Lymington yacht haven and looked on the screen and could see a IOW ferry , looked like it was leaving in front of me but it was heading in the opposite direction to the vector on my screen as these ferrys go in both directions, not a problem but something to watch out for.

An AIS receiver will tell you about the IOW ferry ... so not quite sure why the AIS transponder is worth having .....

 

[PaulGooch]

Have used AIS quite a lot and its very good and worth having, you can also track your boats movements using www.marinetraffic.com
was recently about to leave Lymington yacht haven and looked on the screen and could see a IOW ferry , looked like it was leaving in front of me but it was heading in the opposite direction to the vector on my screen as these ferrys go in both directions, not a problem but something to watch out for.

I don't quite understand that, your AIS system should show the ferry travelling in the actual direction that's she's moving.

 

[Hurricane]

I don't quite understand that, your AIS system should show the ferry travelling in the actual direction that's she's moving.

Because AIS transmissions include the heading as well as other data.
I believe that even the helm info is transmitted so that you know which way they are turning.
Only class A transmissions - very little transmitted on class B.

 

[PaulGooch]

Because AIS transmissions include the heading as well as other data.
I believe that even the helm info is transmitted so that you know which way they are turning.
Only class A transmissions - very little transmitted on class B.

Yeah, i know that. The bit that's confusing (if confusing is the right word) is where aquapower says "but it was heading in the opposite direction to the vector on my screen"

 

[SolentPhill]

Ive got a transponder and its a pain cause everyone knows where I am. You can go online and find me easily, so when you sneak off your found and some online sites show you movements over 24 hrs previous so they know where you have been.

 

[idpnd]

You can turn that off you know!

 

[timbartlett]

An AIS receiver will tell you about the IOW ferry ... so not quite sure why the AIS transponder is worth having .....

When riding a bicycle at night, I always find it a good idea to keep my eyes open so I can see other traffic. Not quite so sure that there's any point having lights, though

 

[Hurricane]

Yeah, i know that. The bit that's confusing (if confusing is the right word) is where aquapower says "but it was heading in the opposite direction to the vector on my screen"

Yes I understand him - its HEADING can be in a different direction from its COURSE.

Course deoted by the vector and the little arrow denotes its heading.

 

[kcrane]

When riding a bicycle at night, I always find it a good idea to keep my eyes open so I can see other traffic. Not quite so sure that there's any point having lights, though

Transponders are for use in the dark. I didn't realise that. I see lots during daylight, people must forget they have them turned on.

 

[fireball]

When riding a bicycle at night, I always find it a good idea to keep my eyes open so I can see other traffic. Not quite so sure that there's any point having lights, though

Depends if the other drivers are going around looking at their sat nav or on the road infront of them doesn't it?!

 

[SolentPhill]

You can turn that off you know!

I love to agree with you, but the guy who put it in said it was a good security feature it comes on when you turn on the iginition, maybe he should have put a hidden switch in it so I can turn it off.

 

[fireball]

I love to agree with you, but the guy who put it in said it was a good security feature it comes on when you turn on the iginition, maybe he should have put a hidden switch in it so I can turn it off.

Hmm - that's the problem really isn't it ... using what should be an Aid to Navigation as a security tool ...

I think if I had a charter boat I would probably have one fitted as it would mean I can keep a virtual eye on the boat.

I'm not convinced of the benefit for collision avoidance yet - I have been on the bridge of a fast cat and they used Mark1 eyeball as primary & radar as secondary (it was good vis) - AIS was just 3-4 lines on a txt read out.

I encountered a classB transmitter in the Solent 2 years ago whilst testing alarms & triggers on Shipplotter on the laptop - unless you could set triggers for class B separately and have a different display icon the alarms will become the equivalent of 'shouting wolf' and the display will become so cluttered that you will not be able to see the chart ...

I do use AIS received data in the solent - mainly during the transit between Cowes and the forts - I check to see if there are any large vessels going to use the water and plan my course accordingly - yes I could do it visually, but I get a little more warning via AIS - this would be trickier if I cannot quickly identify Class A & B traffic (my chartplotter currently does not display ClassB and I have no intention of upgrading it so it does!)

For me - the future of Class B could go two ways:
1) it just rolls out as it is - AIS will become unusable in crowded areas
2) the software will allow selective filtering on ClassB and for the transponders it should allow selective transmissions too.

 

[Hurricane]

Hmm - that's the problem really isn't it ... using what should be an Aid to Navigation as a security tool ...

I think if I had a charter boat I would probably have one fitted as it would mean I can keep a virtual eye on the boat.

I'm not convinced of the benefit for collision avoidance yet - I have been on the bridge of a fast cat and they used Mark1 eyeball as primary & radar as secondary (it was good vis) - AIS was just 3-4 lines on a txt read out.

I encountered a classB transmitter in the Solent 2 years ago whilst testing alarms & triggers on Shipplotter on the laptop - unless you could set triggers for class B separately and have a different display icon the alarms will become the equivalent of 'shouting wolf' and the display will become so cluttered that you will not be able to see the chart ...

I do use AIS received data in the solent - mainly during the transit between Cowes and the forts - I check to see if there are any large vessels going to use the water and plan my course accordingly - yes I could do it visually, but I get a little more warning via AIS - this would be trickier if I cannot quickly identify Class A & B traffic (my chartplotter currently does not display ClassB and I have no intention of upgrading it so it does!)

For me - the future of Class B could go two ways:
1) it just rolls out as it is - AIS will become unusable in crowded areas
2) the software will allow selective filtering on ClassB and for the transponders it should allow selective transmissions too.

There's definately a difference with mobos.
AIS has a much greater range than radar - now thats a sweeping statement!!!
But its true, you will see AIS targets far further away than radar ones.
So, my point is that a mobo which is travelling a lot faster than a sailing boat will see the benefit of AIS on open passages much more than sailing boats. It is (kind of) like a waring for the radar.

I have both radar and AIS fitted - our AIS is a transponder as well and, yes, we do have a covert (hidden) switch.

 

[PaulGooch]

<snip>
I'm not convinced of the benefit for collision avoidance yet - I have been on the bridge of a fast cat and they used Mark1 eyeball as primary & radar as secondary (it was good vis) - AIS was just 3-4 lines on a txt read out.

I think it has benefits for collision avoidance, but i think they are very limited. It certainly doesn't replace MK1 eyeball, or radar. It cannot be relied up to pick up all targets, i have seen some large ships that have not been shown on the AIS, mostly at anchor. It does provide some additional information that is sometimes useful. Not necessarily in terms of collision avoidance, just generally useful. It quickly tells you the big ship in the distance is at anchor, not heading your way. It quickly tells you he's heading the other way. It tells you the name of the fast cat that is on a collision course, to enable you to hail him on the VHF. It's a useful aid in busy areas, with lots of heavy shipping, as you mention.

I encountered a classB transmitter in the Solent 2 years ago whilst testing alarms & triggers on Shipplotter on the laptop - unless you could set triggers for class B separately and have a different display icon the alarms will become the equivalent of 'shouting wolf' and the display will become so cluttered that you will not be able to see the chart ...

<snip>

For me - the future of Class B could go two ways:
1) it just rolls out as it is - AIS will become unusable in crowded areas
2) the software will allow selective filtering on ClassB and for the transponders it should allow selective transmissions too.

I hear you there. I seem to be coming upon more and more class B transmitters on pleasure craft. So far, they've all been on mid range yachts, not that that makes a difference. I agree with point 1 and 2 above. A simple software rewrite by the various plotter manufacturers could easily fix that.

The problem with implementing it, is COLREGS rule 5. To keep watch "by all available means appropriate". Filtering class B AIS reception would breach rule 5.

 

[fireball]

I think it has benefits for collision avoidance, but i think they are very limited. It certainly doesn't replace MK1 eyeball, or radar. It cannot be relied up to pick up all targets, i have seen some large ships that have not been shown on the AIS, mostly at anchor. It does provide some additional information that is sometimes useful. Not necessarily in terms of collision avoidance, just generally useful. It quickly tells you the big ship in the distance is at anchor, not heading your way. It quickly tells you he's heading the other way. It tells you the name of the fast cat that is on a collision course, to enable you to hail him on the VHF. It's a useful aid in busy areas, with lots of heavy shipping, as you mention.

I really meant for AIS class B transponders - many ships do not (yet) use AIS in the way us leisure users do - mostly they have perfectly adequate radar and visual means for lookout - therefore Class B transponder should not be relied upon to make you visible to shipping.

I hear you there. I seem to be coming upon more and more class B transmitters on pleasure craft. So far, they've all been on mid range yachts, not that that makes a difference. I agree with point 1 and 2 above. A simple software rewrite by the various plotter manufacturers could easily fix that.

The problem with implementing it, is COLREGS rule 5. To keep watch "by all available means appropriate". Filtering class B AIS reception would breach rule 5.

Contrary to Class A - (as things stand) Class B will become an hindrance in busy areas as there will be too much traffic to contend with - and as small ships do typically hold constant course/speed in these areas the AIS Class B data will become almost irrelevant to collision avoidance - thus selective filtering & selective alarms will become a necessity if Class B data will be used effectively.
Colregs rule5 will not be broken - as it has the term 'appropriate' in it - which is open to subjective discussion. I believe if 2 class B boats did collide - the fact that one (or both) were not monitoring AIS class B would be a less significant issue to visual lookout - assuming reasonable vis!

My thoughts on a selective filtering on Class B would be as such:
Display - user selectable icon to differentiate from Class A and a range & time to range filter so only class vessels B within X minutes of becoming closer than X Nm (could be fraction of) would be displayed.

Alarm - separate alarm triggers for Class A & B having independent settings as stated on those above.

If I had that facility then my display for Class B would be set to 10 minutes @ 1Nm - so any vessel that will be "within 1Nm of me in the next 10 minutes" would be displayed.
For Alarm on Class B - it would be off most of the time - but I would probably want an alarm on 10 minutes on 0.02Nm (<40m) max.

For AIS alarms in general - Standard Horizon have a 'problem' ... if a vessels forecasted track comes within the guard zone it triggers the alarm - which is fine - except you have to acknowledge it - then, if the track goes outside the guard zone (by any amount) the alarm is reset - and once it comes back in again then the alarm sounds once more. - There needs to be a buffer zone so you're not constantly 'alarmed' by vessels that will pass on the fringe of the guard zone. Actually - thinking slightly deeper than that - vessels on the fringe could trigger a double beep that doesn't need acknowledging - whilst those that would enter an inner guard zone get the full warning ...
Damm - I wish I was a programmer!