a thought on AIS

[oldvarnish]

I posted a couple of days ago an interesting assessment of AIS http://www.ybw.com/forums/showthread.php?463876-Class-B-AIS-pros-and-cons and there were some thoughtful replies.

However, I've notice that whenever we discuss AIS the emphasis seems to be on boasts such as "I've received ships at 100 miles and yachts at 30", as if that was the most important thing.

I'm not so certain.

When crossing the Channel, for example, AIS is God's second best gift after GPS, but I wonder if it quite as valuable in closer situations.

This summer I was approaching Peterhead at dawn in thick fog with the radar spinning. I asked the HM for permission to enter, was given it, and he advised me that there was a yacht, with an AIS transmitter, leaving the marina on a reciprocal track to me, and I should keep a sharp lookout.

The yacht was clearly seen on the radar but not on my receive-only AIS (Vesper, and very reliable - I too can get ships many, many miles away)

The visibility was about 30 metres, quite thick. I proceeded dead slow. Then the AIS bleeped a collision alarm and the yacht appeared for the first time on the screen. Less than ten seconds later the yacht appeared out of the fog. We passed port to port, waved, and all was well. I used the radar to set a course for the marina but noticed the AIS was still showing a collision alarm, and did so for some time even though I knew for certain she was by now well astern of me. I was alongside and secure before the AIS jumped and showed the yacht's true position, now a mile out to sea.

So don't worry about how far you can see, worry more about what might be so close that AIS class B is just too slow to deal with it.

 

[maby]

That is an unusual set of circumstances though. Class B AIS is on a 3 minute transmission schedule and the other boat had presumably only just started moving when you approached the marina - hence the delay in the first report. In the vast majority of cases, the boat will have been moving and in range for many minutes before it becomes a danger to you, so still a valuable safety measure.

 

[PaulRainbow]

Fair point, if he was traveling at less then 2 knots he'll only broadcast every three minutes, if over 2 knots it'd be every 30 seconds. If he was a class A vessel traveling at anything up to 14 knots it's be every 10 seconds, unless he was changing course, then it'd be every 3.3 seconds.

 

[duncan99210]

I think oldvarnish's post highlights nicely the inherent problem in relying only on AIS in poor visibility. Whilst radar gives real time picture of other vessels, there is always going to be a lag in AIS data as his story shows, especially when the target is using class B with its longer period between transmissions. I don't yet have AIS fitted (on the wish list but can't justify it yet in the Ionian) but on the odd occasion when fog has descended, I doubt it's usefulness in our particular circumstances, as too few folks out here have it fitted. Better using the radar despite the poor returns from small wooden or grp boats.

 

[Rivers & creeks]

AIS data over 6M is pointless and over 3M largely irrelevant as well. Sure I've had signals from over 100 miles away, sure I get lots from 20 plus miles away but what am I going to do with that information, bear it mind for future reference? Maybe in wide open expanses of ocean they may be the only other thing out there but I sail the south coast and North Sea where shipping makes frequent changes of direction and I want to know what's got a TTCPA of less than 30 minutes, for that it's brilliant.

 

[rogerthebodger]

I read somewhere that class B AIS transmissions can be prevented in areas with a lot of class A traffic and class takes precedence over class due to shortage of transmission slots.

I know where I moor is a commercial harbour with lots of class vessels and a smallish number of class B and I have had times when I could not pick up local class B boats in the marina where I know their AIS transceiver was on.

IMHO and AIS receiver connected to an AIS DSC radio is important as it allows you to call a vessel direct without knowing it name if a collision course persists.

I do think a AIS class B transponder is a less a value as its up to me to in the end avoid and collision and not rely on the other vessel seeing you.

I must admit large vessels where I sail do mostly see you from their radar without and AIS transmitter.

AIS is very good but not the silver bullet some my think.

 

[Champagne Murphy]

I find it of more use in large ship avoidance situations. Knowing the speed of a distant ship and it's course helps me make a judgment on when to expect it. I've never found Class B transmissions to be reliable enough to be of a great deal of use although it might well happen one day!

 

[Gryphon2]

I had a receive only AIS when crossing theIndian Ocean 2years ago. Very good for a passagelike that where nothing is to be seen for days on end. However when we were alerted to a ship on a converging course I had an interesting conversation with the watch officer.
At about 3 miles I asked him if he had seen us either via radar or visually. When he eventually responded it was clear from his comments that he hadn't and that his chief watch keeping method was AIS. He said my AIS cannot have been working. I pointed out that I only had a receive set, which he seemed to disbelieve! Be warned therefore that AIS may be being relied upon too much in the wastes of the oceans.

 

[PaulRainbow]

I also find it very useful for shipping, but less so for class B.

 

[tudorsailor]

I recently passed a huge motor boat in the Aegean. He had no flag flying and no AIS transmission. So I called him on Ch16 and helpfully advised him that his AIS was not working. His snotty reply was that he was exempt from showing it. Turns out the boat was owned by the ex-Prime Minister of Qatar, called the Al Mirqab


Seems that the rules do not apply to him! Nevertheless, I still love my AIS!

TudorSailor

 

[rogerthebodger]

I recently passed a huge motor boat in the Aegean. He had no flag flying and no AIS transmission. So I called him on Ch16 and helpfully advised him that his AIS was not working. His snotty reply was that he was exempt from showing it. Turns out the boat was owned by the ex-Prime Minister of Qatar, called the Al Mirqab


Seems that the rules do not apply to him! Nevertheless, I still love my AIS!

TudorSailor

It must be classed as a warship then.

 

[Deleted member 478]

I recently passed a huge motor boat in the Aegean. He had no flag flying and no AIS transmission. So I called him on Ch16 and helpfully advised him that his AIS was not working. His snotty reply was that he was exempt from showing it. Turns out the boat was owned by the ex-Prime Minister of Qatar, called the Al Mirqab


Seems that the rules do not apply to him! Nevertheless, I still love my AIS!

TudorSailor

IIRC, a commercial vessel of over 300 tons is obliged to have an AIS, but not obliged to have the transmit on. That boat looks very much like a private leisure vessel.

 

[rogerthebodger]

IIRC, a commercial vessel of over 300 tons is obliged to have an AIS, but not obliged to have the transmit on. That boat looks very much like a private leisure vessel.

Wasn't the yacht Britannia part of the Royal Navy so technical was a warship .

 

[Sandyman]

Hospital Ship

 

[PaulRainbow]

IIRC, a commercial vessel of over 300 tons is obliged to have an AIS, but not obliged to have the transmit on. That boat looks very much like a private leisure vessel.

All ships of 300 gross tonnage and upwards engaged on international voyages, cargo ships of 500 gross tonnage and upwards not engaged on international voyages and all passenger ships irrespective of size.

 

[Polly's Kettle]

I recently passed a huge motor boat in the Aegean. He had no flag flying and no AIS transmission. So I called him on Ch16 and helpfully advised him that his AIS was not working. His snotty reply was that he was exempt from showing it. Turns out the boat was owned by the ex-Prime Minister of Qatar, called the Al Mirqab


Seems that the rules do not apply to him! Nevertheless, I still love my AIS!

TudorSailor

Presumably for security reasons, given his prior position?

Still, I expect he appreciates having a photo of his boat put up on the web and naming him!

 

[Happy Dayz]

This thread reminds me of a tangle a USA warship got into problem.

iirc -;
On picking up a 'hazardous boat' they broadcast a request for it to tack North, reply came back for this warship to change course, started of pleasant a first but the warship captain became annoyed but the other craft still refuse go move over.

after finally announcing in very stern terms he was a USA warship making his guns ready and might open fire on them, he was told he was talking to a light house keeper, and advised he should change coarse.

If true as i hope, just a Classic lol!

Alan

 

[tudorsailor]

Presumably for security reasons, given his prior position?

Still, I expect he appreciates having a photo of his boat put up on the web and naming him!

Not exactly a secret..... Wikipedia has all the yachts details, including:

Name: Al Mirqab
Owner: Hamad bin Jassim bin Jaber Al Thani
Builder: Peters Schiffbau Wewelsfleth, Germany
Yard number: 681
Launched: 2008
Status: Currently in service
Notes:
Call sign: ZCTS4
IMO Number: 1009223
MMSI: 319361000
General characteristics
Class and type: Superyacht
Displacement:
1,440 DWT(summer deadweight)
9,518 GRT(gross tonnage)
Length: 133.00 m (436.35 ft)
Beam: 19.00 m (62.34 ft)
Speed:
20.3 knots (37.6 km/h; 23.4 mph) (maximum)
18.7 knots (cruising)
Capacity: 24 Guest + Owner
Crew: 55

Must have had his AIS on 22nd August since he shows up on Marine Traffic

TudorSailor

 

[vyv_cox]

It must be classed as a warship then.

At least some warships have AIS but choose when to turn it on. There have been many patrol vessels in waters between Greece and Turkey this summer, AIS often displayed as 'NATO warship' or similar. At other times they remain invisible to AIS but in sight.

 

[Daydream believer]

I was following a halberg rassey past the roche douvres in a south west direction about 2 miles behind it. My ais showed a target 2 miles behind me in a north west direction following me. I could not see it even though good visibility.
After a lot of looking to see the supposed target i noted it to pass right over the lighthouse so i can only assume that the hr was giving a spurious signal as several other targets appeared where they should have been- observed by eyeball