Cargo ship not visible on onboard AIS but showing on phone app

[Bertie1972]

A couple of weekends back I passed 400m from a large cargo ship at anchor off Torbay which didn’t show up on my AIS. Brixham trawler Pilgrim was a similar distance away at the time and did show. When I checked ‘Boat Beacon’ on my phone, both Pilgrim and the ship were there.
I have a Garmin AIS 800 connected to a GPS Map 700. On the AIS unit, Power, RX & TX lights appeared as they should with no fault lights showing. My AIS shares the VHF aerial using a splitter.
When I returned to my mooring, I again compared AIS and the phone app. The same number of nearby boats showed on each. However, one boat which appeared on both onboard AIS and Boat Beacon app as being in the same position and with the same MMSI, had a different name in each (not sure if this helps or not).
What do the team advise I should do/test next?

 

[Sandy]

How tall was the ship? You might have been in a spot that was sheilded from their signal. The trawler was not as high hence you could receive it's signal.

 

[ghostlymoron2]

If it was anchored, it may not have had AIS on

 

[neilf39]

What date/time was shown on boat beacon. If it is like marine traffic. It may well be showing the last transmission received which could have been some time ago and it is now no longer broadcasting. Your plotter is only recent signals.

 

[Bertie1972]

Sandy's explanation seems the most likely. At the time Pilgrim and I were both moving and the relative positions of all three vessels on Boat Beacon were accurate.

I'm still bewildered by the different names of one boat discovered later - I looked again today online, and ITU List of Ship Stations accords with AIS and Marine Traffic accords with Boat Beacon.

 

[Daverw]

I see discrepancies between marine traffic and our onboard AIS all the time around us, marine traffic has lots of local dead spots and shows historical positions sometime hours old. Confirms the reason not to use internet based AIS although sometimes difficult to explain to some why

 

[Refueler]

I see discrepancies between marine traffic and our onboard AIS all the time around us, marine traffic has lots of local dead spots and shows historical positions sometime hours old. Confirms the reason not to use internet based AIS although sometimes difficult to explain to some why

I have full service on Marine Traffic - but that does not mean all data / targets shown are real time ... (we use it in my business to track the vessels we are working / appointed for). Approx 30 - 50% of plots shown are historical ......

All other APP's for AIS are same or worse.

 

[Bertie1972]

I see discrepancies between marine traffic and our onboard AIS all the time around us, marine traffic has lots of local dead spots and shows historical positions sometime hours old. Confirms the reason not to use internet based AIS although sometimes difficult to explain to some why

I completely agree.
My concern was that on the day in question, for me it was the other way around.

 

[johnalison]

I completely agree.
My concern was that on the day in question, for me it was the other way around.

But your internet result was only coincidentally more ‘correct’ than your boat’s. In a moving situation, access to the latest information is always going to be more useful than historical info, even to the point of being critical.

 

[Sandy]

If it was anchored, it may not have had AIS on

Big ships, Class A AIS, are required to transmit AIS 24/7.

I've heard Plymouth VTS, I currently sail out of Plymouth, call up a ship because they were not transmitting.

When all the liners were anchored off Tor Bay during COVID they and their launches all transmitted.

 

[Refueler]

Big ships, Class A AIS, are required to transmit AIS 24/7.

I've heard Plymouth VTS, I currently sail out of Plymouth, call up a ship because they were not transmitting.

When all the liners were anchored off Tor Bay during COVID they and their launches all transmitted.

The word 'required' .......

AIS is supposed to be transmitted by all ships continuously with status of transmit changed to indicate ships state at the time ... anchored / steaming / alongside etc.
But contrary to 'publics' belief - ships do turn off AIS contrary to IMO. There is good reason for this. >>

Quote from IMO : (Last section on Security)

"

AIS transponders​

• Home
• Our Work
• Maritime Safety
• AIS transponders

Automatic identification systems (AIS) transponders are designed to be capable of providing position, identification and other information about the ship to other ships and to coastal authorities automatically.

Regulations for carriage of AIS​

SOLAS regulation V/19 - Carriage requirements for shipborne navigational systems and equipment - sets out navigational equipment to be carried on board ships, according to ship type. In 2000, IMO adopted a new requirement (as part of a revised new chapter V) for all ships to carry automatic identification systems (AISs) capable of providing information about the ship to other ships and to coastal authorities automatically.

The regulation requires AIS to be fitted aboard 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. The requirement became effective for all ships by 31 December 2004.

Ships fitted with AIS shall maintain AIS in operation at all times except where international agreements, rules or standards provide for the protection of navigational information.

A flag State may exempt certain ships from carrying an AIS. Performance standards for AIS were adopted in 1998.

The regulation requires that AIS shall:

• provide information - including the ship's identity, type, position, course, speed, navigational status and other safety-related information - automatically to appropriately equipped shore stations, other ships and aircraft;
• 
  
• receive automatically such information from similarly fitted ships;
• monitor and track ships; and
• 
  
• exchange data with shore-based facilities.

Maritime security - AIS ship data​

At its seventy-ninth session, in December 2004, the Maritime Safety Committee (MSC) agreed that, in relation to the issue of freely available automatic information system (AIS)-generated ship data on the world-wide web, the publication on the world-wide web or elsewhere of AIS data transmitted by ships could be detrimental to the safety and security of ships and port facilities and was undermining the efforts of the Organization and its Member States to enhance the safety of navigation and security in the international maritime transport sector.

The Committee condemned the regrettable publication on the world-wide web, or elsewhere, of AIS data transmitted by ships and urged Member Governments, subject to the provisions of their national laws, to discourage those who make available AIS data to others for publication on the world-wide web, or elsewhere from doing so.

In addition, the Committee condemned those who irresponsibly publish AIS data transmitted by ships on the world-wide web, or elsewhere, particularly if they offer services to the shipping and port industries."

 

[graham]

The online AIS apps continue to show the last sighted position resulting in ghost targets on the screen.

 

[oldgit]

When my automatic switch between the VHF and AIS failed it caused problems.
Cheapest option was to fit a new VHF antenna for the AIS.
Never did find where the switch was hidden in the boat.

 

[Ardenfour]

If it was anchored, it may not have had AIS on

It's on his phone...

 

[Refueler]

It's on his phone...

Was his phone receiving AIS live from onboard receiver or from an APP .......

My phone and tablet can receive via WiFi live AIS from my ONWA - or I can use Marine Traffic APP .....

 

[Bilgediver]

Was his phone receiving AIS live from onboard receiver or from an APP .......

My phone and tablet can receive via WiFi live AIS from my ONWA - or I can use Marine Traffic APP .....

I believe he was using an App Marine Traffic or similar. Unfortunately this information is gatherers from various sources including g volunteers around the coast who receive the data and then send via Internet to Marine Traffic These stations are not always in the best location and this means that there can be dead areas within their range caused by structures or topographical features. For instance the source for information regarding g the River Forth Estuary is a ham Station at Kirknewton . This is a few miles south of the upper Forth estuary. This results in transmissions from some vessels being interfered with by the three bridges at Queensferry. However the station happily receives data from the seaward end of the Forth Estuary. Sometimes these systems continue to show the last transmission received for a number of hours.

If you go to the Web site aprs.fi then you will see Marine targets and on this site they indicate the receiving station.

 

[westernman]

AIS transmits every few seconds when the ship is underway, and only every few minutes or so when anchored.
May be you had only just turned on your AIS set, and it had not had enough time to catch all the anchored message transmissions?