AIS in open sea ?

[grafozz]

I am watching a good friend Malcolm Campbell as he makes his way around the world on his 38 ft yacht Grace .
He fitted an AIS transponder and we are keeping track of him so far on Marine Traffic.com ,
he left last week from Kefalonia and is north of Scicily now ,
will we be able to "see " him as he ventures across deep sea ?

 

[AntarcticPilot]

I am watching a good friend Malcolm Campbell as he makes his way around the world on his 38 ft yacht Grace .
He fitted an AIS transponder and we are keeping track of him so far on Marine Traffic.com ,
he left last week from Kefalonia and is north of Scicily now ,
will we be able to "see " him as he ventures across deep sea ?

You won't see him after he's out of VHF range from the land stations that MarineTraffic relies on. AIS operates on VHF radio frequencies, which are restricted to line of sight only. MarineTraffic and similar systems rely on receiving the boat's AIS transmissions at shore stations (you should be able to find out where they are from the web-site). The exact range available depends on the height of both receiving and transmitting antennae, but is unlikely to be much greater than 25km; 50km at a push.

 

[RichardS]

You won't see him after he's out of VHF range from the land stations that MarineTraffic relies on. AIS operates on VHF radio frequencies, which are restricted to line of sight only. MarineTraffic and similar systems rely on receiving the boat's AIS transmissions at shore stations (you should be able to find out where they are from the web-site). The exact range available depends on the height of both receiving and transmitting antennae, but is unlikely to be much greater than 25km; 50km at a push.

The tracking sites are now sometimes using satellite VHF receivers as well so the OP might get much better coverage than he is expecting. I'll bet that it won't be long before AIS tracking is global.

Richard

 

[AntarcticPilot]

The tracking sites are now sometimes using satellite VHF receivers as well so the OP might get much better coverage than he is expecting. I'll bet that it won't be long before AIS tracking is global.

Richard

Given the low power of Class B AIS transmitters (2 Watts), a satellite in a Low Earth Orbit (~700km up, and on average a lot further away horizontally) is still going to struggle to receive much, especially as it wouldn't be able to use a directional receiving antenna. A Class A transmitter is a different kettle of fish, but each installation has to be certified, and requires equipment that would be onerous for a yacht to carry.

If AIS tracking is made global, it will probably only be for Class A transmissions, which are of use in checking for things like illegal fishing as well as the obvious operational uses. For recreational use, there are plenty of alternative tracking systems available without over-loading AIS systems.

 

[Koeketiene]

Given the low power of Class B AIS transmitters (2 Watts), a satellite in a Low Earth Orbit (~700km up, and on average a lot further away horizontally) is still going to struggle to receive much

AIS is already global.
There are several (paying) website that offer such a service as well as some military/government sites not accessible to the public.
These sites do indeed use satellite tracking.

LEO can be as low as 160km. A satellite derived AIS position will not be 'live', but will be subject to a time lag measured in seconds - so irrelevant.
As for the power of the transmitter: the transmitter carried on board the Voyager spacecraft - currently at the verge of interstellar space - is only a 20W one. And NASA is still in contact with those spacecraft.

 

[AntarcticPilot]

AIS is already global.
There are several (paying) website that offer such a service as well as some military/government sites not accessible to the public.
These sites do indeed use satellite tracking.

LEO can be as low as 160km. A satellite derived AIS position will not be 'live', but will be subject to a time lag measured in seconds - so irrelevant.
As for the power of the transmitter: the transmitter carried on board the Voyager spacecraft - currently at the verge of interstellar space - is only a 20W one. And NASA is still in contact with those spacecraft.

Yes, LEO can be at 160 km - but not for a long-lived satellite. Atmospheric drag at that elevation is high. Also, the satellite is only in view of a small footprint at a time at that height, so you'd need a very large number of satellites to achieve a latency of seconds. Finally, satellites in very low orbits are only in view for a very short time, which might not be sufficient to receive an AIS packet.

Higher orbits are needed to get world-wide coverage, with the consequent reduction in signal to noise ratio. Iridium is probably as low as you can go and get world-wide simultaneous cover, at 780 km.

And yes, we can receive a 20w transmitter from out beyond Pluto - using highly directional antennae at both ends, and a vast collecting surface at the Earth end. It isn't a comparable problem to having to receive a signal from anywhere in half the sphere, which is what the satellite has to do, and most AIS transmission antennae I've seen tend to maximize transmission in the horizontal plane -i.e. not towards a satellite.

As you say, the systems exist, and I know of their use in tracking illegal fishing in the Southern Oceans (A ship that attempts to hide by switching off its AIS is under suspicion automatically!). But Class A transmissions are over 6 times more powerful than class B ones, and repeat the position report every 2 seconds instead of every 30 seconds. It isn't impossible for a yacht to carry Class A AIS, but the requirements for certification of the system are such that it is unlikely. So, while Class A AIS is capable of being received by satellite, I think that we are a long way from doing the same with class B.

 

[Koeketiene]

As you say, the systems exist, and I know of their use in tracking illegal fishing in the Southern Oceans (A ship that attempts to hide by switching off its AIS is under suspicion automatically!). But Class A transmissions are over 6 times more powerful than class B ones, and repeat the position report every 2 seconds instead of every 30 seconds. It isn't impossible for a yacht to carry Class A AIS, but the requirements for certification of the system are such that it is unlikely. So, while Class A AIS is capable of being received by satellite, I think that we are a long way from doing the same with class B.

Lat year, I tracked a friends boat in the ARC all the way across. Class B AIS - not constant, 'live' tracking, but I did get a position update every 3 hours or so, which was more than adequate to track a yacht. Not to mention a great comfort for the family back home.

 

[AntarcticPilot]

Lat year, I tracked a friends boat in the ARC all the way across. Class B AIS - not constant, 'live' tracking, but I did get a position update every 3 hours or so, which was more than adequate to track a yacht. Not to mention a great comfort for the family back home.

Fair enough - observation trumps theory every time!

 

[dslittle]

We use our SPOT tracker to back up our AIS for friends. The SOS facility also backs up the EPIRB so all in all a good bit of Kit.

 

[geem]

We use a Delorme Inreach. Tracking every 2mins if you want it and as many texts messages as you want for $65/month. Great when crossing Oceans

 

[tcm]

Lat year, I tracked a friends boat in the ARC all the way across. Class B AIS - not constant, 'live' tracking, but I did get a position update every 3 hours or so, which was more than adequate to track a yacht. Not to mention a great comfort for the family back home.

ARC participants all carry a loaned Yellowbrick satellite transponder enabling them to be tracked in open sea - You sure their positions (on the ARC fleet viewer) wasn't from that??

 

[tcm]

We use a Delorme Inreach. Tracking every 2mins if you want it and as many texts messages as you want for $65/month. Great when crossing Oceans

Well, it's fairly great. I feel moment-by-moment tracking gives the impression of extra safety, rather than any actual increased safety. It's really only of "use" to friends and family on land. Rescue services aren't monitoring such devices in the style of "hm, looks like they've slowed down and we'd better get ready to go help!" You would still have to raise any alarm, and of course, lots of serious problems (e.g. medical) could occur with the tracking device working away merrily. As such, in practice, my experience is that the alarm that such devices can cause when they fail (or get disconnected, or the battery runs down) completely counteracts their advantages.

 

[geem]

Well, it's fairly great. I feel moment-by-moment tracking gives the impression of extra safety, rather than any actual increased safety. It's really only of "use" to friends and family on land. Rescue services aren't monitoring such devices in the style of "hm, looks like they've slowed down and we'd better get ready to go help!" You would still have to raise any alarm, and of course, lots of serious problems (e.g. medical) could occur with the tracking device working away merrily. As such, in practice, my experience is that the alarm that such devices can cause when they fail (or get disconnected, or the battery runs down) completely counteracts their advantages.

What utter nonsense. The device has an emergency button. You can contact authorities if you need to. It has 100 hr battery life but we run from ships supply so it can always have 100 hrs use if you had to take it into the life raft. It's waterproof as well. It's an extra safety device not the be all and end all of safety. It's nice to get weather routing from a sailing friend who can tell us what's coming our way or better heading South a little or North a little. We also have SSB so we can contact people in an emergency if we had to. The bottom line is it tracks us so friend and and family can see where we are and stay in touch with us. If the get a medical emergency you can actually communicate with people to help assist a situation. Why denigrate a piece of additional equipment that could save a life? They also only cost a couple of hundred pound so an excellent piece of additional safety equipment for very little money if you are crossing Oceans

 

[RAI]

Well I have had first hand experience of satellite AIS working with Class B transceivers. I sailed (drifted) from the Azores to the Algarve at the beginning of this month. Friends had been told that we thought the weather predicted would have us across in about 6 or 7 days. It took 11 days, we had our own doldrum in tow. On day 8 or 9 our American friend got worried and called the US coast guard, reporting us as over due. The USCG looked us up on AIS for that area, called via satellite phone to tanker Fidelius, seen on AIS as being near to us. Fidelius called us on channel 16 and checked we were ok and satphoned the answers back to the USCG. I expect we are now in the NSA database too.

 

[geem]

Well I have had first hand experience of satellite AIS working with Class B transceivers. I sailed (drifted) from the Azores to the Algarve at the beginning of this month. Friends had been told that we thought the weather predicted would have us across in about 6 or 7 days. It took 11 days, we had our own doldrum in tow. On day 8 or 9 our American friend got worried and called the US coast guard, reporting us as over due. The USCG looked us up on AIS for that area, called via satellite phone to tanker Fidelius, seen on AIS as being near to us. Fidelius called us on channel 16 and checked we were ok and satphoned the answers back to the USCG. I expect we are now in the NSA database too.

Cool! Technology has its benefits! My pal sails single handed with little technology onboard other than vhf and a GPS. From Bahamas up to St Martin nonstop. He had a slow trip so asked a passing ship to email his wife to let her know he was ok. I find it funny that the yacht and the ship are at opposite ends of the technology spectrum but you can still get the message through!

 

[grafozz]

the info posted has encouraged me to look at alternative AIS sites
and the suggested Vessel finder is even better ,
I have found Malcolm anchored off San Vito , nw Scicily ,
its great to have more than one tracking site .
thanks , forumites .

 

[demonboy]

According to marinetraffic we are leaving Langkawi doing 5.2 knots in a NW direction. Have been for the two years, apparently.

 

[Heckler]

AIS is already global.
There are several (paying) website that offer such a service as well as some military/government sites not accessible to the public.
These sites do indeed use satellite tracking.

LEO can be as low as 160km. A satellite derived AIS position will not be 'live', but will be subject to a time lag measured in seconds - so irrelevant.
As for the power of the transmitter: the transmitter carried on board the Voyager spacecraft - currently at the verge of interstellar space - is only a 20W one. And NASA is still in contact with those spacecraft.

My Delorme Communicator only has two AA batteries in it that last two days or more when it is left on for ocean crossing so I doubt it is transmitting more than a couple of watts and that connects fine to the satellites.
S

 

[oldvarnish]

My Delorme Communicator only has two AA batteries in it that last two days or more when it is left on for ocean crossing so I doubt it is transmitting more than a couple of watts and that connects fine to the satellites.
S

Yes, but it's not working on VHF AIS frequencies, which is the point.

 

[geem]

Yes, but it's not working on VHF AIS frequencies, which is the point.

As has been said in earlier posts, AIS class B is working with satellites so what point are you making? AIS class B transmits at 2W far more effectively vertically than horizontally so range to satellites is achievable.