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Old 27-06-2020, 21:59   #1
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AIS through satellites.

Hi all,

For the first time since I installed AIS on this boat Iíve managed to sail out of coverage by land based AIS receivers. This is expected, the area near American River on Kangaroo Island is masked from the receiver at Warrina by the headland.

My Class B AIS works very well, I had full land based receiver cover all the way down the gulf, when many boats do not. And Iíve had confirmation from a few ships over time that they are receiving my signal from as far as 20 miles out.

The AIS antenna is a stubby little thing, mounted on the davits about ten feet above the water.

However, what I had expected was that now, 12 hours after sailing out of land based cover, that Iíd appear as an unknown boat on Marine Traffic, here in American River.

No luck.

Which is a bit annoying because here in Oz I can easily track friends out of land based cover by looking for unknown boats about where I would expect them to be. I was hoping Iíd be able to do the same thing with my boat.

Has anyone got any idea of how to to improve or test satellite performance for AIS, short of putting the antenna on its side?

Matt
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Old 27-06-2020, 23:20   #2
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Re: AIS through satellites.

I have Manera 15 hours ago via Yankalilla...

The Sat positions displayed aren't instant... sometimes they show a time stamp 5 minutes ago.. sometimes 15 hours ago... bide your time.. maybe you will show up manana.

Mine seems to come up OK via Sat... simple VHF whip on the taffrail.....

The sats don't neccessarily need to be over head ... as long as they can see you... vhf signals just keep going and going..

With ducting I have worked ships a few hundred miles away...the record used to be a ship near Aden working another ship near Bombay..during the NE monsoon..

See how it looks tomorrow... bet you turn up...
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Old 28-06-2020, 00:47   #3
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Re: AIS through satellites.

It seems like the casual user using Marinetraffic doesn't get to see satellite derived positions unless they open their wallet.

If so, then you are dark to me Matt until you get closer to a shore based AIS receiver!
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Old 28-06-2020, 00:56   #4
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Re: AIS through satellites.

It's all that TP soaking up the signal energy
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Old 28-06-2020, 01:53   #5
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Re: AIS through satellites.

Maybe consider a masthead antenna.

A.
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Old 28-06-2020, 01:55   #6
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Re: AIS through satellites.

Quote:
Originally Posted by Wotname View Post
It seems like the casual user using Marinetraffic doesn't get to see satellite derived positions unless they open their wallet.

If so, then you are dark to me Matt until you get closer to a shore based AIS receiver!
I'm as tight as a crab's bum at 40 fathoms - as is my wallet - and have no problems seeing offshore yachts... with no identity info.

They do seem to be trying to sell the monetized details.... this pop up window - VVVV - is new ....
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Old 28-06-2020, 01:56   #7
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Re: AIS through satellites.

Quote:
Originally Posted by JPA Cate View Post
Maybe consider a masthead antenna.

A.


Iím not sure being 50 feet closer to the satellites will make much difference.
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Old 28-06-2020, 01:58   #8
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Re: AIS through satellites.

Quote:
Originally Posted by StuM View Post
It's all that TP soaking up the signal energy


Well, thatís a problem because I came to Kangaroo Island to buy up their supplies as well,
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Old 28-06-2020, 02:01   #9
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Re: AIS through satellites.

If you are running the TP blockade (and CV19 border closures), you will welcome the lack of AIS surveillance....
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Old 28-06-2020, 02:10   #10
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Re: AIS through satellites.

Quote:
Originally Posted by El Pinguino View Post
I have Manera 15 hours ago via Yankalilla...

The Sat positions displayed aren't instant... sometimes they show a time stamp 5 minutes ago.. sometimes 15 hours ago... bide your time.. maybe you will show up manana.

Mine seems to come up OK via Sat... simple VHF whip on the taffrail.....

The sats don't neccessarily need to be over head ... as long as they can see you... vhf signals just keep going and going..

With ducting I have worked ships a few hundred miles away...the record used to be a ship near Aden working another ship near Bombay..during the NE monsoon..

See how it looks tomorrow... bet you turn up...


Fingers crossed, I hope that you are right.

That last report came about an hour after I gybed off to port. Nothing like gybing an asym at 2 am to keep you on your toes.

We will head back out into land based cover some time tomorrow morning, so thereís another, maybe, fifteen hours for us to show up.
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Old 28-06-2020, 02:12   #11
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Re: AIS through satellites.

Quote:
Originally Posted by Wotname View Post
It seems like the casual user using Marinetraffic doesn't get to see satellite derived positions unless they open their wallet.

If so, then you are dark to me Matt until you get closer to a shore based AIS receiver!


Very true, and fair enough too, though I reckon their satellite-use plans are a little eye watering.

But Iíve been quite successful at tracking friends in and out of shore based cover just by looking for unknown sailing boats about where Iíd expect them to be from their last shore based position.
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Old 28-06-2020, 03:03   #12
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Re: AIS through satellites.

I agree Gilow, that to be visible to satellites, the location of antenna does not make much difference, just the quality of wiring and antenna itself.
For visibility to other ships and you seeing them, an antenna high-up would be better. I can see usually ships from 20-40 NM, and I hope they can see me. My aerial (dedicated to AIS only) is on top of the mizzen. Sometimes I can see them 50-70 Nm away.

Regarding MarineTraffic (and similar websites), I noticed the last 2 years, when I am at home, that when boats leaving the local harbour, very soon the boat info disappears (as it would be received by the local land based station), and remaining a boat-icon with just the caption "cargo/leisure etc vessel position received via satellite". Sometimes this occurs less than 10 Nm from the local harbour where the aerial is mounted ?60 mt high up. In the past the same ships were reported with all details 40-50 NM away. Not anymore, at least not where I live and know the boats. I noticed similar situations of friends sailing around OZ or abroad. It is near impossible to track them (as a non-paying voyeur).

As has been said up-thread, the website owners might be trying to monetise their website, and registration for satellite derived information is not cheap.

Looking into the future, who knows, AIS might well become an satellite based information system.

Edit: just checked and right now all boats/ships within 30 Nm radius on MarineTraffic show their boat name, course, speed etc.
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Old 28-06-2020, 03:19   #13
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Re: AIS through satellites.

As a generalisation, a sail boat AIS antenna does not need to be very high to be visible enough to shipping because most (all?) ships have their antennas mounted quite high. The radio horizon is dependant on the height of both antennas.
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Old 28-06-2020, 04:57   #14
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Re: AIS through satellites.

Quote:
Originally Posted by Wotname View Post
As a generalisation, a sail boat AIS antenna does not need to be very high to be visible enough to shipping because most (all?) ships have their antennas mounted quite high. The radio horizon is dependant on the height of both antennas.

Yes, I often see shipsí AIS signals on the plotter before I can see them with the binoculars. Usually they become visible within the next ten minutes or so, suggesting their antennas are poking above the horizon before the rest of the boat.
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Old 28-06-2020, 05:06   #15
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Re: AIS through satellites.

Quote:
Originally Posted by HankOnthewater View Post
I agree Gilow, that to be visible to satellites, the location of antenna does not make much difference, just the quality of wiring and antenna itself.
For visibility to other ships and you seeing them, an antenna high-up would be better. I can see usually ships from 20-40 NM, and I hope they can see me. My aerial (dedicated to AIS only) is on top of the mizzen. Sometimes I can see them 50-70 Nm away.

Regarding MarineTraffic (and similar websites), I noticed the last 2 years, when I am at home, that when boats leaving the local harbour, very soon the boat info disappears (as it would be received by the local land based station), and remaining a boat-icon with just the caption "cargo/leisure etc vessel position received via satellite". Sometimes this occurs less than 10 Nm from the local harbour where the aerial is mounted ?60 mt high up. In the past the same ships were reported with all details 40-50 NM away. Not anymore, at least not where I live and know the boats. I noticed similar situations of friends sailing around OZ or abroad. It is near impossible to track them (as a non-paying voyeur).

As has been said up-thread, the website owners might be trying to monetise their website, and registration for satellite derived information is not cheap.

Looking into the future, who knows, AIS might well become an satellite based information system.

Edit: just checked and right now all boats/ships within 30 Nm radius on MarineTraffic show their boat name, course, speed etc.


Iíve been an avid watcher for a while now and Iíve come to the conclusion that the main issue for the Marine Traffic site is the reliability of their land stations. There are very few land stations with very high availability/reliability so where the stations are not close together you do see gaps in cover from time to time.

What has been most interesting to me is watching friends who travel in company with other boats, and how much variation there is between reception ranges with shore stations. Friends who get around with a masthead shared vhf/ais antenna regularly get ten more miles of cover than the boat they travel with who have their ais antenna on the aft rail.

I, personally, really donít like splitters in my vhf path so Iíve compromised and put the antenna on the davits for now, figuring ten feet is better than six. But one day I will run ANOTHER wire up the mast and put the ais antenna where it really belongs.
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