AIS through satellites.

[JPA Cate]

We, too, use masthead, and splitter.

A.

[GILow]

Originally Posted by El Pinguino

..l

and in that link we find this...

'Signals from vessels that sail in remote areas can only be covered using Satellite AIS. The positional updates provided by this service may vary from a few minutes up to several hours (regardless of how often the subject vessel transmits positions). On average, we get one position update per hour for ocean-going vessels equipped with a Class-A AIS transponder.'

And that’s where I am a little concerned. I’ve observed that behaviour and I’d moderate their description to say it seems to be around six to eight hours on average around the south eastern Australian coast between a boat sailing out of land based cover and appearing as an unknown sailing vessel via satellite. I’ve seen the odd instance where it was only an hour or two for a friend’s boat in this part of the world, but those were rare.

Maybe there is a factor of how much satellite cover marine traffic has access to for this part of the globe?

But it has taken me around 36 hours to appear on their satellite cover this time. Very slow.

So maybe I need class A power levels to reach the satellites from here or maybe my antenna doesn’t radiate well upwards? My antenna theory says vhf spread will be less focussed with the short antenna?

[StuM]

Originally Posted by GILow

So maybe I need class A power levels to reach the satellites from here or maybe my antenna doesn’t radiate well upwards? My antenna theory says vhf spread will be less focussed with the short antenna?

Or maybe you need an Inreach if you want people to be able to track your progress reliably

[sailjumanji]

Again, GiLow, why do you care when your boat shows up on a website?

[GILow]

If you read the first part of my post, you’ll see that I describe how it is possible, here in Australia, to track people pretty well on Marine Traffic by looking for their last land based cover, then tracking forward to look for an unknown satellite vessel.

I do this all the time with friends’ boats and well over half the time it is possible to be pretty accurate about where they are.

This is mostly possible because of the very light recreational boat traffic around Oz. I don’t think it would be practical in some other parts of the world.

I am not a total cheapskate, but I simply cannot afford/justify the cost of accessing the satellite data on marine traffic. Sure, if this was a business need I’d pay happily.

Likewise, I’d like my family to able to follow me when I sail out of range, without them having to shell out for satellite subscriptions. And if they DO decide to pay the money, I’d like to know they would be getting their money’s worth.

[GILow]

Originally Posted by Jubilee39

4. Although never designed for the purpose, VHF signals can also be detected by satellites.
This enables AIS signals to be detected mid ocean hundreds of miles from any land based receiver.
The drawback: Due to the nature of satellite orbits and their trajectories, satellite AIS receivers
cannot pick up AIS messages as frequently as terrestrial receivers which are in a fixed position.
Also, VHF signals received by satellite do not use time slots, meaning that satellite detected AIS
data provides valuable but less granular vessel position records than land based receivers.

This is from marine intelligence website

Thank you. Good summary.

[GILow]

Originally Posted by StuM

Or maybe you need an Inreach if you want people to be able to track your progress reliably

See my costs remark, but if I were really serious, yes, I’d look into some of these options.

As it is, marine traffic is good enough. Anyone who knows me and is likely to be interested in my location would know I was going to Kangaroo Island this week. It’s nice to know they can check marine traffic and see I went to American River, rather than Kingscote. Particularly if they want some tourist souvenirs.

[El Pinguino]

If you go to MarineTraffic, set the filter to only show pleasure craft, then click on a few random boats...I just did that across the S Pacific, Indian and N Atlantic.. all of about a dozen are showing under 10 minutes... so your boat is an outlier along with a couple of others in the Tasman/Coral Sea area...

Now is this caused by your antenna or your AIS, by your geographical location , by something to do with the satellites they are using?

I honestly don't know.... you would need to have another boat fairly near by to see if it is boat related...

Moving right along... just switched all the filters off and looked at ships in the eastern Bight.... all are under 10 minutes....
I'd be checking my instalation... and you could also have a look at the Yankalilla stats https://www.marinetraffic.com/en/ais.../stations/3635 and see how it goes on your run back to Port....

Re positioning of the Ant... I wouldn't be too fussed about putting it up the mast... frinstance max line of site from your current ant position down aft to that Yankalilla station is about 35 miles... to a bog standard cargo ship with a HoA ( height of Antenna) of 100 feet is about 15 miles.....

PS this long delay... You will be getting your signal out to sats with a pretty low altitude .. forget about overhead passes- thats why we use QFH and turnstyle ants for NOAA weather stations on 137 mHz.

So... if you have high ground nearby .. Ballast Head f'rinstance ? ... you may not 'see' the sat..
Just had another look at MT.. ...... two yachts almost alongside each other in the Rio Valdivia....one on 19 hours, the other on 2 hours... both have high ground close north.... ships in the river in the minutes range....

Sorry about the stream of conciousness... waiting for lunch to heat up...

[StuM]

Originally Posted by El Pinguino

Just had another look at MT.. ...... two yachts almost alongside each other in the Rio Valdivia....one on 19 hours, the other on 2 hours... both have high ground close north.... ships in the river in the minutes range....

Apart from anything else, there's a lot of data being picked up by satellites in real time that has to be fed via other satellites and cable to the Marinetraffic and other receivers. There's only a limited numer of receiving satellites, certain amount of bandwidth and number of time slots available so a great deal of that data just gets dropped. Class A transmissions get priority.

[GILow]

Gotta love an El-Ping stream of conscience.

Yep, good point about ballast head, and when I thought about it a bit, I remembered that I was often surprised by the delay in boats showing up down here on Marine Traffic. Might be related.

And, to add to the confusion, my girlfriend had subscribed to the trial of position updates a while back and forgotten all about it. She got an email yesterday that we now realise showed our position when we anchored outside of American river on the first night, waiting for daylight. That’s satellite cover, and it was sent to her within a couple of hours of us leaving the land based cover.

It’s all jolly strange, but reassuring none the less.

Now we are pinned down by some pretty ordinary weather so plenty of time to contemplate.

I do hope your lunch was worth the wait E.P. I’ll try for the comedy net again tomorrow, turns out I can’t use Jim’s antenna trick so it’s all down to your whip tomorrow.

[GILow]

Originally Posted by StuM

Apart from anything else, there's a lot of data being picked up by satellites in real time that has to be fed via other satellites and cable to the Marinetraffic and other receivers. There's only a limited numer of receiving satellites, certain amount of bandwidth and number of time slots available so a great deal of that data just gets dropped. Class A transmissions get priority.

I was thinking along similar lines, but also wondered if there was some back end processing required for boats that first appear to satellites without corresponding land signals.

A long bow, I agree, but I can imagine a database algorithm that might need to be triggered and completed before the data is displayed on the main site or apps.

[El Pinguino]

Let me know when you find out what sats they are using..

[GILow]

A quick reference case...

Friends sailed out of terrestrial AIS reception 4 days ago, but Marine Traffic tells me there is a satellite position report available that is four hours and thirty seven minutes old.

A quick scan of the unidentified boats to the north of them finds them up a creek with a satellite time stamp of four hours and thirty seven minutes ago.

Easy.

And yes, I could have paid $1.49 to get the same report, but I don’t care THAT much, I was just curious.

[GILow]

Originally Posted by El Pinguino

Let me know when you find out what sats they are using..

Thanks for that question, I just spent an hour on Wikipedia when I should have been studying. But if I were a guessing man I’d say they might be using the Canadian based exactEarth network. That seems to be the biggest if I read things correctly.

[StuM]

Originally Posted by El Pinguino

Let me know when you find out what sats they are using..

MarineTraffic.com

"By combining data from the world's largest network of coastal receiving stations with the power of the three leading satellite AIS providers, you can now see more than ever before."

Probably the constellations operated by three of these four:
Satellite Opperator | Company Types | AIS Reporter
ORBCOM
exactEarth
KONGSBERG
Luxspace


A few years ago, they only used ORBCOM.


As a WAG, I'd go with KONGSBERG being the one they don't use
(It looks as though they produce satellite AIS receiver hardware but don't operate their own satellites.)