AIS and MarineTraffic

matt1

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When not sailing I can often be found lurking on marine traffic being nosey about what vessels are out there, doing what etc

There seems to be good coverage around the south coast ...except for when I look at my own boat which appears to disappear whenever I leave the Solent. I’ve tracked a mate most of the way across the channel before with the same standard ais tx set up as me, albeit my aerial is on a much taller mast. To be fair, I would expect the signal to be lost once offshore, but how is it that some are tracked further afield. MarineTraffic is awash with boats through the channel. As an example, when I got home last night and looked on MarineTraffic I saw that it didn’t have any positions for me at all in Christchurch bay after leaving the needles channel
 

Sandy

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Marine Traffic rely on people running receiving stations on the coast. Perhaps somebody forgot to put 50 pence in the meter?

I am always amazed at what it does report, a friend was returning from the Azores in February and we saw them for about an hour some 200 nm off the Brittany coast. It must have been some fluke in atmospherics.
 

[3889]

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Internet AIS is also relayed via ships' satellite connections. We were tracked right across Biscay. You will see many yachts far from land on there.
 

capnsensible

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A couple of days ago I saw a very large vessel in the straits between Lanzarote and Fuertaventura. Unusually large, not seen anything that big running through there before. It was not on Marine Traffic.
 

GHA

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Internet AIS is also relayed via ships' satellite connections. We were tracked right across Biscay. You will see many yachts far from land on there.
Think that's just not so about ships repeating ais messages, any links to back up that statement?

If you were tracked all the way them more likely through atmospheric ducting.

Not much long distance today ...

kiF3jS2.jpg
 

JumbleDuck

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Internet AIS is also relayed via ships' satellite connections. We were tracked right across Biscay. You will see many yachts far from land on there.
MarineTraffic also pick up standard VHF AIS transmissions by satellite, but you have to pay heavy and per named vessel to see the details. Otherwise you just get a ship type.

Ogrp5rB.png
 

Blue Sunray

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A couple of days ago I saw a very large vessel in the straits between Lanzarote and Fuertaventura. Unusually large, not seen anything that big running through there before. It was not on Marine Traffic.

Could it have been this, you won't find her on AIS often.

US_MVC_OceanTrader.jpg
 

capnsensible

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Interesting looking vessel. What is it?

The one I saw was a bulk carrier, green hull, light brown top sides, heading east. Quite unusual in the Bocayna Straits.
 

DJE

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Arrived in Dartmouth yesterday. Vessel Finder tracked us all the way from Poole and lost us just outside Dartmouth. It shows no positions since then. Marine Traffic shows our current position in Dartmouth. It all seems a bit random. Vessel finder shoes very few yachts in Cherbourg most of the time.
 

GHA

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It’s about ships repeating AIS data as Quiddle said.
You are mistaken. Repeated AIS messages have a field in the message set so you can see that it has been repeated, yet to see that from a ship, though it will be set for virtual AtoN's. Your link was about sending data over the internet to a web site, not repeating AIS over VHF.
Happy to be proven wrong if someone can show examples of a message from a ship with the repeated field set but it must be uncommon, yet to see. And just searched through 13Mb of real saved AIS messages, not one had the repeat field set.



Table 6. Common Navigation Block
Field Len Description Member T Units
0-5

6

Message Type

type

u

Constant: 1-3

6-7

2

Repeat Indicator

repeat

u

Message repeat count

.
.
.


The Repeat Indicator is a directive to an AIS transceiver that this message should be rebroadcast. This was intended as a way of getting AIS messages around hills and other obstructions in coastal waters, but is little used as base station coverage is more effective. It is intended that the bit be incremented on each retransmission, to a maximum of three hops. A value of 3 indicates "Do not repeat".
AIVDM/AIVDO protocol decoding
 

johnalison

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It can be a very Big-brotherish experience to investigate one's own vessel on AIS sites. On Live Ships Map there is a photo of our boat in a German marina, posted by a German, according to the legend.
 

JumbleDuck

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It can be a very Big-brotherish experience to investigate one's own vessel on AIS sites. On Live Ships Map there is a photo of our boat in a German marina, posted by a German, according to the legend.
I googled my Citroën DS registration number and found a shot of me driving it in the Netherlands. And no, not on a police website!
 

RichardS

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For the last 10 years I have never been able to see my boat on Marine Traffic or Vessel Finder once I enter the channel between the hills which leads to the marina. The signal is always lost about 1/2 mile out.

I turned on my AIS a few hours ago just to test it and I've just checked on Marina Traffic. As usual, none of the half dozen boats in the marina which are broadcasting are visible. However, on Vessel Finder, all the boats in the marina with a signal, including mine, are all visible.

It wasn't like this last year but things have obviously changed.

Richard
 
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