Sometimes one service will show a ship in port and another will show it’s departed.
Anyone have any insight into this? Is one better than the others in some areas? Or is it just random?
Lately I’ve been using MarineTraffic.
I strongly suspect it depends on their network of reporting stations.
Dunno about others, but with Marinetraffic you can go to the layers menu on the left and tell it to show you the stations and their status. Individual station stats are available.
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Marine Traffic works for me. I have a shore station that feeds into their network too.
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So presumably each AIS service uses a network that is a mix of public and private sources.
Mostly private I think. Some are on ships – OSV Nordhoek Pathfinder PBYN -PD0RQX for example gives them a feed from her main AIS transponder.
You can find details on any Marinetraffic station by clicking on it.
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That’s good info but it’s not practical to evaluate the network by looking at the details of each station.
Of course. Even someone like me with no life could only sample a few that way.
When they were new they were giving away equipment to people willing to set it up and join the network. I wrote to them but apparently they didn’t think that 40m elevation near the head of Narragansett Bay was going to be worth their investment.
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On MarineTraffic, if you activate the stations, you will see the status of the terrestrial stations immediately, green = active, red = inactive.
At least that says, if in doubt, how reliable the presentation should be.
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orange = active but with limited reception area.
You can also get this:
https://www.marinetraffic.com/en/ais/details/stations/314/_:66f57680fd6abd374096b1ee4eb5a9d8
I got mine free 
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Phthphth! 
I use FindShip. Works great and it’s free
GTrax came out a year before MarineTraffic and solved the problems you speak of but… it was $5 /month and, as your title suggest, you want free so it went under.
Unfortunately you get what you pay for when it comes to antenna data… so no, nothing today is very reliable.
The best is probably marine traffic but they use mostly ham radio operators so the data isn’t 100% solid.
They claimed to be giving out free equipment but they also claimed that their motives were nonprofit… which is how they got so many ham radio operators to send them free data.
I don’t care if they make s profit or not. My equipment was still free either way. They like hams because they know how to set it up z
Do you have a Comar SLR 350N yacht_sailor?
What is your rated NM reception distance?
I see they currently have 4181 partner stations worldwide in there data base.
You don’t care now because it’s the norm among hams but many of you guys sure did care back then.
There must be some odd backstory I am missing.
Marine Traffic was never a charity. They are not tricking anyone in any way. Hams do not take some kind of vow to never use any other kind of radio nor restrict their interests to only ham bands. The only overlap between hams and AIS is Marine Traffic knows hams are more likely to be able to set up the gear without messing it up.
I am quite happy to have my shore station, I provide coverage where there was none before including my own slip,which makes working on my AIS gear a lot easier. I certainly get my money’s worth for the tiny amount of electricity it uses.
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Yes there is. gCaptain built the first AIS iPhone app well ahead of everyone else but we needed Data. We spent months trying to convince Hams to give us data but most refused because we charged a small fee to unlock premium features. I can’t tell you how many hams told me personally that the ham community is 100% not about money and wouldn’t participate in a paid service of any kind. But then they flocked to marine traffic because it was 100% free and the data was funding research.
But once they got most hams aboard they started charging just like we did.
Because we were unable to convince enough hams to join and because users didn’t want to pay anything at the time… Marine Traffic launched an app and steamrolled us.
I’m not saying this with any bitterness, MT won fair and square and I cannot blame hams for wanting to donate data to research. And I can’t blame MT for wanting to monetizing a successful research project (that’s exactly what google did).
I spent a full year of my life on the project and invested tens of thousands of dollars so don’t try to tell me “Marine Traffic was never a charity” or that hams didn’t sign up under false pretenses… because that’s just false:
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The Greeks are known as world class philanthropists 
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