These days I feel obliged to include a warning every time I write about AIS over the Internet. What you see in a nice app like ShipFinder HD probably does not include every vessel that is transmitting AIS info, even in fairly well-covered areas like the Miami/Lauderdale area, and many areas aren’t covered at all. That’s because what most of us see on computers, phones or tablets that are connected to the web is target data collected by patchy networks of volunteers, whose shore antennas may miss weaker 2-watt Class B AIS transmissions, even from fairly close by, or stronger 12-watt Class A signals that are obscured by buildings or terrain. (Or they may suddenly go offline because the volunteer’s kid trips on a power cord!)

One particularly good source of free Internet AIS is MarineTraffic (MT), which seems to have attracted a large number of volunteer listening stations and recently added a slew of new features along with a completely redesigned web interface. However, MarineTraffic has simultaneously become a commercial AIS tracking operation, and I’ve had unhappy experiences with that kind of transition before. Currently, MarineTraffic seems to have the best global coverage with the most user features among the free sites, but will a hunger for subscription revenues mean decreased AIS tracking for freeloaders like me?

So far so good, and I especially like the “free forever” notation on the basic membership plan. The overall plan list is also a good place to see all the features MarineTraffic offers, including satellite tracking of vessels beyond shore stations. Thus far, about the only new limitations for free users that I can detect are a limit of five vessels in “My Fleet” and only three days of vessel-track history. I think those features remain pretty useful, and I particularly like being able to tag friends’ vessels so that I get emailed when they enter or leave a specified port.

My own personal My Fleet isn’t limited to five vessels and my screen remains ad-free, because MT gave free premium subscriptions to all its volunteer station-keepers when the plans were introduced, and I was maintaining a receiver here in Camden, Maine, at the time. That was a nice gesture. It’s also neat being able to zoom into targets on a high-quality (Jeppesen C-Map) nautical chart anywhere in the world—another perk of a premium subscription.

There really can’t be too many AIS receiving stations, and I continue to think it’s a great opportunity for marinas and other coastwise marine businesses to “add a little value” and do a little marketing at a low cost. In fact, one reason I’ve been lax with my home station is that Wayfarer Marine set up a reliable station in Camden Harbor, and the in-house installer, Alden Cole, enjoys maintaining a volunteer station so much he also minds a home system high in the hills behind town.

Beyond that, there’s a station at the Lyman Morse boatyard in Thomaston, and retiree Walter Barnard recently opened another station in the north bay, while yet another station just popped up in Searsport.

Unfortunately, while it looks like the east side of Penobscot Bay will be well covered on MarineTraffic when spring arrives and lots more boats finally appear, the same cannot be said everywhere. Indeed, in many other places around the U.S. coast, there’s no Internet AIS coverage at all. If you have a spot and a few hundred dollars to invest, please consider becoming a MarineTraffic volunteer. In the interest of free-market competitiveness, I think we volunteers should also hedge our bets and contribute our feeds to other sites like AISHub, ShipFinder, and FleetMon as well, so MarineTraffic doesn’t end up cornering the market.

For more on Internet-based AIS, search “how to put AIS online” at panbo.com