Yes, over a certain size. AIS class A transponders are mandatory on ships over 24meters. Smaller than that, and many people use them anyway because it’s convenient. Many recreational boats use class B with lower transmit power.
Anyone can operate an AIS transponder in receive-only, enabling you to receive the data yourself. This is how sites like that operate - Many volunteers who receive and forward the NMEA string to the site. Hell, if you have one of those cheap USB-SDRs you can roll your own at minimal cost. Decoding the relevant NMEA strings (AIVDO and AIVDM, readable at 38400 baud) is a bit of a pain in the ass, as it’s built around a 6-bit ASCII table. But I managed to do it with a perl hack once upon a time, so it’s highly doable.
NB: While not legal, it’s very easy to disable an AIS transponder temporarily. War ships often do this.
Tumbleweed
I’m glad you asked; A more reliable method for establishing position is by sending a position request via DSC (VHF channel 70 or MF 2187.5kHz), as that’s a lot harder to disable. You’re gonna need an ROC or GOC to do this legally, though. As well as a MMSI, come to think of it.
Source: I used to work with maritime comm systems, including installation of both VHF radios, MF radios, and AIS transponder. I have a GOC.
I just got a hackrf and it has an AIS tool built in. It’s real neat, I’ve got to play with it a while. It plots them on a map, but it’s extremely low res. My city is like 4 pixels. I’d really like to be able to fix that somehow.
I’ve also noticed a lot of the information it reports seems wrong. Like the same boat can be reporting anchor down and 5 knots. And even more are under way with engine but 0.0 knots. I’m not a boat captain but that doesn’t seem right.
It’s still endless fun just reading the names of the boats as they pass
The ship state (at anchor, etc) is a manual setting that the bridge crew will have to change. Same goes for destination. And bridge crew has enough on their plates already, so updating it isn’t exactly a priority. That’s why you often see “Ch 16” set as destination, as it’s basically shorthand for “If you really need to know, ask us on VHF Ch 16”.
As for receiving AIS data, if you’re able to decode the data, it’s easy to plot it yourself. AIS messages (AIVDO is the one you’re interested in) consists of several messages, and most of them contains the ships position. Every so often, the ships name is transmitted (The MMSI number is the primary identifier).
Well that’s a bit of confusion cleared up, thanks! I did actually notice I’d get some information and then a little later the name would show up too. I figured it was just bad reception missing the full message, but you’re saying they’re sent separately? I guess I’ll stop fiddling with my antenna
The fact they just put their contact info for destination is hilarious to me. I should get a radio license.
Yeah, your antenna is fine. AIS contains more information than can be fit into a single packet, so it’s spread out over several. Every packet contains the MMSI of the ship, which you can use to link every packet together. If I remember correctly, there are three or so packet types. Position and speed is sent relatively often. And static info such as name and other info that doesn’t change a whole lot is sent much more infrequently.
Maritime radio license is easy to get. An ROC which covers the basics is a day or two. It’s basically just a course on how to properly operate a VHF. GOC covers a lot more (telex, inmarsat, EPIRBs, etc) and basically certifies you as a radio operator for any ship. It takes about a week.
Trivia time!
Yes, over a certain size. AIS class A transponders are mandatory on ships over 24meters. Smaller than that, and many people use them anyway because it’s convenient. Many recreational boats use class B with lower transmit power.
Anyone can operate an AIS transponder in receive-only, enabling you to receive the data yourself. This is how sites like that operate - Many volunteers who receive and forward the NMEA string to the site. Hell, if you have one of those cheap USB-SDRs you can roll your own at minimal cost. Decoding the relevant NMEA strings (AIVDO and AIVDM, readable at 38400 baud) is a bit of a pain in the ass, as it’s built around a 6-bit ASCII table. But I managed to do it with a perl hack once upon a time, so it’s highly doable.
NB: While not legal, it’s very easy to disable an AIS transponder temporarily. War ships often do this.
Tumbleweed
I’m glad you asked; A more reliable method for establishing position is by sending a position request via DSC (VHF channel 70 or MF 2187.5kHz), as that’s a lot harder to disable. You’re gonna need an ROC or GOC to do this legally, though. As well as a MMSI, come to think of it.
Source: I used to work with maritime comm systems, including installation of both VHF radios, MF radios, and AIS transponder. I have a GOC.
import memeify memeify.memeify(source='Paw Patrol turns off body cam', image='Russian warship', text='*Turns off AIS*')This guy transponds!
I just got a hackrf and it has an AIS tool built in. It’s real neat, I’ve got to play with it a while. It plots them on a map, but it’s extremely low res. My city is like 4 pixels. I’d really like to be able to fix that somehow.
I’ve also noticed a lot of the information it reports seems wrong. Like the same boat can be reporting anchor down and 5 knots. And even more are under way with engine but 0.0 knots. I’m not a boat captain but that doesn’t seem right.
It’s still endless fun just reading the names of the boats as they pass
The ship state (at anchor, etc) is a manual setting that the bridge crew will have to change. Same goes for destination. And bridge crew has enough on their plates already, so updating it isn’t exactly a priority. That’s why you often see “Ch 16” set as destination, as it’s basically shorthand for “If you really need to know, ask us on VHF Ch 16”.
As for receiving AIS data, if you’re able to decode the data, it’s easy to plot it yourself. AIS messages (AIVDO is the one you’re interested in) consists of several messages, and most of them contains the ships position. Every so often, the ships name is transmitted (The MMSI number is the primary identifier).
Well that’s a bit of confusion cleared up, thanks! I did actually notice I’d get some information and then a little later the name would show up too. I figured it was just bad reception missing the full message, but you’re saying they’re sent separately? I guess I’ll stop fiddling with my antenna
The fact they just put their contact info for destination is hilarious to me. I should get a radio license.
Yeah, your antenna is fine. AIS contains more information than can be fit into a single packet, so it’s spread out over several. Every packet contains the MMSI of the ship, which you can use to link every packet together. If I remember correctly, there are three or so packet types. Position and speed is sent relatively often. And static info such as name and other info that doesn’t change a whole lot is sent much more infrequently.
Maritime radio license is easy to get. An ROC which covers the basics is a day or two. It’s basically just a course on how to properly operate a VHF. GOC covers a lot more (telex, inmarsat, EPIRBs, etc) and basically certifies you as a radio operator for any ship. It takes about a week.