AIS Unknown Vessel

[Ded reckoner]

Has anyone experienced this or know of its cause?

Several boats were anchored in proximity in Sandy Hook Bay. They could be identified by boat name and vessel type on AIS. Each went up the East River a couple of days later and each lost their AIS specific identification. They appeared on a chartplotter but with the general identification of Unknown Vessel and no detailed information. While AIS was fully functional on their vessels for their own use, this meant they couldn’t be hailed by name by someone else. This was confirmed by chartplotter. And Marine Traffic apparently had, and kept, the boat location at which AIS was lost.

A power down, hard reset of the AIS unit restored specific identification and Marine Traffic recognized the boat’s correct location again. I don’t know how, but Marine Traffic restored the track from where the AIS was lost.

I had observed vessels before on the chartplotter with AIS with the identification Unknown Vessel. This seemed to be a proximity issue because, in most cases, the specific identification would appear as the boat got closer. This seems to be a different phenomenon.

[Paul L]

What you are experiencing is normal behavior. AIS transmits the ID data approximately every 7 minutes (if I remember correctly). So you need to wait awhile for the ID packet to be both transmitted and received. Not all packets are correctly received, so it can take awhile before the names fill in. Position data is transmitted much more frequently, like every 30 seconds for a moving Class B AIS. In this case you can fail to receive many position packets and still see the vessel position on your chart plotter.