AIS data is messy and sometimes a message might be received with a corrupted or erroneous position. In the past (before September 2022) Starboard’s algorithm for dealing with vessels that were sharing a MMSI may have incorrectly split a vessel into multiple instances because of these corrupted messages.

For these legacy “split vessels”, it is therefore useful to analyse the group of vessel instances of the same vessel together, to avoid missing portions of the track history that might have been assigned to another vessel ID.

To differentiate between vessel instances, they are numbered from #1 onwards. Starboard marks the primary vessel as #1 which contains the most number of positions, and subsequent vessel instances are ranked by the number of AIS positions.

Vessel instances have the same MMSI, but other static identification details like name and callsign may be different between the entities, depending on what static details were transmitted at different times of the vessel’s life.

Only the primary vessel (marked #1) is assigned risks, additional information from S&P Global Market Intelligence, and RFMO registrations. Tags can be assigned to any vessel instance.