OK, I've made progress through trial and error and come to understand these options much better to the extent that it now does what we need. For the benefit of anyone wanting to do something similar here's the story.
Turns out that there are several settings at play in this scenario and how they interact can be quite subtle and even unexpected.
The settings are:
o AIS>Show AIS Target Tracks [aka AISTracks]
o Options>Ships>AIS Targets>Lost Targets (both settings) [aka LostTargets]
o Options>Ships>MMSI Properties>New>Tracking [aka Tracking]
o Options>Ships>AIS Targets>Show targets tracks length (min) [aka Tracklength]
Also Options>MMSI Properties>New>Tracking>Persistent is always required to be checked.
So I add an MMSI into the MMSI Properties table. If Tracking
is set to "Always" then it will be tracked when the vessel begins to broadcast AIS data. Trouble is, if LostTargets values are checked then once the vessel stops broadcasting, it will eventually be marked as "lost" and deleted. The track stays but the vessel seems to remain "lost" even if it recommences broadcasting and it doesn't get tracked until OpenCPN is restarted. If instead LostTargets are not checked, the vessel is always tracked as one single
very long track from whenever the vessel starts broadcasting to whenever OpenCPN is shut down. Recording recommences once OpenCPN is restarted and the vessel starts broadcasting.
What I ended up with was Tracking
set to "Default tracking". That required AISTracks to be checked and meant that all AIS targets are tracked. Tracklength was set to a reasonable value so as to avoid too much screen
clutter. I found 10-20 minutes was OK. Most importantly, LostTargets were both checked and set to reasonable values (for us that's 20 and 30 mins). So when the vessel hasn't transmitted for 30 mins it is marked "lost" and removed from the AIS target list. The track however remains indefinitely, unlike most targets whose track is removed once they are lost
. Once our vessel starts broadcasting again then a new track is recorded in the Route & Mark Manager.
So there we have it. Our selected vessels (only) are tracked every time they go out. Should we ever have need to provide evidence of our vessel track or location then we can get that. This can be essential for us given our vessels perform search and rescue