Not encountering any battle opportunities

Hello - this may be straightforward. I have tried wikis and threads to no avail.
I’ve had SS for a while now, but initially found the navigation to hard for battles so I left it alone for a few months.
I returned recently and after losing my first couple of captains, switched to Merciful Mode.
Since then I have mastered the navigation skills, but have not encountered a single monster or enemy ship after about 40 hours of gameplay. I’ve only ever perished due to running out of supplies.
Not sure if I need to do something to trigger enemies appearing, or if this is a bug.

Are you using the Zubmarine? I heard that some people had this problem underwater but that monsters started appearing later, you may want to send a bug report to Failbetter either way since it is probably not intended.