PLC’s are hard to hack as they are not casually connected to WAN’s. The supervisory system on ships are not connected to WAN’s, just local networks, not the internet.
I have never worked on a cargo ship where the enginecontolroom panels/computors have hade internet/satelite connection. It might exist somewhere, but I have never seen it.
Maersk Engineer (note - an act of terrorism is usually not covered by insurance, so it would be in Maersk's interest for it to be that under force majeure, good luck)