You could just settle for alerting you when someone is trying to steal your boat for starters. For that lorawan is quite suitable, maybe ideal. This thread may be a good starter for that one:
I'm curious as to what sensor you would use? Clearly you could use a PIR sensor on the inside of your boat, however it would be much more desirable to know before they've broken in. Boats would pose a particularly difficult problem here. A pir sensor would see way past the boat. Boats rock so you can't use that. You could use pressure sensors but installation is not trivial. That approach may provide the best working solution though if you could achieve it realistically. I've considered using upwards pointing microwave movement detectors for that purposes, mounted under the deck, however my experiments with microwave movement detectors have not yield good results.
Let me know if you find a good sensor approach. If you have that solved, I can help on the other side of it. The alerting and a node for example