If you launch and follow your boat as it's travelling some distance, you could get to a point where the RTH/distance/battery level calculation tells the drone it time to go back and the drone heads for where it was launched, way back in the distance.
You don't want that happening.
To prevent this situation, reset the homepoint every 5 mins or so to keep the homepoint closer to where the boat actually is.
Retrieving the drone on a boat that's moving in 3 dimensions can be much harder than landlubbers can imagine.
Make sure that you have enough battery to allow for several catching attempts and go-arounds.
And practice everything you'll need to do while on land.
Out on a moving boat is the worst place to be learning new techniques or trying to find features in the app.