.. of a small moving boat. 
Firstly - horizonal speed. It will immediately try to be stationary with respect to the world .. NOT the boat. So there’s a good probability that before you can get the speed right it will be going backwards, relative to the boat, at the boat’s speed. So, NEVER launch with ANYTHING between the drone and the stern of the boat.
Secondly - boats bob up and down. Once you’ve started the motors, as soon as there’s any downward motion the drone will try to hover. Just an inch or two of movement is enough. And, of course, it will attempt to hover stationary to the world, not the boat. So, again it will be zipping off to stern.
Had you bothered to search, you’d have found some things are STILL very relevant.
This post, and the subsequent one, show how little bobbing movement is needed for this potentially dangerous situation to occur, possibly endangering other occupants of the boat.
Unless the motors stop the moment you land .. you can be back into the bobbing boat scenario and it will be off again.
So .. simple rule for launching and landing from a small boat .. stand/sit at the very back of the boat, no rigging/superstructure aft of you, and hand launch/land.
And by small, I mean one that has vertical motion of more than an inch or so, but I’d still be at the very stern of the boat .. to make sure.