A new tethered drone system from Volarious enables DJI drones for boats. The system allows a commercial off-the-shelf, Mavic 2 drone to autonomously take off, follow, and land safely on small vessels . The drone can remain in the air as long as it needs, as it is powered by the tethered line.
Interesting concept
I can think of several scenarios where drone video would be useful if not limited by battery life
I’m not familiar with boats, why would you need a birds eye view of where you are? Can’t you just look out of the window to see what’s in front of you? 
Search and rescue. On water, for someone who is 1.8m tall (for example) the horizon is 3 miles away. But at 50m above sea level, the horizon is a distance of 16 miles away.
Or in other words, the area that a person can see is 28 square miles at sea. Whereas an area that a drone can see (at 50m) is 804 square miles. That is more than 28 times the search area than “looking out the window”.
Interesting, thanks Chris 
Despite the hype, the Earth is not flat 
Could have done with that on the Broads recently, couldn’t see a thing out of the windscreen every morning cos of the condensation. Ended up sliding the canopy off, standing up & dressing like an Eskimo 
I’ve seen the truck mounted options in the States but not sure about the off the shelf compatibility, looks like a great idea though
I can see it’s use in Search and Rescue at sea, especially if fitted with an IR camera - much easier to see a casualty in the water from a few metres up whereas at sea level they can easily be obscured by waves.
I can also see uses for a van mounted version e.g. crowd control at large events
