Jadran .. best to check with your country's civil aviation authority for their rules.
In many countries (but not all) you can fly and photograph for recreational purposes without a licence as long as you follow their safety guidelines.
To correct a few misconceptions .. the popular drones are the size of a seagull and unless the flyer is doing crazy things, the ship's crew probably wouldn't even notice it when you are photographing.
And these things are the world's worst spy devices. With an extreme wideangle lens, flashing LEDs and a sound like 100000 killer bees, you can't sneak up on anyone or get recognisable photos of a person without them knowing well be fore you would be in range. If you are concerned about privacy, drones come way, way down the list with mobile phones, cameras, binoculars etc etc 100 times more effective for spying.
I suspect that at least some of the rash of recent sightings by airline pilots are not recreational drones at all. The reports rarely give any details but when they do, many are definitely not the common quadcopters and are more likely to be birds, balloons, other planes, Venus or any other thing that used to cause UFO reports.
On the positive side, a drone is just magic for ship photography.
It opens up so many angles and perspectives that weren't possible without hiring a helicopter.
Tanker or car carrier looks boring?
Just get some elevation and show a little deck detail and water on both sides of the ship and it lifts your photos.
Sun on the wrong side of your ship?
No problem ... just zip across to the other side and shoot with the sun instead of against it.