I think that is is much safer, because no people are endangered if pirates attack. And if there are no humans on board such a ship can be designed to be un-openable and un re-directable by outside parties. There will always be someone who can break into the system and re-program it, but its much more complex than to take 3 men and a few kalashnikovs an board in.
homo datensis 
This is incredible to watch but how they gonna work we have to wait and see. But one thing i doubt is that these ships may be easily attacked by pirates. That too too expensive where €3.5m to develop
an autonomous ship is very expensive. Source: http://www.ship-technology.com/news/newsrolls-royce-to-develop-drone-cargo-ships-4185296
I think that is is much safer, because no people are endangered if pirates attack. And if there are no humans on board such a ship can be designed to be un-openable and un re-directable by outside parties. There will always be someone who can break into the system and re-program it, but its much more complex than to take 3 men and a few kalashnikovs an board in.