Re: Safety?
I disagree that "intelligent" autopilots on ships are more difficult to implement than on aircraft, or that the probability of collision is higher. Ships may need tens of miles to stop, but aircraft have an infinite stopping distance! Vessels equipped with AIS (i.e. just about all vessels these days, even including large buoys and most small yachts that venture offshore) can detect a potential collision situation tens of minutes away, and the navigation/autopilot computer can plot a course between moving vessels even in pretty crowded waters well within the time needed to make the appropriate course adjustments, whilst aircraft may have only seconds to detect and react to a collision situation.
The added safety of having humans on ships is debateable. In fact the *illusion* of increased safety may well cause it to be *less* safe. Ships (like airliners) are being controlled by autopilot 99% of the time anyway, and human lookout is more fallible than an automated collision detection system based on radar and AIS - especially so in fog and heavy squalls. When sailing a small yacht (my only personal experience of navigating a vessel at sea), I would far prefer to rely on an AIS plotter or radar proximity alert than my eyeballs. It's very easy to daydream or doze off, or fixate on looking in the wrong direction, or become engrossed in a book, meal preparation or passage planning etc.
Leaving and entering a port and docking is something else entirely, and I doubt that can be reliably automated - but unlike aircraft, a pilot crew can be taken off a ship after clearing port, and put on as it approaches its destination, leaving the ship unmanned during the days or weeks of the en-route portion of its passage.