When will we get robotic cargo ships with no crew on them?

We put this question to Tristan Smith from UCL...

I think this would be a good thing as long as you weren't a ship's captain or a crew member! I think there's a lot of electronics that could be done and the technology is probably feasible, but the legal implications of having unmanned ships sailing around the world are probably a bit tricky to sort out - if you have an accident who's going to try and remedy the situation or salvage anything? How do you avoid the collision in the first place? Can you actually make sure that the ship's computers are going to be reliable enough in order to stop that? So, there are lots of detailed practical issues, but certainly, the technology could be there and it's something that there are researchers who are working quite hard to achieve at the moment.