Economics of robotic clipper ships

Lets talk about a completely robotic sail boat that caries 500 containers.  There is no human habitation on the thing, so all human support equipment is gone, i can even dip in the water. The design is simple standard container carrier, easy off and easy on. Mass production unit costs? About 20 million.

In the business, these are herded, 20 at a time, across the Atlantic. Along with the herd of clippers is a maintenance yacht and a few humans who ride shotgun. This outfit generates about 2,000 in shipping fees per container, a million per trip. 20 trips and the thing is paid for, and at 15 days per trip, that is about a year payback.  That is very good stuff, if you can keep the capital costs down.

I am not saying that this is what Google is up to, but if they have the boats, then go for it.