Lack of predictability.

I attended a maritime academy and worked in the industry for a year before switching to computers.

The modern transportation is built on reliable ETAs. Mechanical propulsion changed shipping from an industry of uncertainty to one in which you 'could make your own ETA'. Sail doesn't give you that kind of certainty.

It is worth noting that there are technologies (SkySail, for example) on the market now that use sail as a form of auxiliary power so that ships can save on bunkers.

(edit: formatting)

Is there any kind of cargo with logistics of "eh, as long as it gets there eventually"?

A curious thought just popped into my head. Deliveries tend to be time critical. I can't think of many deliveries that would tend not to be. However ocean cleanup struck me as a type of 'collection' that may hypothetically find sail power to be an advantage. I've done zero research and have absolutely no background in the area, however I do recall from my years fishing that at least surface garbage tends to follow wind patterns. If this can be exploited by an autonomous vehicle in some way, perhaps it could prove to be an advantage? Clusters of networked vessels could work together to provide enough live data on wind direction to avoid errors with localised high frequency changes in wind direction perhaps.

The down sides would be that once the vessel has a full cargo, it may take longer than a powered vessel to return to wherever it will offload the waste (perhaps a larger 'mothership' could follow?), and with no sailing expertise, I suspect that it may be harder to direct such a vessel than just using a powered one with the appropriate sensors aboard.

For non-perishable goods, you can compensate for this by keeping larger stockpiles at the destination to prohibit shortfalls. However, this obviously costs more in terms of warehousing, risk, and sunk capital.

By the way if you want to know what it was like at (almost) the very last moments of sail freight I very highly recommend "The Last Great Grain Race" in which Eric Newby writes of his experience working aboard a wind powered grain freighter from Europe to Australia in 1939. Sail shipping was suspended during the war and finally ended for good in 1949.

(In typical Newby style he had zero sailing experience when he signed on, though he was an excellent writer).

>> "It wouldn't be autonomous..."

There are plenty of autonomous sailboats, such as https://ubcsailbot.org/, http://saildrone.com/ etc.

These tend to be small because they're not often run for commercial purposes, but you could surely build one bigger.

There's a proposal (not proven economically sound AFAIK) to develop an airfoil-assisted cargo vessel powered by LNG: http://www.cnn.com/2015/01/16/tech/vindskip-wind-powered-con...

I remember seeing this kite-like concept in a magazine a long time ago: http://www.skysails.info/english/

Crew is expensive today, especially when compared to the 19th century when conditions were horrid and you could impress people into your crew.

> compared to the 19th century when conditions were horrid and you could impress people into your crew

Impressment was not used for merchant shipping.

Ya wanna bet? https://en.wikipedia.org/wiki/Shanghaiing

Why not an autonomous sailboat?

Sailboats devote a lot of structure and surface area to propulsion. All that stuff gets in the way of loading and unloading containers.

Also, they're slow.

An electric boat is probably slow also.