A lot of ship cargo consists of things that (1) we need a steady supply of, and (2) have a very long shelf life. For such cargo it doesn't matter how long the transit time for any particular shipment is, as long as shipments are arriving at the destination often enough.<p>I wonder if we could make unmanned cargo boats that spend most of their time drifting?<p>Drifting can be quite effective at long distance ocean transport. For an example look at the Friendly Floatees accident [1]. A ship accidentally lost 29 000 floating bath toys in the middle of the Pacific. Over the next 15 years they reached land in on both the Pacific and Atlantic coasts of North America, the Pacific coast of South America, Australia, and Europe, and came close to Japan.<p>I'm imagining a ship that drifts, occasionally using an engine to get into known currents that will help it toward its goal or avoid currents known to hurt.<p>Places where two or more significant currents pass through the same region could be used to route traffic. They could have tow ships stationed there that can move drifters between the currents<p>We could have a large fleet of such drift ships carrying suitable commodities with very little environmental impact, with a smaller fleet of normal cargo ships providing fast transport to fill in the gaps caused by the randomness of the drifting fleet arrivals.<p>The above idea is based on the proposals I've seen to do something similar in space. Briefly, there are orbits that can move an object from Lagrange points of one pair of bodies to Lagrange points of another pair using very little energy, but they can take a very long time.<p>The proposals are to start using those to regularly send supply ships to various moons and planets that we think we may want to send humans to later. Suppose the path to some particular moon takes 30 years. If we start sending supply ships down that path now, sending one every 6 months, say, then 30 years from now they start arriving. Then we can send the humans. The ship with the humans only needs to take enough supplies for the trip out, making the trip much more feasible.<p>[1] <a href="https://en.wikipedia.org/wiki/Friendly_Floatees" rel="nofollow">https://en.wikipedia.org/wiki/Friendly_Floatees</a>