If the world’s shipping fleet were a country, it would be the world’s sixth leading emitter of greenhouse gases. To reduce those emissions — and, not incidentally, to conserve expensive fossil fuels — cargo ship designers are now turning to the oldest source of power there is: the wind.

The new vessels, mainly still on drawing boards and in prototype, look nothing like the graceful schooners and galleons of centuries past. Last spring, for example, the University of Tokyo unveiled a model of its UT Wind Challenger at the Sea Japan trade show. It has nine masts, each 164 feet tall, with five rigid sails made of aluminum and fiber-reinforced plastic; the sails are hollow, designed to telescope into one another in rough weather or at anchor.

Then there is the 328-foot, 3,000-ton cargo carrier being designed by B9 Shipping (pronounced benign), part of the B9 Energy Group in Northern Ireland. Its three masts rise 180 feet, as tall as a 14-story building.

Powered by a combination of wind and a Rolls-Royce biogas engine, it is intended to operate with no fossil fuels.