Shofu Maru is a bulk carrier that has been retrofitted with a sail to capture wind energy. The sail creates thrust for the ship that would otherwise have to be generated by bunker fuel. The sail is retractable so that it can be lowered in unfavorable wind conditions or at port.

Outfitting bulk carriers with sails is an interesting concept because a lot of bulk cargo (eg iron ore, coal, grain, etc) is not particularly time sensitive. This will allow the ship to make a more circuitous route and take advantage of any favorable wind along its voyage.