A windjammer is a type of sailing ship with a large iron hull, usually used for cargo in the nineteenth century. They were the grandest of cargo sailing ships, with between three and five large masts and square sails, giving them a characteristic profile. They frequently displaced several thousand tons, and were cheaper than their wooden hulled counterparts for three main reasons: iron was stronger, and thus could enable larger ship sizes and considerable economies of scale, iron hulls took up less space and allowed for more cargo to be carried, and iron hulls were cheaper to maintain than an equivalent wooden hull.
Windjammers were only produced from the 1870s to the 1890s, as the steam engine outcompeted them economically, due to cheap coal. Steel hulls also replaced iron hulls at around the same time. The internal combustion engine forever sealed their fate. Sailing ships in general were expensive to operate, as they required a large crew and used up space for storing sails, and, like all sailing ships, depended on favorable wind conditions, making them unreliable. Companies would rather hire one crew and burn coal (offering reliability) than hire two crews (one to man each method of propulsion) and have minor savings in coal costs but retain its reliability.
Today, some aspects of a windjammer design are again appealing in light of the soaring costs of diesel fuel in shipping and the environmental impacts of burning such fuels. However, these ships would be a hybrid design, with sails lessening the fuel required by augmenting the diesel engine with sails, allowing the diesel engine to run at a more efficient rate. Though each design has drawbacks, the governments of Denmark, Germany, Japan, and the European Union have all funded research into such development projects. Using modern materials, fuel efficient designs, and modern computers, these ships could be more fuel efficient and economically feasible than modern cargo ships, and more economically viable and reliable than traditional windjammer designs. A flying kite design could also be useful for passenger ships, since they also pull the ship up and are anchored on the center of the craft, stabilizing the ship's structure, allowing it to rock back and forth less.