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Pioneering wind-powered cargo ship sets sail
(www.bbc.com)
This is a most excellent place for technology news and articles.
I dont think this ship could ever go sail-only. But it can use them as assistance to the engines. It'd need a lot more sails, taller sails, and probably some hull modifications to get anywhere near the same speed on sail only. But it can use the sails to go faster for a given throttle setting.