It must have been a bizarre sight when a freight ship, equipped with two large rotating towers, made its way under the Forth Bridge a century ago. The experimental sail technology, on the rotor ship Buckau, was first demonstrated in 1925 on a journey carrying timber from Danzig - now Gdansk, in Poland - to the Scottish port of Grangemouth. The spinning towers were designed to harness the wind as a way of saving fuel but it didn't catch on for about 90 years. Now the pioneering Flettner rotors