On 25 March 1852, Brunel made a sketch of a steamship in his diary and wrote beneath it: "Say 600 ft x 65 ft x 30 ft" (180 m x 20 m x 9.1 m). These measurements were six times larger by volume than any ship afloat; such a large vessel would benefit from economies of scale and would be both fast and economical, requiring fewer crew than the equivalent tonnage made up of smaller ships. Brunel realised that the ship would need more than one propulsion system; since twin screws were still very much experimental, he settled on a combination of a single screw and paddle wheels, with auxiliary sail power. Although Brunel had pioneered the screw propeller on a large scale with the "Great Britain", he did not believe that it was possible to build a single propeller and shaft (or, for that matter, a paddleshaft) that could transmit the required horsepower to drive his giant ship at the required speed.