Weight of screw 4 tons Diameter of main drum 18 feet Diameter of screw-shaft drum 6 " Weight of coal 1,200 tons CHAPTER X. _STEAM NAVIGATION._ _INTRODUCTION OF THE SCREW PROPELLER INTO THE ROYAL NAVY._ A.D. 1841--1844. ÆTATIS 36--39. APPOINTMENT OF MR. BRUNEL TO CONDUCT EXPERIMENTS FOR THE ADMIRALTY WITH VARIOUS FORMS OF THE SCREW PROPELLER, APRIL 1841--TRIALS WITH THE ‘POLYPHEMUS’--OPPOSITION TO MR. BRUNEL’S EXPERIMENTS--TRIALS WITH THE ‘RATTLER,’ OCTOBER 1843-OCTOBER 1844. Soon after Mr. Brunel had taken the bold step of recommending the adoption of the screw propeller in the ‘Great Britain,’ he was asked to send a copy of his report to the Admiralty. He did so; and in the course of a few months was invited to attend the Board on the subject of some experiments their Lordships proposed to make. An interview took place on April 27, 1841; of which Mr. Brunel gives the following account:-- I attended the Board: Lord Minto stated that he wished a complete experiment to be made on the applicability of the screw to Government boats, and he proposed to place the conduct of the experiments in my hands as a professional man. I stated that I should have great pleasure in doing it, and should take great interest in it, provided they intended to make a good experiment and would place it entirely in my hands, without the intervention of any Government officers, but that I should communicate direct with the Lords, and of course with Sir E. Parry.[135] He said he proposed to build a vessel and engines on purpose, and that he particularly wished it to be left entirely in my hands, and took me apart to the window to impress this last condition on me. Within a fortnight of his appointment, Mr. Brunel invited Messrs. Maudslay and Field and Messrs. Seaward to send him designs for the engines: they were to have been of 200-horse power, with a stroke of 4 feet. The engines were to make a smaller number of revolutions than the screw, the motion being communicated from the engine shaft to the screw shaft by drums and straps. This arrangement was adopted in preference to tooth-gearing, in order to facilitate the variation of the number of revolutions, in the experiments with different screws. The designs ultimately sent to Mr. Brunel for his approval were those of Messrs. Maudslay and Messrs. Forrester. He reported to the Admiralty in favour of Messrs. Maudslay’s engines.