

290 SECTION MECHANICS. 



became the type of screw engines in general use. This ship had a 

 screw-well and hoisting gear for the screw. 



In 1845 tne import nee of the screw propeller for ships of war became 

 fully recognised, and designs and tenders were invited from all the 

 principal marine engineers in the kingdom. The government of f hat 

 day then took the bold step of ordering at once nineteen sets of screw 

 engines of the following firms, viz., of Messrs. Maudslay, Sons, and Field, 

 four sets for the "Ajax," "Edinburgh," " Niger," and " Desperate ;" of 

 Messrs. Seaward and Capel four sets, for the "Blenheim," "Hoguc," 

 "Conflict," and "Teimagant;" of Messrs. Jno. Penn and Sons two sets, 

 for the "Arrogant" and "Encounter;" of Messrs. Boulton and Watt 

 three sets, for the "Eurotas," "Horatia," and "Vulcan;" of Messrs. 

 Rennie two sets, for the "Forth" and the "Seahorse;" of Messrs. 

 Napier two sets, for the "Dauntless" and "Simoom;" of Messrs. 

 Fairbairn one set for the "Megcera ;" and of Messrs. Scott and Sinclair 

 one set for the "Greenock." 



Of these, the four last-named vessels and the " Desperate "ami "Ter- 

 magant" had wheel gearing. In all the rest the engines were direct 

 acting. The steam pressure in the boilers was from five to ten pounds 

 only above the atmosphere, and if the engines indicated twice the 

 nominal power, it was considered to be a good performance. 



The most successful engines were those of the "Arrogant" and 

 "Encounter" of Messrs. Penn. They had a higher speed of piston 

 than the others, and the air-pumps were worked direct from the 

 pistons, and had the same length of stroke. These engines developed 

 more power for a given amount of weight than other engines of their 

 day, and were the forerunners of the many excellent engines on the 

 double-trunk plan, made by this firm for the navy. 



The engines with wheel-gearing for the screws were heavier, occu- 

 pied more space, and were not so successful as the others, and no 

 more of that description were ordered for the Royal Navy. 



Up to 1860 neither surface-condensers nor super-heaters were used 

 in the Royal Navy. The consumption of fuel was about four and 

 a-half pounds per one horse-power per hour. 



In 1860 a cp was taken in the Royal Navy which receives illus- 

 tration from a beautiful set of drawings contributed by the firm of 

 J. Elder & Co. 



