Editing SS Great Britain (section)

===Machinery===
{{multiple image
| align = left
| image1 =  SS Great Britain transverse section.jpg 
| width1 =  120 
| alt1 = 
| caption1 = Transverse hull section, showing arrangement of gearwheels, gear chains and engine cylinders
| image2 =  SS Great Britain engine and gearwheels lateral section.jpg 
| width2 =  100 
| alt2 = 
| caption2 =  Side view of engines, showing arrangement of gears and gear chains between the engines 
| footer = 
}}[[File:Model of SS Great Britain's engines.jpg|thumb|right|upright| A model of ''Great Britain''{{'}}s engines]]

Two giant propeller engines, with a combined weight of 340&nbsp;tons, were installed amidships.{{sfn|Claxton|1845|p=18}} They were built to a modified patent of Brunel's father [[Marc Isambard Brunel|Marc]]. The engines, which rose from the keel through the three lower decks to a height just below the main deck, were of the [[marine steam engine#Direct acting|direct-acting]] type, with twin {{convert|88|in|cm|abbr=on}} [[bore (engine)|bore]], {{convert|6|ft|m|adj=on}} [[stroke (engine)|stroke]] [[cylinder (engine)|cylinders]] inclined upward at a 60° angle, capable of developing a total of {{convert|1000|hp}} at 18&nbsp;[[Revolutions per minute|rpm]].{{sfn|Fox|2003|p=150}}{{sfn|Claxton|1845|pp=3–6}} Steam power was provided by three {{convert|34|ft|m|adj=mid}} long by {{convert|22|ft|m|adj=mid}} high by {{convert|10|ft|m|adj=mid}} wide, {{convert|5|psi|abbr=on}} "square" saltwater [[boiler]]s, forward of the engines, with eight furnaces each&nbsp;– four at each end.{{efn|Some sources, such as Claxton,{{sfn|Claxton|1845|p=3}} state that there was only a single boiler, but others, such as Fletcher and Maginnis,{{sfn|Maginnis|1900}}{{page needed|date=July 2020}} state that there were three side by side. This apparent discrepancy is explained by the fact that there were three separate boilers or boiler compartments sharing a common housing.{{sfn|Dumpleton|Miller|2013}}{{page needed|date=July 2020}} }}

In considering the gearing arrangement, Brunel had no precedent to serve as a guide. The gearing for ''Archimedes'', of the spur-and-pinion type, had proven almost unbearably noisy, and would not be suitable for a passenger ship.{{sfn|Fox|2003|pp=148–149}} Brunel's solution was to install a [[chain drive]]. On the crankshaft between ''Great Britain''{{'}}s two engines, he installed an {{convert|18|ft|m|adj=mid}} diameter primary gearwheel,{{sfn|Claxton|1845|p=6}} which, by means of a set of four massive inverted-tooth or "silent" chains, operated the smaller secondary gear near the keel, which turned the propeller shaft. This was the first commercial use of silent chain technology, and the individual silent chains installed in ''Great Britain'' are thought to have been the largest ever constructed.{{sfn|American Chain Association|2005|p=10}}

''Great Britain''{{'}}s main propeller shaft, built by the Mersey Iron Works, was the largest single piece of machinery. {{convert|68|ft|m|abbr=on}} long and {{convert|28|in|cm}} in diameter, the shaft was bored with a {{convert|10|in|cm|adj=mid|-diameter}} hole, reducing its weight and allowing cold water to be pumped through to reduce heat. At each end of the main propeller shaft were two secondary coupling shafts: a {{convert|28|ft|m|adj=on}}, {{convert|16|in|cm|adj=mid}} diameter shaft beneath the engine, and a screw shaft of {{convert|25|ft|m|abbr=on}} in length and with a diameter of {{convert|16|in|cm}} at the stern. Total length of the three shafts was {{convert|130|ft|m|abbr=on}}, and the total weight 38&nbsp;tons.{{sfn|Claxton|1845|p=18}} The shaft was geared upward at a ratio of 1 to 3, so that at the engines' normal operating speed of 18&nbsp;rpm, the propeller turned at a speed of 54&nbsp;rpm.{{sfn|American Chain Association|2005|p=10}} The initial propeller was a six-bladed "windmill" model of Brunel's own design,{{sfn|Fox|2003|p=151}} {{convert|16|ft|m|abbr=on}} in diameter and with pitch of {{convert|25|ft|m|abbr=on}}.{{sfn|Claxton|1845|p=13}}