Editing Propulsion (section)

===Marine===
[[Image:Two Main Engines, V12.jpg|thumb|250px|A view of a ship's engine room]]
{{main|Marine propulsion}}
Marine propulsion is the mechanism or system used to generate [[thrust]] to move a [[ship]] or [[boat]] across water. While [[paddle]]s and [[sail]]s are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting of a motor or engine turning a [[propeller]], or less frequently, in jet drives, an [[impeller]]. Marine engineering is the discipline concerned with the design of marine [[propulsion system]]s.

[[Steam engine]]s were the first mechanical engines used in marine propulsion, but have mostly been replaced by [[two-stroke engine|two-stroke]] or [[four-stroke engine|four-stroke]] diesel engines, outboard motors, and [[gas turbine engine]]s on faster ships. [[nuclear marine propulsion|Nuclear reactors]] producing steam are used to propel [[warship]]s and [[icebreaker]]s, and there have been attempts to utilize them to power commercial vessels. [[Electric motor]]s have been used on [[submarine]]s and [[electric boat]]s and have been proposed for energy-efficient propulsion.<ref>{{cite web |url=http://www.ivt.ntnu.no/imt/electricship/ |title=Energy Efficient - All Electric Ship |access-date=2009-11-25 |url-status=dead |archive-url=https://web.archive.org/web/20090517060017/http://www.ivt.ntnu.no/imt/electricship/ |archive-date=2009-05-17 }}</ref> Recent development in liquified natural gas (LNG) fueled engines are gaining recognition for their low emissions and cost advantages.