The top of this chain of command is the Chief engineer (or first engineer), who is in command of engine room and auxiliary areas that would relate. Then comes the first assistant engineer, or second engineer, second assistant engineer (third engineer, and then the third assistant engineer, or fourth engineer. These are the officers within the engine company of a standard ship.
The general duties for a third assistant engineer (fourth engineer) differ from ship to ship. Generally speaking, third assistant engineer (fourth engineer) are tasked with controlling the main propulsion systems, water systems,Purifiers,Air compressors,Sewage Treatment Plant,Fresh water Generator, actively involving in bunkering operation,Record keeping of fuel tanks sounding as instructed by chief engineer and anything else tasked to them from up in the chain of command. A third assistant engineer (fourth engineer) is part of the engine company’s chain of command.