Life at sea for a marine engineer is 3-D ie: its Dangerous, Dirty and Difficult. Every day is a challenge at sea. You got to fight the nature at its worst and even then not loose your cool. The ship is exposed to the rough sea conditions and there will be rolling and pitching. You will have to learn to balance when the ship rolls and pitches, then there is sea sickness, the empty oceans and 8-12 hrs of work. These are not the cons of this filed, its a part and parcel, one should learn to survive in these conditions to be a successful marine engineering officer. These conditions make the life of a marine engineer rough and challenging, but once adjusted it becomes second nature.
A fifth engineer will be under the seniors and will have to carry out maintenance related work on-board. There will be minimum sleep and he has to be active at all times. This field demands moderate knowledge and very high observational skills. These traits are imparted to the trainees during their training as a Fifth engineer. It might take 1 month to get adjusted to the life at sea and to the challenges of this profession, but once adjusted this will be the best decision of your life. All I can say is that the "life at sea" is worth it!