Answer:
If after studying mechanical engineering you feel you could work on a ship you must go to a college to do all the practical based requirements in a workshop like welding, machining, filing etc and all your safety courses like first aid at sea and fire fighting etc then go to the MCA and take an oral examination to receive your marine engineering officers ticket. If you do not ( as its a completely different world ) then you must go to a Maritime Academy and do a degree in marine engineering.