Marine engineering includes the engineering of boats, ships, oil rigs and any other marine vessel or structure, as well as oceanographic engineering. Specifically, marine engineering is the discipline of applying engineering sciences, including mechanical engineering, electrical engineering, electronic engineering, and computer science, to the development, design, operation and maintenance of watercraft propulsion and on-board systems and oceanographic technology. It includes but is not limited to power and propulsion plants, machinery, piping, automation and control systems for marine vehicles of any kind, such as surface ships and submarines.
The purely mechanical ship operation aspect of marine engineering has some relationship with naval architecture. However, whereas naval architects are concerned with the overall design of the ship and its propulsion through the water, marine engineers are focused towards the main propulsion plant, the powering and mechanization aspects of the ship functions such as steering, anchoring, cargo handling, heating, ventilation, air conditioning, electrical power generation and electrical power distribution, interior and exterior communication, and other related requirements.
In some cases, the responsibilities of each industry collide and is not specific to either field. Propellers are examples of one of these types of responsibilities. For naval architects a propeller is a hydrodynamic device. For marine engineers a propeller acts similarly to a pump. Hull vibration, excited by the propeller, is another such area. Noise control and shock hardening must be the joint responsibility of both the naval architect and the marine engineer. In fact, most issues caused by machinery are responsibilities in general.
Not all marine engineering is concerned with moving vessels. Offshore construction, also called offshore engineering or maritime engineering, is concerned with the technical design of fixed and floating marine structures, such as oil platforms and offshore wind farms.
Oceanographic engineering is concerned with mechanical, electrical, and electronic, and computing technology deployed to support oceanography, and also falls under the umbrella of marine engineering, especially in Britain, where it is covered by the same professional organisation, the IMarEST.
Source: https://en.wikipedia.org/wiki/Marine_engineering