The purely mechanical ship operation aspect of marine engineering has some relationship with naval architects. 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.