Marine engineers typically do the following:

• Prepare system layouts and detailed drawings and schematics
• Inspect marine equipment and machinery, and draw up work requests and job specifications
• Conduct environmental, operational, or performance tests on marine machinery and equipment
• Design and oversee the testing, installation, and repair of marine equipment
• Investigate and test machinery and equipment to ensure compliance with standards
• Coordinate activities with regulatory bodies to ensure that repairs and alterations are done safely and at minimal cost
• Prepare technical reports for use by engineers, managers, or sales personnel
• Prepare cost estimates, contract specifications, and design and construction schedules 
• Maintain contact with contractors to be sure that the work is being done correctly, on schedule, and within budget

Naval architects typically do the following:

• Study design proposals and specifications to establish basic characteristics of a ship, such as its size, weight, and speed
• Develop sectional and waterline curves of the ship's hull to establish the center of gravity, ideal hull form, and data on buoyancy and stability
• Design entire ship hulls and superstructures, following safety and regulatory standards
• Design the complete layout of ships' interiors, including spaces for machinery and auxiliary equipment, passenger compartments, cargo space, ladder wells, and elevators
• Confer with marine engineers to design the layout of boiler room equipment, heating and ventilation systems, refrigeration equipment, electrical distribution systems, safety systems, steering, and propulsion machinery
• Lead teams from a variety of specialties to oversee building and testing prototypes
• Evaluate how ships perform during trials, both in the dock and at sea, and change designs as needed to make sure that national and international standards are met

Marine engineers and naval architects apply knowledge from a range of engineering fields to the entire water vehicles' design and production processes. Marine engineers also design and maintain offshore oil rigs and may work on alternative energy projects, such as wind turbines located offshore and tidal power.

Marine engineers and naval architects who work for ship and boat building firms design large ships such as passenger ships and cargo ships, as well as small craft such as inflatable boats and rowboats. Those who work in the federal government may design or test the designs of ships or systems for the Army, Navy, or Coast Guard.

Ship engineers, who are sometimes called marine engineers, operate or supervise the operation of the machinery on a ship. Their work differs from that of the marine engineers discussed in this profile. For more information on ship engineers, see the profile on water transportation workers.