Marine Engineering

Marine engineering includes the engineering of boats, ships, oil rigs and any other marine vessel or structure, as well as oceanographic engineering, oceanic engineering or ocean 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.  

Challenges specific to marine engineering

Hydrodynamic loading
In the same way that civil engineers design to accommodate wind loads on building and bridges, maritime engineers design to accommodate a ship being flexed or a platform being struck by waves millions of times in its life.
Stability
A naval architect, like an airplane designer, is concerned with stability. The naval architect’s job is different, insofar as a ship operates in two fluids simultaneously: water and air. Engineers also face the challenge of balancing cargo as the mass of the ship increase and the center of gravity shifts higher as additional containers are stacked vertically. In addition, the weight of fuel presents a problem as the pitch of the ship cause the weight to shift with the liquid causing an imbalance. This offset is counteracted by water inside larger ballast tanks. Engineers are faced with the task of balancing and tracking the fuel and ballast water of a ship.
Corrosion
The chemical environment faced by ships and offshore structures is far harsher than nearly anywhere on land, save chemical plants. Marine engineers are concerned with surface protection and preventing galvanic corrosion in every project.   Corrosion can be inhibited through cathodic protection by utilizing pieces of metal known as sacrificial anodes. A piece of metal such as zinc is used as the sacrificial anode as it becomes the anode in the chemical reaction. This causes the metal to corrode and not the ship’s hull. Another way to prevent corrosion is by sending a controlled amount of low DC current to the ship’s hull to prevent the process of electro-chemical corrosion. This changes the electrical charge of the ship’s hull to prevent electro-chemical corrosion.
Anti-fouling
Anti-fouling is the process of eliminating obstructive organisms from essential components of seawater systems. Marine organisms grow and attach to the surfaces of the outboard suction inlets used to obtain water for cooling systems. Electro-chlorination involves running high electrical current through sea water. The combination of current and sea water alters the chemical composition to create sodium hypochlorite to purge any bio-matter. An electrolytic method of anti-fouling involves running electrical current through two anodes (Scardino, 2009).[3]These anodes typically consist of copper and aluminum (or iron). The copper anode releases its ion into the water creating an environment that is too toxic for bio-matter. The second metal, aluminum, coats the inside of the pipes to help prevent corrosion. Other forms of marine growth such as mussels and algae may attach themselves to the bottom of a ship’s hull. This causes the ship to have a less hydrodynamic shape since it would not be uniform and smooth around the hull. This creates the problem of less fuel efficiency as it slows down the vessel (IMO, 2018). This issue can be remedied by using special paint that prevent the growth of such organisms.
Pollution control
Sulfur emission
The burning of marine fuels has the potential to release harmful pollutants into the atmosphere. Ships burn marine diesel in addition to heavy fuel oil. Heavy fuel oil, being the heaviest of refined oils, releases sulfur dioxide when burned. Sulfur dioxide emissions have the potential to raise atmospheric and ocean acidity causing harm to marine life. However, heavy fuel oil may only be burned in international waters due to the pollution created. It is commercially advantageous due to the cost effectiveness compared to other marine fuels. It is prospected that heavy fuel oil will be phased out of commercial use by the year 2020 (Smith, 2018).
Oil and water discharge
Water, oil, and other substances collect at the bottom of the ship in what is known as the bilge. Bilge water is pumped overboard, but must pass a pollution threshold test of 15 ppm (parts per million) of oil to be discharged. Water is tested and either discharged if clean or recirculated to a holding tank to be separated before being tested again. The tank it is sent back to, the oily water separator, utilizes gravity to separate the fluids due to their viscosity. Ships over 400 gross tons are required to carry the equipment to separate oil from bilge water. Further, as enforced by MARPOL, all ships over 400 gross tons and all oil tankers over 150 gross tons are require to log all oil transfer is an oil record book (EPA, 2011).
Cavitation
Cavitation is the process of forming an air bubble in a liquid due to the vaporization of that liquid cause by an area of low pressure. This area of low pressure lowers the boiling point of a liquid allowing it to vaporize into a gas. Cavitation can take place in pumps, which can cause damage to the impeller that moves the fluids through the system. Cavitation is also seen in propulsion. Low pressure pockets form on the surface of the propeller blades as its revolutions per minute increase (IIMS, 2015).Cavitation on the propeller causes a small but violent implosion which could warp the propeller blade. To remedy the issue, more blades allow the same amount of propulsion force but at a lower rate of revolutions. This is crucial for submarines as the propeller needs to keep the vessel relatively quiet to stay hidden. With more propeller blades, the vessel is able to achieve the same amount of propulsion force at lower shaft revolutions.
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