Why do diesel engine vessels usually have independent lube oil systems for the main engine and main reduction?

Using independent lube oil systems for the main engine and main reduction gears is crucial primarily because contaminants produced during engine operation can potentially damage the reduction gears. Diesel engines generate various by-products, including metal particles, soot, and other contaminants, which can affect the performance and longevity of the lubrication system utilized by the reduction gears. By having separate lubrication systems, the lube oil for the reduction gears remains free from these harmful contaminants, thus ensuring optimal operation and protecting the integrity of the gear systems.

While enhancing fuel efficiency, reducing system weight, and adhering to safety regulations are important considerations in marine engineering and design, they do not directly address the fundamental reason for separating the lubrication systems. The primary focus is maintaining the health of the reduction gears by preventing contamination from the main engine's lube oil.