Do you know that full displacement yacht usually install big derated engines and sometimes those engine are coming out of the commercial lineup of the engine maker. Basically they install a big engine but tune it in such a way that it gives less power the process is called derating. Derating a marine engine means to reduce the engine maximum speed (maximum continues running) in order to match the load point with the desired engine output needed for that yacht. There are multiple advantages of derating an engine. For sure a longer engine life is one of the decision making factor. A lot of people will argue but also reliability is better in fact all the components of your engine are designed for much bigger loads so using them at lower loads preserves them in the long run. Derated engine work with lower loads this allows not only to save fuel but also to save on maintenance cost in terms of wear and tear.