I don't think that it's just inefficiency at certain power levels: The big table on https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption https://en.wi

I don't think that it's just inefficiency at certain power levels: The big table on https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio... has the Marine Trent rated less efficient than some car engines. And that table is peak efficiency, not efficiency at some arbitrary inconvenient power level. But you are right in so far as efficiency at the low end of the power range is very important in commercial shipping. Because the energy demand (at the drive shaft) of a given trip is highly dependent on the desired speed and if going show ruins your engine's efficiency any dip in demand will ruin you economically (because others on the market are much better at compensating the dip by "slow steaming")