Fuel oil, especially residual fuel grades, has historically been ordered by viscosity, although distillate fuels are often ordered by using other criteria.
Whilst viscosity is an important characteristic, it does not give an indication of the other fuel qualities. With viscosity as the sole criterion for ordering, engine operators remain unaware of these other characteristics.
Similarly, the designers of machinery and fuel oil systems have not always been informed of the fuel characteristics to which they should be designing. It is therefore necessary to define the quality of the bunker oil during fuel oil bunkering over a range of parameters to which the engine plant is sensitive.