We have three diesel generators that operate in parallel with a steam turbine generator (STG) on a tanker, of course there is a Main Engine. The excess steam generated from the heat value of VOC gases during cargo loading operations is utilized to drive the steam turbine generator (STG).

Should the diesel generators be referred to as Main Generators, Auxiliary Generators, or Essential Generators? Similarly, considering that the STG operates intermittently in parallel with the diesel generators, would it be classified as a Main Generator, Auxiliary Generator, Essential or Non-Essential Generator?

 

Note: it's been a while since I was in that world (over 20 years), and I was never a designer who had to make those decisions. No one has replied, so I'll throw out a question to help refine things maybe.

Do those terms carry regulatory weight? In other words, are there different requirements for Main, Aux, or Essential/Non-essential generators? If so, you'll have to refer to the regulations for details on how to identify which each one is. It all comes back to the definitions of those terms.