It depends on what I'm trying to represent. In a concept phase, I mainly use standard output formats from the naval architecture software: for example, in a tank plan all tanks and void spaces are colored. The same applies to various damage stability outputs - flooded compartments are filled with nice light blue sea water. If I'm drawing something on top of a fully-deveped general arrangement, such as a structural fire protection plan or a lining scheme, I typically use hatches and also make sure they work when printed in black and white even when the drawing is plotted in color.
The last remark is a legacy habit and required by certain clients; most deal with the documentation in electric format and/or have color printers so it's not always mandatory.