Machinery volume and SHP/ton

I had not really been aware of the volume issue, although I knew that some of my designs might have problems with insufficient volume for the machinery. Boiler room volume per SHP looks like a hyperbolic function where the volume per SHP is a function of the SHP/ton of machinery. I have plotted this over the range of 10 SHP/ton up to 75 SHP/ton, so I have a reasonable coverage. I have some fast battlecruisers designs that work strictly from a weight analysis, but would fail on volume, if the SHP/ton were not increased. I also have realized that I need to be able to specify the "vitals" height, as a destroyer "vitals" would occupy the full depth, minus a double bottom, if there was one. A battleship would have the "vitals" below the armor deck.