A little perpective on SHP per ton of machinery weight

I was looking at D.K. Brown's book Nelson to Vanguard, where I was looking for data about machinery weight. In one table, he lists pounds per SHP. I prefer to turn that around to SHP per ton of machinery weight. The Queen Elizabeth class battleships were originally 26 SHP/ton of machinery. The WWII-era King George V class were 60 SHP/ton of machinery. The former used large tube boilers, and was designed about 1912. Using D.K. Brown's figures, the battlecruiser Hood, with small tube boilers achieved 34 SHP/ton of machinery. This was a 1916 design. The modernized Queen Elizabeth class ships had a plant that was 51 SHP per ton of machinery. Cruisers had long had lighter-weight machinery. Again, using D.K. Brown's figures:

• Kent: 43.7 SHP/ton
• Exeter: 45.7 SHP/ton
• Leander: 47.8 SHP/ton
• Amphion: 55 SHP/ton
• Arethusa: 52.4 SHP/ton

These are all 1920's-early 1930's ships.

Destroyer machinery weight bases seem harder to find. The WWI Admiralty R-class had machinery weighing 395 tons. The power output was 27,000 SHP designed. This gives us 68.35 SHP/ton for a ship designed in 1915. For comparison, the WWII Hunt class machinery was 285 tons. The power output was 19,000 SHP. That gives a machinery weight basis of 66.67 SHP/ton. That was for a plant designed in 1938-1939. There was no improvement in output.