Vertical expansion engines and efficiency

Vertical engines returned once larger steel ships gave designers more space below deck and shifted the main constraint from height to length. An engine type could become useful again when steel construction and hull scale changed the problem it had to solve. Single, compound, triple, and multiple expansion differed in how many stages of useful work high-pressure steam could perform. Each successive stage extracted more energy before the steam was exhausted, making mature triple-expansion machinery the product of roughly a century of incremental refinement. That long development history explains why proven reciprocating machinery could still compete with newer turbines when efficiency and reliability mattered.