Boiler pressure and shaft horsepower do not convert on a one-to-one basis. Hotter, higher-pressure steam can make the turbine plant more efficient and lets designers choose between fewer boilers for weight and fuel savings or similar boiler numbers for greater power. The US Navy's 600 psi M-type plant, associated with ships including the Iowa and Fletcher classes, provides a practical comparison for the proposed 850 psi system. A later explanation separates boiler horsepower, a measure of steam-generating thermal output, from shaft horsepower, the mechanical power delivered by the engine's output shaft. The design question is how the complete boiler-and-turbine plant converts steam conditions into usable range, cruising efficiency, and shaft output.
Chapter · 5:30-9:20
What higher steam pressure changes
Higher boiler pressure can reduce fuel use and boiler count while increasing turbine efficiency, shaft power, range, or speed.