Dockside steam and warship support systems

Why did some ships blank over steam ports when in harbour?

Dockside steam could run or maintain systems without shipboard boilers, but that depended on port infrastructure.

External steam could support or maintain shipboard systems without lighting the ship's boilers. That arrangement saved the effort and fuel required to keep machinery running in harbour. It depended on compatible dockside infrastructure, which made it more practical for ships returning regularly to the same home ports. A globally deployed fleet could not assume that support would exist at every anchorage, including Scapa Flow.