Physical space is only one test of whether a ship can accept new equipment. A higher hotel load may require additional electrical generation, which in turn needs machinery space and fuel. Carrying that fuel while preserving the ship's range creates further weight and volume demands. A warship is a system of systems, so a local change propagates into its supporting engineering. An apparently straightforward upgrade can therefore become uneconomic even when the new component fits through the available opening.
Notable Point · 27:37-29:24
Power, fuel, and range can block a simple upgrade
Look beyond whether new equipment fits: its standing electrical load, generation, fuel demand, range, and supporting systems may make the whole ship change.