Why most floating dry docks were not self-propelled

Were any floating dry docks self-propelled?

A few had propulsion work, but as a rule they were towed because engines would take space needed for lifting and repair functions.

Most Admiralty floating docks relied on towing rather than carrying their own propulsion plant. A few received some work in that direction, so the rule was not absolute. The basic design trade-off favoured using internal volume for the dock's lifting and support functions instead of engines. Long-distance mobility came from arranging tugs or warships to tow the dock to its station. A strategically mobile facility did not need to be independently powered.