Why shipyards limit fleet expansion before training does

How long would it take to train new Royal Navy personnel to effectiveness during a major fleet expansion?

Less time than it would take to build the ships, especially because the necessary shipyards would have to be created first.

The question separates the human and industrial sides of expanding the Royal Navy. New personnel would become effective sooner than new warships could enter service. A larger program would first have to create or expand shipyards before construction itself could proceed. The bottleneck therefore moves upstream from recruiting and training to industrial capacity.