Iron hulls preserved buoyancy under heavier fire

Was shipboard machine-shop capability the main reason navies adopted iron hulls?

It was one factor; heavier gunfire and the need to preserve buoyancy through protected citadels also mattered.

Machine-shop capability is accepted as part of the explanation for iron construction. Heavier guns also made wooden hulls less able to withstand damage. Preserving enough buoyancy after being hit supported the development of protected citadels, particularly in British designs.