Why converting line-of-battle ships into ironclads was costly

Could a first-class line-of-battle ship be converted into an ironclad at acceptable cost?

It was possible and sometimes considered, but the conversion was usually expensive enough to make navies hesitate.

Existing ships could be razeed and considered for ironclad conversion, but the expense quickly undermined the apparent savings. Adding armour was not a simple refit because the hull, stability, propulsion, and internal arrangement all had to support a different kind of fighting ship. The work could become nearly as demanding as a new design. That cost helps explain why navies often preferred new construction while large wooden ships remained on hand.