Let's say that some big coal- and oilfields aren't discovered ITTL. Consequently, fuel is less widely-available, and ocean-going vessels, including ironclads, continue to be made with sails for long journeys after their OTL phasing-out date in the 1880s.
How would this affect the development of ironclads? IOTL, the abandonment of sails enabled the construction of bigger vessels with thicker armour and bigger guns (as they no longer needed to worry about getting the barrels tangled up in the rigging). ITTL how big could ships reasonably get, and what sort of armour and armament would they carry? How would their guns be arranged? And what effect would all this have on naval tactics?