Why tank armour logic does not scale cleanly to ships

Do the rules that make modern composite armour viable for tanks scale to ship-grade armour?

Not really: naval protection faces salt water, large weapon effects, and compartment survival problems that make bulkheads and splinter protection central.

Shipboard protection still exists, but much of it is aimed at splinters, heat, and compartmental survival rather than stopping the largest incoming weapons outright. Naval damage is framed in terms of bulkheads and compartments, where being on the wrong side of the hit can matter more than fine gradations of armour performance.