Iron plates would become eroded so easily by sea water that they were unfit for a long-term use, therefore, they were substituted by copper plates, which can be said to have made a reasonable development from a tekkosen.
鉄板では海水によって腐食するため長期の運用は不可能であり、そのため銅板に換えたと考えられ、鉄甲船からの順当な発展型と言える。