Bryan is correct. The turtle ships were, I think, wooden vessels with iron plating.
The Nemesis, built by Lairds for the Bengal Marine, a naval arrm of the Honorable East India Company, was an iron-hulled paddle frigate. Ordered in 1835 and launched in 1839, she was armed with two 32-pounder and four 6-pounder guns and served with distinction during the First Opium War (1841-43).
Over to you again, Bryan.