The consensus of British naval opinion after the Crimean War favoured the large steam-powered two-decker line-of-battle ship with 101 or 91 guns. The designs for two-decker evolved. "The 101-gun type were redesigned with an extra 400 tons and engines of 800 nhp, to produce the "Duncan" class. The 91s were given similar engines, while their smaller increase in size was largely taken up with an additional overall for a finer length-to-beam ratio and improved lines in ." In the 1859 programme the two types were merged to produce a 91-gun ship with the dimensions of the 101-gun type. Two ships built on this plan - the "Bulwark" and "Robust", the latter having been commenced as a 101-gun ship - were preserved on the stocks until 1872, the remaining seven being converted into ironclads. These last two-deckers were overall, that they all displayed all the classic symptoms of weak construction, such as leaky seams, demonstrated that wood was no longer suitable for the construction of the largest classes of warships.