Brunel, anxious to ensure the avoidance of hogging in a vessel of such unprecedented size, designed the hull to be massively redundant in strength. Ten longitudinal iron girders were installed along the keel, running from beneath the engines and boiler to the forward section. The iron ribs were in size. The iron keel plates were an inch thick, and the hull seams were lapped and double riveted in many places. Safety features, which also contributed to the structural strength of the vessel, included a double bottom and five watertight iron bulkheads. The total amount of iron, including the engines and machinery, was 1,500 tons.