This is one of Lusitania's 4 propellors. She was salvaged from the wreck in 1982 and was rescued by Liverpool maritime museum in 1989, where she now remains an outside exhibit.
The 4-blade props replaced the original 3-bladed props in 1909 and gave an extra 1 knot speed. Each prop is 23 tons of bronze and rotated at 3 times a second to give 26kts. The cone however is cast steel. The props show clear signs of wear from many Atlantic crossings, but also from lying on the sea bed for so long.