sentences:  "Dolphin"s hull was inspected in 1768 after the ship had twice circumnavigated the world; there was significant corrosion of the hull's iron components, which had to be replaced.In 1769 another attempt was made at coppering a ship's hull, this time on a new ship that had been constructed using bolts made from a copper alloy.The results were far more favourable this time, but still the problems with the bolting remained.