The Cobb has been destroyed or severely damaged by storms several times; it was swept away in 1377 when 50 boats and 80 houses were also destroyed. The southern arm was added in the 1690s and rebuilt in 1793 after it was destroyed in a storm the previous year. It is thought that mortar was used in the Cobb's construction for the first time in this rebuilding. It was reconstructed in 1820 using Portland Admiralty Roach, a type of Portland stone. After the Great Storm of 1824, Captain Sir Richard Spencer RN carried out pioneering lifeboat design work in the Cobb harbour.