thumb|Nancy Blackett at [[Woodbridge, Suffolk, in 2009.]]
Nancy Blackett is a , 7-ton (Thames Measurement), Bermuda rigged sailing cutter built in 1931. The boat is now owned and operated by The Nancy Blackett Trust.
Built by David Hillyard and originally named Spindrift at her launch in 1931 (and then renamed Electron by her next owner), she was bought by children's author Arthur Ransome in 1934 and renamed Nancy Blackett after the major character of the same name in his Swallows and Amazons series of children's books. He sailed her mostly on the east coast of England and the southern North Sea from her home port of Pin Mill near Harwich.
Ransome's cruises also provided material for another book Secret Water (1939) set in the Walton backwaters.
Ransome sold Nancy Blackett in 1939 but always said that she was "the best little ship". In 1988, she was found rotting in Scarborough and subsequently purchased and restored.
The Nancy Blackett Trust was formed as a registered charity to preserve and sail her and to promote the sort of sailing activities dear to Ransome. The trust's patron is Ellen MacArthur.