What specific invention, patented in 1821, featured hinged flukes intended to bite simultaneously?

Answer

Richard Francis Hawkins' 'Stockless' or 'Patent' anchor

Richard Francis Hawkins patented a Stockless or Patent anchor in 1821 which incorporated hinged flukes designed to ensure both flukes bit into the seabed at the same time.

What specific invention, patented in 1821, featured hinged flukes intended to bite simultaneously?
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