 The Graving Dock lock was only long, and so could take a single barge, but all the others were long enough to take two barges end to end.The first Jetty Marsh lock was much bigger, at 215 ft long and 45 ft wide (65m by 13.7m), but carries the inscription "Duke of Somerset, 1841", and so it would appear that it was reconstructed as a basin, so that barges could wait in it for the tide.The Graving Dock lock is probably unique in the United Kingdom, in that it was reconstructed with a dock at its side, which could be used as a dry dock when the lock was empty.