As I know it was first time designed by Captain John Schank in 1774
John Schank was known as a man with a particular mechanical understanding. So he designed a bed that could be raised or lowered when in use. This earned it the nickname Old Pulley. In 1774, in Boston, he designed a private boat with a lowerable keel suitable for shallow waters. He later presented his invention to the Admiralty. Two identical ships of 13 tons were ordered, one with a lowerable keel and the other without. Since the design proved successful, several ships with lowerable keels were built, such as the HMS Cynthia and the research ship HMS Lady Nelson.
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Sliding keel designs by Captain Schank for an unnamed boat (1774) and and unnamed cutter (no date)
Scale: 1:48. Plan showing the profile of a boat with one long sliding keel built at Boston in 1774 for Lord Percy, Duke of Northumberland; and a section and four profiles of a cutter (no cutter) illustrating how the sliding keels can be used depending upon the angle and strength of the wind. The plan has an explanation key.
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Cynthia (1796)
Scale: 1:48. Plan showing the inboard profile for Cynthia (1796), a 16-gun Sloop fitted with three sliding keels, building at Rotherhithe by Messrs Wells.
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Lady Nelson (1799); Passenger vessel; Brig
Contemporary full hull model of the ‘Lady Nelson’ (1799), built at a scale of 1:32. The model, which is decked, has been constructed in the solid from planks of wood assembled in the 'bread and butter' fashion. The frames have been drawn onto paper, which has then been glued to the hull and painted with a layer of varnish. This in some ways uses the 'navy board' style to highlight the overall shape of the very shallow hull, which enabled the 'Lady Nelson' to carry out survey work around the shallows of the coastlines. To help overcome leeway and sail efficiently with a shallow draught, sliding keels designed by Captain John Schank (1740-1823) were fitted. The casings for these can be seen on the deck of the model by the main hatch, deckhouse and windlass.
The 'Lady Nelson' was originally rigged as a cutter but this was changed to that of a brig when it was fitted for the long voyage to Australia for survey work in 1800. The vessel was later destroyed by the inhabitants of Babber Island, Timor in 1825.
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there are only 20 of them. How to do it?
