Iron Ship, Patent Model

James Kerr, William Grant, and John Potter of Pittsburgh, Pennsylvania, used this two-part model to demonstrate their 1842 method for lining the hulls of iron vessels with watertight chambers.
Iron shipbuilding was in its infancy when James Kerr, William Grant, and John Potter came together to patent their improved iron hull in 1842. American ship owners were particularly slow to adopt iron (and later steel) for their hulls because the nation's abundant forests and wealth of skilled carpenters made wood construction significantly more cost effective. Nevertheless, those few iron vessels that were built in the 1840s and '50s-almost all of them British-tended to receive considerable attention in the press. Even European reporting circulated widely in the United States, brought over by express steamship and transmitted internally by riverboat. Perhaps it is not surprising, then, to find Kerr, Grant, and Potter familiar with "the usual way" of building iron vessels: covering a skeleton of angle-iron ribs with horizontal rows of iron plate, "as is now generally done." Their idea was to line the interior of such a structure with additional plates. The spaces between these inner and outer plates would form watertight chambers between the ship's ribs. The chambers would render "the vessel more buoyant if she sprang a leak, as each chamber was insulated from the others. "It will thus be evident that should the outer sheathing of the vessel be injured between any two or more of the ribs, that chamber only will fill with water, the rest of the vessel continuing to retain its buoyancy." In addition, this inner lining of sheet iron would make the hull more stiff, "and the necessity for bulkheads is entirely superseded."
A reissue of Kerr, Grant, and Potter's patent in October 1842 incorporated a fuller description of their idea. The main revision it outlined called for the interior plates be bolted to the ribs, instead of riveted, in order to facilitate inspection and maintenance.
Currently on loan
date made
patent date
Kerr, James
Grant, William
Potter, John
Associated Place
United States: Pennsylvania, Pittsburgh
Physical Description
copper (overall material)
overall: 29 1/2 in x 6 1/2 in x 4 1/2 in; 74.93 cm x 16.51 cm x 11.43 cm
ID Number
catalog number
accession number
patent number
Patent Models
See more items in
Work and Industry: Maritime
America on the Move
Data Source
National Museum of American History


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