The hulls were tied together athwartship by the deck beams of the gun deck and spar deck, except in the wake of the paddle wheel. Knees were placed along the sides of the race at alternate gun-deck beams. In addition, the 12 1-foot-square timbers, crossing the race at the rabbets of the hulls, (mentioned by Montgéry) are shown. These must have created extraordinary resistance, even at the low speed of this steamer. The deck details shown are the results of reconstruction of the inboard works.
The use of catamaran hulls, or "double-hulls," has been periodically popular with ship designers since the time of Charles II of England. The earliest of such vessels known in the present day were four sloops or shallops designed 1673-1687 by Sir William Petty, who was an inventor in the field of naval architecture and received some attention from Charles II and from the Royal Society.
The first Petty experiment, the _Simon & Jude_, later called _Invention I_, was launched October 28, 1662. She was designed with two hulls cylindrical in cross section, each 2 feet in diameter, and 20 feet long. A platform connected the hulls, giving the boat a beam of a little over 9 feet. She had a 20-foot mast stepped on one of the crossbeams connecting the hulls, with a single gaff sail. In sailing trials she beat three fast boats: the King's barge, a large pleasure boat, and a man-of-war's boat. This "double-bottom," also called a "sluiceboat" or "cylinder," was later lengthened at the stern to make her 30 feet overall.
The King did not support Petty, to the latter's great disappointment, and Petty next built a larger double-bottom, _Invention II_. This catamaran was lapstrake construction. Not much is known of this boat except that she beat the regular Irish packet boat, running between Holyhead and Dublin, in a race each way, winning a £20 wager. She was launched in July 1663; what became of her was not recorded.
A third and still larger boat, the _Experiment_, launched December 22, 1664, appears to have been a large sloop. This vessel sailed by way of the Thames in April 1665 and went to Oporto, Portugal. She left Portugal October 20, 1665, for home, but apparently went down with all hands in a severe storm.