er 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.

[Illustration: Figure 7.]

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 L20 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.

[Illustration: Figure 8.--DANISH COPY OF ORIGINAL SAIL PLAN of Robert
Fulton's _Steam Battery_, dated September 12, 1817, in Rigsarkivet,
Copenhagen.]

[Illustration: Figure 9.--LINES OF FULTON'S _Steam Battery_, as
reconstructed for a model in the Museum of History and Technology.]

[Illustration: Figure 10.--A RECONSTRUCTION OF INBOARD WORKS of the
_Steam Battery_, for construction of the model in the Museum of History
and Technology.]

For 18 years Petty did no more with the type, but finally, in July
1684, he laid down a still larger sloop with two decks and a mast
standing 55 feet above her upper deck. She was named _St. Michael the
Archangel_ and is probably the design in Pepys' _Book of Miscellaneous
Illustrations_ in Magdalene College, Cambridge, England. This vessel
proved unmanageable and was a complete failure.

[Illustration: Figure 11.--MODEL LINES REDRAWN to outside of plank to
show hydrodynamic form of the _Steam Battery_.]

Though the double canoes of the Pacific Islands were probably known to
some in Europe in 1662, there is no evidence that Petty based his
designs on such craft. He appears to have produced his designs
spontaneously from inde