completed in the Deptford Yard as a sailing ship. Under the name
_Congo_ she was employed in the African coast survey. Her plan is in the
Admiralty Collection of Draughts, at the National Maritime Museum,
Greenwich, England.

The double hull continued to be employed in both steam and team
ferryboats in the United States and in England and France. A few river
and lake steamers were also built with this design of hull. Continued
efforts to obtain fast sailing by use of the double hull produced a
number of sailing catamarans; of these the Herreshoff catamarans of the
1870's showed high speed when reaching in a fresh breeze.

Designs for double-hulled steamers appeared during the last half of the
19th century; in 1874 the _Castalia_, a large, double-hull, iron,
cross-channel steamer, was built by the Thames Iron-works Company at
Blackwall, England. She was 290 feet long, and each hull had a beam of
17 feet. The paddle wheel was placed between the hulls and, ready for
sea, she drew 6-1/2 feet. She ran the 22 miles between Dover and Calais
in 1 hour and 50 minutes, a speed much slower than that of the
paddle-wheel, cross-channel steamers having one hull. Another
double-hull steamer was built for this service by Hawthorn, Leslie and
Company, Newcastle-on-Tyne, Scotland, in 1877. First named _Express_,
she was renamed _Calais-Douvres_ when she went into service in May 1878.
Her length was 302 feet, her extreme beam 62 feet, and each hull had a
beam of 18 feet, 3 inches. She drew 6-foot 7-1/2 inches ready for sea
and the paddle wheel was between the hulls. On her trials she made 14
knots and burned coal excessively. Sold to France in 1880, she was taken
out of service in 1889. Though popular, she was not faster than the
single-hull steamers in this service and had been a comparatively
expensive vessel to build and operate.

The many attempts to produce a very fast double-hull steamer and large
sailing vessels have led to disappointment for their designers and
sponsors. In the history of naval architecture, since Petty's time,
there have been a number of periods when the new-old idea of the double
hull has become popular. Craft of this type have been commonly well
publicized but, on the whole, their basic designs have followed the same
principles over and over again and have not produced the sought-for
increase in speed and handiness.

In very recent years there has been a revival in interest in sailing
double-hull boats that