ated by a channel, or "race," 15-1/2 feet wide, running
the full length of the vessel. The two hulls were joined by a deck just
above the waterline, as well as by an upper deck, and also connected at
their keels by means of 12 oak beams each 1 foot square. The vessel was
152 feet long, 57 feet beam, and 20 feet deep. Sides were 4 feet 10
inches thick, and the ends of the hull were rounded and alike. There
were two rudders at each end, one on each hull, alongside the race. The
eight paddle blades, each 14-1/2 feet by 3 feet, turned in either
direction by stopping the engine piston at half-stroke and reversing the
flow of steam. Rigged with two lateen sails and two jibs, the ship
sailed either end first. The engine of 120 hp was in one hull and two
boilers were in the other. Other sources, Marestier, and Colden in
_Proces-verbaux des Seances de l'Academie des Sciences_,[14] gave
additional information (some of it incorrect): the engine was inclined,
with a 4-foot-diameter cylinder, 5-foot stroke, direct-connected to the
paddle wheel, which was turned at 18 rpm. The boilers were 8 x 22 feet
with the fireboxes in inside cylinders, each about 5 feet in diameter,
and extending about half the length of the boiler from the fire doors.
Two fire tubes, each about 3 feet in diameter, returned the gases from
the inside end of the fireboxes to the stacks at the firing end. Except
at the fire-door end, the firebox was completely surrounded by water.
The boiler pressure of about 6 psi was not maintained, varying somewhat
with each stroke of the engine.

Water level in the boilers was indicated by try cocks. The safety valve
was controlled by a counterbalanced lever. A jet of salt water was
injected into the exhaust trunk to form a vacuum by condensation. An air
pump transferred condensate and sea water into a tank from which it
passed overboard. Only about a tenth of this water was returned to the
boilers.

Montgery stated also that only the lower or gun deck was to be armed. No
bulwarks were on the spar deck, only iron stanchions to which were
fastened a breastwork of wet cotton bales when the _Steam Battery_ was
in action.

The _Battery_ was designed to carry 30 guns (32-pdr.), with 3 guns in
each end and 12 on each side, but no guns in the wake of paddle wheel
and machinery. Hatches to give air to the stokehold were located
amidships. The _Battery_ was to have been supplemented at the ends of
each hull by a Columbiad "submarine