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The contemporary descriptions of the Fulton Steam Battery do not agree. This was in part due to differences between the dimensions given out by Fulton during the negotiations with the Federal Government, and after the ship’s construction was authorized. From the context of various statements concerning the projected vessel, such as that of the naval officers, the changes in the intended dimensions of the ship can be seen. For example, the officers state the model and plan shown them would produce a battery carrying 24 guns (24- and 32-pdrs.), and a letter from Fulton to Jones, shows she was to be 138 feet on deck and 55-foot beam. The final reported dimensions, given by the Supervisory Committee, are 156 feet length, 56 feet beam, and 20 feet depth.

In addition there are a few foreign accounts which give dimensions and descriptions. The most complete was probably that of Jean Baptiste Marestier, a French naval constructor who visited the United States soon after the end of the War of 1812 and published a report on American steamboats in 1824. The Steam Battery is barely mentioned though a drawing of one of her boilers is given. Marestier made another report on the American Navy, however. Extensive searches have been made for this in Paris over the last 14 years, but this paper has not been found in any of the French archives. References to the original text indicate that the naval report dealt very extensively with the Steam Battery. Some of his comments on the battery appeared in Procès-verbaux des Séances de l’Academie des Sciences. Marestier considered the powers of the battery to have been overrated due to fanciful accounts of some laymen writers. He was aware of the shortcomings of the double hull in a steam vessel at the then-possible speeds, but he apparently thought two engines, one in each hull and each with its boilers would be better than Fulton’s arrangement of boilers in one hull and engine in the other. He noted that the paddle wheel turned 16-18 rpm and that steam pressure sustained a column of mercury 25 to 35 centimeters. The safety valve was set at 50 centimeters. Fuel consumption was 3-5/8 cords of pine wood per hour.

In view of the access Marestier is known to have had to American naval constructors, shipbuilders, and engineers, it is highly probable that he not only obtained the building plan of the ship but also some of the earlier project plans from the builders and from Fulton’s superintendent, Stoudinger. It is, therefore, a great misfortune that his lengthy report on the Battery cannot be produced.

A French naval officer who investigated the ship, M. Montgery, also wrote a description, published in “Notice sur la Vie et les Travaux de Robert Fulton."

It should be noted in regard to what Montgery wrote about the Battery, that in 1821 it had been considered desirable to disarm the ship. The engineer in charge, William Purcell, had reported that as there were not proper scuppers, dirt and water had entered the hull and had collected under the engine and boilers, causing damage to the hull, and also that with guns removed, the Battery would float too high for the paddle wheel to propel the vessel; so it had been decided to remove all machinery as well as the armament.

Montgery’s description, published in 1822, was taken from his report to the Minister of Marine and Colonies. It noted the battery was made of two hulls separated 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 Procès-verbaux des Séances de l’Academie des Sciences, 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 gun” (100-pdr.), Fulton’s invention, but these were not fitted. Provision was to be made in the fireboxes for heating shot, and a force pump with a cylinder 33 inches in diameter was employed to throw a stream of cold water, about 60-80 gallons per minute, for a distance of about two hundred feet. This could be done only when the paddle wheel was not in operation. The paddle wheel was housed, the top fitted with stairs to the spar deck. The gun deck, over the race, was used in part for staterooms, of which the bulkheads were permanent. Hammocks for the complement of 500 men were to be slung on the rest of the gun deck. The ship drew 10 feet 4 inches, with the port sills about 5-1/2 feet above the loadline. Burning wood, the vessel could carry about 4 days’ supply of fuel; burning coal, she carried 12 days’ supply.

Montgery said that the vessel would be vulnerable to bombshells and hot shot, and that furthermore she could be boarded. The displacement of the ship, at service draft, was 1,450 tons, a figure Montgery obtained from a copy of the original plan given him by Noah Brown.

In 1935, Lieutenant Ralph R. Gurley, USN, attempted a reconstruction in sketches of the vessel published in his article “The U.S.S. Fulton the First” in the U.S. Naval Institute Proceedings. This reconstruction was based on the Patent Office drawing prepared for Fulton, and published by Stuart and Bennett, and the foregoing French sources. The Patent Office drawing showed the engine was an inclined cylinder and Lt. Gurley shows this in his sketch; in his text he says, “The engine was an inclined, single-cylinder affair with a 4-foot base and a 5-foot stroke.” Gurley’s attempt to reconstruct the Steam Battery is the only one known to the author.