August 22, 1818. Her register shows that she was 98 feet 6 inches in length between perpendiculars, 25 feet 10 inches in beam, 14 feet 2 inches depth in hold, of 31970/94 tons burthen, and with square stern, round tuck, no quarter galleries, and a man's bust figurehead.

These dimensions of the Savannah required the researchers to investigate the method of taking register dimensions in 1818. It was found that the customhouse rule then in effect measured length between perpendiculars above the upper deck, from "foreside of the main stem" to the "after side of the sternpost." The beam was measured outside of plank at the widest point in the hull, above the main wales. If a vessel were single-decked, the depth was measured alongside the keelson at main hatch from ceiling to underside of deck plank; if double-decked, one-half the measured beam was the register depth.[5] However, inspection of the register of a number of ships of 1815–1840 showed that, in practice, double-decked ships commonly were measured as single-decked ships; this obviously was the case in the Savannah. Also, due to the lack of precise measuring devices, the register dimensions were not always accurate, particularly those of the length, which often were in error as much as one foot in a hundred, as was found by investigation of various classes of vessels. Because of inherent difficulties in measuring to the required points, this condition lasted even after steel tapes were introduced late in the 19th century.

The Museum's researchers next turned their attention to examination of the Marestier work, a French report on early American steam vessels that had become known to some American marine historians in the 1920's. The author was a French naval constructor who, on orders from his government, had spent two years in the United States between 1819 and 1822 studying American steam vessels, schooners, and naval vessels. The published report contained only material on steam vessels and schooners. The portion dealing with naval vessels was not published, and the manuscript has not been found to the present time (1960). The publication, a rare book, was available in only a few collectors' libraries or public institutions in the United States. In 1930 the writer translated the chapter on schooners,[6] and in 1957 Sidney Withington translated most of the remainder.[7] As a result of these publications and earlier published references, the Marestier material became widely known to persons interested in ships.

Figure 3.—Marestier's sketch of the Savannah (from plate 8 in Withington's translation of the Marestier report). Heights of lower masts are excessive by all known American masting rules; and, according to Marestier's drawing of the engine (see figure 4), the deckhouse is too short.

Withington's translation states that the Savannah measured 30.48 meters (100 feet) in length and 7.92 meters (26 feet) in beam and that she drew 3.66 meters (12 feet) in port and 4.27 meters (14 feet) loaded. Marestier's sketch (see fig. 3) of the outboard of the Savannah shows a ship-rigged, flush-decked vessel with a small deckhouse forward of the mainmast and nearly abreast of the side paddle wheels. The stack is a little forward of the deckhouse and has an elbow at its top. Netting quarter-deck rail is shown and a bust figurehead is indicated. The position of the hawse pipe shown at the bow indicates the wheel shaft to have been at or about deck level. For structural reasons, and in compliance with the sketch, the wheel shaft would have been just above the deck.

Figure 4.—Marestier's drawings of the Savannah's engine (from plate 7 in Withington's translation of the Marestier report). The graphic dimensions do not precisely correspond to the scale of dimensions in Marestier's text, nor with other recorded measurements.

Marestier's drawings of the engine and paddle wheels[8] are reproduced in figure 4. The nonoscillating engine is inclined toward the paddle-wheel shaft. The connecting rod operates a crosshead to which is pivoted a pitman, or oscillating rod, that operates the paddle-wheel crankshaft. Alongside the steam cylinder is an air pump cylinder, also connected to the crosshead. The steam inlet and outlet pipes enter a valve chest on top of the steam cylinder, which is described as being 1.035 meters (3.4 feet) in diameter, and of 1.5 meters (4.9 feet) in stroke.

The paddle wheels are shown as being of iron, with two fixed arms opposite one another on the hub. The other arms (four above and four below the fixed arms) are pivoted to the hub and held spread by chain stays. These eight blades fold, in pairs, to each of the fixed arms. The wheels are shown in elevation, with the upper pivoted arms folded on top of the fixed arms, and in cross section; the latter shows the shape of the buckets, hub, and outboard bearing of the shaft. The wheels are described as being 4.9 meters (16 feet) in diameter, while the buckets are 1.42 meters (4.65 feet) wide and 0.83 meters (2.72 feet) deep. The two outer corners of each bucket are snyed off at nearly 45°. The wheels are shown folded in the sketch; according to the description, they could be unshipped from the shaft and stowed on deck when desired. The method of removing the wheels from the shaft is not described, but from the drawings it seems probable that they were detached from the shaft by removing a lock bolt outboard and sliding the wheels off the square shaft. The hub seems adequate for this. Marestier states that this removal could be accomplished in 15 to 20 minutes; the logbook shows that it took 20 to 30 minutes to perform this operation at sea.

Marestier states that the ship had spencer masts and trysails on fore and main, and a spencer mast on the mizzen for a spanker; he illustrates these as having royal poles, but with no royal yards crossed.