tom of keel, the displacement of the Powhatan exceeds that of the Susquehanna by 58 tons, or about 1.77 per centum of the latter. The immersed amidship section of the Susquehanna at the above draft is 21 square feet, or 3-4 per centum greater than the Powhatan's. At 19 feet 6 inches draft, the same difference of 21 square feet holds with the immersed amidship section, but the displacement of the Powhatan now exceeds that of the Susquehanna by 41 tons. At 19 feet 6 inches draft, the Susquehanna's displacement per inch of draft is 23 tons, while the Powhatan's is 22,1 tons. It thus appears the Susquehanna has the greater capacity at the load line, while the Powhatan has the greater capacity in the lower lines; which also follows from the fact that the centre of displacement in the Susquehanna at 18 feet 6 inches draft is 7.167 feet below the water line, while in the Powhatan, at the same draft, it is 8.86 feet below the water line, or 1.693 foot lower; also the height of the metacentre above the centre of gravity of the displacement in the Susquehanna at 18 feet 6 inches draft is 11.208 feet, while in the Powhatan it is 10.87 feet, or 0.338 foot lower.

.

ENGINES.--Two inclined, direct acting, condensing engines.
Diameter of cylinders,

70 inches.
Stroke of piston,

10 feet. Diameter of the disks of the steam valves,

143 and 16 inches. Diameter of the disks of the exhaust valves,

151 and 161 Space displacement of both pistons per stroke,

534.51 cubic feet. Steam space between cut-off valve and pistons, at one end of both cylinders,

26. PADDLE WHEELS, of the common radial kind. Diameter from outside to outside of paddles,

31 feet. Length of paddles,

10 Width of paddles,

26 inches, Area of two paddles,

43} square feet. Number of paddles in each wheel,

23 Number of paddles in each wheel in water at 18 ft. draft, 5

Immersion of lower edge of paddles at 18 ft. draft of water, 4 feet 11 inches. Boilers.—(Plate III.)—Four copper boilers with double return ascending flues. Length of each boiler,

16 feet. Breadth of each boiler,

15 3 inches. Height of each boiler, (exclusive of steam chimney)

13 Total area of heating surface in the four boilers,

7706 square feet. Total area of grate surface in the four boilers,

356
Aggregate cross area of the first row of flues in the four boilers, 75.720
Aggregate cross area of the second and third row of flues in
the four boilers, (each row),

55.906
Cross area of the smoke chimney,

63.617 Height of the smoke chimney above the grates,

65 feet. Weight of the four boilers and appurtenances,

199.75 tons. Weight of sea water in the four boilers, (calculated,)

84.38 The total length occupied in the vessel by machinery from bulkhead to bulkhead, is the same as in the Susquehanna, 102 feet 9 inches; but the bunkers stow only 800 tons of coal, being 100 tons less than the Susquehanna, owing to the steam pipes of the Powhatan, two in number, being carried through the side bunkers, while in the Susquehanna the single steam pipe is carried between the engines.

66

66

66

Table of the Performance of the U. S. Steamship Powhatan, under steam assisted by sail.

commencement of 3 99733833933

221

9.679

18

1

5 0

16:45

104 12.027

66

202

2

3951

The mean results from the above log would compare as follows, viz: Comparative performance of the Powhatan, under steam and sail, and under steam

alone.

Assisted Unassisted
by sail.

by sail Total number of hours,

223 221 Speed of vessel per hour in knots of 60824 feet,

10-474 9.679 Mean draft of vessel,

18 st 1 in. 18 ft. I in. Immersion of lower edge of paddle,

5 ft 5 ft. Slip of the centre of pressure of the paddles in per cents. of its speed,

9.25 16.45 Oblique action of the paddle,

18.48 18.48 Steam pressure in boilers per gauge, per square inch above atmosphere in pounds,

10.1 10.4
Steam pressure in cylinders per square inch above atmos-
phere, in pounds,

6.1
Double strokes of piston made
per minute,

12.600 12.627 Part of stroke of piston, steam cut-off at from commencement in inches,

56

56 Proportion of throttle valve open,

.273 •292 Back pressure in condenser per gauge in pounds,

2
Mean effective pressure per square inch of piston in pounds, 13:35 13.6
Horses power developed by the engines,

784:7 801:1
Pounds of Cumberland bituminous coal burned per hour, 3665 3951
Tons of 2240 pounds of Cumberland bituminous coal burn-
ed per 24 hours,

39.27 42:33 Pounds of steam evaporated per hour from sea water of twice

the natural concentration, by one pound of coal, with the
temperature of feed water, 1000 including the waste
by filling the cylinder nozzles and clearance, and by
blowing off to maintain the sea water at twice the natural
concentration,

• 6.511

6:135 Moderate breeze Gentle breeze shaft the beam, forward the and moderate beam and

smooth sea.

.

6.4

2

.

Remarks on the preceding Log. The speed of the vessel (taken by the chip log) comprised in that portion of the table under the head of “performance under steam unassisted by sail,” has probably been a little overlogged. This opinion may be arrived at by a comparison of the size of the hull with the size and immersion of the paddles in connexion with their slip, the average of which by the log is only 16:45 per centum, whereas it could not have been less than 20 per centum. If the latter slip be taken, the speed of the vessel will be reduced from 9.679 knots to 9.267 knots.

The performance of the engines and boilers may be depended on, the double strokes of piston being taken by a counter, and the point of cutting off ascertained by an indicator applied at both ends of each cylinder. The amount of coal burned is also probably very near the truth; all the furnaces were kept in operation.

The steaming recorded in the preceding log comprises the run from New York to Havana, from Havana to Vera Cruz, from Vera Cruz to Pensacola, and from Pensacola to Norfolk, Va. During the whole time there was fine weather and smooth seas.

The evaporation by the boilers has been calculated from the number Vol. XXV.-THIRD SERIES.–No. 2.-FEBRUARY, 1853.

12

of cylinder charges of steam, using the data furnished by Regnault's experiments for the latent heat of steam. The difference in the evaporation in the two cases is nearly 6 per centum of the greater, an amount within the limits of errors of observation, enhanced also by the greater rapidity of the combustion in the case giving the lesser result, as with bituminous coal increased rapidity of combustion is attended with decided effect. The temperature of the engine room appears to have averaged 20° above that of the deck.

Indicator Diagrams. No. 1 was taken November 25th; steam pressure in boiler per gauge, 7} pounds per square inch above atmosphere; back pressure in condenser per gauge, 14 pounds per square inch; temperature of hot well, 100° F., throttle, şths open; double stroke of piston per minute, 13.

Nos. 2 and 3 were taken from both ends of the same cylinder, November 20th; steam pressure in boiler per gauge, 21 pounds per square inch above atmosphere; back pressure in condenser per gauge, 14 pounds per square inch; temperature of hot well, 115° F.; throttle, kths open; double strokes of piston per minute, 17ļ; speed of vessel, 12 knots per hour by chip log; consumption of Cumberland bituminous coal per hour, 5000 pounds; draft of vessel, 17 feet 10 inches forward, and 18 feet 4 inches aft; immersion of lower edge of paddles, 5 feet; slip of the centre of pressure of the paddles, 21 per centum of its speed. Fresh wind on port bow, moderate sea, and no sail set.

Sec. on CD