Mr. Collins, under the advice of his engineer, originally intended to use fresh water entirely in these boilers, previously condensed from sea water, and an arrangement was made with J. P. Pierson, the inventor of the “double vacuum condenser,” to furnish condensers. But the tubes, which had been manufactured in England, were lost at sea, and the vessels were equipped without them.
Bituminous coals alone were used until the superior qualities of anthracite were in several particulars shown to be of great importance in ocean steamers, when it was determined to use the former only on the return trips; and such became the established practice, resulting from an extended and careful series of experiments.[199]
The Pacific was a three-decked ship, very high on the water, and consequently much more comfortable for passengers than the other vessels; while the straight line of her bows, and freedom from encumbrances on her upper deck, offered less resistance to the wind. Her model under the water-line resembled somewhat the river boats; she had a flat bottom, her immersed section being not far from a parallelogram. Her bows and stern were formed by nearly plain surfaces, which, joined together, constituted an angle much more acute than was considered safe for adoption in ocean navigation some years ago.
Engines.
The Pacific was provided with two engines, each supported upon a large and solid bed-plate 32 feet long, and 9 feet broad, which was fastened to the keelson and ship’s bottom by bolts of large dimensions previously fixed in the wood; it was a single casting having a channel below in which there was a foot valve, and above it the cylinder bottom, the air-pump seat, and also a great part of the condenser, through which the side-lever shaft passed: it also had upon it sockets for the different pieces of the frames. On the cylinder bottom, at the extremity of the bed-plate, the cylinder itself was bolted, the largest at that time ever cast: its diameter being 96 inches, calculated for a stroke of 9 feet, and length, flange to flange, 10 feet 6 inches. The lower steam-opening being cast with the bed-plate, the upper one alone belonged to the cylinder. The steam exhaust valves were on the plan generally adopted in the United States and arranged with Stevens’s “cut off,” so as to let the steam expand one-half its volume.
The steam passed from the boiler to the upper steam-opening by a large pipe 2 feet in diameter and about twenty feet long, and after doing its duty in the cylinder, escaped by the middle of the exhaust side pipe, and reached the condenser, which was not more than 1 foot distant, through a pipe of the same section.
The condenser and the reservoir were formed by a single casting inside which was a partition between them of the same casting. This piece was ornamented in the same style as the steam-chest, and supported a beautiful turret used as an air reservoir, which rather resembled an old castle of the Middle Ages than a steam engine of the nineteenth century, and gave an imposing appearance to the whole structure. The steam, arriving in the condenser between two horizontal iron plates, which were pierced over the whole surface, causing the condensing water to fall in small streams through them, so as to be soon condensed; then passing through the foot valve under the condenser, it reached the air-pump, which was situated on the other side of the condenser.
The condenser was so much elevated that the steam required to make a vertical descent of 11 feet, mixed with cold water, before reaching the channel way, thereby furnishing the means of quick condensation with a condenser of comparatively small size. All the pieces of the engine, cylinders, levers, connecting rods, &c., were calculated upon the best rules then known,[200] and the straps, keys, gibs, ribs, mouldings, &c., were so disposed as to produce the maximum of strength and security against accidents: but the pre-eminent success was in the design of the frame.
Frame sustaining engines and dead weight.
Any scientific engineer can calculate the thickness of a cylinder or diameter of a connecting rod necessary to resist the force they have to resist, but the disposition of the frame becomes difficult when the action of dead weight, and the various pressures produced by the working of the engines are complicated through the motion of the ship herself, which alters their modes of action. The usual practice had been to sustain the engines by a frame so massive as to present ten times the strength necessary, and accordingly a useless and costly weight took permanently the place of cargo: but in the engines of the Pacific, the difficulty was completely overcome: two large hollow pillow-blocks which sustain the paddle-wheel shafts on each side of the cranks were supported in each engine by four wrought iron columns on the forward extremity of the bed plate, the centre of the shaft being 23 feet above the keelson. The pillow-blocks thus supported were connected by two strong inclined braces to the cylinder, by means of solid facings cast with it, on each side of the steam opening. To maintain this skeleton, a number of braces, small in appearance, were so disposed as to effect the purpose.