Steamboat Machinery


The earliest steamboat engines were similar to both those used on shore for industrial purposes and those used in early, seagoing vessels. They were typically upright engines, working a piston in the vertical axis. The piston was connected to a pivoting cross-beam above moving like a child’s see-saw, that transferred the up-and-down motion of the piston to the crank on the paddlewheel. Over time, the vertical engine was replaced by one laid horizontally, and the indirect action of the cross-beam would be replaced by an arrangement in which the forward-and-back, reciprocating motion of the piston would be transmitted directly to the crank on the paddlewheel by means of a connecting rod or, as it came to be called on the river, a “pitman.”

By the mid-1830s, when Western Rivers-type boats began plying Buffalo Bayou on a regular basis, the vertically-arranged engine had been abandoned, and many boats were operating with a single, large, horizontal cylinder set up along the centerline of the boat, turning a large flywheel, eight or ten feet in diameter, that smoothed out the motion of the engine. The boat’s sidewheels turned on the same axis as the flywheel; either could be disconnected, allowing power to be applied to the single wheel on either side, or both simultaneously. (Operating both wheels in opposite directions, or in the same direction at different speeds, was not possible in this arrangement.) A single example of this early type of Western Rivers steamboat machinery arrangement survives, in the wreck of the 1832 sidewheeler Heroine, snagged and sunk in the Red River near Fort Towson, Indian Territory (Oklahoma) in 1838. Many of the earliest boats on Buffalo Bayou likely had similar arrangements, including Henry Austin’s Ariel, Grayson’s Laura, Yellow Stone and Auld’s Constitution.

George Catlin’s depiction of the sidewheeler Yellow Stone at St. Louis, Missouri. Yellow Stone later was brought to Texas and operated on the Brazos River and Buffalo Bayou. The exhausting steam from the boat’s single engine is visible as white puffs coming out of the ‘scape pipe at the center of the boat.

By the 1840s, though, the same priorities that had resulted in a distinctive combination of features in the construction of steamboat hulls – lightweight, simple to build and maintain, and specialized to the river environment to the point of being too fragile to work elsewhere – had worked their influence on the engines that propelled them. Engines became much smaller, more compact, and therefore lighter in weight. Where before one large cylinder provided power to both of a boat’s sidewheels, ultimately two smaller, single-cylinder engines came to be used, one driving each sidewheel. (This had the added advantage of allowing the two wheels to work independently of each other, improving the boat’s maneuverability considerably.) Later on, as sternwheel boats gradually replaced sidewheelers, this two-engine arrangement continued, with each engine turning a crank on either end of the sternwheel’s shaft. The cranks were offset 90 degrees, so that as one engine reached the end of its stroke and was contributing no force to the rotation of the wheel, the other engine was in the middle of its stroke, transferring its peak power to the opposite side of the wheel. These two-engine arrangements proved to be perfectly-suited to particular demands of Western Rivers boats, and have been retained, with minor refinements, down to the present day on the handful of boats, mostly built for tourist excursions, that still operate. The arrangement is simple, easy to maintain, and efficient enough to be practicable.

In keeping the propulsion machinery simple and easy to maintain – the expectation was that most repairs could be made by the boat’s own engineers with the use of simple tools and a small, portable forge carried on board – boats on the Western Rivers did away with many of the features common to the powerplants of seagoing vessels. Notable among these was the lack of a condenser, the device used to convert “spent” steam vented from the engines back into clean, liquid water for recirculation back into the boiler. Such a device added expense, complexity and weight to a steamboat, so it was quickly dispensed with. Without a condenser to capture the spent steam coming off the engines, steamboats like those used on Buffalo Bayou vented the steam directly into the atmosphere from ‘scape (“escape”) pipes extending up vertically from the engines. The boats, like their counterparts on the Mississppi and Ohio Rivers, made a distinctive huff-huff-huff sound as they steamed along, each puff being made by a slug of spent steam being shot up the ‘scape pipe as the engine’s piston moved forward and back.

Because the boats lacked condensing equipment to cool spent steam back into liquid form and return it to the boilers for another cycle, there was a continual need to replenish the boilers with new water from overside. For many years, this presented a continual problem for steamboat engineers, who had to maintain a precise level of water in the boilers to prevent a catastrophic failure of the boiler structure and the resulting explosion or release of scalding steam. This problem was largely resolved in the 1840s with the introduction of a small feed pump that, it was widely said, cured all the ills of the steamboat, so the pump itself came to be known simply as the “doctor.” While there were, in fact, plenty of problems it did not solve, the doctor did greatly improve the overall safety of steamboat operations.

But it was the boiler itself that was, in the words of the late Captain Alan L. Bates, “the heart and soul” of the boat’s steam plant:

It does not move – it merely sits there and cooks water – a dull proposition at best, but a little study will show it to be the most dynamic unit in the system. A boiler full of superheated water is a fused bomb, ready to explode at the least provocation, and is a prima donna fully as demanding and far more deadly than an operatic diva.

The boilers used on Western Rivers boats, including virtually all those on Buffalo Bayou from the 1840s on, were of the same basic design. A surviving boiler from a boat that operated on Buffalo Bayou in the early 1870s, Mary Conley, serves to illustrate the basic features, and is typical of a mid-19th century Western Rivers steamboat boiler. The Conley boiler is known as a “fire tube” boiler, in that hot exhaust gasses from the furnace passed though large-diameter tubes, or flues, which transferred the heat to the water contained within the larger boiler shell. The boiler shell is comprised of twelve rings of rolled iron plate, with the resulting tube closed at either end by a cast-iron cap. The boiler is fitted with five flues, and is most similar to the preserved boilers of U.S.S. Cairo, preserved at the Vicksburg National Military Park in Mississippi. The Mary Conley boiler is cylindrical, 24 feet 3 inches long, and 41 inches in diameter. Five, 10¾ inch diameter flues run the complete length of the boiler. There is about 1¾ inches of spacing between the flues at the fore head of the boiler, where they are riveted inside. At the aft head the individual flues are flanged and riveted on the outside. The flues are tapered, such that the fore openings are one inch wider than the aft openings. Engineers designed the flue flanges to be overlapping, such that the center flue shares rivets with each adjacent flue. Above the flues at the aft end of the boiler is an oval-shaped opening, measuring approximately 15 by 9½ inches. This opening allowed a worker to crawl inside the iron shell to clean, inspect or repair the boiler.

Boiler recovered from the wreck of the former Buffalo Bayou steamboat Mary Conley, now preserved near Liberty, Texas. The five large flues are clearly visible.

A medium-sized boat like Mary Conley would normally have had at least two, and likely three or more, of these boilers arranged side-by-side in a “battery,” all enclosed in an iron casing lined with firebrick. Under the forward end of each boiler was a firebox, where the boat’s firemen kept a hot fire burning. The firebox doors opened directly toward the front of the boat, allowing the vessel’s forward motion to assist in fanning the burning fuel. Western Rivers boats burned either wood or coal interchangably, depending on which was readily available. Coal became the preferred choice on the Ohio and Upper Missisisspi early on in the 19th century, but wood was much more common on the lower reaches of the latter river. With timber plentiful and cheap in Texas, and coal correspondingly rare, wood was used almost exclusively as fuel for the boats on Buffalo Bayou, and it later became common for boats running between Houston and Galveston to bring a barge towed alongside, stacked high with extra cordwood for the furnaces.

Three-boiler battery and “doctor” (feedwater pump) of the steamboat Arabia, wrecked on the Missouri River in the 1850s. Image via the Steamboat Arabia Museum.

The hot gasses from the battery’s furnaces flowed aft, around and along the underside of the cylindrical boiler shells to the aft end of the battery casing, where it swept around the back ends of the boilers and passed forward again through the boiler flues. Mary Conley’s boilers each had five flues, but many had only two, of somewhat larger diameter. More, smaller flues, like those on Mary Conley, were more efficient for transferring the heat from the furnace exhaust gasses into the surrounding water, as they had more surface area. One frequent cause of boiler explosions in the early years was the problem of water levels dropping too low inside the cylindrical boiler casing, to the point at which the top surfaces of the flues was exposed above the water and in the pocket of steam above; steam is a much poorer conductor of heat than liquid water, so the iron flues, unable to transmit the heat within to another medium, would soften and collapse under pressure. This would blast superheated steam and water into the flues, the battery casing, fireboxes and out onto the deck within seconds. Even if the boilers did not explode violently, as sometimes happened, the injuries to those caught nearby could be horrific. The doctor, by helping to maintain a safe volume of water in the boilers, helped reduce such accidents substantially.

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