Specification

Displacement: 1,132 tons (1,788 tons fully laden) Dimensions:

Length: 281ft 6in. (279ft 6in. between the perpendiculars) Beam: 36ft

Draft: 8ft 6in. (10ft fully laden) Propulsion: Two oscillating engines and four boilers, powering two sidewheels, producing 350hp, and a maximum speed of 16 knots. Armament: Unarmed

Blockade Runner Boiler

William G. Hewes

William Hewes

William G. Hewes

Blockade RunnersBlockade Runner BlueprintsUss Stettin

F: Aries and the USS Stettin, March 1863

Aries Blockade Runner

G: Government-run blockade runners

Blockade Runner Bat

G: Government-run blockade runners

G2: Bat

Blockade Runner Bat

G2: Bat

Axis Blockade Runners

During the mid-19th century the general design of sidewheel engines improved, but they still took up a considerable space, which could otherwise be used to hold cargo. This longitudinal section of a side-lever engine is typical of the machinery installed in most blockade runners of the Civil War. (Mariners' Museum, Newport News, VA)

end of a large side-lever, an oval-shaped beam pinned at its center. Another connecting rod at the opposite end of the side-lever was attached to the paddle shaft. Each engine was a self-contained unit, and was usually fitted with "parallel motion mechanisms" to ensure the pistons rose vertically regardless of the ship rolling, and had its own steam system running from the boiler, complete with condensers and escape valves. During the decade before the Civil War, improvements were made to the condenser system, improving the reliability of the engines, and steam pressure was increased, allowing engines to operate at greater speeds. This design became the standard form of engine used in sidewheel-powered blockade runners during the Civil War.

Sidewheel Blockade RunnersBlockade Runner Steam Engines

The small iron-hulled British-built sidewheel steamer Merrimac became a blockade runner, making two successful trips into Wilmington before she was captured in late June 1863. She was acquired by the US Navy and used in the blockading squadrons until she foundered in 1865. (US Naval Historical Center, Washington, DC)

The drawback of the side-lever engine was its weight and size. While this was relatively unimportant on the high seas, it became vital when blockade runners needed to outrun pursuers, or had to operate in shallow water when entering the smaller ports of the Confederate seaboard. An alternative design gained favor during the 1820s. The oscillating engine had no connecting-rod system, as the piston was attached directly to the paddle shaft by means of a crank lever. The piston pivoted (or oscillated) around its central axis due to the motion of the crank, but the motion caused steam leakage problems, so complicated mechanisms had to be devised the better to control steam flow and exhaust. Although the basic system remained the same, there were wide differences between designs, depending on where or by whom the engine was made. As higher steam pressures became available, steam leakage became more of a problem, and consequently oscillating engines fell from favor during the mid-19th century.

The ideal form of design was the direct-acting engine, where there was no intermediate moving machinery between the piston and the paddle shaft or paddlewheel crank apart from a single connecting rod. This "holy grail" of marine propulsion was first introduced by Marc Brunei (the father of Isambard Kingdom Brunei) in 1822 when he developed a system of inclined engines and pistons pointing directly at the crank, but this was considered too bulky a mechanism for practical use. His son perfected the design when the availability of higher steam pressure permitted the use of smaller cylinders. From 1860 this type of inclined engine became increasingly popular, and was adopted by several late-war blockade runners.

By this stage the first compound engine had been developed, where steam was expanded in two stages, in two different cylinders (one high-pressure and the other a smaller low-pressure version). After the Civil War this led to the triple-expansion engine which became the standard type of marine engine by the close of the century, albeit one which became linked with screw rather than sidewheel propulsion. The standard variant used in blockade runners was the "diagonal" engine, where the cylinders were mounted behind and below the paddlewheel shaft, inclined at an angle of around 15 degrees. With the "double-acting" system, waste steam was vented into a seawater-cooled condenser, then circulated back into the boiler, which increased efficiency. This venting of steam created a vacuum, which helped improve the "pull" of the piston, and increased its effectiveness. Usually the paddlewheel shafts of both sidewheels were connected, and turned at the same speed, but if required they could be disconnected, so that each engine could run independently, either in

The small iron-hulled British-built sidewheel steamer Merrimac became a blockade runner, making two successful trips into Wilmington before she was captured in late June 1863. She was acquired by the US Navy and used in the blockading squadrons until she foundered in 1865. (US Naval Historical Center, Washington, DC)

forward or reverse drive. Engines of this type were capable of producing around 150hp, although some oscillating engines could produce double this power (300—350hp), but these larger engines meant increased weight, increased displacement, and speed loss.

The 1860s were a time of great technical innovation, and it seemed as if every new ship which was launched had better, faster, and more compact engines than the one before. While some blockade runners used screw propulsion, this remained relatively uncommon, as by the 1860s, in identical conditions the paddlewheel still produced a greater sustainable speed through the water than its rival. The archetypal blockade runner was therefore a sidewheel steamer, albeit one with a particularly powerful and compact pair of engines. Every method was used: beam engines, oscillating engines and various types of direct acting engines. The propulsion system was a reflection of what was available, and represented a balance between power and weight which made the Civil War blockade runners virtually unique in maritime history. These sleek vessels were the fastest steamships of their day, and therefore represented the latest word in marine propulsion. Like the drug-smuggling "cigarette" speedboats of the late 20th century, they were created for a specific purpose, where speed equated to success and survival.

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Responses

  • Alannah
    What powered blockade runners?
    6 years ago
  • abbondanzio
    Who made steam engines for blockade runners?
    3 years ago

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