Boilers

U.S.S. Cairo's flue boilers are among the oldest and best surviving examples of the type designed for boats plying the western waters. Five matched flue boilers were mounted side by side along the centerline of the boat.  Five wrought-iron pipes called flues, carried fire and smoke through the length of each boiler to the front.  The boilers were joined together in four places.  At the rear end a common fire box included gratings on which the coal was thrown to burn.  Just forward of that, the bottoms of each boiler were joined by a mud drum, used to collect sediment that settled out of the river water used in the boiler. Periodically the muddy silt was blown out of the mud drum by high pressure steam. At the forward end of the boilers, they were joined by a steam drum across their tops and the smoke box.  The smoke box gathered smoke and hot gasses which then traveled up and out of the two tall smoke stacks. The boilers operated at 140 pounds per square inch steam pressure and consumed almost a ton of coal per hour.

Iron boilers were built to hold tons of water and steam under pressure. Steam, generated in the boilers, powered the engines which turned the paddle wheel. Boiler explosions occured often enough to give the commercial western steamboat a poor reputation for safety.

The fire room was a hot, stifling place to shovel coal for hours on end.  Because a steamboat without steam could not move and was helpless if attacked, the gunboats kept fires burning, and steam pressure built up even when they were anchored. Coal, burned in the fire boxes, created hot gases which circulated by flues through the boilers.  Water turned to steam and passed through the steam drum to the engines, and the hot gases vented through the chimneys.

The Boilers

Type:	Return flue
Number:	5
Size:	36” diameter x 24’ long
Fuel:	Coal
Pressure:	140 lbs. sq. in.
Fuel consumption per hour:	18 to 20 bushels, 1980 lbs.

Vicksburg National Military Park