page_title: USS Monitor
section_title: Design and description
hierarchical_section_title: USS Monitor / Design and description
caption_attribution_description: Polski: USS Monitor - przekrój
context_page_description: USS Monitor was an iron-hulled steam-powered ironclad warship built for the Union Navy during the American Civil War, the first such ship commissioned by the Navy. Monitor played a central role in the Battle of Hampton Roads on 9 March 1862, where, under the command of Lieutenant John L. Worden, she fought the casemate ironclad CSS Virginia to a standstill. The unique design of the ship, distinguished by its revolving turret which was designed by American inventor Theodore Timby, was quickly duplicated and established the monitor class and type of armored steam-powered warship built for the American Navy in the next several decades.
  The remainder of the ship was designed by the Swedish-born engineer and inventor John Ericsson, and hurriedly built in Brooklyn, New York on the East River beginning in late 1861 in only 101 days. Monitor presented a new concept in ship design and employed a variety of new inventions and innovations in ship building that caught the attention of the world.
context_section_description: Monitor was an unusual vessel in almost every respect and was sometimes sarcastically described by the press and other critics as "Ericsson's folly", "cheesebox on a raft" and the "Yankee cheesebox". The most prominent feature on the vessel was a large cylindrical gun turret mounted amidships above the low-freeboard upper hull, also called the "raft". This extended well past the sides of the lower, more traditionally shaped hull. A small armored pilot house was fitted on the upper deck towards the bow, however, its position prevented Monitor from firing her guns straight forward. One of Ericsson's prime goals in designing the ship was to present the smallest possible target to enemy gunfire. The ship was 179 feet (54.6 m) long overall, had a beam of 41 feet 6 inches (12.6 m) and had a maximum draft of 10 feet 6 inches (3.2 m). Monitor had a tonnage of 776 tons burthen and displaced 987 long tons (1,003 t). Her crew consisted of 49 officers and enlisted men.
  The ship was powered by a single-cylinder horizontal vibrating-lever steam engine, also designed by Ericsson, which drove a 9-foot (2.7 m) propeller, whose shaft was nine inches in diameter. The engine used steam generated by two horizontal fire-tube boilers at a maximum pressure of 40 psi (276 kPa; 3 kgf/cm²). The 320-indicated-horsepower (240 kW) engine was designed to give the ship a top speed of 8 knots (15 km/h; 9.2 mph), but Monitor was 1–2 knots (1.9–3.7 km/h; 1.2–2.3 mph) slower in service. The engine had a bore of 36 inches (914 mm) and a stroke of 22 inches (559 mm). The ship carried 100 long tons (100 t) of coal. Ventilation for the vessel was supplied by two centrifugal blowers near the stern, each of which was powered by 6-horsepower (4.5 kW) steam engine. One fan circulated air throughout the ship, but the other one forced air through the boilers, which depended on this forced draught. Leather belts connected the blowers to their engines and they would stretch when wet, often disabling the fans and boilers. The ship's pumps were steam operated and water would accumulate in the ship if the pumps could not get enough steam to work.
  Monitor's turret measured 20 ft (6.1 m) in diameter and 9 ft (2.7 m) high, constructed with 8 inches (20 cm) of armor (11 inches in front at the gun ports) rendering the overall vessel somewhat top heavy. Its rounded shape helped to deflect cannon shot. A pair of steam-powered donkey engines rotated the turret through a set of gears; a full rotation was made in 22.5 seconds during testing on 9 February 1862. Fine control of the turret proved to be difficult; the steam engines would have to be placed in reverse if the turret overshot its mark, or another full rotation would have to be made. The only way to see out of the turret was through the gun ports; when the guns were not in use, or withdrawn for reloading during battle, heavy iron port stoppers would swing down into place to close the gunports. Including the guns, the turret weighed approximately 160 long tons (163 t); the entire weight rested on an iron spindle that had to be jacked up using a wedge before the turret could rotate. The spindle was 9 inches (23 cm) in diameter which gave it ten times the strength needed in preventing the turret from sliding sideways. When not in use, the turret rested on a brass ring on the deck that was intended to form a watertight seal. In service, however, this proved to leak heavily, despite caulking by the crew. The gap between the turret and the deck proved to be a problem as debris and shell fragments entered the gap and jammed the turrets of several Passaic-class monitors, which used the same turret design, during the First Battle of Charleston Harbor in April 1863. Direct hits at the turret with heavy shot also had the potential to bend the spindle, which could also jam the turret. To gain access to the turret from below, or to hoist up powder and shot during battle, the turret had to rotate facing directly to starboard, which would line up the entry hatch in the floor of the turret with an opening in the deck below. The roof of th
caption: Transverse hull section through the turret
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