New technique advances carbon-fiber composites.
The USS Constitution, a floating piece of history and the world's oldest commissioned warship, is painstakingly maintained to ward off the ravages of time, but inspecting some parts of the ship is difficult or impossible. In a few years, however, remote-controlled robots and other devices may be put in inaccessible areas of the hull and rigging, sending pictures and information about conditions back to Old Ironsides' human caretakers.
Professor Steven Dubowsky of mechanical engineering is heading a research project to design and develop equipment that will assist in the conservation, inspection and restoration of architectural and archeological treasures such as the Constitution. Ideas that the group is exploring include devices that can remotely inspect and measure the underside of the ship, the upper reaches of the masts and rigging, and the narrow space between the ballast floor and the hull.
The Constitution is now in dry-dock in the midst of an extensive three-year repair and restoration project slated to be completed before the ship's 200th anniversary in 1997. While the vessel is out of the water, another MIT scientist, Professor Heather Lechtman, director of the Center for Materials Research in Archeology and Ethnology, is also doing research on some of its copper spikes to try to determine if any of them could have been made by Paul Revere (see accompanying story).
Dr. Dubowsky's project will have applications for other historical structures as well. Robots could reduce the time, expense and physical risk of working around historic sites, and they could also overcome drawbacks of some current methods that can result in unavoidable damage or deterioration. For example, to support human activities on large monuments, scaffolding anchors must be drilled into the monument itself.
"We're using the USS Constitution as a demonstration site for the advanced technology we are developing," Dr. Dubowsky said. "The technology we're working on is very broad." Other possible applications, he added, include inspecting and working in areas too dangerous or inaccessible for people, such as toxic-waste sites, gas line interiors and bridge superstructures, or exploring other planets or Egyptian tombs.
One part of the Constitution that now can be inspected only when the ship is dry-docked (which happens only every 20 years or so) is the sub-ballast area in the hold. Between the outer hull and the inside floor beneath the ballast-which consists of rocks, chains and other heavy objects dating from the ship's construction in 1797-is a four-inch-high space which is subject to damp, rot-inducing conditions. Diagonal riders divide the sub-ballast area into sections, making inspection even more difficult. A small autonomous robot with legs to climb over the riders could do the job when the ship was afloat, recording conditions with an on-board video camera and sensors.
A second system being developed by Dr. Dubowsky and his colleagues (who include Nathan Rutman and Craig Sunada, both graduate students in mechanical engineering) employs an array of sensors attached to the keel to measure the hog, or the keel's shape. Viewed from the side, the bottom of the Constitution is almost a straight line between the rudder and the start of the rise to the bow. Due to the stresses of water and supporting the ship's 2,200 tons, however, the keel eventually warps and sags at the ends, which necessitates repairs. This problem was exacerbated by the removal of some supporting beams in the 1800s.
The sensors would be attached to seven carefully selected spots on the keel to measure water pressure, which is a function of the distance to the surface of the water. A computer within the ship would then compare the data from the different locations and immediately infer the hog. This is an improvement over the costly and less efficient route of sending divers down twice a year to take measurements manually, or taking indirect measurements from inside the hull. The information gained could be used to correct hog by shifting ballast without having to put the ship in dry-dock.
Other hard-to-reach areas of the Constitution are the masts and rigging. Checking for rot involves either unsightly and unwieldy cranes, or hazardous climbs of up to 220 feet by an inspector. Dr. Dubowsky's group is examining two alternatives: a climbing robot, or a long-reach manipulator system consisting of a long articulated arm controlled by a mobile unit on deck and topped with an intelligent inspection device. Such a system is similar in structure to one being proposed for in-orbit maintenance of NASA's space station Freedom.
The Constitution, which is slated for relaunch in November 1995, is now undergoing repairs and refitting with historically accurate components, said Patrick Otton, acting historian at the Naval Historical Center's Boston section. Over the years, parts were changed and removed for financial reasons and also because the ship's role evolved from warship to training ship to dockside museum (she has not sailed since the 1880s). Among the parts being restored according to the original specifications are the diagonal riders designed to resist hog, as well as deck strakes and gun deck supports. The project will cost $12 million over four years, compared to more than $2 million a year for routine maintenance, he said
Dr. Dubowsky's project is currently supported by the National Science Foundation and is being done in collaboration with engineers and scientists from NASA, the Getty Conservation Institute and the Naval Historical Center, Boston.
A version of this article appeared in the November 16, 1994 issue of MIT Tech Talk (Volume 39, Number 12).