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A very brief reference to gyros in Sea Magazine:
http://www.seamagazine.com/Newsletter/Article/Gyros-Deliver-Stability

Gyros Deliver Stability

Posted: August 1, 2012

By: Roger McAfee

It sure does. Gyro stabilizers operate on the principle that a spinning mass resists efforts to move it in any direction. As kids, we used to play with a spinning top. Once the top got spinning, the surface on which the top was spinning could be moved, tilted and angled, but the top continued to spin in a vertical position. This is a gross oversimplification of modern gyro stabilizers, but it makes the point. In 1922, a 120-ton gyro stabilizer was installed on an oceangoing passenger liner, Hawkeye State, operating between Baltimore and Honolulu. Modern gyros can be fitted on outboard-powered boats as small as 40 feet.

Unlike fin stabilizers, gyros work whether the vessel is at rest or under way, and there are no through-hull fitting requirements.