Eagle Wind Heel Project
Sail training vessels are used worldwide as platforms for teaching and learning; additionally the vessels act as ambassadors for the countries they serve. These powerful icons symbolize strength and beauty; unfortunately, in recent years, the safety of these vessels has been questioned due to a series of accidents caused by vessel knockdown, a sudden and extreme heeling from a strong wind or gust of wind. The most recent incident occurred on February 17, 2012, when the 188-foot sail training vessel Concordia was knocked down and sank off the coast of Brazil. Other sail training vessel sinking incidents include the 316-foot Pamir (1957), the 117-foot Albatross (1961), the 117-foot Marques (1984), the 137-foot Pride of Baltimore (1986) and the 125-foot Maria Assumpta (1995).
At the U.S. Coast Guard Academy, Professor Susan Swithenbank of the Naval Architecture and Marine Engineering faculty and LCDR Jessica Rozzi-Ochs, a faculty member in Mechanical Engineering and the prospective Executive Officer of the U.S. Coast Guard Cutter Eagle, led a group of cadets to use experimental, numerical, and analytical methods to research the issues surrounding sailing vessel heel and knockdown.
U.S. Coast Guard Cutter Eagle, known as “America’s Tall Ship”, is a three-masted Barque rigged sailing vessel used to train the U. S. Coast Guard Academy cadets, U. S. Coast Guard officer candidates, and National Ocean and Atmospheric Administration prospective officers. Eagle was constructed in 1936 at the Blohm and Voss Shipyard in Hamburg Germany and has belonged to the U.S. Coast Guard since 1948. Using data and information collected from Eagle, the team of professors and cadets are determining the wind speed required to knock down Eagle and develop heeling arm curves to evaluate the stability and safety of Eagle.
In 1982, Eagle underwent a major overhaul to make her compliant with current military vessel safety regulations. At the time of the overhaul, a stability analysis was completed that calculated the righting and heeling arms for high wind conditions; this informed the crew of the highest wind speeds Eagle could endure. However, since 1982 there have been significant advances in the field and to the technology used to analyze the stability of a ship. The Academy’s team believes that the current stability data is not completely accurate and could be updated and revised to improve the overall safety of the vessel. With the help of the Coast Guard Marine Safety Center, the team built a 3-D model of the Eagle. Using the model and modern software, the group was able to determine more accurate righting arm curves for Eagle, as well as heeling arms.
The team also modeled Eagle’s sails and used the wind tunnel at the Academy to determine the lift and drag coefficients of the sails in the upright and inclined positions. Because square sails are uncommonly used, little research has previously been done on them. By determining more accurate lift and drag coefficients for these sails, more accurate heeling arm curves for Eagle can be determined; this method then could be applied to other sail training vessels.
The group has already determined preliminary results for Eagle that will help the crew better understand how to handle the ship in high wind conditions. These findings will likely lead to new Coast Guard regulations for sail training vessels so that future tragedies can be avoided.