3/20/98 Lifeline Study Update
SAFETY AT SEA SUBCOMMITTEE REPORT
US SAILING MEETING, TULSA, OK
MARCH 20, 1998
RALPH NARANJO, VANDERSTAR CHAIR
U.S. NAVAL ACADEMY
Lifeline Study Interim Update
The results of Phase One of the study indicated that bow and stern tubular pulpits and pushpits play a crucial role in the structural integrity of the overall lifeline systems. The research done by Mechanical Engineering majors at the U.S. Naval Academy revealed that wire and swage fittings, utilized in the lifelines of Navy 44's did not fail until tension loads exceeded 5,000 lbs.. However, when the full system was actually tested using loads that simulate hiking crew members leaning against the lower lifeline, failure of the system occurred at 1,200 lbs., and was caused by deflection of the stern pushpit and subsequent collapse of individual stanchions.
The midshipmen involved in the project determined that the support geometry of the tubular pushpit was a poor choice for a structure intended to resist the deflection caused by lifeline loads. This resulted in the tubular support legs, which were at right angles to the lifeline loads, to crimp neat the base and fold forward, causing the slackened lifelines to cease holding stanchions in column, resulting in premature failure of the entire system.
Further testing, using substantial weldments in lieu of a pushpit and pulpit, provided a structure less prone to deformation and collapse under load, and the results showed that the system could handle well over two times the amount of lifeline tension before stanchion collapse occurred. This prompted research aimed at determining the optimal geometry for bow and stern pulpits/pushpits, a major component of the Phase Two portion of the project.
Work in progress includes a review of standard industry practice and current design theory behind differing pulpit/pushpit configurations, choice of tube wall thickness and diameter. In addition, midshipmen researchers are also preparing to do a failure analysis as well as computer modeling of a wide range of pulpit/pushpit options. This will include the open bow pulpit that has grown more popular in recent years. The testing will be done on the full scale steel box beam jig created for phase one testing, and will measure the effects of both static and dynamic loads on the system.
This testing will be a demonstration project for an entire section of mechanical engineering students at the US Naval Academy and has been endorsed by Dr. Russell Smith, Chairman of the Mechanical Engineering Department. Testing will be done during September and October and results presented shortly there after.
Funding and in-kind assistance for the project will once again be handled through the US Naval Academy Sailing Program and the much appreciated support of the Cruising Club Of America's Bonnell Cove Fund. Several commercial interests have offered assistance with this research, however, Director of Navy Sailing Captain Jerry Farrell feels that such involvement would be inappropriate and in conflict with institutional goals.