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SAFETY AT SEA
SUBCOMMITTEE REPORT
US SAILING MEETING, TULSA, OK
MARCH 20, 1998
SUBMITTED BY
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.
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