Towline
Failure is the Leading Cause of Injury and Death in Parasailing Accidents
Tying knots in the towline may significantly weaken it
The problem
A bowline knot, the knot
most commonly used by parasailing operators in their towlines. This type of
knot can weaken a brand-new rope by as much as 70 percent
Towline failure is the leading cause of injury and death in
parasailing accidents. See Coast Guard
safety alerts “Know Your ROPES,” 2011 and 2013.
The NTSB recently studied several parasailing accidents and verified
that the knot most commonly used by parasailing operators to fasten their towlines
is a bowline knot (www.ntsb.gov/doclib/reports/2014/SIR1402.pdf). In subsequent
laboratory testing, the NTSB confirmed that this knot (and any knot in general)
can reduce towline strength by as much as 70 percent, even on brand-new,
otherwise-strong ropes.
The NTSB tested three types of rope commonly used by
parasailing operators: 3/8”- and 7/16”-diameter double-braid polyester, and
5/16”-diameter single-braid polyethylene. When
the testing also factored in sun and saltwater exposure, sudden “shocks” by
wind gusts or other overloads, and general wear-and-tear, the ropes weakened
further.
Although most parasailing operators may be aware that tying
knots in the towline reduces rope strength, they may have no idea just how
drastic the weakening really can be. This
lack of awareness can potentially be deadly.
·
Recognize that although a particular rope may be
rated at 10,000 pounds, the moment you tie a knot in it, the rope strength can drop
by half or more. This is before factoring in the rope’s age, use, etc.
·
Frequently and carefully inspect your ropes to ensure
that they are in good overall condition with no sign of external abrasion or other
damage, and that they are suitable for the intended operation.
·
At the parasailing location, use an anemometer or
other device to measure wind speeds to ensure that those speeds fall within the
parasail canopy manufacturer’s recommendations.
·
Use steady and consistent speed and force on the
winch when deploying and recovering the canopy towline.
·
Maintain logs about rope usage and examinations.
These should include information on the type of ropes you’re using, their time in
service, and details of every examination. A usage log is a great way to determine
if excessive tension or shock-loading has occurred and weakened the ropes.
·
Store your ropes in a clean and dry location out
of direct sunlight.
·
Trim back the working ends of the ropes as needed,
and replace your ropes frequently. For more specifics, consult a recognized source
of information such as the Cordage Institute on the selection, care, and disposition
of ropes. In addition, refer to the standards for parasailing equipment, currently
being developed by ASTM International.