Why Polyester not Nylon for marine craft lifting slings..
The ‘Web Sling and Tie-Down Association’ conducted two long time exposure test study on the degradation effects of polyester- and nylon web sling when exposed to sunlight. The first test was done in 1981, and the second test series was done between 1997 to 2004. The full test report is published by WSTDA, a copy of which can be obtained by Unirope.
One of the main conclusions reached by WSTDA:
“The polyester samples tended to undergo most of their strength loss during the first twelve months of exposure and then leveled off approximately a 30% loss in strength. The nylon 6 and nylon 6.6 sample showed a general trend of consistent strength loss over the entire 36 months exposure period, with strength loss levels approaching fifty to sixty percent after 36 months for some sample tests.”
Based on the test results and conclusions reached, Unirope has decided to discontinue the use of NYLON webbing material for Boat Lifting Slings.
However, it must be noted that, although Polyester webbing seems less affected, even polyester slings will undergo a significant strength loss leading to a DECREASE in strength. Consequently, the DESIGN FACTOR for such slings will DROP from a 5:1 value to at least a value of 4:1
Reference: http://unirope.com/sling/why-polyester-and-not-nylon-for-boat-lifting-slings 29.1.2016