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At 10:00 PM -0400 6/25/98, Jim Cobb wrote: >Take 2 brass rings. Zip them together with the best, most costly zip tie >on planet earth. Pull the rings, seems pretty strong, huh? Now twist the >rings while pulling. Whoops! There go's an essential piece of dive >equipment. Why did it break? Zips are simply not designed to take >torsional stress of any kind. Let me add my $0.02 to this thread (which seems to come up periodically). When I took a cavern / intro cave course from JJ we all set up our gear at the beginning to be scrutinized before hitting the water the following day... We all were rigged strict Hogarthian (which only reenforces the arguments for standardization, since 4 people coming from four corners of the world could all find emergency gear on their team members after never having met each other before!... but that's another issue). I had gotten two of Barry Miller's bullet-proof delrin back-up lights and dutifully fixed them not with one but TWO heavy duty zip ties to stainless steel bolt snaps rigged to 1" pieces of bicycle inner tube to my personally hand-made harness. My rig was beautiful... I was SO proud! <g>. JJ came along... gave my rig general good marks... pulled out one of my lights... held it up for the rest to see.. gripped it with just his thumb and index finger and twisted... Both zips just snapped with so little effort it was over before I even realized what he was up to! Jim is right. You MIGHT be able to lift an elephant with zips with longitudinal pull, but zips have little strength in lateral shear mode. I use them to hold my regulator mouth pieces, but that's about all. One strand of #26 cave line has a breaking point of about 200 lbs (and you usually end up wrapping it several times which only multiplies the effect). When fixed properly, you literally could almost lift an elephant! Robb W ==================================== CDR Robert B. Wolov, MC, (FS), USNR Orthopedic Pathology / Aerospace Medicine Dept. of Orthopedic Pathology Armed Forces Institute of Pathology Washington, DC 20306-6000 wolov@hi*.co* (preferred) wolov@af*.os*.mi* -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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