At 05:45 AM 2/4/2006, Rich Osman N1OZ wrote:
>I'm putting together a 45 ' temporary mast package. I'm using the 4'
>military surplus sections that it seems you see at every hamfest.
>
>I've got 3/16" double braid Dacron rope for low stretch guys. Most of
>the double layer rope I've used in the past was pretty finicky about
>treating the cut end, both in terms of how the cut is made and
>processed, and also the way it is looped and knotted on the D ring. The
>big problem I've seen is unequal tension on the inner and outer weaves
>leading to failure of one and the the other.
I don't know about this specific rope, but in kernmantle type ropes (e.g.
climbing ropes), the strength is in the center core. The outer braid is
just there for abrasion resistance. The braided jacket can be expected to
stretch a fair amount, just like any other knit, so the jacket (the mantle)
stretches to acccomodate whatever the core (the kern) does.
>I emailed the manufacturer and they were surprisingly unhelpful, saying
>in essence "use a hot knife, we only make it, we know nothing about
>application."
>
>I'd like to engineer a solution rather than hack one. Starting with the
>guys I want to be able to calculate the real guys strength. I'm
>concerned that the terminations will end up being the weak points.
What about proof testing? Seems like you think your application has a
large degree of "workmanship effects" and is not primarily a strength of
materials issue.
Make up a bunch of test articles, and test them to failure. Not only will
you get a "real" number for how YOU assemble them, but you'll also get an
idea of the spread.
You're probably right that the failure point will be at the
end/knot/attachment. All those twists, turns, and bends. However, there's
probably some clever end attachment scheme that preserves most of the
strength (e.g. proper thimbles and crimped connectors for wire rope)
Jim, W6RMK
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