For everyone reading this thread, the following is part of a private disscussion that I thought would
shed some light on the why's and wherefore's, good and bad, about using the
Circus Hitch,
this half
hitch to
wire rope I think the real problem, applying the end
fitting - no matter if clip or
Circus knot, but I wouldn't think it proper if it has half hitches in it, and I assume the cause of failure.
In my own training and readings, the half
hitch should never be used on
wire rope.
Actually, The half hitches were, like the
circus knot wraps, merely a way to prevent slipping at the
clove hitch should there be
momentary "bounces" or slack or
shock loading in the rig. They actually took no weight and were tied with the same degree of looseness as the
circus hitch loops in the picture at the top of this thread. The double half
hitch method, taught as common practice in the '50's and 60's, was an out growth of hemp
house or fiber rope rigging, which was an out growth of navel rigging on sailing vessels, when attaching to a wooden or pipe
batten with a
clove hitch. The reason we used to use clove hitches was to prevent the rope from sliding along the pipe, that is really the way a
clove hitch is designed to work, to
cinch around a smooth beam, spar, mast, log,
etc and not slip even if there is only one
line doing the lifting.
When using a 10 ton test rig for destructive testing, subjecting this, and various other methods of attaching
wire rope to a pipe using clove hitches, the knot always, repeat always, failed at the
clove hitch where the
live end first entered the knot. Usually at about 40% to 50% of the rated
breaking strength of the
GAC. If you think about it or look at it, a well tied
clove hitch bends the
line, whether
wire rope or hemp rope or
cord,
etc. at a hard 90 degree
bend right there, thus tremendously weakening the
line.
I do not use nor will I allow workers working for me to put
any knots in
wire rope. As noted above, the
clove hitch is the failure
point, not half hitches or
circus knot wraps.
Real question before I install some on some pipe is if the
clove hitch followed by the proper amount of
drop forged
wire rope clips proper to use? And is the
clove hitch one of only two knots permissable for
wire rope - assuming the
Circus Knot is the second and only with proper (it would seem differences in them) local training in tying them? Or have rigging practices changed in the
clove hitch no longe in favor? Terminating how ever it's done in wrapping the pipe. Is it only
pipe clamp now permissable or the
clove hitch around the pipe when properly terminated also permissable?
For permanent installations, no knot is permissible in
current common practice. Today I would NEVER use a
clove hitch with
wire rope on a permanent installation. The proper way to terminate a
line to a
batten is with
trim chain and rated and properly moused screw pin shackles, or rated and properly moused turnbuckles attached to a
batten clamp.
If for some reason you must attach
wire rope directly to a pipe
batten, wrap it 1 1/2 times around the pipe and then attach the proper number of clips for the
wire size. Attach the first clip at least the diameter of the pipe away from the pipe, (the
spacing is to prevent a sharp
bend where the
GAC enters and leaves the clip, thus weakening the
GAC) i.e. if using schedule 40, 1 1/2" pipe, the closest clip should be at least 2" away. This should NOT be done as a permanent
batten attachment, but only as a temporary, single event rigging. This will be at least twice as strong any attachment method that uses a
clove hitch (or any other knot in the rope.
Don't know and looking to your advice on this and the above questions about different styles of application of such a knot seemingly. I think the
Clove hitch is fine when terminated on Nico press oval sleeves or
wire rope clips dependent on the install.
The properly used
circus hitch now is used for short term installs such as short run aerialists, one or two week
road shows and such types of uses. They are designed to be easy and very quick to install and
strike without tools of any kind and with no parts or hardware to find, store or lose. They should only be used by knowledgeable, professional (preferably
ETCP Certified) riggers and the cable or
GAC being used is derated by 50% at least.
Hope this helps.