Author Topic: Knot suggestions for in-line pull on an I beam?  (Read 6257 times)

knot rigger

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Knot suggestions for in-line pull on an I beam?
« on: May 04, 2015, 01:58:46 AM »
I'm dissatisfied with a current knot attachment with something I use at work, and I thought it might be an interesting puzzle for the collective group.

I am looking for a good hitch to use on an I beam, for a length-wise pull.  The I beam is approximately 6" high and 5" wide, and the current line used is 1/2" static kernmantle.  The current attachment is a bowline, with most of the loop protected by a rubber hose a chafing gear.  However, the bottom flange of the I beam has no chafing gear, and has chafed the rope significantly over time.  The I beam and rope both are constantly underwater.  The I beam is a fixed structure, that the line is tied too it, and the free end is then used to temporarily position a raft. It is wrapped around a smooth pipe on the raft (again, underwater) and kept in tension by hand (I actually use an awning hitch, but I doubt anyone else does).  The orientation of the pipe is horizontal to the I beam, at about the same height (depth) as the bottom flange of the I beam.  As the line is kept in tension by hand, other people step onto the raft, so the line is dynamically loaded, and it bounces a bit on the beam, contributing to the chafe.  I have about 2 or three inches of beam area to hitch upon, and I can use chafing gear to help minimize wear.  But it would be really slick if I could tie a great hitch and not need the chafing gear at all!

Hopefully I've described the problem at hand. 

My initial instinct is a variation of the rolling hitch, but this hitch doesn't perform so well on square shaped beams (let alone I beams).

I'm interested with what you all may suggest.

andy

roo

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #1 on: May 04, 2015, 03:24:36 AM »
I'm dissatisfied with a current knot attachment with something I use at work, and I thought it might be an interesting puzzle for the collective group.

I am looking for a good hitch to use on an I beam, for a length-wise pull.  The I beam is approximately 6" high and 5" wide, and the current line used is 1/2" static kernmantle.  The current attachment is a bowline,
How is a bowline taking a lengthwise pull?  Is it fairly tight?
« Last Edit: May 04, 2015, 06:20:00 AM by roo »
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knot rigger

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #2 on: May 04, 2015, 05:40:53 AM »
Quote
How is bowline taking a lengthwise pull?  Is it fairly tight?

No it's loose.. it load's sorta diagonally, and there is a groove that has rusted into the top flanges of I beam over time that it has settled into (with the chafing gear tube) so that it doesn't slip along the I beam.  There is also an attachment flange on the I beam on the end closest to the raft, that the loop of the bowline would eventual check up against, if it ever slipped.

roo

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #3 on: May 04, 2015, 06:31:54 AM »
Quote
How is a bowline taking a lengthwise pull?  Is it fairly tight?

No it's loose.. it load's sorta diagonally, and there is a groove that has rusted into the top flanges of I beam over time that it has settled into (with the chafing gear tube) so that it doesn't slip along the I beam.  There is also an attachment flange on the I beam on the end closest to the raft, that the loop of the bowline would eventual check up against, if it ever slipped.
OK.   You've got a tough situation there with little room.  You could try to make a few turns around the beam as you deem appropriate and finish with a Gnat Hitch.  Just be sure to get things as tight as you can before applying a lengthwise pull.

You may still have to deal with chafing.  I would be mighty tempted to look for an easier attach point, maybe sacrificing a cheap clamp to attach to a flange or web of the beam.
« Last Edit: May 04, 2015, 05:10:27 PM by roo »
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Fairlead

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #4 on: May 04, 2015, 10:47:06 AM »
The "Double Overhand Noose" aka "Poachers Noose" aka "Scaffold Hitch" might suit your needs - pulled up taught it stays firm and will take a pull in any direction.  Try it on the legs of a chair, which will replicate the four edge contact points of your I beam - prepare to be amazed!

Gordon


Tex

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #5 on: May 05, 2015, 03:30:43 PM »
It seems to me the scaffold hitch holds well, but I'm not sure about the chaffing issue.  It does "take" a pull in any direction, but as the direction changes around the object the two loops roll rope from one into the other.

Ropes don't have to solve everything, permanently.  Other tools do exist.


Dan_Lehman

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #6 on: May 05, 2015, 07:01:36 PM »
The simple solution --using your rope-- is to make several
wraps around the I-beam and essentially hitch to these;
and a Portuguese bowline is a model for doing this.
The SPart loads the mid-span of the multi-wraps, and
thus acts like "frapping turns" in drawing them tighter
--and giving a terrible angle for aggravating forces on
the wraps, except that they have strength in number.
It will be hard to slide such wraps along the beam.

One could also tie --around *space*-- an anchor/fisherman's bend
and take its tail around & around as the wraps, tying off with
something simple.

Note that in some situations a hitch such as the poacher's h.
suggested here will aggravate chafing aspects, as they
put force entirely on the line's turn around the object,
whereas an eye splits force between its legs.

FYI re chafe guards : I recall one study with rope over
some cliff edge (not necessarily a severe "edge") in which
there was more rope degradation WITH a guard than
without --a matter of heat generated with, IIRC, a carpet
(vs. what was presumably pretty smooth, stone-cold rock).


--dl*
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knot rigger

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #7 on: May 05, 2015, 10:18:49 PM »
Thanks all

I'll play around with all the suggestions and let you know what works and what doesn't.

I haven't used the Gnat hitch much (yet) roo.  That fact that it's not well know is something of a drawback, as this line will be inspected by my co workers, who are almost certain not to know this hitch.

Farilead:  I haven't ever tried a scaffold hitch on a square object.  Thanks for the idea.  I'll play with it.  A scaffold hitch has the advantage that it's widely known, and therefore easily verifiable.

Quote
Ropes don't have to solve everything, permanently.  Other tools do exist.

Tex!  What's the fun in that?  ;)  I didn't post this on the "international weld a bracket to an I beam guild forum"  ;)  I can easily just leave it as it, replace the chafed line with new, and call it a day.  Or drill and bolt in an eyebolt, but it occurred to me that there must be a better Knot to use without resorting to other mechanical devices.

Dan, you have an intersting idea of a two step solution: tie a binding hitch to the beam, with a leg loaded hitch tyed to the the binding hitch.  That could be the ticket to minimizing the chafe the best.  It's a little complicated, I was really hoping for an elegant single hitch solution.

How do you all think an anchor bend would deal with an lengthwise pull on a square I beam?

thanks for the help
andy

roo

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #8 on: May 05, 2015, 10:37:01 PM »
I haven't used the Gnat hitch much (yet) roo.  That fact that it's not well know is something of a drawback, as this line will be inspected by my co workers, who are almost certain not to know this hitch.
It's a good chance for them to learn, and it's simple.  I'm surprised that your coworkers are going to be inspecting an underwater attachment.  If it works, their recognition of the knot or knots shouldn't really matter.  Are you expecting them to remove it and re-tie it on a regular basis?
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SS369

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #9 on: May 06, 2015, 12:07:50 AM »
Hello knot rigger.

I think that I would consider a beam lashing, leaving a tail long for securing the raft the way you do.

If you wrap over the previous round turns and frap in the free area till snug, there will be very little, to none, chafing.
The first wraps will cushion the outer wraps and this will be basically permanent. Should be very easy to inspect if you use knots your compatriots are familiar with as well.
Should handle the varying loads at all angles.

SS

alpineer

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #10 on: May 06, 2015, 07:24:54 PM »
Looks like a job for xarax! And waddaya know, he's silent. But not for long, I suspect. :)
I like the lashing concept similar to the method mountaineers use to secure a coiled rope. The rope would be doubled along the beam, the tail end crossing over the standing part first, then continue wrapping away from the lead line toward the bight's closed end, and the tail then passed through the bight's loop. The lead line is then pulled tight to secure the tail. I imagine the tail may need further securing of some sort.
« Last Edit: May 06, 2015, 10:40:03 PM by alpineer »

knot rigger

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #11 on: May 07, 2015, 02:05:15 AM »
Quote
  I'm surprised that your coworkers are going to be inspecting an underwater attachment.  If it works, their recognition of the knot or knots shouldn't really matter.  Are you expecting them to remove it and re-tie it on a regular basis?

Roo, perhaps my co-workers would see a new attachment and miss-identify it as a "hope Knot" and erroneously determine it as inadequate.  It's the kinda thing I might do.  It's a challenge to using an unfamiliar knot. 

Quote
I think that I would consider a beam lashing, leaving a tail long for securing the raft the way you do.

SS369, I'm not familiar with a "beam lashing" or maybe know it by another name.  Maybe you could cite a reference or a picture?

Quote
I like the lashing concept similar to the method mountaineers use to secure a coiled rope.

I like this idea a lot,  It's easily recognizable, and solves the problem well.  I am curious how tight I could get it to avoid chafe, as there are no frapping turns in this method, but it seems that the load would tighten it to some degree.

thanks



SS369

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #12 on: May 07, 2015, 03:19:36 AM »
Quote
I think that I would consider a beam lashing, leaving a tail long for securing the raft the way you do.

SS369, I'm not familiar with a "beam lashing" or maybe know it by another name.  Maybe you could cite a reference or a picture?


I'll have to use a found picture to better convey my suggestion. I've no access to an I-beam at present or I would construct it.

In the left side of the attached picture, substitute your beam for the rope cables.

Yes, it is similar to the way a rope is coiled, just one side of the coil though. Whatever that side is named.

SS
« Last Edit: May 07, 2015, 03:21:04 AM by SS369 »

knot rigger

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #13 on: May 07, 2015, 09:35:52 PM »
SS

I see what you mean now, thanks for the pic.

It seems like you and Alpineer are suggesting essentially the same idea.  I'll let you know how it works, but it may be some time until I'm scheduled back in the water at work.  But in the mean time, I'll try and mock up the same scenario on dry land.

cheers
andy

alpineer

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Re: Knot suggestions for in-line pull on an I beam?
« Reply #14 on: May 08, 2015, 07:12:50 AM »
 
SS

I see what you mean now, thanks for the pic.

It seems like you and Alpineer are suggesting essentially the same idea. 

Only insofar as they are both lashings.

The lashing carries the same form as the Heaving Line Knot shown here   http://cs.maritime.kobe-u.ac.jp/Rope2/rope/nagesakumusubi/00.htm   Ignore the first 2 of 7 images.

Here's what it looks like in the finished form:
« Last Edit: May 08, 2015, 01:42:05 PM by alpineer »