Help me choose a proper knot

[Murphy625]

Hello,
I need help with choosing which knot to use for my application. I'm a newbie with this stuff.

We are pulling tree stumps on the farm using ropes and pulleys for mechanical advantage. I purchased 200 feet of Notch Kraken 5/8 rope (18,000 lb tensile), several 3/4 clevises, several snatch blocks, and tree saver straps... all rated for some pretty high forces.

We're using the farm tractor to pull on the rope.

So I learned how to splice a loop in the end of the Kraken rope and that worked out pretty good for the end of the rope at the anchor tree.. Then the rope feeds through my pulleys back and forth and then finally to the tractor where we use a clevis on the tow-bar.. Problem is, I can't figure out which knot to use to attach the rope to the clevis. We usually have an extra 50 to 100 feet left over so whatever I use, it has to work in the middle of the rope and I need to be able to move it after each pull. So far, my experience has shown that we make a pull and the tractor moves forward 50 feet or so, then we have to back up and adjust the tie-in point of the rope to take out the slack.

I tried the mid-line Alpine Butterfly knot and that sort of worked, but on our last pull it got jammed up pretty good and its going to take some time for me to get it unbound.. I'd rather not run into that problem again.

I also tried purchasing some 1/2 inch AMSteel Blue, which has a crazy high tensile strength.. I bought 6 feet of it and turned it into a Prusik Hitch. It was easy to untie and adjust, but I can see that its eventually going to melt and possibly damage my 5/8 Kraken rope. My Tractor weighs about 5000 lbs and working in our soil, I estimate it exerts about 3000 lbs of pulling force before the tires break traction and just start digging a hole.

Is there a mid-line anchor loop knot that would work better then the Alpine Butterfly? Easier to untie? Or maybe a device I can purchase that grabs the rope and is easy to remove?

Thank you to the experts!

 

[pdqdl]

You should not ever tie a knot in Amsteel. As you suspected, it will cinch down so tight it will melt and cut itself in half at the knot. It should only be used with spliced ends and winches, as it does not tolerate knots.

I presume that you are pulling in the direction of the "anchor tree". In order to capture the loaded end of the rope, you should rig up a prussic knot at the end of a rope separately tied to your anchor tree, running down and attached reasonably close to the block tied to the stump being pulled. When you pull with the tractor, your prussic knot will follow the line being pulled without interfering in any way, as it is not under a load. When you get to the end of your run with the tractor, slide the prussic knot down the loaded line as far as your anchored line will allow. Back the tractor up just a ways, the prussic will hold, then you rig to the tractor and tow again.

By the way: attaching a rope to a clevis isn't really a good habit. The clevis is probably too small a diameter to retain full strength with the rope, and it is easy to bind knots on as well. If you have a tow bar of some sort that is rigidly attached to the back of your tractor, just make about 5 wraps around a steel component that doesn't have sharp edges, then tie it off to itself with two half hitches. The steel will pull the load, and the knot won't be bound down so tightly.

There are friction devices used in the tree business that capture these forces and protect the rope from damage. Rigging one to the back of your tractor would be an excellent plan. If you were to attach a bollard of some sort or a portawrap to the back of your tractor, you could use "wraps" rather than knots, and almost eliminate the need for any fancy rigging. Once you eliminate the knots, Amsteel would be a vastly better rope in light of its great strength, light weight, ease of splicing, and it's reduced stretch.

Your Kraken rope has 1.8% elongation at 10% average breaking strength and is much stretchier than the amsteel, which comes in at .46%. If you were heavily loading down your tractor and the anchor point broke, all the tension on those stretched ropes would create a deadly projectile. So long as nothing breaks, your Kraken will be just fine otherwise. In that respect, Amsteel is much safer.

When I am using my amsteel rope (only 3/8th in. diameter) to pull out a truck, I always use the steel eye on the spliced end, and my porta-wrap to secure on the other end. When you don't yank suddenly, it's the best rope going. Do not under any circumstances shock load it, however. All that extra energy gets wasted on breaking your rope! This is another reason why Amsteel is completely unsuitable for regular tree work: it does a poor job of absorbing shock loads like falling logs. It's my favorite for hooking up my tractor a long way away from the mud hole my truck is stuck in!

By the way: 5/8th Kraken rope only has a 16,000 lb. ABS ratings. You must step up to 3/4" to get that 18k rating.

 

[pdqdl]

By the way, the prussic rope capture setup might go something like this demonstration.



Your pulleys are probably not well suited for that style of prussic, but you should get the idea.

 

[Franny K]

3/4 inch clevis seems small without a thimble. I would use as big a clevis as fits in the drawbar, go one and a half times around and then use a bowline. With a pair of pilers the knot can be undone.

 

[pdqdl]

That'll be ok, although there is no gain in strength when you go around more than a simple bowline. More rotations just create a shorter path for some fibers than others.

An anchor hitch (bend) would be cleaner and more appropriate.



Never seen one that needed pliers to untie. I use a stopper knot instead of the last hitch, and I put that on my carabiner to hang from a tree with. Sometimes. Other times, I put a double or triple fisherman on my carabiner, depending on the style of 'biner, because you are not going to untie a fisherman's knot unless you can slide the carabiner off.

 

[Franny K]

Maybe I should stop going around 1 1/2 times. Your knot there is all bunched up against the clevis. I was more thinking he wanted to go through the clevis and then back as far as possible towards the block and tackle. I guess you could have a long tag end on your anchor bend knot.

If one would use a trailer hitch ball with a shank the size of the hole in the drawbar instead of the clevis then my 1 1/2 turn thing would pretty easy.

Think what they have at a dock. Sure you hope they throw you a loop end but those things wrap it around a few times and no knot needed. Welding project to attach to drawbar.

 

[pdqdl]

Yes. The anchor hitch definitely bunches up on the clevis. If stretched down tight by testing the limits of the rope, it might be more difficult to untie. Like a bowline, it can generally be rolled out until it loosens up.

When I am using a vehicle to put a rope, however, I generally use a series of marls separated by a foot or more of free space. I don't remember the name of the knot, but I learned it in the Ashley Book of Knots. It never slips or lets go, and it never binds down and cannot be untied. Finding that knot in use on the internet has been impossible, and I've never been into making videos, so I cannot advise you further on that.

Eh... I'll try.

Allow this knot to take up about 6 feet away from your clevis.

1. Set your rope down parallel to the direction of your pull, then pull out about 6 feet of "tail".
2. About 6 inches away from the clevis, make a full marl in the loaded line, then pull the tail through it.
3. Going away from the clevis about 9 or more inches, make another marl, and pull the line through it.
4. Repeat as needed, at least 4 marls should be used, and I generally put in about 6.
5. Pull your line snug to the load, tugging on the tail as needed to balance out all the load on the different marls. If you carelessly yank the load without balancing out the pull on the marls, it will fall apart!
6. Pull your tree over, with the full confidence that the strange knot won't fail.

It will look kind of like this, but the tail of the rope is the dark colored rod, and you will be pulling the tail through the marls as you quickly twist them up with one hand:


And you pull on the line with the marls. Very easy when you learn how, not so easy to describe.