Best knot for kevlar to screw eye for shock cord?

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Marc_G

Marc_G

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Hi folks,

I lost the nose cone of my Hornet a while back, due to the kevlar shock cord untying itself from the screw eye sunk into the nose cone. I had just used a standard double knot, and taped the leftover end back to the main cord, but clearly this isn't the best way. What knots do you use for such things. I'm talking LPR/MPR and think braided kevlar, if it matters. I've noticed that when using 1/8" kevlar I just got, which is heavier duty than what I'm used to, these double knots totally don't get tight.

It's time to up my knot game. What do you guys use?

Marc
 
Go to www.animatedknots.com

I use the 'improved clinch knot' and the 'polamar' more often then others. Look it up under 'fishing' on the home page and learn to tie them!
 
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The best, most reliable, and versatile knot for this application is called the bowline (pronounced boe-lin). It is a standard sailing knot, and one that everyone should know. It pulls tight under pressure and will not release when wet. Here is an example of how to tie it:

https://www.animatedknots.com/bowline/
 
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Everyone has their own favorite knot. Iv done a lot of rock climbing and we always use the figure 8 follow through knot when our lives are on the line so it must be good enough for my rocket. I also like that it forms a loop in my line so that since I have one harness for all my HPRs I just link the carabiner in and I am ready to go.

100 ways to skin a cat. Find the one you like that best.
 
Cyril's Scribe said:
The best, most reliable, and versatile knot for this application is called the bowline (pronounced boe-lin). It is a standard sailing knot,
Click to expand...

While true most pronounce it that way, I would not be hasty to say it is supposed to be pronounced that way. It seems that on a boat the line on the front of that ship would be called the Bow line and the knot for it the Bowline.

Dumb English pronouncing things weird.

(BTW I am more than happy to be wrong with the above statement, its just the story Iv heard)
 
bandman444 said:
While true most pronounce it that way, I would not be hasty to say it is supposed to be pronounced that way. It seems that on a boat the line on the front of that ship would be called the Bow line and the knot for it the Bowline.

Dumb English pronouncing things weird.

(BTW I am more than happy to be wrong with the above statement, its just the story Iv heard)
Click to expand...

The rope on the "front of the ship" is pronounced "bao line" (as in take a "bow", and "end of the "line")
The knot is indeed pronounced "boe lin" (as in tie a "bow", and the name "Lynn")

And yes, the bowline knot is a fine one for attaching shock cords. As is the figure-8.

I have a lot of background both as a rock-climber/rigger, and as a shipman/boatie - each of these groups has their own take on what knot works best for what application. For myself, whenever I need a knot or I'm doing some sort of rope work, sometimes I approach it as a climber, and sometimes as a boatie. And I will get praise and derision in equal measure from members of whichever group happens to be around.

One thing to keep in mind, that lots of folks don't realize, when choosing a knot - ANY knot will actually weaken your rope/line; some more than others. So, remember that your 750lb. cord will NOT hold 750 lbs. of force once you tie a knot it it. This is just one of the reasons you need much more strength in your line than simply the heaviest weight you need to hold. This link from Aerocon ( https://www.aeroconsystems.com/misc/muleknot.pdf ) shows a good alternative to use if you are pushing the strength limits of your shock cord when using webbing.

s6
 
I grew up with a Coast Guardsman father and we were taught a plethora of knots from an early age. The go to knot for me is the bowline, and I learned to tie it one-handed (one hand for the boat, one hand for me)

I use it for everything these days.

G.D.

Sent from my iPhone using Forum Runner
 
I just used the double overhand knot for my parachord to my eyebolt.I put a drop of white glue on the knot .
 
Cyril's Scribe said:
The best, most reliable, and versatile knot for this application is called the bowline (pronounced boe-lin). It is a standard sailing knot, and one that everyone should know. It pulls tight under pressure and will not release when wet. Here is an example of how to tie it:

https://www.animatedknots.com/bowline/
Click to expand...

I agree very strongly. I took a rigging class recently, and the bowline was presented as the preferred method of attatching taglines to the load. With regards to the knot pulling tight under pressure, the best wau to describe the bowline is as the opposite of a noose; the loop will not constrict when pressure is applied. Furthermore, it is important to remember that any knot tied in a rope will introduce a weak spot that can only handle 50% of the rope's rated strength.
 
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Anchor hitch (designed for permanently tying rope to an eye and to not be untied), followed by two (or three) half hitches, and then cover the knot with a short length of heat shrink tube. Kevlar cord is slippery and doesn't compress under pressure so it is more difficult to keep a knot in it. The anchor hitch is a good, secure knot, especially when it is finished off with a couple of half hitches. As the name indicates, it is used to tie a line to an anchor. The heat shrink tubing is a quick and easy way to "fix" the knot and to prevent the Kevlar from doing one of its favorite tricks, which is to untie itself.

Another good, secure knot to use in this situation is a buntline hitch.

Although it is a good knot, the bowline is intended to be a temporary knot (so that it can be untied) and is not as secure as it is made out to be. Under tension it is a secure knot but when it is not loaded it can be shaken loose. The bowline creates a non-slipping loop in a line (under tension it won't become smaller or close up), which has many uses but isn't necessarily what you need to tie a rope to fixed object such as an eye.
 
I have found that with certain Kevlar cords, the bowline has a tendency to work itself loose. If it is in a location I will not be able to inspect (like attached to a CR down in the airframe) I typically dab some epoxy onto it. Like the not itself, this likely weakens the Kevlar itself, but with appropriate cord is not an issue.
 
I am a fisherman, so I naturally gravitated to the uni-knot (duncan loop) or the improved clinch knot. Both can be undone in kevlar or TN with some effort and strong fingernails.

For nose cones, I have since move to the bowline because of its ability to be easily undone if needed. I think quicklinks are uneccessary weight in a rocket, so I like removeable knots instead.
 
I use a Uni-knot for most everything except when I need an independent loop (with no chance of cinching) then I use a Rapala knot.

BTW, Animated Knots has an excellent app for the iPhone so you can have the knot reference right there at the launch site!
 
I don't bother with knots. I sew my stuff. It's a basic loop through the eye bolt and sewing 30# braided fishing line to secure the end of the shock to itself. Hit it with a little CA and you're done.
 
Regardless of which flavor of knot you prefer - Figure 8, Water, Bowline, Surgeons, etc. - the best thing you can do is secure the eyebolt to the cord with a Lark's Head knot.

This prevents uneven loading of the looped end of the knot, promotes stability of the assembly, and is the prefered method of cojoining webbing loops in manned parachute assemblies.


All the best, James
 
I like the figure-8 because it's easier to remember than a bowline and because the two parts of the cord both end up in the same direction (ie- away from the nose cone). The bowline has one end that goes in the other direction.
 
Like many of you, I've used and tied lots of knots for many purposes and if you talk to anyone who has, they will have an opinion.

Yes there are some special situations that call for specific knots.
My own belief is that there are so many knots because sailors had quite a bit of free time on their hands and quite a bit of rope on hand to amuse themselves with.

With that said, here is my opinion:

Just about any knot you can tie with a dab of superglue to seal the deal.
A simple pair of overhand knots is incredibly strong. Add a dab of superglue and the deal is sealed.

I use 2 half hitches because they are easy to tie and rather compact coupled with the obligatory dab of superglue.
Oh and you don't need any rabbits, trees or holes to tie them.

Bones
 
Bone Daddy said:
Like many of you, I've used and tied lots of knots for many purposes and if you talk to anyone who has, they will have an opinion.

Yes there are some special situations that call for specific knots.
My own belief is that there are so many knots because sailors had quite a bit of free time on their hands and quite a bit of rope on hand to amuse themselves with.
Click to expand...

To be fair, I'd figure that certain knots, such as the scaffold hitch, were more likely developed by carpenters in the middle ages. I doubt that sailors would have much use for the scaffold hitch...
 
I use a bowline most of the time. I have found several ipad apps helpful on the field.
 
I use a double figure 8 knot. I also always use nylon harnesses and quick links. All of my rockets have their own full recovery system, harness and chute(s). The quick links are for separating sections of the rocket and for part replacement as needed. Any knot will weaken the material, Kevlar is much more subject to this. Adhesive on the knot weakens it even more, again Kevlar is real bad about this.
 
Don't need to use a fid...just use a 18" length of piano wire bent double.

Procedure:

  • Mark kevlar at finished length (where the end of the loop would be)
  • Mark kevlar where loop will enter back into line (usually, for these applications, 1" back from the finished length)
  • About 4" down the line, push the bent "tip" of the piano wire into the side of the line and into the hollow core
  • Feed piano wire up to the "entry" mark
  • Push piano wire out through the side of the line
  • Stuff about 1/2" of the bitter end into the fold of the piano wire
  • Pull bitter end into line, up through the core, and outside the line
  • Adjust until line is correct length
  • Cut line so that end is as feathered as possible (opposite of a right angle). This increases strength.
  • Pull the cut end back inside.
  • Smooth out and sew to lock fingertrap...only a couple of stitches are necessary, as they do not carry any tension. (there is a "stitchless" method that John Sherman taught me that I use often)


Using this method, a fingertrap takes maybe 15 seconds. Most of the time is spent measuring and cutting.

All the best, James
 
As both a climber and a rocket hobbiest, I use a grapevine (double fisherman's knot) on cord that is slippery and then throw a lark's head on the eye. On flat tubular nylon, I use a water knot to make a loop and then a lark's head on the eye. Make sure the knot is not part of the lark's head or on the bottom where you clip onto it with a quick link.
 
I use the following:

Water knot for webbing.

Figure eight for where I need a loop to attach a quicklink or similar.

Two-half hitch for attaching shock cord to nosecones, eye screws, whatever.

Double fishermans (grapevine) for joining kevlar to elastic.

As others have mentioned, Animated Knots by Grog is a fantastic resource.
 
Adding glue to a knot is going to weaken the line further. It does not allow the individual fibers to equalize load. Therefore the portion of the cord most tensioned will fail first, leading to a cascade failure. Materials with low stretch such as Kevlar will suffer to a greater extent than other materials in this regard.

Try good masking tape instead. For a bowline for instance, wrap the free end with a couple wraps of masking tape to prevent fraying. Now tape that to the loop with a couple wraps. The knot will not come undone without removing the masking tape first.

Gerald
 

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