Perfection Loop knot - another way to tie it

[SolarYellow]

From a discussion of what knot to use in your Kevlar several months ago, I got turned onto the Perfection loop knot as a more secure alternative to the bowline.

https://www.animatedknots.com/perfection-loop-knot
The problem is, it's substantially more complicated to tie, and there isn't an easy to remember story about a bunny, a bunny hole, and a tree.

The steps at Animated Knots are good at demonstrating the geometry of the knot, but if you look at how the loop is actually formed there, it's a non-intuitive PITA if you want to end up with the loop actually passing through something, such as a swivel. Even worse if the loop you want your PL knot loop to pass through is part of something much larger. The way and the sequence by which the loop is formed in those steps makes it virtually impossible to accomplish in that case.

Today, I was repeatedly tying PL knots in light, 150-lb Kevlar cord, with other stuff in the loop. Got to the last one, and the tail of the cord was pretty short. It's unruly, as it's quite stiff and springy, so it's difficult to make it do what you want to do. Especially when you have XXXL hands and everything you're working with is smaller than your pinky nail.

As I was walking out to the garage to find my pointiest tweezers, I had a lightbulb go off about how to finish the knot. I think this overall is a much more intuitive and practical procedure for creating the knot than is illustrated at Animated Knots. Hope it helps somebody.

Start with just a simple overhand knot. Note that the standing part comes out of the loop on top as it head out to the left. You can then pass the working end through whatever loop you want it to hold when the knot is complete.



Pass the working end back up through the overhand knot's loop and back under the standing part.



Now, if you're working with bigger line and you can actually manipulate all the stuff with your fingers, pass the working end back through the knot from the bottom of the image to top, going under, over, under, over.

If you're working with tiny material, trying to make a knot a fraction of the size of your finger tips, feed the tweezers through from the top of the image to the bottom, going over, under, over, under.



Grab the working end with the tweezers and pull it back through. Then pull everything tight.

 

[robbied186]

That's a good idea! I was thinking of an idea of making a loop and gluing it and maybe putting a crimp on it. I fish so I have a crimping set. Maybe a heat shrink wrap?

 

[SolarYellow]

That's a good idea! I was thinking of an idea of making a loop and gluing it and maybe putting a crimp on it. I fish so I have a crimping set. Maybe a heat shrink wrap?

You're new here. Read some threads about Kevlar and knots. You can count on them to break if you glue them. I only use CA on the tails to keep them from fraying and make sure the glue doesn't get into the knot.

The Perfection loop seems more secure and less likely to untie than a bowline. I'm going to put several of them into service without any additional treatment but checking the rigging and snugging them tight before launches.

@cwbullet puts the heat shink sleeve over the Kevlar, ties the knot, then shrinks the sleeve. This gives it body to resist untying, increases the bend radius in the knot (thereby reducing the loss of strength said bend radius causes in the Kevlar), and protects it from ejection charges. Makes a lot of sense to me, though I haven't had a chance to implement it since he mentioned it.

@BEC has posted quite a bit about breaking Kevlar. He's even had it break right at the end of the heat shrink when using HS to protect it from ejection gasses. One idea I have had since reading that is to maybe not shrink the HS tube all the way out to the end. Leave the end unshrunk. Then the transition between shrunk and unshrunk is gradual, so it doesn't concentrate stress in the Kevlar. Kind of like the strain reliefs that are used on stainless steel braided hydraulic hose to pass the DOT "whip test" for automotive brake line use.

 

[Hobie1dog]

knots have always driven me crazy, all the way back to trying to learn the things, anticipating joining the Boy Scouts which I never did.

 

[BEC]

@BEC has posted quite a bit about breaking Kevlar. He's even had it break right at the end of the heat shrink when using HS to protect it from ejection gasses. One idea I have had since reading that is to maybe not shrink the HS tube all the way out to the end. Leave the end unshrunk. Then the transition between shrunk and unshrunk is gradual, so it doesn't concentrate stress in the Kevlar. Kind of like the strain reliefs that are used on stainless steel braided hydraulic hose to pass the DOT "whip test" for automotive brake line use.

That’s an interesting idea. I’ll have to give that a try the next time I’m adding heat shrink to a Kevlar shock cord leader. I mainly put it on to prevent abrasion at the lip of the body tube rather than as a heat protector, but the one that broke right after the heat shrink did surprise me.

 

[robbied186]

You're new here. Read some threads about Kevlar and knots. You can count on them to break if you glue them. I only use CA on the tails to keep them from fraying and make sure the glue doesn't get into the knot.

The Perfection loop seems more secure and less likely to untie than a bowline. I'm going to put several of them into service without any additional treatment but checking the rigging and snugging them tight before launches.

@cwbullet puts the heat shink sleeve over the Kevlar, ties the knot, then shrinks the sleeve. This gives it body to resist untying, increases the bend radius in the knot (thereby reducing the loss of strength said bend radius causes in the Kevlar), and protects it from ejection charges. Makes a lot of sense to me, though I haven't had a chance to implement it since he mentioned it.

@BEC has posted quite a bit about breaking Kevlar. He's even had it break right at the end of the heat shrink when using HS to protect it from ejection gasses. One idea I have had since reading that is to maybe not shrink the HS tube all the way out to the end. Leave the end unshrunk. Then the transition between shrunk and unshrunk is gradual, so it doesn't concentrate stress in the Kevlar. Kind of like the strain reliefs that are used on stainless steel braided hydraulic hose to pass the DOT "whip test" for automotive brake line use.

Yeah I'm not too familiar with Kevlar. Seems like its the way to go even in smaller rockets. I know I'm not using the rubber band shock cords anymore because they all rotted in my older rockets. The elastic cords aren't that great either I suppose.

 

[SolarYellow]

knots have always driven me crazy, all the way back to trying to learn the things, anticipating joining the Boy Scouts which I never did.

I've gotten by for decades just remembering the story of the bunny hole tree. Learned it from my soccer coach sophomore year of high school.

 

[robopup]

Excellent tutorial - I got mine to work following your pictures. Reading online, it sounds like it is much harder to untie than a bowline? Have you flown this yet? If so, what's your experience?

 

[SolarYellow]

I've used these rigs in a few LPR launches. Nothing has come untied or broken, but I wouldn't say I've really put it through the wringer yet. Knots still look good.

 

[robopup]

Copy that thanks. Yes, seems solid, I'm not worried about it coming undone. But have you tried to untie after a flight? (I untie things after every flight - don't use quick links, only loops in the kevlar). That's what I like about bowlines - super easy to untie, even after getting jerked around for 5 minutes.