Knot Question

[Incongruent]

I've read the water knot can back off when not under load as well.

According to Wikipedia, it can.

"Once tied, for additional security each end should be tied in a double overhand stopper knot around the other standing end.

Some testing has shown that the water knot, in certain conditions, can slip very slightly but very consistently, with cyclic loading & unloading at relatively low forces; it is the tail on the exterior that slips (this would be the blue tail in the image presented here). In tests using 9/16 in (14.3 mm) tubular nylon webbing, repeated loading and unloading with 250 lbs (113 kg) caused one of the 3 in (76 mm) tails to work back into the knot in just over 800 loading cycles. Another test showed similar results for Spectra tape (but not for new, 1 inch tubular nylon). And yet the knot can be loaded to rupture without slippage. These results validate the need to leave adequate tails and inspect water knots before each use. With single overhand knot safeties on either end, the combination eventually seized and the slipping stopped.


Although used extensively in climbing and caving, there is some opinion that the water knot is unsafe. According to Walter Siebert, several deaths have been reported due to failure of this knot. In Germany, the knot is sometimes called todesknoten, which means death knot."

The bolded text is a possible remedy. The tails should be long enough.

 

[Woody's Workshop]

I use the "Animated Knots" website for learning knots, check it out. Here's the double fisherman's knot, which I use for tying tubular nylon to kevlar:
https://www.animatedknots.com/doubl...png&Website=www.animatedknots.com#ScrollPoint

At this website, the top right red circle, says home.
That's the knot I would use...what ever it's called.

 

[boatgeek]

A double sheet bend is super-easy. If you're concerned about it slipping, tie the knot and shake it around before pulling it tight again. If anything has moved, adding an overhand knot to the end should take care of it. I've found some Kevlar stiff enough that it wants to untie itself, but the overhand knots take care of it.

Also, the water knot discussion above (slips after 800 cycles of loading and unloading) is ... kinda overkill for rocketry. Let's charitably assume 8 load-unload cycles per flight as the rocket flops about right after ejection. If you haven't checked your knots after 100 flights, you're probably doing it wrong.

 

[qquake2k]

At this website, the top right red circle, says home.
That's the knot I would use...what ever it's called.

The Carrick Bend?

https://www.animatedknots.com/carri...png&Website=www.animatedknots.com#ScrollPoint

 

[MALBAR 70]

Okay, okay, I'll admit it. I can't tie a bowline! My dad was a Navy veteran, and he tried to teach me to tie it as a kid. I have some sort of mental block about it!

I feel your pain, I'm an Eagle Scout and can tie some of the more difficult knots with out even thinking about it. But a Bowline.....forget it! I always have to look it up and give myself a refresher.
For this application, I like the water knot too.

 

[OverTheTop]

The sheet bend was the one I was trying to think of for tying different ropes together. I would secure the ends somehow (I am an electronic engineer so I would probably use cable ties :wink: ) to avoid the knot unraveling.

Having said that, I can reliably tie a bowline and have been known to use that when I couldn't remember how to tie the sheet bend.

 

[Woody's Workshop]

The Carrick Bend?

https://www.animatedknots.com/carri...png&Website=www.animatedknots.com#ScrollPoint

I'm still learning my left from right...DOH
Top LEFT red circle on that main page.
Says Home under it. Sorry