Strength of a knot takes out of climbing line?

[MOG]

So was wondering how much a well dress corretly tied knot, will take out of a climbing line.

 

e.g climbing line 2700kg, knot takes out 1000kg and then splice in end takes out 200kg( = full strength of climbing line 1500kg) or will it just break at

1700kg due to the knot?

 

be helpful if some one could give a exmaple like this but with the correct answer and rating on true strength on rope and knot.

 

1. Bowline?

2. Double Bowline?

3. Alpine Butterfly?

4. Fishermans?

 

be handy to know, cheers matt

[Frank]

any knot reduces tensile strength by about...........erm............wait for it.............cant quite remember now.

Think it is by between 40 and 60 percent.

Scary huh???

[Frank]

why would you have a knot and a splice???

you would have to take into account how worn the rope is aswell.

[Dean Lofthouse]

Lesson Number 1

 

Can you explain WHY a knot takes out strength wee Franky ?

[arbclimber]

Lesson Number 1

 

Can you explain WHY a knot takes out strength wee Franky ?

 

I know, I know. Can anyone answer teacher Dean:laugh1:

[Dean Lofthouse]

I know, I know. Can anyone answer teacher Dean:laugh1:

 

Of course !!

[geoff]

The reduction of two knots dont compound to weaken the rope,but the knot with the bigest reduction in the system is the one that would be relevent regarding max break or SWL.

Otherwise you could put three or four knots into the system and it would (with a 30% loss) fail under its own weight!

 

 

Knot Break Strength vs. Rope Break Strength

[arbclimber]

Of course !!

 

Obviously due to the bend in the rope. But i think it is more specifically due to only a small portion of the diamater of the rope taking the load. Its a bit like tension and compression in wood. The inside of the bend takes little load, with the outside being under tension taking most of the load. As the very outside is loaded severely it can cause a shearing action.

[Dean Lofthouse]

Spot on.

 

What is interesting is most ropes fail just outside the knot, not within.

 

Which would explain the fibres entering the knot on the outside of the radius taking all the load.

 

This was interesting and so is the knot, a blood knot.

 

Google Image Result for http://www.allaboutknots.com/html/7_breaking_files/image004.jpg

[geoff]

I seem to remember that if a rope is shock loaded,then you get friction/heat,and also a distortion of the rope structure by the tightening.