Rope / String Strength Question

[Jag-D]

Swarley said:

Oh and will it take off?

If you swing it fast enough....maybe

[egomeister]

Sounds like the knot is the weak point in test 1 (acting as a stress raiser on the string), and then in the second test the weak point becomes the string itself (although the two failures at the ring suggest that this may be artificially creating a weak point as in test 1)

[jagracer]

SimonV8ster said:

jagracer said:

It's osmosis.

Photosynthesis surely ?

That's what I meant

[mblade123]

Swarley said:

mblade123 said:

Your halfing the loading. Each length of string now takes half the load in the double configuration.
Although I do wonder why it snaps at 3Lbs and not 4.
If you had 2 more scales at the "grany knot end" you would find each should register 1.5lbs

I agree. But at one point (the ring) there is only one strand of cotton that can only hold 2lb. So how can it get up to 3lb at that point?

You would think so but thats not the case. Infact you are still doubling the string. If you had a roller in there instead of the ring it would be different again as you are increasing the MBR. ( Mininmum Bend Radius)

[Swarley]

mblade123 said:

Swarley said:

mblade123 said:

Your halfing the loading. Each length of string now takes half the load in the double configuration.
Although I do wonder why it snaps at 3Lbs and not 4.
If you had 2 more scales at the "grany knot end" you would find each should register 1.5lbs

I agree. But at one point (the ring) there is only one strand of cotton that can only hold 2lb. So how can it get up to 3lb at that point?

You would think so but thats not the case. Infact you are still doubling the string. If you had a roller in there instead of the ring it would be different again as you are increasing the MBR. ( Mininmum Bend Radius)

Ok then, So in that case my cotton could have a tensile strength of 3Lbs, but my knots reduce this to 2lbs. Then at the ring my cotton is working as if it was perfectly straight (ie capable of holding 3Lbs), and the 2 knots are working together (ie 1.3Lbs each).
So I would not have a week link, only slight differences in the cotton itself, this would mean it would never or be unlikely to snap in the same place. It doesn't so you must be right!

Thank you!!!!

[mblade123]

Swarley said:

mblade123 said:

Swarley said:

mblade123 said:

Your halfing the loading. Each length of string now takes half the load in the double configuration.
Although I do wonder why it snaps at 3Lbs and not 4.
If you had 2 more scales at the "grany knot end" you would find each should register 1.5lbs

I agree. But at one point (the ring) there is only one strand of cotton that can only hold 2lb. So how can it get up to 3lb at that point?

You would think so but thats not the case. Infact you are still doubling the string. If you had a roller in there instead of the ring it would be different again as you are increasing the MBR. ( Mininmum Bend Radius)

Ok then, So in that case my cotton could have a tensile strength of 3Lbs, but my knots reduce this to 2lbs. Then at the ring my cotton is working as if it was perfectly straight (ie capable of holding 3Lbs), and the 2 knots are working together (ie 1.3Lbs each).
So I would not have a week link, only slight differences in the cotton itself, this would mean it would never or be unlikely to snap in the same place. It doesn't so you must be right!

Thank you!!!!

Er No. Your cotton still has a breaking load of 2Lbs in single configuration. The breaking load increases if you double it up as you have, in effect, 2 pieces of cotton.
Oh by the way the rule is that you decrease the SWL (Safe working load) by 20% for a knot.
Example.
A 1t SWL strop choked around a pipe is down rated to 0.8t SWL.

Ref LOLER and North sea lifting

Edited cause I jumped the gun and didnt read your answer correctly lol

Edited by mblade123 on Wednesday 5th May 19:54

[CyprusCraig]

Reently done a banksman slinging course?? haha

Also depending on the angle of the lift aswell.

[mblade123]

CyprusCraig said:

Reently done a banksman slinging course?? haha

Also depending on the angle of the lift aswell.

Correct the angle is all important lol.

Stage 3 North sea lifting course.
Advanced Rigging and lifting.
Deck Foreman on heavy construction vessels.
LOL

[Swarley]

mblade123 said:

CyprusCraig said:

Reently done a banksman slinging course?? haha

Also depending on the angle of the lift aswell.

Correct the angle is all important lol.

Stage 3 North sea lifting course.
Advanced Rigging and lifting.
Deck Foreman on heavy construction vessels.
LOL

I defiantly found the right person for my problem then!

[mblade123]

mblade123 said:

CyprusCraig said:

Reently done a banksman slinging course?? haha

Also depending on the angle of the lift aswell.

Correct the angle is all important lol.

Stage 3 North sea lifting course.
Advanced Rigging and lifting.
Deck Foreman on heavy construction vessels.
LOL

Although my bits of Cotton tend to be 55mm thick and lift a couple of hundred tonnes

[working class]

I think the op is stringing us all along