bull rope advice

[Paul Smith]

14mm polydine for me all the way, great general purpose rigging rope, good for a ton I believe.

 

Hama, that's if you use the 5:1. I use it all the time with my GRCS.

[Tony Croft aka hamadryad]

Hama, that's if you use the 5:1. I use it all the time with my GRCS.

 

I take it you mean 1/5th of full breaking strain as working load limit?

 

as in 14mm polydine over 5000kg rating 1/5th of that being 1000kg or a ton.

 

and lets face it who rigs down over a ton in one everyday?

 

thats a rare job, easy to swith to a 16/19 mm and impact block for the cords:thumbup:

[Paul Smith]

The figures for 14mm from Yale are for the average breaking strain @ 6800kg divide by 7 = 971.4 . We should be working out the safety factor from the minimum breaking strain which Yale haven't given?

 

I totally agree, to rig a 1 ton lump we probably haven't got any gear in arb to do it safely!

[arbmark]

i've a whoopie sling, stein 2000. a 16mm pulley with a 16mm dead eye, a smaller pulley with slings etc and a old climbing rope at the moment.... not been putting big lumps on it though.....

 

if i went 16mm i'd have to upgrade to a 19mm dead eye.

 

i think 14mm may suffice but know 16mm would be the way forwards...... hmmmm

 

very similar predicament then! ive got the rc2000, 2 x 19mm slings and a 150kn block

 

what is wrong with my maths:

the highest strain is in the top pulley and sling so you choose your rigging line relative to their failure yes?

sling MBS rating => 9409kg = 90kn so safe load then is 9kn on textile

block - 150kn => safe load 30kn on metal

so the block is far stronger....the sling is the limiter

rope experiences half the load of anchor point so you can put no more than 4.5kn on your line. fine - 450kg

back to the failure - the rope has to fail before top sling (so well below half the slings MBS) so it should fail at no more 40kn

even a 12mm lowering line has a MBS of 40kN! should i get the bails string out!???!?

[Paul Smith]

Do you call MBS minimum, maximum breaking strain or even mean? There should be a set standard for terminology. All too often Kn and Kgs are cross referenced. Even rope diameters are in mm or inches!

[Tony Croft aka hamadryad]

Do you call MBS minimum, maximum breaking strain or even mean? There should be a set standard for terminology. All too often Kn and Kgs are cross referenced. Even rope diameters are in mm or inches!

 

doesnt help that the yanks havent gone metric:thumbdown:

[arbmark]

Do you call MBS minimum, maximum breaking strain or even mean? There should be a set standard for terminology. All too often Kn and Kgs are cross referenced. Even rope diameters are in mm or inches!

 

sorry guys just watched a film - i was thinking it meant minimum because that means the gear never fails, but in the case of rope failure we need the maximum to be sure the rope fails before the anchor as the rope is supposed to be the fail 'safe'. To my knowledge:

1kg =10N so

1tonne (1000kg) =10kn

 

i'm now thinking that my top sling i have isnt strong enough as it hasnt got more than twice the breaking strain of my rope.

 

so i need the 24mm sling (blimey!) which has a beaking strain of 17182kg = 170kn, this should comfortably hold when a 16mm 60kn braking strain rope doubled over (180deg)the block would fail

 

i may have this wrong but to summarise - if you want to run a 16mm rope you need a wopping great sling on the block to be sure the rope fails before the sling

[Tony Croft aka hamadryad]

I wanted to be sure of a 1 ton sling I had, so tested it to its limit! I know the limits of my gear, the KN is my guide but im always working WELL under loads so pretty low on the vital scale with regards to specifics. These new impact blocks from DMM are rated at 300 KN, you would uproot most trees with that!

[arbmark]

tony you're more of an intuitive guy than me - give it up and embrace you inner control freak!!!!!

its just that i have heard the whole thing simplified by saying you need a size bigger slings in the system than the rope but my maths head is telling me (on a saturday night!) that it needs to be bigger on the top attachment, so thats what i'm buying.

off to bed mate to escape myself!!!!

cheers

Mark

oh done your PTI yet mate? i passed - you'll breeze it barefoot

[Tony Croft aka hamadryad]

tony you're more of an intuitive guy than me - give it up and embrace you inner control freak!!!!!

its just that i have heard the whole thing simplified by saying you need a size bigger slings in the system than the rope but my maths head is telling me (on a saturday night!) that it needs to be bigger on the top attachment, so thats what i'm buying.

off to bed mate to escape myself!!!!

cheers

Mark

oh done your PTI yet mate? i passed - you'll breeze it barefoot

 

listen, basket your slings, it doubles them, splices instead of knots in the rope and everyones a winner:001_cool: