Abbreviations: A ... Anchor (e.g. tree) w ... Weight (e.g. slackline) T ... Tension Br... Resetable Brake
How to arrange the rope pulleys the best way? These are some basic and easy pulley systems to setup a slackline. Let's assume you are able to pull with a force of T. Depending on which of the following pulley systems you use, the slackline has a tension of four or five times T.
5:1 A
4:1 A T
2T
2T T
T T
2T
2T Br T
5:1 A
T T
T T
T T
2T
2T
T
T 2T
Br T
2T
T
T
T
2T
2T
5T
w
w
T
T
5T
4T
Br T
T
T
2T
T T
T T
T T T
2T
2T
w
How much force is on the brake? When you stop pulling the brake should hold the tension of the slackline. The force on the system - caused by "w" - is still the same as it was when you were pulling with a force of T.
T
T T
T T
T T
2T
2T
Br
2.5T
2.5T
1.25T 1.25T 1.25T 1.25T
T
^1 T = / 4 Fw
2T
1.25T
4T w
2.5T 5T w
2T
2T
T T
T T Br T 1.25T ^ = 1/ 4 F w
1/ ^ = 5 Fw T
T
T
T T
T
2T
Br
2T
5T w
What does this mean? You can tighten the slackline with... 4x
5x
The brake has to be able to hold... 1/ 4
5x ... times of your strength.
1/
1/ 5 ... of the slackline tension.
4
tlins
How to make a 15:1 pully system 5:1 3:1 A A A 2T
T T
T
T
Ph
2T
2T
T T
T T T Pr
Pr
T T 2T
T
T T
T
+
2T
... Prusik knot to haul the rope (connected to a rope pulley) ... a brake that can be reseted (e.g. Petzl I'D, Edelrid Eddy, ...) ... Tension ... Force on the resetable brake ... Force at the weight side (e.g. force of the Slackline) ... Anchor
5T
Ph Pr T FPr Fw A
T Ph
2T
3T
15:1 compound A
6T
(5:1)(3:1)
A
A
6T
3T 3T 3T 3T
2T
Pr
T T
T
T T Ph2 T 3T Ph1 15T
3T 3T 3T 6T
3T 6T
2T This part will be loosened during (to move the prusik Ph2) and at the end of the tensioning process. Pr has to hold the tension.
FPr=3T, Fw=15T
FPr = 1/5 of Fw tlins
Why not a 27:1 with the same components? 15:1 compound A
6T
(5:1)(3:1)
A
A
18T
2T
Pr
(3:1)(3:1)(3:1)
A
A
6T
3T 3T 3T 3T
27:1 compound
9T
3T Ph1 15T
6T
3T 6T
FPr=3T, Fw=15T
FPr = 1/5 of Fw
*
T
3T Ph3 Ph2
2T
9T Ph1 27T
T
T
2T
3T
Ph2 T 3T 3T 3T
T
3T
9T T T
2T
Pr
T
T T
A
6T
18T
6T *
FPr=9T, Fw=27T
FPr = 1/3 of Fw
!
There are many many ways to build much higher efficiency setups with the same amount of role pulleys used in the the 15:1 setup. But this assumes that we have an extremely high strength braking device. The only reason we have more pulleys before the brake (Pr) is so that we can reduce the load at this point in the system. The brake is typically the weakest link in the pulley system. So it's always best to limit the load here for safety reasons. The multiplicational part (*) will be loosened during the tension process and can be remove when the slackline is tightened enough. This means that the break has to hold 3T in the (15:1) system. That's a fifth of the force caused by the load or slackline (15T). For the (27:1) system it holds 9T. This is a third compared to the load-force (27T)! So the force on the (27:1)-break is 1.67 times higher than in the (15:1)-setup! tlins
45:1 compound A
(5:1)(3:1)(3:1)
18T
A
9T
Ph1 45T
9T 18T
A
6T
6T
A
A
6T
2T
Pr T
T 3T
2T
3T
9T
(9:1)(3:1)
T
3T Ph3
Ph2
A
6T
T
T 3T
A
2T
6T
Pr
9T
A
A
18T
27:1 compound
3T
3T
T
T
3T
T Ph2
6T
3T
3T
6T
Ph1
18T
27T
FPr = 1/5 of Fw
6T
6T
2T
6T
FPr = 1/9 of Fw
81:1 compound A
18T
A
(9:1)(3:1)(3:1)
18T
A
18T
A
18T
A
A
2T
6T
Pr T 3T 9T
9T
9T
9T
3T
T
Ph3 3T Ph2
9T Ph1 81T
9T 18T
18T
18T
FPr = 1/9 of Fw
T
T
2T
6T
18T
tlins