Rope Wrench feedback

[Old Mill Tree Care]

Ddrt only puts your weight on the anchor point, where as a base anchored Srt system will exert 2x the force on the anchor point thats why its encouraged not to isolate your line, i wouldnt say you could exert the same force Ddrt on your anchor point as you could with a base anchored srt system.

 

Yes that's correct.

Draw a picture and that will explains it.

[Ewan Murray]

Yeah i was looking for a good diagram, on the web but couldnt find one.

[Tommy_B]

Yeah i was looking for a good diagram, on the web but couldnt find one.

 

I'm not trusting your drawing skills mate!! haha!!

[Ewan Murray]

I'm not trusting your drawing skills mate!! haha!!

 

Haha good point mate

[WorcsWuss]

Presumably the amount of friction around the limb will affect the amount if force necessary on the opposite side to counter act the force from the climber?

[Ewan Murray]

Presumably the amount of friction around the limb will affect the amount if force necessary on the opposite side to counter act the force from the climber?

 

Well the rope is static so i dont think it would make a difference.

[WorcsWuss]

Well the rope is static so i dont think it would make a difference.

 

True, but presumably a large limb with say 400mm of rope in contact with it will exert an amount of friction on the rope which will reduce the force required to resist the force, the same principal as using friction to lower cut timber....?

And I guess a smaller diameter limb would create less friction requiring more force to counteract the exerted weight. Only over a friction free pulley would the force be the same both ways. But I would still have thought half the exerted force, the main principle behind ddrt?

[WorcsWuss]

Not arguing by the way, just want to make sure I fully understand the principles behind it!

Explanation appreciated!

[Ewan Murray]

In DDrt you are your suspended over a limb so you have a hundred percent of your weight on that limb then the load is shared between your spliced eye and friction cord etc, the friction at your anchor point wouldnt change the force exerted on said point just allows you to hold your weight as the branch takes some friction, Imagine how much friction it would take in order to hold 100 kg with the other end not attached, i think the friction on the branch would make an almost negligible amount of difference, the most important thing in SRT or SRWP is understanding the forces behind what you are doing and knowing your tree species. When anchoring over more than one branch its important to remeber that you could be pulling the stems together or exerting force over the weaker axis of the tree so just be smart and climb safe!

[WorcsWuss]

In DDrt you are your suspended over a limb so you have a hundred percent of your weight on that limb then the load is shared between your spliced eye and friction cord etc, the friction at your anchor point wouldnt change the force exerted on said point just allows you to hold your weight as the branch takes some friction, Imagine how much friction it would take in order to hold 100 kg with the other end not attached, i think the friction on the branch would make an almost negligible amount of difference, the most important thing in SRT or SRWP is understanding the forces behind what you are doing and knowing your tree species. When anchoring over more than one branch its important to remeber that you could be pulling the stems together or exerting force over the weaker axis of the tree so just be smart and climb safe!

 

 

Still don't get it, I never was much cop at applied mathematics and engineering....!

 

What I can't fathom is how one end of the rope being attached back to the climber makes any difference to the force applied to a limb when compared to one end of the rope attached to a static point.... I'm having a thick day!

 

Ref the tie in point, if a limb is suspended by natural rigging with a rope thrown over a branch, a small amount of friction is generated to aid controlled lowering. If the piece you're lowering is heavier, you take a couple of turns round it to reduce the amount of force needed in the tail of the rope to lower it, same principal as a capstan. So the force on the tail (or theoretical base anchor) is reduced, but the force on the limb you're rigging from remains the same.

 

So while i understand the reasoning, i can't understand the maths which mean a 100kg suspended on a loop from a point exerts 50kg down each leg, 1kn in total, but if you unclip it from itself and fix it back to a static point all of a sudden it generates 2kn of force on the limb...? (Have I got the units right there?)

 

This is why I use structural engineers when I'm designing a building!!