Funny but serious by all accounts!!

[Paul Barton]

DdRT is definitely a 2:1 system. Again it's one of teh advantages of it because when bodythrusting you shove yourself up a foot and pull 2 foot of rope through. You gain a foot for 2 foot of rope pulled through.

 

It can't be! If you pull 2 foot through but only go up 1 foot, your rope must be magically getting longer.

 

The double rope technique (that I am aware of) is a re-directed 1:1 system.

 

Look here: Pulley Systems | ropebook

[Amelanchier]

Well every day is truly a school day. The mechanical advantage gained by a system depends on where you are when applying the force - so yes a climber experiences 2:1 as he pulls himself up with each leg of the rope holding half his weight (i.e., you guys are right) but a ground based person pulling the same rope beneath the climber would only experience 1:1 - pulling on all the climbers weight (so I'm not entirely wrong... )

 

How about that...

Edited February 12, 2014 by Amelanchier
sp.

[Paul Barton]

Huh? I challenge you to explain that...maths was never my strong point. Or physics!

[BenR]

Huh? I challenge you to explain that...maths was never my strong point. Or physics!

 

The point you are missing is that you are attached to both sides of the line in a DdRT system. If the groundy pulls you simply become the load and the prussic is not loaded. Takes some getting your head around. I would suggest looking at taylor hamels videos on RADS discussion. It is a slightly different subject but the principles are applicable..

 

However, Ive never been pulled up a tree by my groundsman, so if using DdRT its a 2:1 in terms of the effort the climber puts in.

[MattyF]

The thing I find is climbing on a vt with rope guide I dont break a sweat to pull my self up and around a tree.. I try the same with SRT and working off a rope wrench and I end up a sweaty knackered mess... Maybe its to late for me to change but I would like to compare the two in a work climb with you one day Adam.

[Amelanchier]

Each leg of rope holding a static load must bear half the load. So if you are the load, then you only need to apply a force greater than half that load to move yourself. If you are not the load then you must apply a force greater than the load to move it. Simultaneously both a 1:1 and a 2:1 depending on where you are...

[BenR]

The thing I find is climbing on a vt with rope guide I dont break a sweat to pull my self up and around a tree.. I try the same with SRT and working off a rope wrench and I end up a sweaty knackered mess... Maybe its to late for me to change but I would like to compare the two in a work climb with you one day Adam.

 

That's because you are conditioned to climbing DdRT and have not going SRT planning and muscle memory down yet. Stick at it and it will come

[Gary Prentice]

Each leg of rope holding a static load must bear half the load. So if you are the load, then you only need to apply a force greater than half that load to move yourself. If you are not the load then you must apply a force greater than the load to move it. Simultaneously both a 1:1 and a 2:1 depending on where you are...

 

Each leg bears the full load Tony, the load has a force downwards equal to the force that is keeping it in situ. If you weighed a 100kg, threw a rope over a limb and put 100 kg on the other end you wouldn't move - balanced:thumbup1:

[Amelanchier]

Each leg bears the full load Tony...

 

Even when the load is attached to itself? If you had two legs attached to a static load through a pulley that'd be the same as a single leg surely? The anchor point couldn't be experiencing double until it moved? So the legs experience half then full load dynamically?

[BenR]

If you had two legs attached to a static load through a pulley that'd be the same as a single leg surely? /QUOTE]

 

Correct.. It all depends on the point of attachment guys.. Its not that complicated.