Double Whipped Tackle (DWT)

[Rupe]

Not sure if this has been discussed here or not. I learned it from Tom D at Tree Buzz. Many people have probably used it, but I just thought we could confirm the terminolgy as DWT instead of the many possible names for it.

 

Like with SRT, DdrT, Drt, RaDs etc etc. its best to all know what we are on about.

 

DWT, is a method of doubling the lifting power of your riggin device. Either GRCS, Hobbs or Regs new one, of for fiddle block lifting sytems that some use in conjunction with capstans and other none lifting lowerign devices.

 

By attaching a pulley on the object to be lowered, and passign the rope through and tieing off high in the tree you creat a 2:1 advantage at the load, this is thne in addition to the liftign advantage of your rigging device.

 

So the GRCS has an mechanical advantage (MA) of 44:1 (mine does, the newer ones are higher I believe) so adding a DWT give you 88:1, so your doubling the power available or halvign the power required depending on which way you see it.

 

A simple method is like this...

[Rupe]

Another great advantage of this is to create a "virtual" rigging point between two actual points. If you have two stems and the ideal drop zone is between the two then this sytem allows you to lower into that drop zone, even if you don't need the extra MA.

[Stephen Blair]

cool never done it, thanks

[Tom D]

Sounds good, however I'm always mindfull when using the hobbs that the weakest part of the rigging system is, in most cases, the tree, further increasing this load could be a litle dodgy.

Having said that for pulley setups such as the one that Reg does on his lowering device things it could be ideal. I reckon the hobs and grcs have too much power to try doubling it.

 

BTW have you ever found something the GRCS wouldn't lift? I haven't with the hobbs.

[slack ma girdle]

Do you not wory with all this extra mechcanical advantage, that you are going do overload the limbs that have to carrying this extra weight. As i seam to remember from my 41 training, when a rope goes over a pully you are doubleling the load to the anchor point. Or do you have a cunning method for dealing this

[Rupe]

Totally agree, loading is an issue, especially if the two anchors are far apart. This is where some maths would be helpful, but I'm not gonna overcomplicate stuff.

 

Basic rules of thumb is how I work and the rule here would be that if the stuff you are liftifng is that big then you should (in theory) move all you pulleys lower down the tree. You might start a dismanlt with pulley as high as possible but when you switch to bigger ropes and lifiting big stuff then you should think about movign the pulleys. After all the big stuff is lower and closer in to the tree and so the pulleys can be too.

 

The only limits I've found with the grcs are rope strenghts and rope slipping. 13mm can be wrapped more so doesn't slip but 16mm can only get three good wraps. Plus mine is a bit polished now.

[Rupe]

Do you not wory with all this extra mechcanical advantage, that you are going do overload the limbs that have to carrying this extra weight. As i seam to remember from my 41 training, when a rope goes over a pully you are doubleling the load to the anchor point. Or do you have a cunning method for dealing this

 

Your right, and part of the cunnign method is in my last post. Another thing though is that the load is shared on the two ropes above it, so if the load is doubled over the pulley it is still only equal to full load and not double it as it would be in normal lowering.

[Tom D]

 

The only limits I've found with the grcs are rope strenghts and rope slipping. 13mm can be wrapped more so doesn't slip but 16mm can only get three good wraps. Plus mine is a bit polished now.

 

Thats interesting, I can get 4 or five wraps of 16mm on the hobbs. Like you say you tend to move pulleys down as the job progresses. Although given a multi-stemmed tree I'll always (within reason) leave the thinnest stem till last and lower the second last off it, as that way you're butt hitching the smallest stuff and tip roping the heavy stuff, sometimes the last stem is even a cut and chuck.

[slack ma girdle]

I humbley bow to your worldly knowedge. I have got some fun rigging over a caravan this week, and i shall give it a go. And when it goes belly up i will know who to blame:marchmellow::bowdown:

[Rupe]

Although given a multi-stemmed tree I'll always (within reason) leave the thinnest stem till last and lower the second last off it, as that way you're butt hitching the smallest stuff and tip roping the heavy stuff, sometimes the last stem is even a cut and chuck.

 

Absloutly agree. You work out the best method for every job, and DWT off the smalles remaining stem might not work so you wouldn't use it.