# Double whip tackle



## Bradley (Mar 2, 2002)

Could someone explain what a "double whip tackle" is, what it's applications are, maybe other common terms for this setup. How do you guys use it and in what situations? What gear is needed to build and run it? I may know what it is but under a different name. Thanks, Steve.


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## John Paul Sanborn (Mar 2, 2002)

The DWT name was found in nautical rigging.

In our usage the working end of the rope is anchored then run through a block at another point so the the line runs ove the work area. A pullu or biner is place on the line so that the load can be attached.

This can be used a number of operations such as where a single rigging point can not be set atover the work, or where you want to rig up high enough that you feel you need to share the load between two points.

In normal rigging operations you need a rope that is greater then twice the distance to the rigging point. With DWT it needs to be greater then 3 times. Dont want the groundie holding ontop the rope end with the load still off the ground!

If you ask Mike Maas nicely he may dray a few varients.


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## Kneejerk Bombas (Mar 2, 2002)

Here's one deviant...err...I mean varient...


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## Bradley (Mar 3, 2002)

Thanks for the drawing, I've used that several times before, didn't know what to call it. I like the mechanical advantage advantage you get with it, but you lose it as the load is raised. Can you think of any more advanced variations of that? Thanks, Steve.


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## Kneejerk Bombas (Mar 3, 2002)

Here's another varient, have you used this one????


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## Joe (Mar 3, 2002)

It's funny the topic dwt would come up at a time Sherrill's has cmi pulleys on sale at 20% discount off their regular price. This would be a good time to invest in some pulleys and give this rigging configuration
a good trial run. 

equipment needed:

2 rescue pulleys with as large a sheave diameter as possible for the type of rope being used

2 carabiners-steel screw lock will work

Rigging sling for rigging point pulley-a whoopie sling will work. Set it up so the pulley can twist as the rope rotates or you'll ruin a pulley. 

rigging slings for load attachment, any slings Sherrill sells

extra-long work line

The dwt in the tree industry is a rigging configuration that creates a 2:1 mechanical advantage by employing the use of an extra pulley in raising or lowering limbs and wood. The power comes from the extra floating pulley which divides the line in half. Essentially, there ends up being 2 legs of line to hold the load.

With the dwt you 1)reduce all loads in the rigging gear. 2)incorporate more line in the rigging system which is always welcome. 3)reduce the speed of lowering which in turn reduces rigging point stresses during that time. 4) your ground people don't need to worry as much about burning their hands to control load decent. 5) you'll get a kick out of seeing the look on the ground peoples faces when they use it for the 1st time, especially the experienced guys. 

The system is not infallible and has a few problems of it's own. The parts of the rope with the floating pulley tends to twist on itself adding friction to the system. The only real remedy is to take the system apart, remove the twists, and set the system back up. Do I find it worth the trouble? Yes I do. There are more benefits to using this system than pitfalls. 

Here's a link given to me by Tom Dunlap which shows the double whip tackle(dwt):

http://www.alberta-ck318.freeserve.co.uk/tackles.htm

Have fun with this one.

Joe


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## rbtree (Mar 3, 2002)

Hey Mike,

Trying to get some blood flow to the head, eh?

Beats drinkin' on the job, i reckon! 

Better get Kwotica to pencil in some stomach rip to help u regain uprighticity.

Gotta love (and appreciate) your drawing and ideas.

Now try rapping out inverted, as my demented head tried friday.


...back to the padded cell........


Rog


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## rbtree (Mar 3, 2002)

Rare flowers.......
.
.
.
.
Cannabis giganticus?


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## X-man (Mar 3, 2002)

I agree with Joe on this one!

DWT can do things that a standard single block can't. I prefer to use it in most of my rigging. Depending on where you place the two anchors, your landing zone is established. It's added Mechanical Advantage aids in pretensioning the line, or lifting the limb(DWT(2/1) in tree-(4/1) or Rachet at base). The DWT can also be re-directed easily with a double-pulley choked off by a rigging strap. The Hockling or twisting above the floating pulley can be reduced by using a rated swivel at the dead-end. The dead-end can also be carried around in the tree to be reset for desired landing zones(like a traveling re-direct). I like clipping a large rigging plate to the floating pulley end for multiple straps. I try to balance out the limbs with two or three straps, and triangulate them into the plate. This lets your limbs come off clean and balanced(most of the time!) and decreases load on the system, plus it's always nice to know the limb is strapped by a two or more slings(just in case!). Tag-lines can also be added easily to the plate.
One thing is for sure, you don't want to rig wood off of it-self with DWT! The Standard single block slam dunk is still king for this. I think the extra pulley adds distance to the fall of the piece which would be more load, or so I think! Never the less, the pulleys can become cross-loaded or twisted in the fall which may be disaster. It works if everything is set perfectly in-line and there is no slackin the system from the bottom of the main anchor to the attachment on the above piece. I still prefer single blocking wood off of itself!
This system has made my work alot easier and allowed me, and my crew to do jobs safer and faster. I remember afew jobs that could of only been done using DWT. Glad I learned it! I do have a few pictures of DWT that I could e-mail upon request, and get some of the CMI pulleys for 20% off before I buy 'em all! 

Rigging it Down,
X-man


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## Kneejerk Bombas (Mar 3, 2002)

What's the deal with those CMI pulleys anyway?
Some are steel some are aluminum. Some are rated 10,000 lbs some are much less. Some have bushings, some have bearings. I'm so confused...they all look the same.
Does the rating come from the cheek plates, the size of the axle, or the type of bearing/bushing?

When I overload one of these light/med. pulleys I see the cheek plates bend where they hook up to the carabiner. Although, I have a couple CMI pulleys with fried bushings.


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## John Paul Sanborn (Mar 3, 2002)

Xian, howbout uploading the pics to the board?

There is an attache file option under the message input field.


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## rbtree (Mar 3, 2002)

Mike, there are 3 2.37" pulleys that I am aware of, and have each.

The only one rated at 10000 lb has steel cheeks. There are two alum. cheeked models, one with lexan, one with alum, sheaves. I dont think any of these have bearings. i have a four inch SMC with bearings, which aren't as good in gritty conditions. Plus it runs with no resistance, if you forget to tie off an unattended line, it may well zing its way out!!

I've never deformed the cheeks from overloading, but once twisted an aluminum one, which messed it up a bit. I've seen a four inch CMI pulley toasted from slam dunking wood onto it. Not the tool for that!!

Gonna get another 5/8 CMI from Sherril's and maybe a few more.

Anybody think of a use for the new double mini pulley?


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## John Paul Sanborn (Mar 3, 2002)

Watch tackle for asecnding while dead dog tired?

Prusick it as high as possible on the line, run through a single on harness put friction device on







MAybe someone else can adapt the sailing smack graphic.

hauling heavy loads into the tree with a WT.

I cannot see any rigging due to the bend ratio.


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## X-man (Mar 3, 2002)

I like the steel CMI pulleys with bushings for rigging(seem to take more abuse), aluminum with bearings for climbing(bearings give great action, and mainly used in cleaner areas). They make the double-ender single pulley which has attachment holes, top and bottom, great for running a 2/1 MA climbing system or a little extra pulling power for lifting. We used DWT once with our Hobbs to lift all of one side of a white oak up and over in pieces and back down into a small dropzone via tag-line. The limbs overhung and actually touched in some spots the OLD spanish tile that was formed on indians thighs! It was really cool, wished I could of speed-lined it instead, but there was No Access. DWT saved the day, and made it happen.... 

I would like one of those new CMI double pulleys that Sherrill is going to have for a retrievable re-direct I have for my climbing system. It would be perfect! 
I'll see if I can get the pic's off the site and post them here!

Hope this Helps,
X-man


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## John Paul Sanborn (Mar 3, 2002)

Let's see if this works Xian.


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## John Paul Sanborn (Mar 3, 2002)

I'm in netscape and can right clik on the pick click on "copy image location" and then paste it into the MSG


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## X-man (Mar 4, 2002)

*DWT Pics Link:*

Guys,


Here's a link to some of the pics, when I find the tape with the rest, I'll post them here! Enjoy!
http://community-2.webtv.net/acutabovetree/RiggingGallery/


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## John Paul Sanborn (Mar 4, 2002)

MAAAAANNNNN! It worked yesterday! [email protected]&*#)@)*#@*( internet falky BS!


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## TheTreeSpyder (Mar 4, 2002)

In adden-dumb- the 2/1 advantage can be maintained high, if the anchors are close together; such as one; or even a dropeye. In a 3/1 or other odd/1; there is an odd leg on one side that can be used to pull to that side.

Mike's second pic that is pulling the limb up hill with truck;is 1/2 because it carries the pulley on the pulling force, that splits the input power between 2 legs, one of which is an anchor. Thus, the load will move 2x as far in the same amount of time as truck (faster), it will have 1/2 power of truck's pull in trade; ie 1/2ma;fractional mechanical advantage.

There are 3 basic positions: input,output and anchor. If the pulley is on the input it splits that power between load and anchor; the anchor 'consumes' 1/2 the pull(1/2power=1/2ma; 2x as fast in trade). If the pulley is on the load; it splits it's forcebetween input and anchor; the anchor is holding 1/2 the load(2xinput=2ma;1/2speed in trade). If the pulley is on the anchor (redirect) it splits it; with equal pulls on each leg (2xload=1mano speed or mechanical advantage). These figures assume 0 friction; though always present.

All these things can be explained by the Law Conservation of Energy; this law also defines why screws, ramps , levers, gears,impacting etc. Understanding this and friction can take you very far with motion studies


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## Tom Dunlap (Mar 5, 2002)

Mike,

This morning I put my glasses on and looked at your picture. Ooops...I goofed. Sorry 

You're right, I was wrong...

Tom


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## Kneejerk Bombas (Mar 5, 2002)

I disagree, big mechanical advantage, the load moves twice as far/fast as a single rope.

It's not always about lowering the load, when you have too much power and not enough speed or distance, this is the ticket.


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## rbtree (Mar 5, 2002)

Good discussion,guys, I edited my rather basic comments.


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## TheTreeSpyder (Mar 5, 2002)

The mechanidal advantage is fractional i beleive; ie. 1/2 power therefore 2x speed; from same input.

This is because 1/2 the pull is exerted on anchor, and 1/2 on load; because the input is divided between these 2 by pulley on truck. As the truck pulls forward 1'; it shortens both legs into the pulley by 1' at same time; therefore truck will move forward 1' and load will move forward 2' (if line is already stretched); in the same amount of time as truck moves forward. This is where the speed comes in, as it is traded for power. So this could be used for shorter pulls than load movement and speed; when there is reduced run for input; but loads more power than needed; the opposite of having plenty of run; and not enough power.

Mechanical advantage is a multiplicative operation; whereby "0" advantage is more properly expressed as "1"; 2x power as 2/1; 2xspeed as 1/2. The resistance of any load is a set, singular number to be overcome by force; anytime the input moves a diffrent measured amount than the load; the ma is not none or "1"; it is either fractional or positive. If the input effort moves farther than load, that input energy is concentrated into a shorter distance; power increases; mechanical advantage is positive. If the input effort moves a shorter distance than load; the power of the input is 'diluted' over a longer distance; ma is fractional, power drops; but speed increases in trade. Since the load that must be overcome is a set number that = power x speed; as one of the 2 multipliers change; the other must change reciprocally to still equal same force/distance in time needed to move a given load. In other words; irrespective of friction, in simple (non-compound) machines; the change in power x change in speed will equal 1. ie. a 2/1 will move 1/2 as fast; so the total effort to move a given load will be the same; just manipulated bertween speed and power. Putting 2 mechanical advantage systems on a load parallel to each other will increase their power arithmetically; putting them in series (compound) will increase their power geometrically.

If you learn to see this daily in levers, screws, ramps, gears etc.; it will be easier to see and decode from our operations. For it is all the same; exactly the same but diffrent: trading back and forth speed and force to equal same product in an equation.


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## TheTreeSpyder (Mar 6, 2002)

Joe and i were conversing on simple physics and he suggested that i post these 2 web sites:

http://www.sciencejoywagon.com/physicszone/lesson/05work/consofenergy.htm 

http://www.sciencejoywagon.com/physicszone/lesson/05work/workpower.htm

Of course if you took the open system (control line off load); and put a climber on the lowering pulley; gave the climber the control line (closed system=control line attatched to load; doubling as another support leg) it would make the 2/1 DWT a 3/1. Write?

If you use a dropeye pulley (my favorite) on the anchor; with another pulley on the dropeye; you can redirect the terminating end from the dropeye back to the load. This would give 3 lines of support on load for an open system; 4 if a closed rig; for 3/1 or 4/1. Looking at single anchors here.

Raising from 2/1 to a 3/1 will put less pull on the anchor per same load in an open system. In a closed system the pull on anchor will be = to the load itself. In an open system the pull on anchor will always be greater; than the load. Looking at single anchors, no friction here, ground controlled.

The pull on anchor, open system, with pulleys i beleive could be expressed as = (load) + (load x (the inverse of the mechanical advantage)). That would be 100# [email protected] 'no' mechanical advantage would be=(100)+(100x(1/1))=200#. For 100#@2/1 that would be =(100)+(100x(1/2))=150#. For 100#@3/1; anchor pull would be = (100)+(100(1/3))=133etc. So another considerationfor using a mechanical advantage system; is manipulation of anchor load as well as direction,distance ,time (speed) and power.


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## Joe (Mar 10, 2002)

You posted a reasonble reply KC. You're math seems to work for figuring overall rigging point loads when using pulleys for rigging. Another point in your post you didn't mention was the fact the rigging point sling needs to handle no more than the load instead of twice the load.

I've figured in the past a system using pulleys with 2" diameter sheaves(the small cmi pulley with steel cheek plates like at Sherrill) and 1/2" 16 strand line(breaking strength new=7000 lbf) to handle about 900 Lb•ft of work with many cycles to failure for the dwt. This means one can do quite a bit of lowering with this system without fear of the system failing.

The best part about the physics links you posted is they're very easy to understand.
The concepts jump out at the reader and there is no misunderstanding which concept is being discussed. If one is being introduced to physics for the 1st time, this is a good link for which to start learning. It's also a good and quick review for the people who've forgot the material.
Thanks for sharing them.

Joe


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## TheTreeSpyder (Mar 10, 2002)

Hmmmmmmm thanx Joe................

But, i would think that the sling on the anchor would carry the same load as the anchor. Actually, that the anchor, sling, biners, pulley etc.; would be taken as a 'redirect' unit, ie. all carry the same load? So, that in a simple redirect, no friction, 1/1, they all would be carrying 2xload? 

Personally, i prefer the 2.37" pulleys from Sherrill. For as the numbers expressed by Samson; for a 1/2" braided line; the percentage of maintained line strength is up 20-25% over the 2" pulley. Also, 5/8 can be run through them; and they are rated at a higher capacity characteristically. i think the dropeye is the most flexible; and use it as a standard pulley, on my belt.

Still don't understand your previous statement that a redirect with friction puts more load on anchor than redirect without friction (pulley). It seems to me that the total load on anchor would be sum total of all lines (support and control) of pull. On a pulley that would match load, with friction, brake force on control line would be less i think. Wereby if total stopping or braking were employed at anchor; control line load would reduce to '0', and anchor would only bear force of load, as there would be no brakeforce redirecting to ground. As, less friction was allowed on anchor, control line would have to make that up to maintain enough brake force to control load, as this force is on contrlo line pulling on anchor, load on anchor increases; to my feeble way of thinking...............


i also have quite a lot of success with choking a sling and pulley on a vertical spar and and using as a back up anchor for delivery point anchor; place over lwering zone. In this way i can adjust somewhat how much each anchor carries by sliding system up and down on the spar, adjusting for diffrent loads and primary anchors around the tree from this central point. So an anchor point that is excellent for where it lowers too, but questionable for load; can be used with this backup support! Also, in this way, rigging line runs in upside down "U" rather than "V"; keeping groundies from being pulled into load.


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## Joe (Mar 10, 2002)

> _Originally posted by TheTreeSpyder _
> *Hmmmmmmm thanx Joe................
> 
> But, i would think that the sling on the anchor would carry the same load as the anchor. Actually, that the anchor, sling, biners, pulley etc.; would be taken as a 'redirect' unit, ie. all carry the same load? So, that in a simple redirect, no friction, 1/1, they all would be carrying 2xload?
> ...


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## TheTreeSpyder (Mar 22, 2002)

Thanx, for correcting me on that Joe!

i just assumed that the rated diameter of the sheave would be of the necessary info for calculating line percentage strength! Especially when rated that way by a manufacturer of both line and device! But as you pointed out i missed that in "Arborist Equip.". And it is no small diffrence to me for i still state this is the part of the graph were the line strength is decreasing quicker per drop in sheave diameter! So in my mind; putting a 1"pulley on a 1/" line to load is really pushing it, especially with human cargo! 

As far as not using a 5/8 line in these pulleys; it kinda goes both ways i think! i wouldn't load them with 5/8 singlely because of the small bight per rope diameter. But, in an application with 2 anchors; like super strong high anchor, sending force straight into ground all day; then 'floating' one of these pulleys around with the 5/8 in it; placing it to run off another anchor too; in this way loads are shared, and the line doesn't make such a sharp bight, so is safe i believe. This is a very strong, flexible strategy for working diffrent loads to diffrent positions, with less swing all day.

One interesting way i've used it is to make the 'primary' anchor (the one the load lowers directly from?) a springy limb for rigging slight lift. Pulling tight gives 2/1 on tightening this spring; till it got 'bow' tight of course. But it can help pull around a hinging load horizontally by taking up line slack! In doing so the 'primary' anchor bends down some; the lower it bends the more the 'other' anchor takes the load for it is now higher in comparison! The 'other' anchor can also be backup in case of total failure. i find these to be very interesting features to manipulate! And once again as i can understand the flow of the math; can make informed decisions.

See ya; gonna go play!


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