Bill Burke Recovery Training

Hulk

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Keep in mind that the vehicle above probably only weighs 6,000 lbs. You're not going to put 27,000 lbs of force on the tree when winching with the triple-line pull in that scenario.
 

DaveInDenver

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Keep in mind that the vehicle above probably only weighs 6,000 lbs. You're not going to put 27,000 lbs of force on the tree when winching with the triple-line pull in that scenario.
Indeed those numbers are at each connection point given a maximum pull of a 9k winch at the first layer. If the truck requires 6,000 lbf and not 27k to get unstuck then all the forces are reduced relatively but until you do an analysis you don't know.
 
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Inukshuk

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If you want to halve the work the winch is doing put the sheave on vehicle B in your scenario and connect the winch line back to the vehicle with the winch.

View attachment 84011

Notice though that the winch will still be capable of the full amount of force and the thing to watch is the point with the block in this case could actually see 2x that, so you need to do stuck analysis and consider safety, such as the recovery point strength and the need to use a bridle.
In the 9,000 lb pull above, single line would be expected to see 9,000, double to see 4,500 each, and triple to see 3,000 each. The tree should always see 9,000. But the winch sees 9,000, 4,500, and 3,000 respectively and the vehicle moving speed declines by 1/2, then 1/3.

To be clear, and Dave says it, the above example is of the potential "max load", so I agree with Dave saying "the winch will still be capable of the full amount of force and the thing to watch is the point with the block in this case could actually see "max load", so you need to do stuck analysis and consider safety, such as the recovery point strength." If your pull resistance calculation is off or the vehicle gets seriously hung up - which thus increases the total resistance. So a 9,000 lb winch could in theory exert a 27,000 lb load.

I'd also not leave my tree strap ends "open". Have the tree strap ends come together so in the event of uneven pull you don't yank the pulley or winch line round the anchor point.

Its hard to draw good diagrams!
 
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