No partner or ground guy yet

[Greener]

This weekend warrior has finally moved to utilizing a block in chunking down and need some feedback please.

On a dynamic load, I need some theories how much the need for WLL capacity increases for each foot a chunk of wood drops before it torques on the block? In other words. Is the weight of a log doubled for every ten feet it drops? Ok, I'll be honest, the block I'm using only has a working load of only 750 lbs. Any suggestions. (Don't worry, there is no house below and there is clearance way out on one entire side of the tree! Big drop zone.) The tree diameter is only about 14-16" across at the point I will be rigging.

 

[sgreanbeans]

No theories to it, its all math. Google it and read about vectors in force. If you have a big LZ, then let em run.

 

[ddhlakebound]

This weekend warrior has finally moved to utilizing a block in chunking down and need some feedback please.

On a dynamic load, I need some theories how much the need for WLL capacity increases for each foot a chunk of wood drops before it torques on the block? In other words. Is the weight of a log doubled for every ten feet it drops? Ok, I'll be honest, the block I'm using only has a working load of only 750 lbs. Any suggestions. (Don't worry, there is no house below and there is clearance way out on one entire side of the tree! Big drop zone.) The tree diameter is only about 14-16" across at the point I will be rigging.

As a very general guideline, you can multiply the weight of the chunk x the distance of drop in feet, but then you've gotta remember to add in the original weight after the multiplier.

Ex. 200# chunk, 3' of fall = 600#, + the original 200 = 800#.

Does this mean that the rig point will experience 1600# of loading?

No, not necessarily, because there are many other variables unaccounted for than the size of the chunk, and the distance of the fall. These include length and stretch of rope, flex of rig point/stem, how much run, air resistance, hinge usage and strength, (or lack of any of these), and more.

With a 750# WLL pulley, and applying a 10:1 safety factor, you shouldn't be dropping more than 75# on it anyway. In a good rigging scenario, that'll always keep your loads below WLL.

You mentioned a 14-16" rig point......Does that mean you're planning on dropping the top from that point into your rigging?

 

[ATH]

Just curious...If there are no worries about the landing zone, why rig them down? Can't you just cut and drop?

 

[Greener]

Just curious...If there are no worries about the landing zone, why rig them down? Can't you just cut and drop?

This customer does not want his lawn messed up and his patio is also within about 10-12 feet, opposite side from the fence.

 

[Greener]

As a very general guideline, you can multiply the weight of the chunk x the distance of drop in feet, but then you've gotta remember to add in the original weight after the multiplier.

Ex. 200# chunk, 3' of fall = 600#, + the original 200 = 800#.

Does this mean that the rig point will experience 1600# of loading?

No, not necessarily, because there are many other variables unaccounted for than the size of the chunk, and the distance of the fall. These include length and stretch of rope, flex of rig point/stem, how much run, air resistance, hinge usage and strength, (or lack of any of these), and more.

With a 750# WLL pulley, and applying a 10:1 safety factor, you shouldn't be dropping more than 75# on it anyway. In a good rigging scenario, that'll always keep your loads below WLL.

You mentioned a 14-16" rig point......Does that mean you're planning on dropping the top from that point into your rigging?

Ddhlakebound. Thanks for the excellent response. You know your stuff. Very helpful. Knowing this, I'm glad I just spent the money and bought a 4,000 lb block. With your analysis, which seems pretty logical, the 750 lb block will not be useful for me in most of my jobs. And, no, I had not planned to drop the entire top from where the trunk is 14-16 inches. I was just trying to give an idea of the size of the work that would be rigged at the middle section of the tree. I was planning to rig 1-200 pound chunks, but not with that block. I knew there are many variables but your post reminded me of all that is in play. Thanks again.
Colby

 

[BCbound]

Glad to see you grabbed a bigger block. Keep that little guy handy. The more rigging you do the more systems you'll have to invent. It'll be great for change of directions, keeping your rigging line in a clean position and light duty limb removals.