Omni-Block 1.5

Thanks Sherwood.

Looking at green lot weights, I researched this a little more, and my eyes started to gloss over imagining how it would apply to tree-work.

Is there a simpler formula we could use that would apply to swing, and maybe one for drop? I know there are no accurate measures in our business; too many unknowns and variables. And I know we don't want to max-out our equipment. I'd guess we'd be best to stay at least a third beneath our threshold?
 
The easiest way to calculate loads is with the weight x distance of fall. In a drop of a piece of doug fir of average diameter 22".

Green log weight is: 103 lbs for a 1' section with 22" dia. Now you play with the length.

a 4' piece is 4 x103 = 412 lbs. Drop that piece straight down for 3' and you've got 1236 lb force. If it makes it easier round the weight to 100 and it is simpler and still accurate enough for what you want to do. That is the force that will be felt in the system if it were tied off. Or at least near enough for our purposes.

If that piece is swinging then the faster it's moving the greater the force, exponentially. The longer the radius of the swing (the more rope) the lower that force is on the anchor point of the rigging.

If you can do the basic calculation and understand some of the basic relationships between force, speed, distance then you can figure out the amount of load you'll be putting on your system and how close you may be to the SWL's.

To actually get into the real math you're getting into differential equations that involve momentum, stress, tensions, and all sorts of fun. Not the kind of thing that you can do in your head. If you can then may I suggest a career in rocket science instead of this.
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for sure. I have never seen a formula for figuring out how the force is distributed on a dynamic system(tree,rope,rigging,let it run). Prob would not understand the formula if I saw it... The static calculations are a good place to start. I just always try and doulble check myself anytime Im dropping big wood when butt hitching(insert your perfered name)Usually dont have to worry as much about the force when you tip tie. Also tip tie and butt tie(less swing). Best of all, have uncle smoothy working the lowering device. All the correct rigging stuff that has been talked about before. The big take home from all this, 300lbs isnt really 300lbs if you are dropping it into a rigging system.
 
Yeah, been doing this for 14 years and never really tried to determine even the log weight, much less the loads: except maybe when I first started in the business, and on crane jobs. But for the most part have either doubled up on rigging or cut smaller to guarantee we remain well within the SWL.

It's still nice to see how it's calculated even if just to appreciate the sheer force of the stuff we're working with.

Thanks again for the schooling.
 
For sure man. 14 years for me too. Always trying to pick up new stuff every year. I never really think about log weight either.( at least not in terms of lbs) just rig based on experience and situation. The biggest thing for me is making sure to listen when that little voice in my head says, "are u sure u want to cut it there...."
 
Doing the math in my head helps to keep it interesting and me focused. I try to remember the green log weight/cubic ft then figure out the log volume. then what the drop may be.

When the piece is slowed over distance then the load is distributed over that same distance and time. Friction in the system, dynamic v. static rope, amount of rope, distributed loads and the angles of the rope running from point to point (vector analysis). Having some fundamentals of math, physics and mechanics gives me a greater level of confidence in rigging systems and an understanding of how and why I'll set up a given system.

If nothing else, it makes the day go by quickly and I'm not prone to my mind wandering.
 
I learned this in 2012 from Eric ( oceans )....he knows some cool rigging stuff...was very creative til he got that damn GRCS...still is I guess...that dude always impresses me....
 
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