Moving Rocks with High Lines and Levers

“Give me a place to stand on, and I will move the Earth.” Archimedes

Archimedes_lever_(Small)

While it’s not likely that Archimedes “invented” the lever, according to Plutarch he did help fashion block and tackle for lifting items into boats. If we don’t have excavators or helicopters, levers and block/tackle are still how we move heavy items on trails today, and I imagine into the future as well.

ROCK BARS

When did the advantage of using a lever first become apparent? Was the knowledge handed down by word, until finally written? I’m not sure, but rock bars are a staple tool for leveraging advantage for trail work in rocky areas. As shown in the image below, the ratio of the load arm to effort arm determines advantage, the most advantage being achieved from using the shortest load arm length practicable, or conversely the longest effort arm.

rock-bar-lever1

^60 inch class one rock bar lever set up

rock-bar-lever2

DRAGGING ROCKS WITH A GRIP HOIST

draggingrocks-side-view

Straight/direct or directional pulls, dragging rocks, and perhaps assisting with rock bars, is often easier than rock bars alone, though sometimes quite destructive as most things in the way get plowed under. Adding a block to get lift can significantly increase the ease of a pull as friction and tensions are reduced.

MORE ADVANTAGE

2, 3, and 4 times easier, but with 2, 3, and 4 times the strokes to move the same distance as a direct or directional pulldraggingrocks-2-1-ratio

HIGH LINES or TRAMWAYS

lester-kenway-first-highline-articleUsing high lines for trail work seems to have started with Lester Kenway in Maine, as way to move rocks far and fast without damaging sensitive habitat; and as means to not move rocks with rock bars. Lester wrote an article titled “New Rock-Moving Method Saves Fragile Terrain (Tramway System Used by Katahdin Crew),” which appeared in The Register (Appalachian Trail), Vol.13, No.2, April 1990 (original article).

My first experience with high lines was with Bellfree contractors when building steps for the Sea Dahlia trail in Palos Verdes, CA.

It was Lester though, who came for an SCA and Americorps training at the Welch Trail Education Center that really pushed me to explore high lines in greater detail. He also repeated the Archimedes ditty at the top of this page to us. Lester left enough information to inform, and enough to push me to go much deeper into the physics than most workshop participants would have the patience for.

I created this rigging handbook for the NYNJTC designed exclusively for trail work with Ama Koenigshof, a protege of Lester’s. The handbook contains everything I would post on this page. Rather than write it twice, I suggest a look at the handbook.

rigging-set-up-topIf you’ve seen my jump design and turn design calculators it’s obvious I like to apply physics and math to trail work, i.e. trail “science.” Perhaps my greatest accomplishment in understanding rigging use for trails was the eureka moment I had when laboring over this Excel Spreadsheet for the physics and safety limits of high lines: Rigging-for-trails-math-Excel.

It’s still a work in progress, but nearing completion in 4/15.

This older version needs updating, as it assumes VERY rusty pulleys, if not clamps, not pulleys: old version. What you see in the new spreadsheet began simply enough, but snowballed into something complicated, yet practical and useful for those wanting to use high lines to move rocks, and other heavy items.

Perhaps the only thing I have not explained in full in the handbook and  spreadsheet is this little item, the Sagitta:rigging-set-up-pathThe Sagitta is what caused the snowball to initially roll, though it turns out that I should have been thinking ellipse instead of circle…long story. Lester had talked about tensions, and even had a Dynamometer, but I failed to understand how tension could stay the same during the entire trip as the line angles would change, and therefore the tensions. I hypothesized the tensions would have to be unequal, except for the lowest point along the path, when both angles were the same (assuming the same block height), which is what Lester showed us on paper. He was right, I was mistaken…sort of. They would change, but not on each side of the fly block pulley. Turns out pulleys ‘equalize’ the tensions so they are the same throughout the fly line, but still, changing angles would change tensions. Realizing the missing information, I knew I needed to determine the arc of travel, which at first I didn’t know existed, or how to figure out…as the Taconic trail crew I worked with always said, “challenge accepted.” The challenge led me to use the stagitta, and in turn create the spreadsheet. I finally fully grasped the inner workings of high line physics…well at least as far as I wished to take it, but it was pretty far considering that I started with almost nothing and had to do a lot of research and deduction to arrive at the answers, and beauty of balanced equations….and then Wayne contacted me and the ball deflated, got patched, and started rolling again, but not without some resistance from me.  Wayne pushed me in a new, correct, direction, but there were a number of unknowns to still discover. Wayne thought I could help him with high line problems he was trying to solve, but first I had to leave the rust behind, so to speak, and rethink the variables involved in flying objects on high lines. The new spreadsheet is just that.

flying-excavator^image from from Peter Jensen, courtesy of Eddie Walsh of Tahawus Trails

I don’t know what more I can say here in regards to high lines, as the handbook and spreadsheet do most of the explaining. Enjoy, be safe, and you are welcome.

Belaying a big rock on a steep slope, no Portawrap

 

The big rock in the images below was moved with rock bars, the descent into place controlled with a belay line. At 150-175 lbs/ft3 the rock is approximately 3x3x1.5= 13.5ft3x165= 1220 lbs.

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