Progress capture - efficiencies of various devices

 

So, we have more than few options for ratchet devices. But which one’s best, in terms of minimizing evil friction in our MA system?

I did a simple observational study on the efficiency of different pulley, carabiner and ratchet systems, and found some to be dramatically better than others.

Here’s how I set up my study.

  • All 1:1 pull with a redirect through the anchor, no mechanical advantage

  • Fixed anchor point around head level, could be pretty much anything

  • About a 9 mm dynamic rope

  • 10 pound barbell plate

  • Various types of pulleys / ratchets clipped to anchor point

  • Inexpensive spring scale from Amazon, about $11, cloved to the pull rope, LInk: https://www.amazon.com/gp/product/B00ZWNGZFO/

The set up looks something like this. The scale is cloved hitched to the left side “pull rope”.

carabiner efficiency test.JPG

I set up the pulley or ratchet, then slowly pulled the spring scale to raise the weight and noted the scale reading during the steadiest pull I could manage. The measured force is approximate as I used a cheap spring scale, but I think it’s accurate enough to give a rough idea of efficiencies.

I tested pretty much every flavor of pulley or ratchet mechanism that I owned.

All of the pulling force listed below is for a 1:1 redirected pull of a 10 pound weight.


Here’s a summary of the raw data.

Screen Shot 2019-02-17 at 8.11.33 PM.png

and here’s a bar chart:

Screen Shot 2019-02-03 at 5.54.54 PM.png
 

Here are some takeaways.

  • Never use a garda hitch or ATC in guide mode as the ratchet. Friction is HUGE, it took about 60 lbs of pull to move a 10 lb weight! (If this is your only option as a progress capture, you’re probably better off setting up a separate 2:1 on the load to lift it, and then when the rope has some slack, use the hitch or ATC to capture the progress of the loose rope.)

  • Pulling force of round stock vs “I-beam” carabiners is pretty similar, not really noticeable in the real world.

  • DMM Revolver carabiners did not seem to reduce friction very much, comparable to a plain round stock carabiner in this study. (They were actually worse.)

  • 2 identical carabiners side by side did not change the friction much compared to a single carabiner.

  • If a prusik if jamming in your pulley even a little (as I had), it adds noticeable friction.

  • Using a 5.5 mm Spectra cordelette gave better efficiency than a 9 mm diameter climbing rope. This gave the best efficiency of 87%.

  • Pulley ratings from manufacturers are probably calculated under ideal lab conditions, and not under real world testing conditions like I tried to model.