In the last two articles, we focused on the foundation of mechanical advantage systems (MAS). We also touched on both anchor and belay systems. By now you should have a good base of knowledge regarding these topics so we'll dive into some of them a little deeper.
Our main focus in this article is going to be anchor systems. Simply put, without a good anchor system nothing else is possible.
We previously discussed anchor classifications. Those classifications being bomb-proof, questionable, and manufactured. Remember, we're always going to strive to achieve the bombproof rating. It may take some redirecting of ropes but as a wise chief of mine once said, you can "make it happen."
One of the most important features of an anchor system is the angle you create building it. This will apply to all anchor systems and their components.
Let's first look at a basic cache of anchor systems you should know inside and out.
Look at the single point anchor system. This is created by attaching the rope itself or the rope via an anchor strap to a single anchor point such as an I-beam or cement column. The load is focused on a single point.
If the load I was supporting or hauling was 500 pounds the anchor would see a load force of 500 pounds. If you choose to utilize a single point anchor system, one method that works well is referred to as a tensionless wrap. A tensionless wrap works by utilizing friction and here's how.
The rope is wrapped around the object a minimum of four to six times. Smaller anchor objects will need more wraps to achieve the needed friction. As the load force is applied the torsional load placed on the wraps causes them to tighten and form a secure anchor system. The terminal end of the rope (the piece you used to wrap the anchor with) will have a Figure 8 Bight tied in it and will get connected back onto itself (see Figure 1.)
One of the biggest positive characteristics of this anchor method is because the wraps take all the force and the rope itself retains 100 percent of its strength.
Anchor straps and slings also work well for single point anchor systems however you must ensure they are of the proper length to avoid unwanted directional loads on the software (see Figure 2.)
We must touch on critical angles or the angles created by components in our anchor system.
If you look at Figure 2, you will see a triangle is created by a length of half-inch static kernmantle rope. That angle should stay between 45 and 90 degrees.
Let's take a load of 100 pounds. If we create an angle of 45 degrees each side of the anchor strap will see about 52 pounds. Let's increase the angle to 90 degrees, now each side of the anchor strap will see a load force of approximately 70 pounds. If we take that angle and bump it up to 123 degrees, the load force on each side of the anchor strap is now around 100 pounds.
Look at the bigger picture. Those loads are transferred back to the anchors and anchor system components. The less stress and unneeded load force we create in our system, naturally the better off we'll be.
Now that we've talked about angles created in anchor systems and the importance of keeping them within the suggested guidelines let's move onto more means of anchoring.
Webbing is a tool you can use to create anchor systems with. Webbing is strong by design. You'll find webbing in two forms, flat and tubular. One-inch tubular webbing has a load rating of 4,000 pounds, where as one-inch flat webbing has a load rating of 6,000 pounds. One-inch diameter webbing is probably the most popular choice for rope rescue operations.
The "wrap three, pull two" is a quick efficient way to create a strong single point anchor system (Figure 3.) One-inch tubular webbing is used which is rated for four thousand pounds. By wrapping the webbing around the anchor object three times then pulling two loops of the webbing to create a connection point, we create an anchor system rated for approximately 16,000 pounds.