In rock climbing, whether you use the SRENE/ERNEST system, or another method you may have learned, the fact is you should always use multiple anchors. It does not matter if you are trad climbing, top roping or sports climbing. Two anchors are the minimum for rock climbing. Three anchors won't hurt you either.
Creating rock climbing anchors is, in fact, creating a dynamic engineering systems to handle a suspected or expected maximum impact force. As with all dynamic systems, the need to build a system that multiplies the load handling capability is required. You would not build a step ladder that would only hold your weight, you would build one that can hold a great deal more than your weight. The same is true of climbing anchors. Given a choice you should build yours with a 2:1 or better safety factor. If you can generate almost 3,000 pounds of energy you better have a system designed to take a least 6,000 pounds.
We've all heard stories about people taking a 20 ft. flyer on a #1 stopper. These people are just plain lucky. A 150 lbs. climber taking a 10 ft. fall generates roughly 1,100 lbs. of energy. A 180 lbs. climber has the ability to generate roughly 2,900 lbs. on a major fall of 20 ft. or more.
Components of an anchoring system
9.8 mm rope 1,825 lbs.
10.5mm rope 2,025 lbs.
11 mm rope 2,090 lbs.
locking carabiner 4,950 lbs.
non-locking carabiner 4,500 lbs.
6mm cord 1,500 lbs.
7mm cord 2,090 lbs.
8mm cord 3,150 lbs.
5.5mm spectra cord 3,800 lbs.
19mm climb spec webbing 4,900 lbs.
9/16" climb spec runners 2,250 lbs.
9/16" spectra runners 6,075 lbs.
1" tubular webbing 4,000 lbs.
Rawl 1/2" x 3" bolt 7,300 lbs.
Rawl 3/8" x 3" bolt 5,200 lbs.
Hilti 3/8" x 3" bolt 4,500 lbs.
Petzl 10mm x 61mm bolt 4,000 lbs.
This is impact force, not weight.
As we can see from above, all but the 9.8mm-11mm rope and the 6mm-7mm cord can withstand an impact force of 3,000 lbs or greater. The 9.8mm-11mm rope can actually handle heavier loads due to it's dynamic ability. By stretching, it distributes the load over a larger area and distributes some of the heat and impact on the rope. However, you must take into consideration these tests are only estimates, done in laboratories, under ideal conditions, using brand new materials. Very far from the real world. If you take as an example the 1" tubular webbing add a knot or two, 4 or 5 falls on it, a year of rough edges, grit, rain and sunlight it's strength may be reduced to 25% of it's original strength or about 1,000 lbs. Not enough to hold a leaders fall. Not enough to safely top rope either.
It is obvious that a single anchor point is not secure enough to protect a climber even in a top rope situation. In Part II we will show you some of the methods used to equalize your anchors.
SETTING A TOP ROPE ANCHOR USING THE ERNEST SYSTEM
Anchor: Where you are actually attached to the rock, tree or bolt hanger Anchor Point: The place where all anchors converge to create a single point for suspension
Determine your Anchor Point. This is the place where you want the rope to hang from. Avoid or pad sharp edges. Make sure the rope is not running over the rock or edge (if possible)
Make a through check for anchors. Look for trees, horns, large boulders or flakes. If you can not get at least two 100% solid anchors move to a different climb.
Begin to build your anchor point in ERNEST
All anchor points should be sharing the load, try to have the anchor point match in overall length
Make sure that you are backed up in every part of your anchor. Have at least two anchors
If you choose one very large and solid anchor, use more than one piece of webbing
Use two (2) locking carabiners for the anchor point, make sure that the gates are OPPOSITE, OPPOSED and LOCKED
If you are in doubt about your anchors add another anchor. 2 is better than 1 and 3 is better than 2
* No Extension
Try to eliminate or minimize any movement at the anchor point should an anchor fail. This will reduce shockload on the anchor system
Make sure all anchors are as solid as possible
Is that tree large enough, healthy and deeply rooted enough to take the load?
Is that boulder heavy enough to take hundreds or thousands of pounds of shockload?
* Timely (simple and efficient)
Keep you anchors as simple as possible Do everything you can to avoid confusion and tangled webbing or ropes Take your time, it takes minutes to check an anchor system and an eternity to lay in a grave
Double check your anchors and anchor point All knots are tied properly with back-ups and at least two to three inches of tail Both locking carabiners in the anchor point are locked All climbers have double checked the anchors and their own gear
After setting up your first (primary) anchor, put on the 2 locking carabiners and the rope. The weight will help you tie the rest of the webbing to the proper length. Your rope should not be on the edge of the rock.
Always keep in mind the direction of the load and any multiplying factors in your system such as the angle of the pull, going from walking on the face to free rappel, etc.
Think of what will happen if one of the anchors fails. Will the second or third hold by it's self?
If you can, have someone belay the person rappelling from another secure setup at the same time
Check your system every time someone rappels. Just because someone got down last time doesn't mean it's always safe for the next person.
Carry several different lengths of webbing (suggested at least 3 of each 15, 20 and 30 foot lengths of 1 inch tubular webbing is the standard. Use the same color for each length, that way you will know that red, or whatever color, is always 30 feet, yellow is 20 feet, etc. I also always carry one 50 foot length. It has come in very handy on more than one occasion.
At least 3 locking carabiner but you may want to carry 2 extra locking carabiners for certain top rope systems (plus the ones for your harness)
For climbing and rappelling you need a dynamic rope. If you just want to only rappel you can use a static rope. A static rope is not for climbing.
Climbing Anchors and More Climbing Anchors by John Long