The Standard Machete Descent: Is It Time for Rap Anchors?

[Bruce Hildenbrand]

Brad, I am listening.  Thanks for making a 50m work!  One comment.  I would have liked to see the two bolts at each anchor closer together.  The farther apart they are the less the load of the rappel is shared between the two bolts and you can quickly reach a situation where each bolt has 100% of the load.  The Rawl/Powers spec for concrete says that one bolt length is sufficient between bolts.  That should probably also apply to good rock at the Pinnacles.

[schrammel]

Thumbs up on this.

Charles

[MUCCI]

The Rawl/Powers spec for concrete says that one bolt length is sufficient between bolts.  That should probably also apply to good rock at the Pinnacles

.

I have to disagree Bruce.  I have seen "bomber" placements of original bolts.  Removed them only to find that a 6" piece of the "rock" came out by the time I was done.

3.5" between bolts goes against the conglomerate theme.

Here is a great write up:

http://webcache.googleusercontent.com/search?q=cache:Xh_WM3Ab_kcJ:https://www.thebmc.co.uk/Download.aspx%3Fid%3D216+&cd=4&hl=en&ct=clnk&gl=us

A hand length between bolts has always been a term I have heard thrown around.  This article references 200mm between which is roughly 7.25".

What are you're thoughts on the status of the matrix behind the surface?  Holes and other irregularities we have all found after drilling for a few inches.  Then we get spinners and unseated bolts.

I would not even consider 3.5" apart on granite, let alone an anchor that would need to have hauling forces applied.

I am a product of you, Clint, roger, brad, Greg et al online information, and guidance.  I have always appreciated all that you guys do for the community, that is why the comment struck me odd.

[Bruce Hildenbrand]

Mucci,

good comments.  Here is a chart I found about Powers power-bolt(the standard 5-piece SS bolt that is used at the Pinnacles).

http://www.powers.com/pdfs/mechanical/06914.pdf

On page 9 of the document it states that the minimum spacing is one length of the embedded depth where the bolt has 50% of it's strength.  At two lengths of the embedded depth, the bolt achieves 100% of the load.  The rub is that as you move the bolts farther apart, they have to hold more of the load to the point where each bolt can be holding 100% of the load. So, would you rather have a bolt spacing of one embedded depth which is 50% strong, but is potentially only holding 50% of the load or a bolt spacing of two embedded depths which will is 100% strong, but is holding 100% of the load.

Obviously, this is a lot of speculation.  Clearly, if the rock is good the maximum distance between bolts should be no more than two times the embedded depth(which is around 7 inches as you point out).

I was unable to find the exact document that I read discussing this whole issue in depth(no pun intended).  I will continue to look for it and will post up when I can find it.

There is a similar discussion on SuperTopo:

http://www.supertopo.com/climbers-forum/1464361/Results-of-2-inch-bolt-spacing-pull-test

More interesting reading on anchor spacing:

http://www.rockandice.com/lates-news/climbing-anchor-and-belay-stations

[Brad Young]

Bruce, I gotta disagree on this one. I'll go with my gut.

Every time I see bolts that close together it makes me really nervous. I just don't think it is optimal, maybe not even safe. This feeling is probably more true in Pinnacles rock than in any other that I've ever bolted. It's a gut thing, but Mucci well explained some of the objective factors that make me feel that way.

I would never place bolts that close together.

[mungeclimber]

In granite, no prob. Pinns, only VERY judiciously.

[Bruce Hildenbrand]

Bruce, I gotta disagree on this one. I'll go with my gut.

Every time I see bolts that close together it makes me really nervous. I just don't think it is optimal, maybe not even safe. This feeling is probably more true in Pinnacles rock than in any other that I've ever bolted. It's a gut thing, but Mucci well explained some of the objective factors that make me feel that way.

I would never place bolts that close together.

Brad,

I understand your concerns.  I am just trying to use some physics to make educated decisions. As discussed in the Rock and Ice article I cited above you can generate more than 100% (they say up to 200%!) of the force of the rappel by having the bolts/rings far apart.  This is part of the ongoing discussion of the merits of the American Triangle.

If you place the bolts that far apart one thing worth considering is putting long links of chain on the bolts to reduce the force generated by the ropes going through the rings.

Having said all that I will be modifying my spacing between anchor bolts and leaning more toward the 2x the embedded depth rather than 1x.  Thanks to all of you for your input.

[Brad Young]

Bruce,

I am listening to what you're saying. And I understand that you're talking about more than just these specific bolts.

However, if we do look at just these anchors, in this situation, we rejected chains because the area of the descent stays damp a lot and I felt that they would quickly rust. Also, I felt like simple stainless steel rings would work best where, as here, the amount of weight on these from a 45 degree angle rappel is very, very low.

[Bruce Hildenbrand]

Brad,

Sounds good to me! And if I didn't say it already, thanks to you, JC and KC for doing all the hard work.

[JC w KC redux]

Brad,

Sounds good to me! And if I didn't say it already, thanks to you, JC and KC for doing all the hard work.

No problem Bruce. It was a fun day and we really felt like we were doing something valuable for the whole community. Brad is right about the angle too - the raps are very mellow compared to most.