While redundancy is generally a good thing, there are time when it simply is not neccessary, or will not work.

And i would dare to say that 2ft trees are one of those cases.

What do you guess will happen when one of the big trees you anchored to will fail?

A few tonnes of wood will fall down towards the earth or the cliff side. I havent yet calculated it or measured it, but falling trees produce quite a lot of force. I have managed to knock over other trees with a falling tree, or to simply completely unroot them, so i guess there is a lot of force involved.

And even if your backup tree and the conncetion to it withstands the other trees fall, try to imagine what will happen if said tree still connected to the other tree swipes over the cliffside.

Again, i havent calculated it, but i imagine a bloody smear all over the cliff, that once was a climber ...

qwert

Assuming each tree is alive, with good root structure, and is solidly attached into the ground . . . .

Trees under 7" diameter - at least three

Trees 10"-18" in diameter - two

Trees over 24" in diameter - one could be fine


Keep in mind you’ll want to sling each tree as low to the base / ground as possible. Also keep in mind that this is only my personal opinion which is based on my experience where I climb with the species of trees that I use as anchors.

Assuming each tree is alive, with good root structure, and is solidly attached into the ground . . . .

Trees under 7" diameter - at least three

Trees 10"-18" in diameter - two

Trees over 24" in diameter - one could be fine


Keep in mind you’ll want to sling each tree as low to the base / ground as possible. Also keep in mind that this is only my personal opinion which is based on my experience where I climb with the species of trees that I use as anchors.

I've ripped trees, thousands of trees at that, out of the ground with heavy equipment and will say this.

Good ground, good tree, one 7" tree will hold any fall!!!!!!
The problem is that you are not an expert at guessing the strength of the rooting abilities of a tree.
Just look at the tree first. and think about the ground the tree is rooted in. Anchor low and go for it!

When trees are < 3" in diameter I will use three depending on where they are located in proximity to one another. I know less will hold yet it makes others feel better to see more.

Ugh... typical half-assed responses.

One big tree is plenty strong enough. Your problem is that if the route wanders, you will be scraping the TR anchor rope or webbing all over the place. If the lip of the clifftop has any sharp edges, your anchor rope will certainly get hung up on it.

Much better to do something like this:

[IMG]http://i51.tinypic.com/294mjvk.jpg[/IMG]

The blue line is the anchor material, the red is the climbing rope.

The small tree is what's known as a "directional". If you set it up right the little tree won't have to hold much force (a little less than half) but it will keep the anchor material from moving around over the clifftop.

Cheers,

GO

After the edge standard was introduced I did a bunch of tests using an actual piece of broken granite as the edge. Even with a fall factor WAAAYYYY below 0.5 none of the certified ropes held. Later I resorted to simply lowering the 80kg onto the rope without dropping. Once the rope was fully loaded with the mass I allowed the rope to roll slightly across the edge. Again none of the ropes held. <snip> The broken piece of granite was pretty damned sharp but I could easily walk up to any granite cliff and find edges that are sharper.

Ugh... typical half-assed responses.

One big tree is plenty strong enough. Your problem is that if the route wanders, you will be scraping the TR anchor rope or webbing all over the place. If the lip of the clifftop has any sharp edges, your anchor rope will certainly get hung up on it.

Much better to do something like this:



The blue line is the anchor material, the red is the climbing rope.

The small tree is what's known as a "directional". If you set it up right the little tree won't have to hold much force (a little less than half) but it will keep the anchor material from moving around over the clifftop.

Cheers,

GO

One swinging fall could mean curtains. It's very easy to cut a rope under tension

Trees under 7" diameter - at least three

Look at it in another way, a large tree weighs a LOT. The fact is when the tree is on the ground it weighs just as much You couldn't possibly move that much around. If the tree failed away from the cliffs edge you might find yourself getting to the top a little faster than anticipated! So redundancy isn't really necessary.

There is no problem with the scraping over the edges where I am, cracklover. There are rugs that people have left at the top of the climbs that are about 2 inches thick that you can place underneath the anchor setup to keep from it abrading any. I know not to place the rope over the edge, I said that in my response that I was extending the anchor set up over the cliff edge.

I am going to see if I can bring along someone from the local rock gyms who have set them up before to check my anchors before I use them.

I was talking about the anchoring rope. I even drew you a diagram. Sheesh, how dense can you be?

And with a single anchor point and your anchor rope moving around, you can easily knock the rug off. But whatever, do as you please.


There ya go. Maybe you'll listen to him.

Cheers,

GO

I know you were talking about the anchor part of the system.

I know not to place the rope over the edge

...Anyway, you're still missing the point. Webbing may be better, but it can still get sliced if it moves around under tension.

Yup, and I'm not convinced it is better than rope.

(see the last reply to this post on the other site)
http://www.mountainproject.com/...06990414#a_106990769

The translation sucks a little but here is a report of some Norwegian climbers that ripped one of the trees in their anchor. They weren't 2-footers but pretty sizable (at least a foot). Carnage.


http://www.ClimbNorway.blogspot.com/2008/april/23/zeefernfailen

Wow, thanks for that link! Pretty definitive, I'd say!

GO

in a top rope scenario your anchor is holding the climber and belayers weight. you should not by any means anchor to a fallen tree.
look for a bfr, cracks for pro, etc.
Assume the tree weighs 1,000 lb (probably more, maybe less). I can personally move that much weight (rolling, dragging etc.) take into account that most cliffs have a slope at the top, you get gravity contributing.
If you find a dead tree lodged in a crevace or crack (acting like a chock), I'd be comfortable with that, but no free lying trees.
Its not a matter of weight, but possition and security of your BFT/BFR/BFA.

Would it be safe enough to set up one tree anchor that is well made on an excellent tree and extended over the edge of the cliff?

I know not to place the rope over the edge

I know you were talking about the anchor part of the system. Your drawing was unnecessary, it did not contribute to teaching me. I knew about the set up already

In the OP I just needed to know if using multiple trees was necessary.

I know how to make the anchors

Don't take this lightly. One swinging fall could mean curtains. It's very easy to cut a rope under tension.

Edited to add the following quote from a guy who makes ropes at Sterling. This is in regards to the "sharp edge test" used to certify some ropes:


GO

Who and where was that said?

Ugh... typical half-assed responses.

One big tree is plenty strong enough. Your problem is that if the route wanders, you will be scraping the TR anchor rope or webbing all over the place. If the lip of the clifftop has any sharp edges, your anchor rope will certainly get hung up on it.

Much better to do something like this:



The blue line is the anchor material, the red is the climbing rope.

The small tree is what's known as a "directional". If you set it up right the little tree won't have to hold much force (a little less than half) but it will keep the anchor material from moving around over the clifftop.

Cheers,

GO

Or if it´s not too extreme I use a cloth covered lifting strop- they are cheap, robust and tested over sharp edges under load.

Another side question, what do you guys think is the limit that a tree should be used for a climb? There are a few more tree closer to where each climber anchor is set up, but they are smaller in diameter, maybe 4-8 inches.

They are the continous loop slings (that´s a strop) rather than the lifting straps with eyes in the end used for general lifting and stuff and are covered in coarse canvas with the working load stamped on it. Inside are the cores.

They sell them in OBI amongst other places, about €5 for a 1000kg rated one and they are robust as hell!

Jim