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Top roping anchor - using a single large boulder

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What are people's thoughts on using a single large (fridge size or larger) boulder as an anchor point for top rope and abseiling in?

I am going to Sennen next week on holiday, but would like to climb there once or twice, I don't have any trad gear, but have lots of slings and rope so I am planning to loop slings round, or tie a static line around boulders. There are a few large boulders at the top, but from memory I aren't sure if there are always enough to double up the anchor with two different boulders. If the boulder is big enough and the rope/sling won't ride up, it seems unnecessary to use two anchor points.

What are people's thoughts on this? And if I am putting slings over the boulder would you suggest putting two over? I'd imagine a single 10mm static line would be fine if that alone was wrapped round it. 

I would then use a 10mm static rope to lead the rope back from the anchor point over the lip.

Thanks

 GrahamD 10 Jul 2021
In reply to ollyp123:

I do it.  Obviously make sure the sling is properly seated and not trapped under the boulder.

In reply to GrahamD:

Thanks that's helpful.

How would you avoid getting the rope or sling trapped under the boulder if the sling can't be positioned in any other ways?

In reply to ollyp123:

The other thing to consider is that a single point anchor will tend to allow more side to side motion of the rope, depending on how far back it is from the edge and the angles involved. Check what edges the rope is running over. Maybe use rope protectors and/or have doubled up independent strands of rope to your master point. Granite can be quite abrasive.

In reply to ollyp123:

Use a bag or jumper or something to protect the rope/sling from any sharp edges or constrictions it could get jammed in.

 mark s 10 Jul 2021
In reply to ollyp123:

1 bomber anchor is enough. your harness only has a single point and no one questions that. as others have said,protect the the rub points

In reply to ollyp123:

Boulder belay rule of thumb:- "If it's smaller than a coffin, you're going home in one"

 C Witter 10 Jul 2021
In reply to ollyp123:

Luke90 is correct that a two-point anchor, set up correctly, will be more stable, which is usually preferable with a top-rope set up. However, it's fine to attach yourself to only one anchor if that anchor is unquestionable and in the right position.

Having said this: no one on this forum is able to assess for you whether these hypothetical boulders are unquestionable and in the right position. At the risk of being blunt, you need to take responsibility for your own safety by making informed decisions. There's no need to attach yourself to a dodgy anchor in this scenario - you're not trying to abseil off the North Face of the Eiger in a storm or to rapidly escape a climb with an injured partner. If in doubt, take the time to find something better or do a different climb that's easier to rig. That's how you continue to avoid accidentally killing yourself.

 Cake 10 Jul 2021
In reply to ollyp123:

> How would you avoid getting the rope or sling trapped under the boulder if the sling can't be positioned in any other ways?

You can put nuts in places where you think the sling will get pinched

 nikoid 11 Jul 2021
In reply to ollyp123:

Another thing to assess - is the boulder sitting on loose material?Large boulders have been known to shift in this situation with surprisingly low forces acting on them. 

In reply to ollyp123:

Main thing IMO is regardless of size, can the boulder move or rock. If yes or suspicion of yes then use another (or additional) anchor.

I'm reminded of the obvious block above Heaven Crack at Stanage that everyone thought was ok until it somehow slipped slightly into a position where it rocked slightly and the obvious thread would became a (no longer a belay) gap when not much force was applied in the rope's direction.

Take your time and take care.

 Andy Gamisou 11 Jul 2021
In reply to Cake:

> You can put nuts in places where you think the sling will get pinched

Maybe someone like "Mad Frankie Frazer" and a Kray brother?  Seems a bit excessive to stop a sling getting knicked, but would do the job I guess.

In reply to ollyp123:

Thanks guys, this is all so helpful. I'll take care of course, but I'm pleased that others are happy to use one bomber anchor - so long as it is larger than a coffin!

Protecting the rope is key, I'll bring a couple of spare rucksacs as that should help.

Thanks so much

In reply to ollyp123:

It's easy to forget, through a (sensible) abundance of caution, the actual forces involved at a single pitch belay. If it doesn't rock, and it doesn't move, and it isn't shaped such that the rope/sling can possibly ride off of it, then I'd not (and don't) hesitate to use a single boulder/block/good-thread-between-blocks belay. You or your mate falling off seconding the pitch, or abbing off, isn't going to generate significantly more force than bodyweight; if you put your shoulder into it and give it a good heft, and absolutely nothing happens, then you're not going to generate enough force by tying a rope to it and putting your bodyweight onto it that way.

If that is the case, and you ensure the rope can't be damaged by the placement, then you're good to go I'd say. Hexes are always good to keep the rope from becoming jammed too - either thread the rope end through the hex or just place it between the rope and block.

I'd take a single solid block over a medley of trad gear any day.

 EarlyBird 11 Jul 2021
In reply to Michael Hood:

Friends of mine were unfortunate enough to see a climber deck out below Heaven Crack when his abseil anchors failed - I wonder if this was the cause?

In reply to EarlyBird:

Quite possibly, the top/back of the boulder leant against a larger piece of rock and formed an obvious thread. When the boulder rocked (which wasn't at all obvious) the thread disappeared.

Offwidth will probably know the details/dates but my (possibly incorrect) rough understanding is:

  • Many years ago the boulder used to be ok.
  • About 3-4 years ago (but I wouldn't be surprised if it's 5-6) the boulder became loose, no idea if it was moved or some kind of erosion of the ground it's on.
  • I believe there were one or two accidents related to this boulder but I'm not aware of any details.
  • Sometime since then, the boulder has slightly moved (or been moved) into a more secure position (where it doesn't rock) but I'm not sure if it's still in this secure position.

Personally, I would no longer trust this boulder on its own however fixed it appears - there are other belays available. The other thing is that you can often sling thread  belays made by boulders in such a way that if the thread "disappears", the sling is still left around the boulder rather than just pulling out - but this requires some awareness of the possibility so that the sling is arranged in the necessary way.

 jkarran 12 Jul 2021
In reply to ollyp123:

Fine if:

The boulder can't spin, roll away or rock to pinch or even release the sling. I don't know Sennen, might not be an issue but it's not uncommon on grit to find wobbly blocks.

The sling can't slip off even if you move off your intended fall line.

No sharp edges.

jk

Post edited at 11:12
 chris_r 12 Jul 2021
In reply to tehmarks:

> Hexes are always good to keep the rope from becoming jammed too - either thread the rope end through the hex or just place it between the rope and block.

Great tip!

 GrahamD 12 Jul 2021
In reply to jkarran:

At Sennen, you often find bomb proof Rock spikes.

 GrahamD 12 Jul 2021
In reply to ollyp123:

I should add that a lot of Sennen might be a bit high to top rope comfortably.   Even if your rope is long enough, beware of rope stretch.

 Hardonicus 12 Jul 2021
In reply to ollyp123:

Stand on in and make sure it does not wobble. Beware slinging between two leaning blocks, I've seen one close call with a partial sling release when a massive boulder turned out to be a rocker while an abseil was going on...

 gravy 12 Jul 2021
In reply to ollyp123:

Put something in the gap to stop the rope/sling wedging.  Typically you've got a rack so an appropriately size nut works. There's usual rocks, sticks and pebbles to hand to accomplish the same task. Top tip: clip your blocker gear to the rope/sling because there is a fair chance you'll forget it later when you just whip the gear off the rock.

Check the boulder is either big enough and stable enough not to move or part of the bedrock.  Failure to do this can result in problems from a mildly difficult sling to remove, through to loss of gear through to "large boulder falls and squashes entire party of climbers and passers by".

As to whether or not it is sensible - I do it all the time and there is little more reassuring than throwing a static rope around a good boulder other than using a substantial tree.

 johnlc 12 Jul 2021
In reply to ollyp123:

How you arrange the sling on the boulder is important as well.  If you simply drop a sling over the top of the boulder, it is vulnerable to the sling getting cut as you only have one thread of the sling going all around the boulder.  An increasing risk with the dental floss type slings that we all use nowadays.  To avoid this you can use two slings of identical length.   The other way is to use a great big sling.   Pass a loop round the back of the boulder so that you have a loop of sling emerging from both sides of the boulder.  Bring them together at the front and knot them both together with an overhand knot.  Stick your karabiner through both of the loops that emerge from the knot.  Now if one of the threads of the sling is quietly rubbing on a bit of broken glass etc, there is some redundancy in that the other thread which is going round the back of the boulder will be unaffected.  All pretty theoretical risks I know but when it comes to the safety of friends and family, every marginal gain is worth it.

In reply to johnlc:

Yep. Even if you can't get 'placement redundancy' you should aim for 'attachment redundancy'.

In reply to johnlc:

Good point, I'll do that thanks so much - you may be a lifesaver, we'll never know!

In reply to gravy:

Very helpful thanks, I'll do that! I like the clipping tip as it must be easy to leave it!

 neuromancer 13 Jul 2021
In reply to ollyp123:

I'm convinced someone's gonna get hurt when the boulder at the top of Threadneedle Street (HS) pitch 1 dislodges. It's only about the size of a sofa cushion, and stuck in some crappy mud. 

 LastBoyScout 13 Jul 2021
In reply to ollyp123:

A general rule of thumb for setting up top rope/ab anchors (as taught to me on an instructing course) is to give each bit of gear a score of 1 to 5, where 1 is marginal and 5 is bomber and aim for a combined score of at least 11.

In theory, that means you need at least 3 anchors, but is really aimed at individual nuts or stakes - 1 of them can't be a camming device, as they can walk.

However, as mentioned above, I'd give a rock solid (excuse the pun) anchor like a sling/rope loop around a stable boulder (or even a big Hex) a score up to 10, as long as it can't get cut/flick off - but I'd still back it up for my own peace of mind to get it over the 11 (and reduce side to side movement).

Incidentally, much better to use static line for building anchors, rather than dynamic rope, as it reduces the sawing effect of stretch. Take a couple of bits of carpet or cheap rubber car mat for protection over edges - tie it to the sling/rope so it can't fall on you.

 Martin Hore 13 Jul 2021
In reply to LastBoyScout:

> Incidentally, much better to use static line for building anchors, rather than dynamic rope, as it reduces the sawing effect of stretch. Take a couple of bits of carpet or cheap rubber car mat for protection over edges - tie it to the sling/rope so it can't fall on you.

This is conventional wisdom but I wonder if it's true. Static rope is not completely static. You get a smaller, but not zero, sawing effect over an edge, but this means the abrasion is concentrated in a shorter length of the rope so the abrasion at this point may actually be greater than if spread out over a longer length of dynamic rope. 

Static rope is still better though IMO - the karabiner at the top-rope point doesn't end up half a metre below the point you set it. And static rope is designed for the job (probably with a stronger sheath) and cheaper to replace when worn. Yes, by all means use a piece of carpet to protect at the edge but made for the purpose rope protectors are not expensive and work better.

All the suggestions for using nuts/hex's to stop the rope getting constricted around the boulder are great - except that the OP did say he doesn't possess any trad gear.....

Martin

 LastBoyScout 13 Jul 2021
In reply to LastBoyScout:

The other caveat is that you shouldn't have more than 2 bits of gear in the same placement - and, even then, not close together.

All of the above is great when you have an abundance of trees, boulders and friendly-shaped cracks and unlimited slings, static rope and karabiners.

When you don't have that, you just have to do the best you can with what you've got available.

 LastBoyScout 13 Jul 2021
In reply to Toerag:

> Yep. Even if you can't get 'placement redundancy' you should aim for 'attachment redundancy'.

Someone once looked at me quite quizzically when I tied 2 fig-8 knots in the middle of my rope and clipped them before dropping both ends off the top of Swanage - until I explained I was now able to ab on 2 separate ropes

Post edited at 23:07
In reply to LastBoyScout:

I can't believe you got a dislike for that!

In reply to ollyp123:

Just to mention if you subscribe to the  Wile E Coyote   school of safety rigging, you must make sure you find a perfectly spherical boulder. Non round ones are no good for the purpose.

Instructional video on ropes and boulders. Hope this helps you in some small way  youtube.com/watch?v=OHmJ_t2EneM&

Post edited at 14:19
 strudles 15 Jul 2021
In reply to CantClimbTom:

I’ve often used a huge rock or spike /pillar to ab off. 
 

I always use static rope around it and make sure there’s no sharp edges etc, if there is something else next to it e.g a crack I can put a cam in I might rig a backup with the free strand as there is no reason not to. I also tend to carry around a rope protector when doing this kind of stuff.

 Michael Gordon 15 Jul 2021
In reply to Toerag:

> I can't believe you got a dislike for that!

Not from me, but I can't say I understood it...

 pete3685 16 Jul 2021
In reply to ollyp123:

Hi ollyp123, 

If you only have a few slings and a static/semi-static rope, then you are going to struggle to rig a top-rope that you will be happy with. There aren't that many boulders at the top of Sennen, especially ones close to the climbs that you might want to do. As already mentioned in the thread, there are some spikes etc, but having a few pieces of trad gear would definitely make the job easier.  

Be aware that Cornish granite has a high attrition rate on fabrics, such as rope, dyneema and nylon. The rock at Sennen varies from being reasonably smooth to super sharp. If you are going to be be top-roping in a similar set up to a climbing wall, you are going to need some serious rope protection, as you'll want piece of mind that all is well with your anchor(s) while belaying at the bottom of the crag.

Its already been mentioned, but certain parts of the crag will require a 50m + rope if belaying from the bottom of the crag.

Also, to access the top of some routes would require you to be comfortable in down climbing at about VDiff standard.

It's also a very long walk/scramble around to the climbing if you don't have access to an abseil rope (or know how to abseil safely).

Finally, be prepared for the crag to be like a furnace this weekend. It's due to be around 25 degrees and the granite/sea reflects and intensifies the sun's rays. Bosigran was ridiculously hot today. 

As for your original question, it depends on each, individual, scenario.

Not trying to put you off, just being realistic.

In reply to LastBoyScout:

"1 of them can't be a camming device, as they can walk."


For many placements it will be obvious a cam cannot walk.

Post edited at 09:02

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