Branch strength

Hi all.

I am new to this so hopefully am doing things right. I am planning on setting up a venture hauling people up big trees for picnic lunches. I can haul 2 people up a tree with a 9 to 1 pulley system with ease and I can calculate all Safe Working Loads with the kit I am using as its rated to a Minimum Braking Strain. Unfortunately the branches I am using do not come complete with certified breaking strains. The tree in question is Eucalyptus and the branches are about 12 inches in diameter. I realise the further out the branch the load is placed, the more leverage and strain is placed on its join to the main trunk. Is there a calculation to ascertain the strength of the join, which will see the most force ? On close inspection I can see there is no rot or damage to the branches.

Hope someone can help.

Cheers,

Andy.

It would be smart to hire an arborist consultant to assess the tree or trees you want to use and to discuss load parameters for what you want to do.

Assuming a healthy tree from bottom to top, placing the rope at the trunk union on a 12" diameter limb is a good start, definitely want an expert on site to do a full assessment.
-AJ

Inspecting the tree and limbs for rot, damage, or other hazards is the first step. Locating a limb of decent size and location is the next step.

For most trees a branch slightly bigger than your wrist will do for a normal tie in point. I always prefer a 6" or larger limb for more brittle or soft wood trees. Watch out for and avoid sucker tops and limbs for tie in points. They are weak and not reliable.

A 12" limb in any species is more than enough for one person climbing as long as the limb is alive and in good condition.

Set your rope as close to the trunk as possible. Consider using multiple limbs if several people are going to climb the same tree at the same time. A cambium saver, rope sleeve, or friction saver will help protect the tree, limb and your equipment for future climbs.

Hi there.

Cheers for the feed back. As you can tell by the diameter of the limb this is a big tree. The main issue with it is I will need to rig about 5 meters along the limb to gain a clear path up through the canopy. It was this leverage distance that was concerning me. As I haul, the limb will bounce also. My main impression of it is that its plenty strong enough for the load but without expert knowledge I cant be sure. The limb will be holding up to 200kg ie two heavy people.

andy and India wrote:

Hi there.

Cheers for the feed back. As you can tell by the diameter of the limb this is a big tree. The main issue with it is I will need to rig about 5 meters along the limb to gain a clear path up through the canopy. It was this leverage distance that was concerning me. As I haul, the limb will bounce also. My main impression of it is that its plenty strong enough for the load but without expert knowledge I cant be sure. The limb will be holding up to 200kg ie two heavy people.

If you need to go 5 meters out I would rig it as a redirect. In other words anchor the system on the central trunk high enough so that bull rope (high strength rigging rope) down to the target limb is 45 degrees. Redirect with a substantial sling and block (the redirect) rated for the loads. The redirect is attached with the sling at the 5 meter point on the limb. Just below the redirect attach the top of your 9:1 system to the bull rope.

Again, you still want some professional assistance to consult on the tree assessment and discuss the rigging plan.
-AJ

My two cents worth is to rig it at the spot you like but then add a bomb-proof tie back from further outboard of your anchor point to the trunk as high as practical. Just as AJ calls a re-direct I call an outrigger. If your consulting arborist has a Hobb's lowering device you will find it lifts nicely. Add an engine driven drill coupled instead of the hand crank and you could lift a Buick, oops make that lift a lory. Dan

Another question (it may be obvious but just in case): Do you have a hauling system that defaults to locking. In other words, when the person hauling lets go of the rope, the person being hauled up stays where they are instead of falling back to the ground? Once they are up there and having lunch, are they tied in to the tree and what are they sitting on?

It all sounds intriguing!
Michael

michaeljspraggon wrote:

Another question (it may be obvious but just in case): Do you have a hauling system that defaults to locking. In other words, when the person hauling lets go of the rope, the person being hauled up stays where they are instead of falling back to the ground? Once they are up there and having lunch, are they tied in to the tree and what are they sitting on?

It all sounds intriguing!
Michael

I was thinking the same thing, some interesting challenges, the design of the system needs careful consideration to keep the people on rope safe from beginning to end.
-AJ

Hi guys.

Yes to explain further, we have a pod built made of willow with a ply wood base which looks kind of like a weaver bird nest !! This is attached to a central rigging plate by 11mm static line. The guest are in harnesses which are in turn attached directly to the rigging plate. This allows the guests to sit in comfort in the pod, but be attached to a separate system than the pod itself.

The load is hauled using a stop or an ID, as a progress capture device. Of course it would be no good if relying on not letting go !!!This is situated on a very strong anchor at ground level, so that the rigging goes from the ground, up to the anchored branches via a pulley and back down to the pod This has a complex pulley system comprising of two hand jammers with pulleys attached. Which each create a 3:1 but piggy backed create 9:1. This is the main haul line. There is also a safety line which is attached to the pod via an anchor system on a separate branch, and again separate ground anchor. Using a stop, ID or GRI GRI for progress capture.(These devices are great as they can be released under load, unlike a toothed device or prussic.) The slack on this is taken in as the pod is hauled to create a back up.

The Karabiners are the weakest part in the system which are rated at 25KN Minimum Braking Strain. Thats about 2500kg. Given a factor of safety of 10 ( which is excessive) I should be safe to haul 250 kg. Because of the safety rope and main haul line I have two of these systems attached at all times, and will back up the areas of most loading with an extra karabineer or sling.

As far as I can tell, unless my guests physically unclip there karabineers and throw themselves out I should be OK. Of course however it is a problem calculating the all important anchor strengths up high. The tree I am using is absolutely stunning and overhangs a little river, the top is maybe 40Meters up and pokes out from the top of the canopy for a very special experience. Unfortunately the branches in question are right at the top and actually rise above and out of the main trunk so a deviation set up, I think you guys called this an out rigger system, is not possible (I had that idea also, with the load taken in compression in a downwards direction on a vertical trunk and not a horizontal branch, much stronger). I think I will do as you guys advise and call in a tree expert to help me assess these branches!!!

I think the system is pretty smooth and safe, but feel free to pass on any more comments. The more eyes the better.

Thanks for all your advice !!

Andy

Andy, do you have a sketch or a photo you could attach?

Michael

Imagine if you can an eight foot round trampoline base secured with a six legged spider of 1" webbing. It is easy if you can. You can go as high as you wish or down low for a 100 foot diameter orbit. I know- I have two: three and eight foot round. It is a flying carpet ride.

Imagine if you can an eight foot round trampoline base secured with a six legged spider of 1" webbing. It is easy if you can. You can go as high as you wish or down low for a 100 foot diameter orbit. I know- I have two: three and eight foot round. It is a flying carpet ride.

andy and India wrote:

Hi guys.

Yes to explain further, we have a pod built made of willow with a ply wood base which looks kind of like a weaver bird nest !! This is attached to a central rigging plate by 11mm static line. The guest are in harnesses which are in turn attached directly to the rigging plate. This allows the guests to sit in comfort in the pod, but be attached to a separate system than the pod itself.

That sounds awesome Andy, good luck with your project, looking forward to seeing photos, especially of the pod, brilliant idea!
-AJ