SRT (Single Rope Technique)
SRT (Single Rope Technique) is a newer advanced way of tree climbing that, uses your biggest muscles in your body, less friction in the system, time saving This will all in the end help productivity in the tree its self.
Climbing SRT has many advantages. It allows the climber to ascend at a 1:1 rate of speed. For every foot they pull on the rope they ascend one foot. This is different from the conventional dDRT (double rope technique) configuration of 2:1. In dDrt the climber must pull two feet of rope to advance one foot.
Concerns about SRT
Some peoples misconception say is is a lot more dangerous then dDRT, because you have one rope in stead of two. To be honest in any a SRT or dDRT you only ever have one rope.
Remember it is best to have knowledge of all systems as some jobs could require one, and another job requires another.
Pictures of some SRT items
Most SRT (Single Rope Technique) setups begin with the installation of a line through a fork (or forks) high in the tree. In general this is done with a throw line or launching device; in taller trees. The suitable fork should be healthy, have no signs of decay, be no less than 100mm in diameter and preferably be close to a main trunk of the tree. The access line is then tied off in a manner such that one side is suitable for climbing. The access line is normally left in the tree whilst the climber is aloft thus giving direct access to the tree should the climber require assistance at any time throughout the climb.
The great strength of SRT, and a way in which it is a time-efficient technique for tree access even in smaller trees, is that you do not necessarily need to isolate the target fork. Although climbers familiar with SRT may find it obvious, it is worth highlighting as it means that SRT becomes a very good option even in small trees where there is a lot of internal growth. So long as you have thrown over a sound fork, the two sides of your line do not need to be parallel for you to start climbing. Simply tie off one side of the line to a suitable anchor on the ground, and the other side is ready for you to climb!
1: Tied off at the Base (Base Anchor)
This is by far the most common method of SRT (Single Rope Technique) tie-off. The great advantage is that you do not need to isolate the target branch in order to install the line. Because the line is tied off at the ground, it is easy to remove from the tree at the end of the climb. In addition, this setup gives you the option of including various types of rescue setup (see Appendix I).
The main disadvantage is that it is
possible to generate up to double the load
on the anchor point. A more thorough
discussion of force vectors and their
applications in tree climbing can be found for now it is enough to say that when the two sides of your access line are hanging parallel from an isolated anchor point and one is tied off at the base, climbing on the other will generate double the load on the anchor point.
The only other disadvantages of this setup are that you have two sides of the access line to deal with whilst conducting work in the tree, and should you need to be rescued your rescuer has to have SRT gear in order to use your access line.
2: Tied off at the Anchor Point (Canopy Anchor)
This setup has two big advantages.
Firstly, only a single load is generated at the anchor point.
Secondly, you have only a single line to avoid whilst working in the tree.
The disadvantages are…..
If you are using your throw line as the retrievable rope, this will be hanging down.
3: Tied off at the Anchor Point with a Running Alpine Butterfly
The alpine butterfly is commonly used like this to pull both sides of a footlocking line together, however it is equally useful in order to lock one side of the line for SRT. This setup is removable from the ground, both sides of the line hang together rather than being in the way, and it generates only a single load on the anchor point. Another great advantage is that other climbers can access the tree without needing SRT gear, either by footlocking on the doubled access line or by pulling out the alpine butterfly and body- thrusting up the line.
One of the main risks of SRT (Single Rope Technique), along with any access method that relies on installing a line high into the tree, is that it is very hard to inspect your anchor point before leaving the ground. Particularly in tall trees, or trees with dense canopies or a lot of internal growth, the anchor point may be hard to see. It is critical that you ensure that you are over a sound and sufficient anchor point before leaving the ground. This can be done by visual inspection, possibly using binoculars, or by performing an on-rope ‘bounce’ test.
You should always have a saftey, access line installed for a rescue purpose and make sure all parties are competent to use them.
Remember that if you are tying off the line at the base, you may be double-loading your anchor point. In this instance, checking your anchor point by getting additional climbers to load your line must be done by both loading the climbing part of the line. It is no good one of you hanging on each side, as this is the same load as you will be applying when you tie off and start climbing. Be aware that ‘bounce testing’ or multiple loading may cause upper- canopy failures, so be ready to move away.
Single Rope Technique is a strong and efficient method of tree access. It does have some drawbacks, however. Almost all are related to the risks inherent in the installation of a climbing line high in a tree, over an anchor point that may be hard to see from the ground. Particularly in trees where the climber has found it hard to install a line, there may be a temptation to accept an anchor point whose safety and sufficiency is hard to determine. Take the time to check it again, and if you aren’t confident then throw again for something lower! In some trees it may not be possible to use SRT; a traditional method of access may be preferable.
In addition, new SRT users should practice an on-rope changeover to a suitable descent device several times near the ground before beginning SRT climbing. The tree may contain insect swarms or other such unforeseen hazards, and with some SRT systems the changeover to a descent device can be involved and time-consuming. New users should also consider the use of a rescue setup, which allow the climber to be lowered to the ground in the event of difficulty.
A very efficient way of using the access line when planning to work in quite a localised area of the tree is to set on the access line.. This is a powerful and efficient technique, but climbers should be wary of some inherent risks.
The great strengths of this technique are that it is quick to set up, and allows the installation of a friction-free anchor point without isolating a target fork or having to climb to the top of the tree.
By setting the access line through the fork in the branch of its larger neighbour, and then over a strong branch in the centre of the tree, the climber has given himself a friction-free high point directly over the tree he will be working in.
Note: “Neither an engaged, frame loaded toothed ascender nor a cam-loaded non-toothed ascender shall be permitted [to be used as the connection point for an anchoring system]. Fall protection anchoring systems must include an approved stopper knot or hitch on the static line below the anchoring system, unless the climbing system is directly connected to an approved knot in the access line.
International Tree Climbing Championship Rule Book, 2010
The additional force applied at the anchor point by tying off one side of the line and climbing on the other was mentioned briefly in the setup section. It is however possible to use an understanding of force vectors to greatly improve the loading on an anchor point. .
Where the climber is exploiting the angle formed between two anchor points to allow him to climb safely out along a branch.
Setups like this which use an understanding of force vectors to improve climbing safety and efficiency are very powerful options, but require a thorough knowledge and familiarity to use well. Climbers unfamiliar with the use of force vectors in climbing and rigging should read the VTIO introductory document, Working the Angles, available separately on the website or abridged in this document as Appendix II.
Whilst the setup shown is extremely strong in the precise direction that the climber has headed, it would become extremely weak if the climber were to head up toward the left hand fork.
Working with forces
FORCE VECTORS (Abridged from “Working the Angles”)
It’s a fairly common scenario in most removals: the climber has snatched off a large piece, and the groundie has brought it to a gentle stop with the lowering rope. Leaving aside for the moment any questions of shock loading, friction, and elastic elongation, how much load is on the pulley?
Almost any experienced climber will tell you straight away: “there’s double the weight of the log.” It seems fairly straightforward, but it’s worth going into it in more depth.
The log weighs 100kg. As it is not plummeting to the earth something must be pulling in the other direction with the same force to keep it in place (Newton’s Third Law). In this case it is clearly the rope which is holding the log in the air.
Over on the other side, the groundie is having to put his whole 100kg of weight on the rope to balance out the weight of the log.
It’s fairly easy to see that in this simple example, where both sides of the rope are pulling down on the pulley with a weight of 100kg, there is a net load on the pulley of 200kg.
To put it another way, when one side of a rope is loaded and the other is locked off,
Ropes running parallel = double the force on the anchor point
This simple statement is really important, and has a great many practical repercussions in tree climbing. The most common examples are rigging scenarios like the one shown above, and the classic Single Rope Technique setup of one side of the access line being secured to a ground anchor in order to make the other side ready for climbing.
Net load on pulley
“Shouldn’t we be talking about forces instead of weights?”
In all of the examples in this appendix the loads are discussed purely in terms of weights. This isn’t strictly accurate, as to work things out properly we should move across into Newtons and use genuine force vectors. This way is much simpler, however, and gives basically the same results..
ROPE ANGLES AND FORCES
So far, so easy. As we saw on the previous page, lowering a section of timber whilst your groundie stands directly underneath causes a force on the pulley of double the weight of the piece being lowered. This is about as far as many climbers go with working out forces, and it is certainly far enough to remove just about any conceivable tree. Simply put your rigging point on the main stem somewhere up near the top of the tree, and then use it to lower off as large a bit as you think it can handle.
But we can do better.
The Angle Rule,
given above right, is a fantastic and simple mental tool to carry in your head when thinking about the forces that your climbing and rigging are going to apply to the tree.
Now same log is being held up by the same groundie. But the setup, and the forces being applied on the tree, have completely changed. By adding a second pulley into the system on the right-hand head the climber has hugely improved the situation. In fact, the weight applied on the tree at each pulley is greatly reduced (The Force Rule), but we’ll get to that in a minute. For now, the most important thing to look at in the picture is the direction in which the weight is applied.
As you can see, the lowering rope is making a right-angle at each pulley. A quick look at The Angle Rule above will remind you that where two forces are pulling at angles to each other, the net resultant force bisects the angle between the two forces. In other words, it pulls exactly half-way between the two of them.
Half of 90° is 45°, so the resultant force on the pulley acts at 45° from the line of either rope. In this case, that means it is acting exactly along the branch. Perfect compression force!
The Force Rule,
The wider the angle made by a rope passing over a point, the less force the rope applies to that point.
“By by spreading your rope over a number of limbs you are then making the forces on each limb less.”
Remember you can make this as ex or inexpensive as you like.
A basic set up: Rope Wrench Climbing system
2, Friction Cord Eye to Eye
3, Friction Device Rope Wrench
4, Stiff Tether
5, Ascending Device/Devices
– Pulley (hitchlimber),
– Foot Acsender
Rope Wrench Climbing Set up
Install you SRT climbing rope, either a base anchor or a Base anchor.
Add the friction hitch to the climbing line
Attach the rope wrench above the hitch,
Attach the weather to the wrench.
Attach the tail of tether to the hitchclimber (rated pulley).
Insert the carbine through the pulley eye to eye legs, and down to yourbriodge.
Attach your foot ascender to your boot and clip on rope. Tie a weight to the rope under where your foot is.
Below is mor devices you can, insert in the system.
Rope runner Bulldog Bone, Unicender (are not CE Marked)
– Hass system
Any good climbingg equipment shop should be able to advise you on equipment.
Keeping the the hitch above your waist, remember to take all your slack out of the system.
(slack can equal a dynamic fall.)
Lift you leg with the foot ascender on it. to 90o angle, and stand up on up
Dress your hitch, and lean back and lift leg and repeat
Lift leg and un attach your foot ascender.
Sit back and pull gently down on hitch.
This is a look brief look into SRT. Information is gatherd from:
– Target Trees ( Ian Flatters )
– TICA (Tree Care Industry Association 1938)
– Vito (Victoria Tree Org)
And Collaborated together By:
– Climbwise Ltd ( David Murison )