How to Mitigate Risk of TIP Branch Breaking?

[Grendel]

Right right, friction loss and all that. Just throwing around broad concepts here. . .

Peter, if you tie that weight to itself double rope style, and lift it, allowing a bit of slack on the tending/prussik side, does the same thing happen?

 

[Raj]

I think my external movement would give false results. I think yoyoman had a video on this.

 

[CurSedVoyce]

Word. Or on a single stem working your way up, easily move the leg of line put of your way to cut limbs. Hardly any tension, while your working.leg is taught.

 

[Bodean]

10lb weight base tied. Just about 20lbs on the scale.
View attachment 81128

Nice.

Sent from my SAMSUNG-SM-G900A using Tapatalk

 

[MasterBlaster]

Climb drt. Don't complicate stuff.

 

[kevin bingham]

the amount of the force is much less important than the direction of the force. Give me a base tie with forces oriented down the stem than a canopy tie with the force directed across the grain of wood.

 

[DMc]

The truth is that any TIP that you would choose and feel safe with for DdRT will also be safe with a base tied SRT system and often can be made safer by changing force vectors, as Kevin stated, to align with the strongest structure that the tree has to offer.

It is not complicated but does require some thought if it is to be used safely, as does everything else we do.

 

[Marc-Antoine]

Word. Or on a single stem working your way up, easily move the leg of line put of your way to cut limbs. Hardly any tension, while your working.leg is taught.

That's because your rope is glued in the crotch by the sap

Grendel, look at it this way :

With a basal anchor in Srt, you try to lift the bottom of the tree when you pull yourself up, (actually, all the tree if the tying point is in an other tree). You get a climber and a part of the tree on the false-crotch !

In Ddrt, you lift yourself up with the passive side of the rope while pulling yourself up on the active side. The rope works for you and takes off a part of your weight. You become "magically" lighter, so you don't have to pull so hard on the active side.
- With a good pulley at the crotch, the passive side takes almost half of your weight and you pull only a little bit over half of your weight. Easy.
- If the rope passes throw a big crotch with a rough bark, it drags a lot and pulls effectively say only a quarter of your weight. You weight apparently the 3/4 of your weight and have to pull 3/4 on the other side of the rope.
- Farer, a pinched crotch (or a sappy one) won't let go the rope. In this case, the rope does nothing for you and you have to help yourself with your full body load.

Look at the different schemes (one number for one rope's leg) : 50+50 ; 25+75 ; 0+100 all of them equate 100 on the tying point.
The limb doesn't look more than your weight (without the dynamic factor).
In Srt the canopy anchor gives 100 too, and the basal anchor gives 100+100 (or more like 75+100 if there's a lot of drag).

 

[Grendel]

Nice, thanks! That helps clear the waters a bit.

 

[Bermy]

Well, double my weight...it might approach 240-50lbs with gear and saw...I don't worry too much about TIP forces when base tying, especially if my down leg goes out a bit over a few branches...think fishing rod.
It's nice to be a small arborist.

 

[CurSedVoyce]

Indeed.
I gained weight this year.
Preferred climbing when I was closer to 150. Guess I should get to a gym soon. The dad bod is emerging...

 

[SeanKroll]

I natural crotched a three-strand rope in a tipped alder for a guy-line, tensioned with my maasdam rope-puller. 2:1 mechanical advantage, right? Double the force, right? One side was slack as the other was tight, with a considerable pull. Rope was bent close to 180°, dry conditions, high friction.

 

[Altissimus]

You just have to learn what to trust , period. Secondary branches are the best backup , if unavailable can always set a sling w a Carabiner further down the trunk and run the line through it. Makes one feel a little better in brittle tops.

 

[theTreeSpyder]

i look at rope forces, as like an electrical path; but with 'geometric consequence'(angles ).
>>electric force has resistors, capacitors, transformers
>>rope tension has friction, elasticity, pulley systems respectively
>>many similarities, i often try to sort in rope schematic with electric symbols
.
Retrieveable SRT/ just line over branch anchored lower/at ground would place 2:1 - friction load.
Non-Retrievable choked running Bowline (you mite possibly climb up and switch over to DdRT) would only be 1x load.
.
DdDRT and non-Retrievable SRT are self contained; only 1 support connection to ground; nominal forces.
.

Retrievable has an extra 'ground connection' that gives an extra loaded leg to the situation, giving higher support load.
Non-Retrievable just has the nominal forces, no other downward pulling leg.
.
SRT on same line would give more elasticity than same in DdRT, because elastic response is a percentage of load weight to tensile strength, and each leg of DdRT is loaded half as much as SRT, so DdRT less elastic response.
.
100# climber pulls down in DdRT 50# on each leg;
>>assume Zer0 Friction; pure inlines example
pull down 50.1 # on tail and start to lift self in 2:1.
As you pull down 50# with hand on tail; this lifts 50 from hitch side and you move up.
You must shorten both legs of line to you 10ft.(20ft. total) to move up 10ft. 2:1 more distance power volume funneled into half as much distance space is 2x denser, more powerful.
Let go of friction hitch and place 100# load on open side of rope as ballast and climber floats;
but; if climber pulls up 50# on load side, can lift (or pretension) 200#
bodyweight :100# (down on belt/seat as ballast to load thru pulley)
arm force in: 50# (up on load)
arm force in: 50#(down on belt/seat as ballast to load thru pulley)
>>lifting 50# makes you 50# heavier on ground, but no other ground, so routes back thru system, chasing ground..
200# for 50# input effort!
.
Use foot cam as force in put on climber belt/seat side :200# input
Hold rope on load side, like doing leg lift: equal/opposite force on load lift: 200#
climber weight : 100#
500# lift or pretension against load
600# support load; because no extra ground connections beside single support, so only nominal climber + load weight force

 

[brydan]

Sure, in theory you can double the force, but this is never the case in tree climbing. After 6+ years of climbing primarily on a base tie I cannot remember how many times I've come down to find that my anchor leg is more or less slack.

Just doing a back of the napkin calculation here with some assumptions I found a 200 lb climber with a base tie going over a natural crotch would result in roughly 42 lbf of tension on the opposite leg of rope. So a little more force at the TIP than DdRT or a canopy anchor but well less than the "frictionless" 400 lbf.

 

[adaycj]

I don't have a load cell, so I can't quantify my suspicions. I think the TIP base tie can be both better or worse depending on things that may be out of the climber's control. Suppose you are basal tied with a "sticky" branch or crotch with lots of friction. The climber is 200#, but he slips and causes a 300# force on the rope for an instant. At the same time the rope slips at the TIP and catches. Now there is 150# "stuck" on the base to TIP side. With a 200# climber still on the line there is even more than double force on the TIP at least for a short time. A sizable number of climbs with recorded forces on the basal side would be useful.

I agree that I have found my base to TIP line nearly slack when I have touched it while climbing. I've also noticed that it sometimes feels even more taught than the climbing line. I know the conversation is about avoiding TIP breakage, but I feel like estimating loads can only go so far. Dynamics play hell on static calculations.

 

[MasterBlaster]

Welcome to the TreeHouse!

Do you have a first name? adaycj seems a tad impersonal... my name is Butch.

Don't be shy about filling out your profile!

 

[brydan]

I don't have a load cell, so I can't quantify my suspicions. I think the TIP base tie can be both better or worse depending on things that may be out of the climber's control. Suppose you are basal tied with a "sticky" branch or crotch with lots of friction. The climber is 200#, but he slips and causes a 300# force on the rope for an instant. At the same time the rope slips at the TIP and catches. Now there is 150# "stuck" on the base to TIP side. With a 200# climber still on the line there is even more than double force on the TIP at least for a short time. A sizable number of climbs with recorded forces on the basal side would be useful.

I agree that I have found my base to TIP line nearly slack when I have touched it while climbing. I've also noticed that it sometimes feels even more taught than the climbing line. I know the conversation is about avoiding TIP breakage, but I feel like estimating loads can only go so far. Dynamics play hell on static calculations.

Fair enough. I don't have a horse in this race (retired from tree work 10 yrs) so 10 seconds calculator time and $0.0001 in pencil lead is good enough for a forum post . Just thought it was interesting that the math, conceptually at least, correlated with Levi's experience.

FWIW, the equation I used is specifically for rotating elements so while static inputs were used for expediency, "dynamic" inputs can be used too.

 

[adaycj]

Think we agree. The friction matters. I wasn't challenging your math, skills, or validity of your post. I apologize. I should have been more considerate of my phrasing. I was only stating that I have a suspicion that dynamic forces could potentially be over the 2:1 value as well a less. Sadly I don't have the equipment to collect the data to prove it. I also am approaching 20 years since my last statics course, so you used more pencil lead than I could already.

 

[adaycj]

I'm Allen. I added my state to my profile.

 

[MasterBlaster]

Welcome, Allen.

 

[Bermy]

I base tied in a Eucalypt the other day, my TIP was a relatively small branch/leader up high with nothing below it for a 'fall back' and my down side was in free air as well, not touching any other branches or leaders, I like to have at least one branch below that would catch if God forbid my tip failed and a bit of 'fishing pole' friction on the down leg...so before going up I got the hubby to really jump on it with me, we made that sucker bend and sway...seemed ok so up I went.
Still here.

 

[brydan]

No worries

Yes I agree that friction most definitely matters. If I run a few different friction coefficients (guesstimates and ballpark #'s I remember off the top of my head) through the scenario I originally posted, 0.5 for a natural crotch (IIRC I saw once 0.4-0.6 for rope on wood), 0.2 for rope on metal rings, and a guesstimate of 0.05 for a pulley. The resulting force at the TIP with a basal anchor and 200 lb climber calculates to 242 lbs, 307 lbs, and 371 lbs respectively. Those numbers may not be super accurate but it's clear friction matters, going from a moderate increase in load with high friction compared to a DdRT/SRT canopy anchor system to a substantial increase in load with low friction.

I don't want to get too far into the weeds with this but just for grins, those numbers are based on 180 degrees of contact with the branch, so the climber and base anchor are directly below the TIP. If the anchor was directly below but the climber was out on a limb walk and the rope angle to the climber was 45 degrees, those forces increase to 262, 325, and 378. Not a ground breaking difference but the increase in force is in combination with an increase in bending stress on the TIP (assuming of course the branch leading up to the TIP is vertical).

 

[DMc]

.... If the anchor was directly below but the climber was out on a limb walk and the rope angle to the climber was 45 degrees, those forces increase to 262, 325, and 378....

For reduced friction sure, but aren't you forgetting something?

 

[Bermy]

well I'm not anywhere near 200lbs