Srt anchor/tip loads

Starting srt here and I've been reading all the posts I can find. Seems like there's different opinions on base ties creating 2x the force on a tip and I've also read just 50% more. For starting out and to keep it simple am I correct in saying that w/o redirects a base tie will put equal/similar force on a tip as ddrt, and that a cinched tip is less or 1x the force.

Base tie will put about double the force on the tip. Cinch tie will be the same as ddrt.

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In theory 2X, but depends on friction and angles:

Newer numbers point more to the 50%+, and that makes sense to me.

Consider how much force is applied by weight, and also how the force is applied to the tree.

Also, consider that an equal distance fall on DdRT is more impacting that and SRT system.



I plan to incorporate a Yates Screamer into my base-tie, expecting it will never deploy.

Ddrt is a 2 to 1 ma so pulling yourself up isn't that putting 2x the load on the tip vs 1x if cinched?

Nice diagram I'm going to try and print that.

SouthSoundTree said:

Also, consider that an equal distance fall on DdRT is more impacting that and SRT system.

Click to expand...

Can u explain

Because you are using twice the rope on a base tie SRT, you also have to consider the stretch percentage per 100 foot in the fall which helps absorb some of the force. Then figure in friction over the limb/crotch/or FS. So it does not act like a 2-1 on a base tie SRT from what studies I have read.

Got it now thanks

Not to say it does not multiply the force... Just not 2-1 .... There will obviously be variances depending on rope length, friction, redirects etc.

This gets tricky. On a base tie, it's inly truly double the force on the TIP if both sides of the line are parallel to one another. Basically straight up and down, no interference, etc. but that's rarely the case, so often times it's less then double the force, because each point where the anchor side of the rope touches the tree or goes over a union, a bit of force is disturbed at that point. It's all about friction and angles. With a lot of redirecting, you can tie into some pretty small stuff, things you wouldn't normally trust you can safely count on now because the force is so distributed, your final redirect or tip actually ends up seeing very little of that full amount of force.


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For safety sake, I always figure 2x my weight with a base tie. I have found that when I use redirects with a base tie, the angle isn't that great for me to feel comfortable with smaller tips. When I do want a smaller tip with a base tie, I usually have to throw to hit several suitable redirects. That usually is fairly time intensive. I think it's best to know several ways to do each (base and cinch tie)

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Those last two posts say it the clearest.

I recently received the Best Practices for SRT book for Christmas. It's a really good reference, and if you can spare the cash (it ain't cheap) I highly recommend it. It covers the above question and lots more.

You can get it from our new site sponsor. Just click on the banner at the top or bottom of the page.

Aahhhh haaaa....good illustration Jack

If I get it right, the more friction where the rope goes over the TIP, the less load on the TIP, so in a tree we'd never really experience a true doubling of the TIP load with a base tie because of the inherent friction of the rope over the limb...did I get that right?

Good replies and info here thanks!
I've been considering the srt book but I wasn't sure of how much more I'd get out of it vs just having an understanding of forces and angles. I'll have to look into that

The amount of line with a base tied system makes a huge difference. In a shock loading fall scenario, a base tied system sees much less force on the suspension point than a ddrt TIP because of the stretch in the rope.

Warning, I've had two strong cups of Joe, and no breakfast. This post may be a bit disjointed.

Bermy said:

Aahhhh haaaa....good illustration Jack

If I get it right, the more friction where the rope goes over the TIP, the less load on the TIP, so in a tree we'd never really experience a true doubling of the TIP load with a base tie because of the inherent friction of the rope over the limb...did I get that right?

Click to expand...

Its absolutely, physically impossible to see exactly two times the load.





All of this is very demo'ed with a branch and a string . For a demo, you can jab a cut branch into the ground to 'plant' your 'tree'

Then base-tie, or trunk tie. Directly (like a 180* scenario), and with lots of crotch redirects. With more excurrent and more decurrent branches/ trees. It will be very concretely experienced, I think. Shock-load the system. Pull to failure. Rig onto it. Whatever. You could use a climber (any weight or toy figure) on the end of the line so you have an constant force (weight...this is a vector force, btw). Hang a 'log' on the rigging line and drop it and watch.


Because I have a BASIC background in this type of physics (year of hs, year of college at an engineering school), and thinking rigging for rock climbing and tree work, I can read diagrams pretty well, as it pertains to me.

It is pretty abstract for some people. Most people experience and can 'read' the force on the line/ base anchor/ redirects, etc in a demo visually and with feeling the pull on the line or tree or whatever.





I suspect that it will do any treeworker well to have a basic, formal concept of vector forces (and friction wouldn't hurt with lowering devices and friction hitches).




Mark Chisholm wrote a good 'Article' on TB about Engineering a Tree Removal. Good diagrams about vector forces.





Jack, looks like you made a good diagram there. Can you make the arrow represent vector forces (i.e., as the force is less, the arrow, which represents the amount of Force and Direction through arrow length and direction would be shorter)?

I think that would more clearly show the forces.







As Erik points to, be conservative (think higher forces) than actual for a cushion.




The more static your rope is (htp, etc), the more you have to consider a shock absorber (Screamer, or the like).

SouthSoundTree said:

...
Its absolutely, physically impossible to see exactly two times the load.
...

Click to expand...

True. But, you can get fairly close ... especially with the "cushion" as suggested.

For example; a rope sleeve is highly recommended, as a true cambium saver, when pruning thinly barked trees, especially in the spring when the sap is rising. A leather, or better yet, a Dan House rope sleeve will greatly reduce friction. A ground anchored working climb line through a rope sleeve or a redirect pulley can generate high enough additional forces that adequate allowances should be part of any work plan. The illustrations and discussions here in this thread should not be received or evaluated for rigorous mathematical completeness ... just an effort to raise general awareness of potential hazards.

http://www.treebuzz.com/forum/showflat.php?Cat=0&Number=375466&an=0&page=0#375466

Here is a link to the tree buzz thread discussing some preliminary testing that Petzl did. I pretty much always opt for a base tie when practical and I feel comfortable going higher with my crotch and redirects than I did with a ddrt Isolated TIP. That's one of the main reasons I fly SRT almost exclusively. Better suspension point, safer climbing.

kevin bingham said:

... I pretty much always opt for a base tie when practical and I feel comfortable going higher with my crotch and redirects than I did with a ddrt Isolated TIP. That's one of the main reasons I fly SRT almost exclusively. Better suspension point, safer climbing.

Click to expand...

I feel the same way, Kevin. It is just amazing how many more options there are with a base tie.

David

What you guys are saying flies in the face of reason.... Unless you mean you always use multiple redirects. It's broad statements like this that cause people to think disbelieve everything SRT guys say.

We have had several speakers over the years come to WI and talk about how great SRT is. They always make it out to be the only method they use and that it's the best method out there but the do a poor job explaining exactly what they mean.
Climbers well versed in SRT will understand what the speaker is saying but someone who has never done it before or who is new will become confused.

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And I'm not trying to be a jerk here. I know what you guys are saying but what I just read on this page of threads could be misunderstood......

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Actually the Pettzl research backs it all up.

http://www.treebuzz.com/forum/showflat.php?Cat=0&Number=375466&page=0&fpart=1&vc=1

I should have said it flies in the face of conventional reason....
Just because it's conventional doesn't necessarily mean it's true.

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