"Safebloc reduces forces on the terminal anchoring point" - is this true?

eyehearttrees

Active Member
Location
Tampa-Area
tl;dr - Had operated under assumption the Safebloc reduces forces on the location it's tethered to, now - after contemplating using a Porty there instead of a Safebloc - I can't reconcile the "lowers forces on the tie-in" with the obvious reality that, if you took 5 wraps on the porty and nearly snub the piece, then obviously it's going to slam that tie-in...yet 5 wraps of friction should be "better", if the logic of 'friction hardware reduces forces" holds....

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I'd been under an impression I'm worrying is false, which is this idea of "Using your Safebloc sling at terminal anchor position helps reduce forces on the tree at that location" and am now worrying it's the exact opposite..

Was just reading about Peter Donzelli's untimely death - I know it's not new-news but for me it is which really sucks, found out by googling his name trying to find newer stuff by him and just went through the rabbit-hole of that terrible incident - and watching a clip that someone (in a Donzelli incident thread) posited may have contributed to Peter's thinking in setting his system the way he did (which turned out to be enough to break the trunk below him) here:
they list the time-in-video but basically Peter notes how the force at the anchor-tie-in was >2x the force-on-rope because of the friction in the block.

So the Safebloc.....it slows the passage of bullrope by inducing friction that is held by the Safebloc's slinging and thus hits the tree (or whatever it is anchored to), how on earth could slowing the rope at that location do anything more than add force to the tie-in-point of the sling? Hell, just picture a Porty instead of the Safebloc (which I've also heard "lowers the forces on the tie-in-point" of the sling), where you can turn-up the friction, obviously the extreme would be >3 wraps and snubbing the piece - obviously that'd shock-load the tie-in-point, not lower forces on it....has thinking any&all friction at an anchor-point adds force to that tie-in-point, inherently and linearly with the increase in friction that the hardware is adding.

Thanks for any thoughts on this one!
 
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Benjo75

Well-Known Member
Location
Malvern
I'm a little unclear on your exact question I think. The way I look at it you don't lock off anything unless there is no other choice. Then go as small as possible. Assuming the groundman lets the load run properly, a pulley block will almost double the load on the rigging point. A Safebloc will take a considerable amount of that load away. A port a wrap has the ability to take different amounts. Depends on the number of wraps. One wrap might be about what a Safebloc could do. Two wraps would be more and three wraps would be almost locked off. Which gets into dynamic and shock loading. Then you're worse off than if you were using base friction and a pulley up top. I use a Safebloc a lot. It definitely decreases the load at the tip. We also couple the Safebloc with base friction for heavier loads. Still better than using pulley. I only use a pulley for lifting or redirects when falling a tree. Everywhere else is Safebloc or rings. I recently had the pleasure of using the Morgan Block for a few weeks. It works very well in this scenario too.
 

Birdyman88

Well-Known Member
Location
Arlington
@eyehearttrees First I want to say that I went back and looked into that Arborpod video, and I gotta tell you, where he said "because of the friction in the block", I take issue with that. Not that it's wrong, only in the possible perceived context in the viewers mind. He's speaking of a dynamic rigging scenario, which cannot be directly compared to a static rigging scenario, which some viewers may [wrongly] try to compare it to. But let me explain.

FIRST. The scenario they were discussing was a straight up, straight down rigging line through block and anchor at base with a friction device. Once that load has dropped onto line and load snubbed, AND load is suspended, AND all motion of load has stopped, then you should theoretically see 2X the load value on the meter between block and rigging point. However, and here is my issue, they show that load dropping. Sooooooo ... at what point are they making their measurement??? Because if they're looking at max force, then yeah, it's probably >2X load, but there is a whole butt load of factors that come into that number - distance from block to COG, line length, line type (poly-poly, poly-nylon), line angle, slippage/running at anchor/friction device - basically dynamic loading - factors which I think is what he was trying to delineate in the latter part of video. But, I don't think the video did a great job of just plainly stating what the load on rigging point was with a perfectly static system that has come to rest with load suspended - which would theoretically be 2X the load.

SECOND. So I'm making a big deal out just plainly stating the rigging point load with a static system ... why? Because that is essentially the most fundamental basis for the claim made by the Safebloc - which is that it reduces the load at the point where it's used, which in your use, is at the rigging point. It DOES do that. It does it by the fact that the up line will no longer be under full tension - because the Safebloc has so much friction that it removes tension from the up line - and thus the load on the rigging point is the result of MOSTLY the tension in the down line supporting the load. So with Safebloc at rigging point, AND a load at rest on line, you should only see <2X on rigging point. Let's just hypothetically say that the Safebloc had so much friction that the load could not even be lowered, even after the groundie released the rope from the anchor device AND removed hands from line, then theoretically you would see 1X load value at rigging point. Hope this makes sense so far.

THIRD. So, let's get back to video. So you have a Safebloc up there and you're running that test, will you see the same >2X they claim in video? Yes, you could. But, you could also see something much greater. BUT, and this is huge to understand, if you ran the same test with the normal block and base friction instead of the Safebloc, AND you snubbed off load, AND you increased distance from block to COG, AND you had different type of line, AND you reduced the length of line in system, then you could get a max load of 3X, 4X, maybe even 10X at rigging point. It has everything to do with the dynamic loading and all it's factors. In fact, it would be my guess that you could repeat that video with any or all of the variables tweaked, and as long as the load was snubbed, the Safebloc would result in lower load numbers at rigging point every single time.

So I guess, in short, the video is apparently referring a dynamic load situation in which the rigging point was dynamically loaded to >2X, but they never came right out and said "hey, this cannot be directly compared to the static load values for if the load is just sitting there dangling". But that is a completely different question than whether a Safebloc can reduce the load if used at rigging point. Yes the Safebloc does that, every time, as long as, in comparison, the load moves in EXACTLY the same manner (acceleration, max velocity, deceleration, time to ground) as it would compared to the rigging setup in the video. Hope this all makes sense.

EDIT: After eating some chili, I thought of some simpler verbage.
What he said: "the load at rigging point was a little greater than 2x load because of the friction in the block"
What he should have said: "the force in the block kept the load at rigging point to a little greater than 2X load - it would have been higher if the block had been frictionless."
 
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KevinS

Well-Known Member
Location
ontario
I’ve heard this since blocks vs natural crotch and I haven’t wrapped my head around it enough to speak with authority.
However, if you have a 200lb log that is your load for this chat it is a fixed weight (force at the rigging point). Now whether it’s a block, fs, pulley saver, xrr, biner, natural, etc your t.i.p for rigging should still be able to hold 1,000lbs because we have the 5:1 safety factor built into each part of our rigging system(s).

How I was taught to rig and build a system your system must be able to do everything from run a piece to hold it locked off suspended. Anything less is inadequate.

You stated the safety block has less force and the only spot in your system I can see that being true is at your basal anchor (let’s say a porti). Your safety block does introduce friction into the system sharing the port I’d burden therefore less wraps on the porti. However, if you lock it off your rigging point will still hold that 200lb load.
As for running it smoother well imo that’s nonsense. The safety block has built in friction so even if your rigger let go and the block screamed out of the tree your top would still see a fraction of that 200lb load. Where if you had a block which gives you as close to 0 friction as you can get that rigging point would only see a sliver of that fraction of a load.

So yes adding different friction points throughout your system is a great tool the only place it effects the load is at the anchor.

Now adding multiple rigging points and using angles to reduce your load is a whole other topic that i think More so covers what you brought up. How to make that 200lb block only weigh 150lbs at your rigging point. That’s all in the angles not necessarily the friction.
 

Bart_

Active Member
Location
GTA
I get a bit of a kick out of how the video is such a teaser with opportunity to lay some hard basics out, quantified, and then just mentions what could be important factors and you should consider them.

Dig around some threads, one or two show dynamometer readings rope types and lengths, snubbing and others delve into rope energy /shock load absorption with numbers, and I humbly submit I've chimed in with acceleration analysis showing you always get x2 log weight (in the rig line, log side, not the tip) with reasonable run and catch, plus or minus based on run hard/soft. Snubbing with plenty of forgiving line seemed to give x2 because the line absorbed so well.

Best way to conceptualize rig point friction is suppose you magically had just the right number of wraps on your overhead porty so the weight of the rope tail alone, like 5 lbs?, ran the log just right - your overhead tip would see log weight plus a smidge. Of course with practical wraps or performance you'll have to grab the rope tail to whatever degree, with the worst case your overhead porty is a really low friction pulley.
 

Birdyman88

Well-Known Member
Location
Arlington
There are some other Arborpod videos that get into the static load calcs, so that may be why that particular video doesn't really get into those.
If you look at only static scenarios, just to keep it simple, here is what is known the be fact. If you have a suspended load on line, line runs vertically up, through frictionless block, vertically down to porty, and locked off, the rigging point (where attached) will see 2X the load. This is because the load creates a tension in line, which is transferred equally to every point on rope. So you have an up leg with tension, and a down leg with the same tension. Physics says the tension on one leg balances the tension in the other leg, hence prevent the rope from being in motion. Both legs act downward on frictionless block, giving 2X load on block, which is transferred to attachment point.

When the block has friction, you have modified scenario. Physics says that the sum of the up leg tension + the block friction must equal the down leg tension. Since the down leg tension is stiil equal to the load, then you can see where block friction reduces the need for up leg tension. Since rigging point load is still the sum of the two leg tensions - and only the leg tensions - then rigging point load is now <2X load. This is all pretty well known, and why base anchored SRT loads the TIP more than DDRT.

So say you have system above, 200 lb load, frictionless block, locked off porty, you would see about 400 lb + rope weight at rigging point.

Now say you have same setup, but instead you have Safebloc up top creating 125 lb of friction - still static, nothing moving - then you would see 275 lb + rope weight at rigging point.

Dynamic loading still follows these rules. You just introduce more variables, like those mentioned in the video. Besides load weight, load deceleration is the most important factor, so anything that affects it, will affect loading of rigging point. Letting a load run wil lower the deceleration and reduce rigging point load. But the basic fundamentals for static loading still apply.

I just wanted to add one thing. If this is all clear, then now you see the exact correlation of safebloc at rigging point to using a natural crotch. Then you can translate that to the effects on force vector of crotch friction in SRT redirects. Then I can explain to you a hitch binding scenario in DDRT when using natural crotches without a cambium saver. But yes, the Safebloc is legit IMO.
 
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Bart_

Active Member
Location
GTA
I threw in my wrap just right scenario somewhat facetiously, but in fact I once had stuff barely run with the BMS belay spool and only the tail weight of the rope.

Punch line on dynamics was with 2 G's on the line you stop as fast as you fall and that leads to 4x log load on the tip, if using a pulley. Work outwards from that baseline. 2 G's on the line means log falls (accelerates) for 10 ft, you slow it down in the next 10 ft of "run". If you have overhead friction, the non-log side sees less tension and the tip sees less than 4x the log weight. Let it run 20 feet to stop might be 1 1/2 G's so only 3x the log weight at the tip. etc Run it only 5 feet might be 3 G's (not the exact answer) and you could be at 6x log weight at the tip.

That all ignores rope stretch/shock absorbing which can apparently be very effective.

I don't know the force multiplication factor i.e. how much hand force controls how much log weight, but you need to be careful about doing the equivalent of using too many wraps on a porty - a little extra hand force can generate big tension spikes on the log side, like snubbing it off. I think by design the safe block is quite limited in that regard. e.g. put something real big on it and you'll burn your gloves, it's like a limited number of wraps in capability. I just checked, they say for big stuff you also need a porty at the bottom.

I agree it's legit device and the principle of operation is sound.
 

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