Ropeman Safety

[griff]

Math or no math I'm still going to use a ropeman on my tethr AND my LB. I'm crazy like that. Too much worrying about minutiae, heck, we all sit in the woods while maniacs are blasting bullets like a war zone, I think I'm good with x amount of KN. The way to make sure it doesnt fail...dont fall, lol.

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The point of this thread isn’t to tell you what to do vs. what not to do. We all take calculated risk when we climb a tree. That threshold isn’t the same for everyone. This thread was to bring to light what the ropeman is and isn’t. This is safety information that needs to be out there for guys that are just starting or guys that are entertaining the use of a ropeman for the first time. Buried in this thread is information that is fact regarding sheath stripping that is documented in testing at as little as 3.5kN.


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[mattsteg]

Math or no math I'm still going to use a ropeman on my tethr AND my LB. I'm crazy like that. Too much worrying about minutiae, heck, we all sit in the woods while maniacs are blasting bullets like a war zone, I think I'm good with x amount of KN. The way to make sure it doesnt fail...dont fall, lol.

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That's fine - it's clearly been widely used in that application by many of us over a period of years and is plenty safe if you keep the slack out. My only concern is people convincing themselves it's like 4x stronger than it is, or that falling a few ft on a static line is no big deal. It's easy to pass from safe to sketchy without knowing it. I just want to raise some awareness of where that line is so that we can all make our own choices. The point where the ropeman fails is about the max you wanna expose yourself to anyway.

 

[dbldrew]

Dude - I've literally taught college courses on this sort of thing. I and other trained/practicing engineers as well as actual experienced and trained rock climbers and arborists have repeatedly chimed in on this sort of topic multiple times over the past year or 2. We know what we're talking about. You don't.

Foot-pounds is either a torque, or an energy. Not a force. Pounds is a force unit.

Impact Forces based on fall factor essentially treat the rope as a long spring, perfectly attached to the climber. There is no dependence on fall distance. This works great, as long as the amount you beend and twist is small relative to how much the rope does so. At very short fall distances, the amount of squish and bend of the climber is large, so the model will be pessimistic about very short falls. You can choose how far you think your back can bend before it breaks and substitute that into the force equation that I used, and if you like the result any more...

Ok so you have "literally" taught college courses and you are saying there is "no dependence on fall distance"?!? WOW

So you say that foot pounds is a torque but not a force.. do you know what torque is? (rotational FORCE) wow again

The fact that you are still trying to defend the model from the website that generates a 10.2Kn from a 2" fall is just ridiculous. I know that your whole argument is based on that, but at this point you just look foolish.

Listen lets just leave it at this.. Saddle hunting and hanging from a ropeman is not for everyone. It could be completely terrifying for some, I mean at any moment that ropman could slice through your tether! So maybe a 10mm steel cable for a tether could be used? or stick to a ground blind might be better?

 

[BenG]

dbldrew, I think you're leaving something out from your own example. It is saying the impact force is 106 kN, so if the calculator is junk so is your example. You keep citing the energy as impact force. When that energy is distributed over a very short distance you end up with some pretty large impact forces. Honestly I can't sit here and say I completely understand impact force, but everything I've found on this points out these high impact forces including your example.

For the record, since the original post I've switched from the ropeman to a blakes or prusik. I use my tether while climbing, so I do end up with some slack at times and don't feel comfortable with the ropeman in that scenario. I agree that if you're not using it while climbing and just hooking your tether up at height then it's highly unlikely you would have issues with the ropeman. I also switched to a dynamic rope to further lesson the impact should I happen to fall a few feet. As a climber you can probably see how that would make a pretty big difference.

I know you and Matt are going back and forth here pretty hard here, but he's fighting the good fight. Most of what he's saying is what I've found after researching this pretty hard. I would have to say for as much as we talk safety on here there isn't a very good understanding of impact force. IMO, it's not enough to say well if it's good enough for climbers it's good enough for me. Without understanding what we're doing, we could be subjecting ourselves to greater forces than a climber would.



Keep going in your example to see that they are coming up with 106kN for the impact force.
Example - a Person falling from a Table
A person with weight (gravitational force) of 200 lbs (lbf) falls from a 4 feet high table.
The energy of the falling body when it hits the ground can be calculated using (4) as
E = (200 lbf) (4 ft)
= 800 ft lb
The impact on a human body can be difficult to determine since it depends on how the body hits the ground - which part of the body, the angle of the body and/or if hands are used to protect the body and so on.
For this example we use an impact distance of 3/4 inch (0.0625 ft) to calculate the impact force:
Fmax = 2 (800 ft lb) / (0.0625 ft)
= 25600 lbf
In metric units - person with weight 90 kg, falling distance 1.2 m and impact distance 2 cm:
E = (90 kg) (9.81 m/s2) (1.2 m)
= 1059 J
Fmax = 2 (1059 J) / (0.02 m)
= 106 kN

 

[dbldrew]

dbldrew, I think you're leaving something out from your own example. It is saying the impact force is 106 kN, so if the calculator is junk so is your example. You keep citing the energy as impact force. When that energy is distributed over a very short distance you end up with some pretty large impact forces. Honestly I can't sit here and say I completely understand impact force, but everything I've found on this points out these high impact forces including your example.

For the record, since the original post I've switched from the ropeman to a blakes or prusik. I use my tether while climbing, so I do end up with some slack at times and don't feel comfortable with the ropeman in that scenario. I agree that if you're not using it while climbing and just hooking your tether up at height then it's highly unlikely you would have issues with the ropeman. I also switched to a dynamic rope to further lesson the impact should I happen to fall a few feet. As a climber you can probably see how that would make a pretty big difference.

I know you and Matt are going back and forth here pretty hard here, but he's fighting the good fight. Most of what he's saying is what I've found after researching this pretty hard. I would have to say for as much as we talk safety on here there isn't a very good understanding of impact force. IMO, it's not enough to say well if it's good enough for climbers it's good enough for me. Without understanding what we're doing, we could be subjecting ourselves to greater forces than a climber would.



Keep going in your example to see that they are coming up with 106kN for the impact force.
Example - a Person falling from a Table
A person with weight (gravitational force) of 200 lbs (lbf) falls from a 4 feet high table.
The energy of the falling body when it hits the ground can be calculated using (4) as
E = (200 lbf) (4 ft)
= 800 ft lb
The impact on a human body can be difficult to determine since it depends on how the body hits the ground - which part of the body, the angle of the body and/or if hands are used to protect the body and so on.
For this example we use an impact distance of 3/4 inch (0.0625 ft) to calculate the impact force:
Fmax = 2 (800 ft lb) / (0.0625 ft)
= 25600 lbf
In metric units - person with weight 90 kg, falling distance 1.2 m and impact distance 2 cm:
E = (90 kg) (9.81 m/s2) (1.2 m)
= 1059 J
Fmax = 2 (1059 J) / (0.02 m)
= 106 kN

I think its a typo in the example, converting 1059 J to Kn is not 106kn its 1.059kn its rounded up to 1.06kn they just forgot the "." in the example im thinking? (or my link is also garbage lol)

I mean 106Kn is almost 24,000 lbs.. your not generating that kind of force with a 4' fall that would surpass every manufactured piece of climbing gear.

So if it is 1.06Kn then that would easily fall in the safe zone of the ropeman 1, I mean most people do not have enough slack in the tether to generate a fall farther then that, and that is if they have the ropeman all the way at the bottom of the tether when they fall. Now if people are a heavier person and like to have a lot of slack in your tether and also want the ropeman all the way at the bottom when transferring onto the platform, then maybe a ropeman 2 is the way to go, the ropeman 2 has a clamp design much like most of the other ascenders out there.

 

[mattsteg]

LMGTFY - Let Me Google That For You

For all those people who find it more convenient to bother you with their question rather than to Google it for themselves.

lmgtfy.com

 

[dbldrew]

yeah after thinking about it 1.06kn doesnt make any sense either that is only like 238lbs so that seems way to low for a 4' fall. (and noticed the calculator was for joules per meter to KN) The problem im having is every fall calculator gives wildly different results based on the same numbers I put in for each. I'm sure they put in a lot of "safety" factor but the end results are crazy different.. But this one seems to be a little bit logical..

Calculate the force of a fall while using the fall protection force calculator

Use our free fall protection force calculator to determine the force generated on the body when using fall protection.

wilmes.co

at least when you test it for something small like a 1" fall it doesnt generate 1000s of lbs. So 1" fall generates 216lbs which seems a bit more realistic compared to 2300lbs..

So a 4' fall according to this would generate 1000lbs.. so your past a safe zone of the ropeman 1, (anything past a 3' fall would be past the safe area). So if using a ropeman 1 make sure you have less then approx 3' of slack, or use the ropeman 2

 

[Swingin' Free]

yeah after thinking about it 1.06kn doesnt make any sense either that is only like 238lbs so that seems way to low for a 4' fall. (and noticed the calculator was for joules per meter to KN) The problem im having is every fall calculator gives wildly different results based on the same numbers I put in for each. I'm sure they put in a lot of "safety" factor but the end results are crazy different.. But this one seems to be a little bit logical..

Calculate the force of a fall while using the fall protection force calculator

Use our free fall protection force calculator to determine the force generated on the body when using fall protection.

wilmes.co

at least when you test it for something small like a 1" fall it doesnt generate 1000s of lbs. So 1" fall generates 216lbs which seems a bit more realistic compared to 2300lbs..

So a 4' fall according to this would generate 1000lbs.. so your past a safe zone of the ropeman 1, (anything past a 3' fall would be past the safe area). So if using a ropeman 1 make sure you have less then approx 3' of slack, or use the ropeman 2

I can wrap my head around this

 

[powhound84]

This is the one I have used over the years for rock climbing. Seems pretty accurate but the type of rope and other factors will affect the results.

Fall Factor Calculator

how to fall

ferforge.tripod.com

So, if a 160# guy was standing with his waist level with the tether connection to the tree and there was 2' of slack, you're looking at roughly 8kn of load in the event of a fall if using static rope.


Next, let's assume you climb just above where your tether connects to the tree, with 2' of slack. 12kn:


Now let's assume you climb just above where your tether connects to the tree, with 1' of slack. 16kn:

 

[kyler1945]

Here is and example so you dont have to do any math..

Example - a Person falling from a Table
A person with weight (gravitational force) of 200 lbs (lbf) falls from a 4 feet high table.
The energy of the falling body when it hits the ground can be calculated using (4) as
E = (200 lbf) (4 ft)
= 800 ft lb

How confident are you in this math? At ground level (Your feet at 5' off the ground), would you be willing to fall four feet in a saddle, and have that fall arrested by a static rope as your anchor(tether)? According to your math, that fall would be below the 900lb threshold that OSHA has in place for "belt style/body belt" harnesses. They are ultra conservative, so you should be just fine...

 

[mattsteg]

yeah after thinking about it 1.06kn doesnt make any sense either that is only like 238lbs so that seems way to low for a 4' fall. (and noticed the calculator was for joules per meter to KN) The problem im having is every fall calculator gives wildly different results based on the same numbers I put in for each. I'm sure they put in a lot of "safety" factor but the end results are crazy different.. But this one seems to be a little bit logical..

Calculate the force of a fall while using the fall protection force calculator

Use our free fall protection force calculator to determine the force generated on the body when using fall protection.

wilmes.co

at least when you test it for something small like a 1" fall it doesnt generate 1000s of lbs. So 1" fall generates 216lbs which seems a bit more realistic compared to 2300lbs..

So a 4' fall according to this would generate 1000lbs.. so your past a safe zone of the ropeman 1, (anything past a 3' fall would be past the safe area). So if using a ropeman 1 make sure you have less then approx 3' of slack, or use the ropeman 2

That calculator requires a minimum of 1 ft of "give" in the system. Use a 1 ft stopping distance in the other calculators and you'll almost certainly get the same result. that "give" is however much the saddle slips on you and however much you bend. If you fall legs-down you probably just get a wedgie. If you fall but-down in an extended position...your back will NOT be happy (basically a 2-ft+ forced backbend as the 1 ft is the motion of your average center of mass)

 

[Aeds151]

So being 250lbs and being sold static line as a “saddle tether”, I will just stay on the couch.


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[powhound84]

So being 250lbs and being sold static line as a “saddle tether”, I will just stay on the couch.


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You can minimize the load by using static rope that stretches a bit more, like regular nylon instead of tech cord. I don't like dynamic because it stretches too much for our use but if it was feasible, it would be way safer.

You can also include more dynamic elements to the system, like a friction hitch instead of an ascender. They slip slightly as they tighten, decreasing peak load.

Also keep in mind that your body will bend and squish in your harness when you fall, so the actual load on any 1 element in the system is usually far less than the mathematical calculation.

Any "give" in the system lessens the peak load considerably.

 

[dbldrew]

That calculator requires a minimum of 1 ft of "give" in the system. Use a 1 ft stopping distance in the other calculators and you'll almost certainly get the same result. that "give" is however much the saddle slips on you and however much you bend. If you fall legs-down you probably just get a wedgie. If you fall but-down in an extended position...your back will NOT be happy (basically a 2-ft+ forced backbend as the 1 ft is the motion of your average center of mass)

even static ropes have elongation, the standard for static vs dynamic is based on the % of elongation with a 80kg weight, a static rope with a 80 kg hanging can have up to 10% elongation, a dynamic rope can have up to 40% so that 1' is pretty close

 

[dbldrew]

This is the one I have used over the years for rock climbing. Seems pretty accurate but the type of rope and other factors will affect the results.

Fall Factor Calculator

how to fall

ferforge.tripod.com

So, if a 160# guy was standing with his waist level with the tether connection to the tree and there was 2' of slack, you're looking at roughly 8kn of load in the event of a fall if using static rope.
View attachment 18383

Next, let's assume you climb just above where your tether connects to the tree, with 2' of slack. 12kn:
View attachment 18385

Now let's assume you climb just above where your tether connects to the tree, with 1' of slack. 16kn:
View attachment 18384

this is the calculator that does not work. Your example of having 2' of rope is not the fall distance, thats how much "bungee" effect the rope has, the longer the rope the more give you have. The distance from last anchor is the fall distance (fall distance is 2 times distance from the last anchor) so you are hanging from a 2' rope and have NO fall distance at all and the calculator generated 8kn.. again this calculator is way off in its calculating

 

[powhound84]

this is the calculator that does not work. Your example of having 2' of rope is not the fall distance, thats how much "bungee" effect the rope has, the longer the rope the more give you have. The distance from last anchor is the fall distance (fall distance is 2 times distance from the last anchor) so you are hanging from a 2' rope and have NO fall distance at all and the calculator generated 8kn.. again this calculator is way off in its calculating

You are just misinterpreting the math.

2' of rope out and 0 distance from last anchor means you are standing with your waist parallel to the anchor and there is 2' of rope hanging between you and the anchor. You fall 2' with 2' of rope out, giving a fall factor of 1. If I climb to the end of my tether above the anchor point and fall, it's a fall factor of 2. If I'm below my anchor and fall, it's a fall factor of <1.

You need to keep in mind that this calculator has the lead climber in mind, where we always climb above our last anchor point. If you are below your anchor point, you will have a negative "distance from last anchor" number.

There are MANY conversations about fall force over at mountainproject between people who have been falling on ropes for fun for several decades. I encourage you to educate yourself instead of spreading false information.

Another example: If you have 2' of rope out and are 1' below the anchor point (-1 distance from anchor), you have 1' of slack in the system. The fall would be 1' with a FF of .5:

 

[dbldrew]

You are just misinterpreting the math.

2' of rope out and 0 distance from last anchor means you are standing with your waist parallel to the anchor and there is 2' of rope hanging between you and the anchor. You fall 2' with 2' of rope out, giving a fall factor of 1. If I climb to the end of my tether above the anchor point and fall, it's a fall factor of 2. If I'm below my anchor and fall, it's a fall factor of <1.

Edit: There are MANY conversations about fall force over at mountainproject between people who have been falling on ropes for fun for several decades. I encourage you to educate yourself instead of spreading false information.

no you are not understanding how it works..

look at this gif..





the climber climbs past the last anchor in the gif he is ballpark 6' past his last anchor when he falls, so 6' above means he will be 6 feet below before the rope starts stopping his fall (plus whatever slack the belayer has given him) so the reason that the calculator also wants the rope length is because of how much stretch a dynamic rope gives, the longer the rope the more stretch or "bungee" effect you get therefor reducing the kn on you and your gear.

what that calculator showed was that if you weigh 160lbs you will generate 1800lbs just hanging from a rope.. that calculator is seriously flawed

 

[powhound84]

I understand 100% how this works. I've been doing it for years. I've also fallen on all sorts of systems. You aren't understanding the input. All the scenarios I showed are falls, it's not dead weight hanging on a rope. Your logic is flawed. Hanging from the rope would be 2' out with -2' from the anchor. If you are hanging, you are at a negative distance from the anchor. Again, the distance is assuming you climb ABOVE the anchor. I can't count how many times this has been discussed in relation to getting gear in the wall immediately after starting a new pitch on a multipitch climb to avoid a FF 2 fall.

Sorry bud, you are flat out wrong. Again, please stop spreading false information.

Example of hanging from rope:

 

[kyler1945]

no you are not understanding how it works..

look at this gif..

View attachment 18391



the climber climbs past the last anchor in the gif he is ballpark 6' past his last anchor when he falls, so 6' above means he will be 6 feet below before the rope starts stopping his fall (plus whatever slack the belayer has given him) so the reason that the calculator also wants the rope length is because of how much stretch a dynamic rope gives, the longer the rope the more stretch or "bungee" effect you get therefor reducing the kn on you and your gear.

what that calculator showed was that if you weigh 160lbs you will generate 1800lbs just hanging from a rope.. that calculator is seriously flawed

In keeping with your example of jumping 4 feet from a table and only generating 800lb of force, I'll ask again.

How confident are you in this math? At ground level (Your feet at 5' off the ground), would you be willing to fall four feet in a saddle, and have that fall arrested by a static rope as your anchor(tether)? According to your math, that fall would be below the 900lb threshold that OSHA has in place for "belt style/body belt" harnesses. They are ultra conservative, so you should be just fine...

 

[powhound84]

@kyler1945, I like the sig