Ropeman Safety

[mattsteg]

Is it possible to combine a ripstop with an ascender like the RM? If so, what would that entail, another biner?

Without testing this is just throwing random hardware at a problem.
In broad brushes

1. Toothed devices seem to cut rope sheaths at 4-5kn or thereabouts. Most ascenders are toothed...because this is normally a good thing in their designed use.
2. Ripstops and similar fall-arrest devices arrest falls at a lower (but not documented) load than just hitting the end of a static rope.

In principle you could design a ripstop device that keeps loads below a specific value for falls up to some threshold. And in principle you could test and validate (at least to your personal satisfaction) what loading you were comfortable with an ascender device absorbing.

But for such an off-label application the onus is on you.

 

[Hubby11]

I confess I have not read all 18 (now 19) pages of this thread but curious whether anyone contacted the company to get their take. For liability reasons, my guess is that they will have some boilerplate response about "only using it for the purpose for which is was designed, etc.", but given it has gotten so popular in the saddle world, maybe they have some sort of position on it's non-ascender use?

 

[mattsteg]

Without testing this is just throwing random hardware at a problem.
In broad brushes

1. Toothed devices seem to cut rope sheaths at 4-5kn or thereabouts. Most ascenders are toothed...because this is normally a good thing in their designed use.
2. Ripstops and similar fall-arrest devices arrest falls at a lower (but not documented) load than just hitting the end of a static rope.

In principle you could design a ripstop device that keeps loads below a specific value for falls up to some threshold. And in principle you could test and validate (at least to your personal satisfaction) what loading you were comfortable with an ascender device absorbing.

But for such an off-label application the onus is on you.

Elaborating on this - the same report documenting the ropeman rope cutting, also tested fall protection absorbers. The products tested produce a higher level of force than the ropeman failed at (presumably the standard is such). So I will definitively state that they are unlikely to be useful here.

If you want a tested device, get a work positioning aid. Or use a prusik!

 

[dbldrew]

didnt read the whole thread but you are comparing 2 different worlds. Rock climbing have to be massively over engendered because of the type of falls that happen. When lead climbing you are "stitching" your way up the rock placing protective gear, so you place a cam or nut into a crack, clip your rope, and then continue to climb past it, so sometimes there is a lot of run out where there is not a good place to put your next piece of protection, so you might be 15 feet past your last protection when you fall. So you are looking at a fall of 30 feet plus slack, so you have fallen ball park 35ish feet before there is any forces applied to your gear. Compared to sitting in a tree where you might fall a few inches with using a ropeman in a saddle. Completely different protection needs..

 

[mattsteg]

didnt read the whole thread but you are comparing 2 different worlds. Rock climbing have to be massively over engendered because of the type of falls that happen. When lead climbing you are "stitching" your way up the rock placing protective gear, so you place a cam or nut into a crack, clip your rope, and then continue to climb past it, so sometimes there is a lot of run out where there is not a good place to put your next piece of protection, so you might be 15 feet past your last protection when you fall. So you are looking at a fall of 30 feet plus slack, so you have fallen ball park 35ish feet before there is any forces applied to your gear. Compared to sitting in a tree where you might fall a few inches with using a ropeman in a saddle. Completely different protection needs..

View attachment 18095

Rock climbers are also hanging from what are effectively giant bungee cords. They absorb shock and cushion the fall. We're hanging from eg. a 3 ft length of static rope. Depending on the rope. Maybe it stretches an inch at 4KN. It's not the fall...it's the sudden stop at the bottom. And Even a short fall is a real sudden stop for us.

 

[dbldrew]

Rock climbers are also hanging from what are effectively giant bungee cords. They absorb shock and cushion the fall. We're hanging from eg. a 3 ft length of static rope. Depending on the rope. Maybe it stretches an inch at 4KN. It's not the fall...it's the sudden stop at the bottom. And Even a short fall is a real sudden stop for us.

yes but that is irrelevant to using a ropeman for saddle hunting, the OP was worried about the ropeman only being rated at 15kn and the "rule of thumb was to be at least 22kn" the 15kn rating is over 3300lbs and you will NEVER reach the 3300lbs of force using a ropeman in a saddle hunting situation. We are talking about slipping off the platform and falling the distance of the slack of the tether.. To give you an idea if you had 4 feet of slack on your tether and had the ropeman at the very end of it and you fell and your body weight was 200lbs you would generate about 800lbs of force. no where near the 15kn rating of the ropeman.. to break the ropeman you would have to have so much slack that you would be about hitting the ground anyway.

My point was because of the possibility of 30-40feet falls in rock climbing that is why the 22kn is the rule of thumb to stick with.

 

[dbldrew]

Hillbilly math ain't right.
Leaving aside however much you bend which may painfully give you some leeway...
A couple of ft. Or less.

Fall Factor Calculator

how to fall

ferforge.tripod.com

this calculator is junk..

having a static rope (take the stretch out of the equation because thats whats used in hunting) distance to the last anchor of 1 foot so you are looking at a 2foot fall (plus slack) the calculator is saying a 200lb man will generate 10.5kn or 2300lbs.. if that was true everytime you jumped playing basketball you would shatter your legs.

Impact Force

Impact forces acting on falling objects hitting the ground, cars crashing and similar cases.

www.engineeringtoolbox.com

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

 

[mattsteg]

The ropeman isn't rsted to 15kn (in tests they've failed as low as 2.5kn, 500 pounds or so), rock climbers see nowhere near 22kn, and guys on a shorr static line have an easier, not more difficult, path to dangerous forces.

yes but that is irrelevant to using a ropeman for saddle hunting, the OP was worried about the ropeman only being rated at 15kn and the "rule of thumb was to be at least 22kn" the 15kn rating is over 3300lbs and you will NEVER reach the 3300lbs of force using a ropeman in a saddle hunting situation. We are talking about slipping off the platform and falling the distance of the slack of the tether.. To give you an idea if you had 4 feet of slack on your tether and had the ropeman at the very end of it and you fell and your body weight was 200lbs you would generate about 800lbs of force. no where near the 15kn rating of the ropeman.. to break the ropeman you would have to have so much slack that you would be about hitting the ground anyway.

My point was because of the possibility of 30-40feet falls in rock climbing that is why the 22kn is the rule of thumb to stick with.

 

[BenG]

this calculator is junk..

having a static rope (take the stretch out of the equation because thats whats used in hunting) distance to the last anchor of 1 foot so you are looking at a 2foot fall (plus slack) the calculator is saying a 200lb man will generate 10.5kn or 2300lbs.. if that was true everytime you jumped playing basketball you would shatter your legs.

Impact Force

Impact forces acting on falling objects hitting the ground, cars crashing and similar cases.

www.engineeringtoolbox.com

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

Energy isn't impact force. Look at the impact force in your example.

 

[mattsteg]

If you decelerate to 0 in 0 distance, that actually requires infinite force.

Taking the car crash example from the page you cite, lets sub in a 200 pound guy stopping in an inch.
After a 2 ft fall you're falling 2m/s or so.
3 ft of sterling Htp stretches about an inch at 4kn. Ropeman shreds rope at around that point.

That sudden stop generates 14kn. Or it would, but the rope breaks and the guy falls.

There's of course some wiggle room from you deforming...but that's not gonna be pleasant either.

this calculator is junk..

having a static rope (take the stretch out of the equation because thats whats used in hunting) distance to the last anchor of 1 foot so you are looking at a 2foot fall (plus slack) the calculator is saying a 200lb man will generate 10.5kn or 2300lbs.. if that was true everytime you jumped playing basketball you would shatter your legs.

Impact Force

Impact forces acting on falling objects hitting the ground, cars crashing and similar cases.

www.engineeringtoolbox.com

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

 

[Smokingbarrel270]

@mattsteg where you on the debate team in high school!? I commend you for keeping up your fight for almost 400 comments.

I had a girlfriend once tell me you have to be able to handle the bite if you want to play so with that being said I think the problem is these limp waisted ropes that cant handle bite haha.

Ok please proceed with your arguments... I feel like I'm watching a new version of the OJ trials...

 

[dbldrew]

The ropeman isn't rsted to 15kn (in tests they've failed as low as 2.5kn, 500 pounds or so), rock climbers see nowhere near 22kn, and guys on a shorr static line have an easier, not more difficult, path to dangerous forces.

i was going off of the OP 15kn on the ropeman and his worry that it was not rated at 22kn..

I fully understand that a static line can generate dangerous forces much easier.. I have been rock climbing for 25+ years I used the static line in the calculator because we all use static lines for saddle hunting. Was just pointing out the calculator does not work so dont believe the numbers its giving

 

[dbldrew]

If you decelerate to 0 in 0 distance, that actually requires infinite force.

Taking the car crash example from the page you cite, lets sub in a 200 pound guy stopping in an inch.
After a 2 ft fall you're falling 2m/s or so.
3 ft of sterling Htp stretches about an inch at 4kn. Ropeman shreds rope at around that point.

That sudden stop generates 14kn. Or it would, but the rope breaks and the guy falls.

There's of course some wiggle room from you deforming...but that's not gonna be pleasant either.

so your trying to tell me that a 2 foot fall generates 14kn or 3147lbs with a 200lb guy.. but a 4 foot fall with the same 200lb guy will only generate 3.6kn or 800lbs

I think your math is off a bit

 

[hogfish24336]

Yea, I think back to when my dad and I used to build treestands when I was a kid and it seems a miracle we never fell. Then we used actual seatbelts from old cars for a while too lol.

same except from jeeps

 

[mattsteg]

so your trying to tell me that a 2 foot fall generates 14kn or 3147lbs with a 200lb guy.. but a 4 foot fall with the same 200lb guy will only generate 3.6kn or 800lbs

I think your math is off a bit

No. Where are you getting this "800 pound" number? It's about as credible as a "25 year rock climber" who hasn't heard of a fall factor.

 

[dbldrew]

No. Where are you getting this "800 pound" number? It's about as credible as a "25 year rock climber" who hasn't heard of a fall factor.

When did i say that I never heard of a fall factor? All I said was your fall factor calculator does not work.. and we know this by just applying a small amount of common sense.. The calculator shows a 2 foot fall with a 200lb person generating 10.5Kn or over 2300lbs of force.. You dont need 25 years of climbing experience to apply simple common sense

I posted the link to the mathematical equations to show the "800 pound number"

But here it is again..

Impact Force from a Falling Object
The dynamic energy in a falling object at the impact moment when it hits the ground can be calculated as
E = Fw h
= m ag h (4)
where
Fw = force due to gravity - weight (N, lbf)
ag = acceleration of gravity (9.81 m/s2, 32.17405 ft/s2)
h = falling height (m)
If the dynamic energy from the fall is converted to impact work - equation 2 and 4 can be combined to
1/2 Fmax s = m ag h (5)
The impact force can be expressed as
Fmax = 2 m ag h / s (5b)
The deformation slow-down distance can be expressed as
s = 2 m ag h / F (5c)

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

 

[mattsteg]

Dude. Ft-lb is not a force unit. It's energy. Energy that is absorbed by the rope stretching. A short length of static rope stretches very little.

And it seems like at best you've heard of fall factor but decided you prefer hillbilly math.

Good god - you even pasted a force formula and then proceeded to ignore it!

Fmax = 2 m ag h / s (5b)
or in other words...
2*85kg*9.81m/s^2*4ft/2in...=40 KN

for sufficiently short drops your body absorbs and damps some of the force, depending on how you fall/swing.

 

[dbldrew]

Dude. Ft-lb is not a force unit. It's energy. Energy that is absorbed by the rope stretching. A short length of static rope stretches very little.

And it seems like at best you've heard of fall factor but decided you prefer hillbilly math.

Good god - you even pasted a force formula and then proceeded to ignore it!

Fmax = 2 m ag h / s (5b)
or in other words...
2*85kg*9.81m/s^2*4ft/2in...=40 KN

for sufficiently short drops your body absorbs and damps some of the force, depending on how you fall/swing.

Yes it is a force unit.. in fact thats actually what its called, foot pounds of force, or pounds of force. When you convert Kn to lbs it converts it to lbs of force.

And you think the engineering website is hillbilly math? lol ok stick with your "fall Factor website" where I put in a distance of .08333 (thats 1") so a 2" fall generated 10.2Kn lol

 

[mattsteg]

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...

 

[PaTrout1]

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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