CT RollNLock vs. Ropeman 1

[NDH]

@ThePreBanMan, I box jump as well. I’m young, athletic and fit. I also like math. No JJ Watt, but I’ve hit 52” inches no sweat. You’re comparing coming down on two feet with flex in the knees to the force on a 11mm rope with a bit of metal surrounding it given the same force.

Jump 36”. Rebound off the box. Straighten your ankle and land directly on your big toe. One of them. Much better representation of the force from a three foot fall connected to a Ropeman 1. Video it. Report back.

 

[NDH]

TL;DR pounds per square inch is a thing.

 

[ThePreBanMan]

@ThePreBanMan, I box jump as well. I’m young, athletic and fit. I also like math. No JJ Watt, but I’ve hit 52” inches no sweat. You’re comparing coming down on two feet with flex in the knees to the force on a 11mm rope with a bit of metal surrounding it given the same force.

Jump 36”. Rebound off the box. Straighten your ankle and land directly on your big toe. One of them. Much better representation of the force from a three foot fall connected to a Ropeman 1. Video it. Report back.

The discussion revolved around the forces generated (thousands of pounds) the previously cited math indicated. How the body bears that force is irrelevant. The point was - are such forces even sustainable? If not then it calls into question the application of the formula and the accuracy of the result. Put a half-ton worth of plates on a barbell and drop the weight on your shoulders from a distance of zero.. Do this with both feet planted firmly on the ground. Bend your knees if you like too. Whatever you gotta do. Video it. Report back.

 

[kyler1945]

I would agree - as a fall arrest device - bad idea. That's not what it's designed for. The manufacturer makes that quite clear. It's an emergency ascender for rock climbing applications. I never advocated nor would ever advocate it's use as such and I do not use it in that capacity myself.

But my take on this thread is that people are coming across as "use it and you're a fool with a death wish:, when in reality nothing could be further from the truth.

The testing results...

http://www.hse.gov.uk/research/crr_pdf/2001/crr01364.pdf

...were examining it for use in industrial applications, not hunting applications. Additionally, the testing also showed that the rope makes a BIG difference. Some ropes doubled the performance of others. The folks here are just selectively taking the results of the poorest performing rope when citing this study as reason to abandon the ropeman. They also say "the ropeman cuts the rope" while neglecting to mention that it took 3 consecutive fall factor 2 drop tests on the same dynamic rope before that happened. I think everyone would agree that once your equipment arrests a fall once - you replace it. Pretty much every manufacturer includes that in their instructions. Everyone I've seen anyway. So again - not applicable to hunting scenarios here. We use static line and it should be replaced after arresting a single fall. So I see people citing the worst-case scenario with a total absence of any context. That test is totally not applicable to our use case.

The testing methodology also included bearing that load for an extended period of time. That is not something that occurs in a hunting scenario. It only needs to bear it for a split second (the moment the fall is arrested)

The 4 tests they conducted included:
Minimum working strength: Device to hold a force of 4 kN for 3 minutes.
Minimum static strength: Hold a force of 12 kN for 3 minutes.
Dynamic performance: Peak impact force and slippage with a fall factor 2 drop with a 100 kg mass.
***but from what distance. The document doesn't say... That's an important piece of the puzzle! It says see appendix 14.4.5 for info and there is no such appendix in the document.

Ultimate static strength: Initially it was intended as a final test to load all the devices to destruction. However, the severity of the minimum static strength test meant that most devices had already reached their limits during this test.

Thanks for clearing up where you were promoting the use of the ropeman as safe - on a lineman's belt.

Reading through - it appears the ropeman was left out of the dynamic performance test. That's odd, as that's the test that's really relevant to the issue at hand.

There are some wildly inconsistent results in that testing, and for many different reasons. This is why you see such a conservative rating on the device. A secondary reason being that you shouldn't be exceeding 4kn of force on your body to begin with.

 

[kyler1945]

The discussion revolved around the forces generated (thousands of pounds) the previously cited math indicated. How that occurred is irrelevant. Put a half-ton worth of plates on a barbell and drop the weight on your shoulders from a distance of zero.. Do this with both feet planted firmly on the ground. Bend your knees if you like too. Whatever you gotta do. Video it. Report back.

You just stated a few posts back that "the test isn't relevant because in hunting scenario it only has to manage the force applied for a split second."

The test above - i'm willing to bet that anyone here could handle 1000lbs of weight set on their shoulders for a split second (let's define it at .5 seconds), with the ability to bend their knees, without incurring any sort of injury. Again, the analogies aren't really relevant...

 

[Ontariofarmer]

For the record I’m not trying to be argumentative with this post but I think it needs to be addressed so that no one misinterprets your logic and inadvertently makes a bad decision. Also for the record, I am a practicing Mechanical Engineer with 30 years of work experience so I’m not making these numbers up. The calculations are very straight forward given some basic assumptions which I will try to make clear as I go.

While it’s true that the speed you develop from a 3 foot fall off a platform is the same as the speed you would develop jumping off a 3 foot step ladder, the force generated from that speed is not equivalent in the two cited instances. The force experienced is the mass of the body multiplied by the rate of acceleration applied to it. In this instance that acceleration is the deceleration from that common speed to the point that you reach a complete stop.

For a 200lb man falling 1 meter from rest (approx. 3 feet) the speed at impact will be approximately 4.43 m/sec (13.9 ft/sec) for both cases.

The major difference in the two cases, jumping off a ladder or falling on a slack line is the distance over which the slowing process is applied. The longer the distance, the lower the rate of acceleration.

When you jump off a step ladder you naturally flex your knees to absorb the impact over some short time/distance. Assume that you flex your knees 6” (.152 meters) from the point you first touch the ground to the point where your motion stops. This relates to an average deceleration of approximately 64.4 m/s^2 and an average landing force of approx. 5.8kN (1300 lbs).

For the case of falling on a 3 foot slack rope assume a total length of rope of 6 ft (3 ft hanging off the girth hitch and 3 ft slack hanging from your bridge). At an elongation factor of 3% for static rope that equates to an expected rope stretch of approximately .18 ft (.055 meters) from the time the rope starts to come taut to when it finishes stretching. In that shorter distance the average deceleration is approx. 179m/s^2 resulting in an average landing force of approx. 16 kN (3650 lbs).

This shows that you will experience a significantly higher force from the sudden stop associated with hitting the end of a rope that you will from landing off of an equivalent height jump to the ground.

This is one reason sport climbers prefer to use dynamic lines with higher elongation factors. A rope with a 10% elongation factor, and the associated longer deceleration distance, reduces the fall force to something on the order of 4.8kN for the same fall.

Again, not trying to be argumentative, just trying to provide some clarification. Hope this helps.

Edit: For the record I really like my Ropeman 1's and still use them on my lineman's belts. I have however quit using them on my tether when I'm one sticking up the tree as I do get slack in my tether when climbing using that method. For me, it's just not worth the risk.

So I like what you had to say. Are you confident your madrock safeguard is a lot better than your ropeman 1 when one sticking


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[ThePreBanMan]

You just stated a few posts back that "the test isn't relevant because in hunting scenario it only has to manage the force applied for a split second."

The test above - i'm willing to bet that anyone here could handle 1000lbs of weight set on their shoulders for a split second (let's define it at .5 seconds), with the ability to bend their knees, without incurring any sort of injury. Again, the analogies aren't really relevant...

I would not be willing to take that test.

 

[ThePreBanMan]

Thanks for clearing up where you were promoting the use of the ropeman as safe - on a lineman's belt.

Reading through - it appears the ropeman was left out of the dynamic performance test. That's odd, as that's the test that's really relevant to the issue at hand.

There are some wildly inconsistent results in that testing, and for many different reasons. This is why you see such a conservative rating on the device. A secondary reason being that you shouldn't be exceeding 4kn of force on your body to begin with.

No it was included. That's the rope they drop tested 3x before it broke. It's written poorly but if you look at the rope they tested, it was the dynamic line. Also the dynamic test was the only test that included an actual "drop". The others were just weight-bearing.

 

[kyler1945]

I would not be willing to take that test.

Haha me neither. Not because I don't believe my opinion - but because I wouldn't trust whatever equipment that was going to unload the weight, and it's an unnecessary risk for me to take. But lordy this conversation makes me miss doing heavy squats...

 

[ThePreBanMan]

For the record I’m not trying to be argumentative with this post but I think it needs to be addressed so that no one misinterprets your logic and inadvertently makes a bad decision. Also for the record, I am a practicing Mechanical Engineer with 30 years of work experience so I’m not making these numbers up. The calculations are very straight forward given some basic assumptions which I will try to make clear as I go.

While it’s true that the speed you develop from a 3 foot fall off a platform is the same as the speed you would develop jumping off a 3 foot step ladder, the force generated from that speed is not equivalent in the two cited instances. The force experienced is the mass of the body multiplied by the rate of acceleration applied to it. In this instance that acceleration is the deceleration from that common speed to the point that you reach a complete stop.

For a 200lb man falling 1 meter from rest (approx. 3 feet) the speed at impact will be approximately 4.43 m/sec (13.9 ft/sec) for both cases.

The major difference in the two cases, jumping off a ladder or falling on a slack line is the distance over which the slowing process is applied. The longer the distance, the lower the rate of acceleration.

When you jump off a step ladder you naturally flex your knees to absorb the impact over some short time/distance. Assume that you flex your knees 6” (.152 meters) from the point you first touch the ground to the point where your motion stops. This relates to an average deceleration of approximately 64.4 m/s^2 and an average landing force of approx. 5.8kN (1300 lbs).

For the case of falling on a 3 foot slack rope assume a total length of rope of 6 ft (3 ft hanging off the girth hitch and 3 ft slack hanging from your bridge). At an elongation factor of 3% for static rope that equates to an expected rope stretch of approximately .18 ft (.055 meters) from the time the rope starts to come taut to when it finishes stretching. In that shorter distance the average deceleration is approx. 179m/s^2 resulting in an average landing force of approx. 16 kN (3650 lbs).

This shows that you will experience a significantly higher force from the sudden stop associated with hitting the end of a rope that you will from landing off of an equivalent height jump to the ground.

This is one reason sport climbers prefer to use dynamic lines with higher elongation factors. A rope with a 10% elongation factor, and the associated longer deceleration distance, reduces the fall force to something on the order of 4.8kN for the same fall.

Again, not trying to be argumentative, just trying to provide some clarification. Hope this helps.

Edit: For the record I really like my Ropeman 1's and still use them on my lineman's belts. I have however quit using them on my tether when I'm one sticking up the tree as I do get slack in my tether when climbing using that method. For me, it's just not worth the risk.

So I like your reply. But I have a question on the bold. You're basically saying that this example human still needs to bear in excess of 1000 pounds over that 6 inches and they actually need to overcome that weight/force it in order for actual deceleration to occur over that 6 inches. That doesn't seem possible. I think there's more at play not being considered.

 

[ThePreBanMan]

Would you mind cutting and pasting, or pointing to the page/paragraph in the paper where it shows that the ropeman was tested in the dynamic performance test?

When you look at the graphic for the results of that test - the ropeman is not included. And when you read the page on the ropeman, that test isn't mentioned in it's summary.

page 51.

51 6.2.12 Wild Country Ropeman Material: Aluminium Weight: 60 gm Design principle: Body loaded, toothed cam Method of use: Work positioning Figure 32 Wild Country Ropeman back-up device (shown with karabiner attached, in diagram) Markings: On one side plate, “CE960120 Ø10-11mm ENGLAND”. On the other plate “WILD COUNTRY Ropeman” and the outline of a figure with raised hand.Performance in use: This tiny device was originally intended as an emergency ascender for mountaineering. Compared to the other devices it will not move freely on the rope, particularly downwards, making it difficult and time consuming to use. To descend the cam must be pulled away from the rope and held while the device is moved. This device is extremely difficult to remove under load. Test performance: In all the tests the results reflect the design of the device. As a small body-loaded, toothed-cam ascender experience has shown a likelihood that the sheath of the rope would be stripped rather than the device slip. In a static pull this occurred at approximately 6 kN. In the dynamic tests this occurred at impact forces as low as 3.5 kN, although on Beal rope a maximum of 6.3 kN was reached. On the third test with Beal the Ropeman actually severed the core as well, breaking the rope. These results are clearly unacceptable for a back-up device. While correct use of a passive back-up device can render only marginally suitable devices safe, in this case the design principles may have been pushed too far. The only advantage the Ropeman offers is that it will operate correctly and safely, even if grabbed by the user. This is a function of its body-loaded design principle rather than a unique feature. It is however, the principle reason why the company concerned adopted it. The reason that the Ropeman was adopted, rather than other devices, is due to the cam design.

 

[kyler1945]

page 51.

51 6.2.12 Wild Country Ropeman Material: Aluminium Weight: 60 gm Design principle: Body loaded, toothed cam Method of use: Work positioning Figure 32 Wild Country Ropeman back-up device (shown with karabiner attached, in diagram) Markings: On one side plate, “CE960120 Ø10-11mm ENGLAND”. On the other plate “WILD COUNTRY Ropeman” and the outline of a figure with raised hand.Performance in use: This tiny device was originally intended as an emergency ascender for mountaineering. Compared to the other devices it will not move freely on the rope, particularly downwards, making it difficult and time consuming to use. To descend the cam must be pulled away from the rope and held while the device is moved. This device is extremely difficult to remove under load. Test performance: In all the tests the results reflect the design of the device. As a small body-loaded, toothed-cam ascender experience has shown a likelihood that the sheath of the rope would be stripped rather than the device slip. In a static pull this occurred at approximately 6 kN. In the dynamic tests this occurred at impact forces as low as 3.5 kN, although on Beal rope a maximum of 6.3 kN was reached. On the third test with Beal the Ropeman actually severed the core as well, breaking the rope. These results are clearly unacceptable for a back-up device. While correct use of a passive back-up device can render only marginally suitable devices safe, in this case the design principles may have been pushed too far. The only advantage the Ropeman offers is that it will operate correctly and safely, even if grabbed by the user. This is a function of its body-loaded design principle rather than a unique feature. It is however, the principle reason why the company concerned adopted it. The reason that the Ropeman was adopted, rather than other devices, is due to the cam design.

Read right over it, thanks!

 

[boyne bowhunter]

So I like what you had to say. Are you confident your madrock safeguard is a lot better than your ropeman 1 when one sticking


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IMHO the cam won't cut the rope as the ropeman might. In addition the Safeguard/Lifeguard are belay devices, intended to arrest falls, if not to you, to another you are belaying. Also, as part of the instruction sheet the following instruction is given:

"DO NOT tie a knot or attach a mechanical braking device to the braking side of the rope. The Safeguard is designed to use the dynamic belay system and requires the rope to slide through the device to absorb the shock. If a mechanical device or a knot is placed at the braking side of the rope while the device is in use it may cause the device to break."

To me this means the camming action is intended to slip and gradually slow you down in a fall condition reducing the high forces of a sudden shock load. By placing something on the rope that impedes the ability of the rope to slip, the forces of a fall can cause the Safeguard to fail.

So in direct answer to your question, yes I feel safe one sticking on the Safeguard. That said, I take care to always maintain 3 points of contact as I don't want to experience any falls while climbing. If I'm on a larger tree which makes it harder to get my free hand behind the trunk when advancing the rope I will put my lineman's around the tree prior to moving the rope up.

On a side note relating to our previous discussion of quieting the clank of the carabiner/safeguard during climbing I have been recently experimenting with using a prussic or Blake's hitch in place of the Safeguard. Still a work in progress but it definitely is quieter.

 

[boyne bowhunter]

So I like your reply. But I have a question on the bold. You're basically saying that this example human still needs to bear in excess of 1000 pounds over that 6 inches and they actually need to overcome that weight/force it in order for actual deceleration to occur over that 6 inches. That doesn't seem possible. I think there's more at play not being considered.

I think the 6" deflection for a 3 foot jump is conservative. It's probably more like a foot to 18 inches( for an old guy like me its probably closer to 3 ft). At 18 inches the average force is down to around 400 lbs. Also, consider the force is only applied for milliseconds. I think these numbers are reasonable. Also, if I do the same calculations using the 6" flex and a 4 ft drop, I get exactly the results listed in the OSHA table (16 ft/sec and 1600 lbs) cited by @GCTerpfan earlier.

 

[ThePreBanMan]

You know I loved physics in college. I took all the classes I could as electives. But the physics I enjoyed involved the really big (starts, planets, black holes) or the really small (molecules, atoms, and particles). Physics 101 which was all the stuff about levers, pulleys, fulcrum points, and really this stuff... not so much. Maybe I should have paid more attention. If a mechanical engineer tells me I'm wrong, I'll have to concede the point.

I'm still keeping my ropeman though.

 

[boyne bowhunter]

You know I loved physics in college. I took all the classes I could as electives. But the physics I enjoyed involved the really big (starts, planets, black holes) or the really small (molecules, atoms, and particles). Physics 101 which was all the stuff about levers, pullies, fulcrum points, and really this stuff... not so much. Maybe I should have paid more attention. If a mechanical engineer tells me I'm wrong, I'll have to concede the point.

I'm still keeping my ropeman though.

Nothing wrong with that. I'm keeping mine too.

 

[Ontariofarmer]

IMHO the cam won't cut the rope as the ropeman might. In addition the Safeguard/Lifeguard are belay devices, intended to arrest falls, if not to you, to another you are belaying. Also, as part of the instruction sheet the following instruction is given:

"DO NOT tie a knot or attach a mechanical braking device to the braking side of the rope. The Safeguard is designed to use the dynamic belay system and requires the rope to slide through the device to absorb the shock. If a mechanical device or a knot is placed at the breaking side of the rope while the device is in use it may cause the device to break."

To me this means the camming action is intended to slip and gradually slow you down in a fall condition reducing the high forces of a sudden shock load. By placing something on the rope that impedes the ability of the rope to slip, the forces of a fall can cause the Safeguard to fail.

So in direct answer to your question, yes I feel safe one sticking on the Safeguard. That said, I take care to always maintain 3 points of contact as I don't want to experience any falls while climbing. If I'm on a larger tree which makes it harder to get my free hand behind the trunk when advancing the rope I will put my lineman's around the tree prior to moving the rope up.

On a side note relating to our previous discussion of quieting the clank of the carabiner/safeguard during climbing I have been recently experimenting with using a prussic or Blake's hitch in place of the Safeguard. Still a work in progress but it definitely is quieter.

I like the prussic with tender from new tribes. It works well. The only problem I see is accidentally releasing it when the tether is not tight if you pull yourself up by the tether instead of the stick
Thanks for answer on the safe guard

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[William74080]

Guess this is a bad time to ask if a 1in cam buckle and strap is safe for teather and line and belt.. lol

 

[Newhunter1]

For anyone not trusting their Ropeman 1, I will pay you $10 each to my door! Trying to help you out here.

John H.

While I still trust my ropeman on my LB, on my two tethers that is not the case...I will however keep them to save you the sacrifice of the 10.00 each. It's the least I can do.

 

[boyne bowhunter]

I like the prussic with tender from new tribes. It works well. The only problem I see is accidentally releasing it when the tether is not tight if you pull yourself up by the tether instead of the stick
Thanks for answer on the safe guard

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That's what I've been playing with. I took one of Aerohunter's plastic D-ring accessory hooks and threaded it on under the prussic to tend it. It works ok, probably would work better if I didn't weigh so darn much. Prussics get really tight when I suspend on them.