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marky
climber
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Topic Author's Original Post - Feb 14, 2007 - 06:54pm PT
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thinking of buying some screamers for ice and aid. Would the garden-variety Screamer be adequate for both, or should I buy the more specialized aid- and ice-specific screamers?
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paganmonkeyboy
Trad climber
the blighted lands of hatu
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Feb 14, 2007 - 06:59pm PT
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I believe the ice and aid screamers have a lower activation threshold ? That would be a significant factor in which you should choose, imho...
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atchafalaya
Trad climber
California
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Feb 14, 2007 - 07:02pm PT
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yates' website has all the details on screamers.
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Nefarius
Big Wall climber
Fresno, CA
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Feb 14, 2007 - 07:31pm PT
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The Ice Screams have a tie-off built in so that the screamer can be used on the shank of the screw, in the manner you would use when tieing off webbing on the shank of a screw. This is actually really convenient.
Zippers are designed for long hard falls. They are smaller/more compact than the regular screamers. They are basically designed to take over where regular screamers leave off.
I'd say get a mixture of them. Maybe a few shorties/zippers for the first few bolts on a lead (ice or aid), where the fall factor will be higher, as well as some ice screams for the placements that will need to be slung.
For aid, I'd also recommend some Scream Aids for shakey hard aid placements.
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climbrunride
Trad climber
Durango, CO
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Feb 14, 2007 - 07:45pm PT
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The Scream Aids activate at a much lower impact force, but also have a much lower ultimate strength for the tie-off loop. They also have a lower energy absorbing capacity, before getting to full-length and turning into a regular runner. So they might save you on really dicey little stuff that even a regular Screamer might allow to rip out.
Shorty Screamers, regular Screamers and Zipper Screamers all activate at the same impact force. The Shortys and regulars absorb about the same total energy before they turn into runners. Shortys might just be more convienient, if you prefer shorter style quick draws. The Zipper is for potentially HUGE loads, and can absorb much more energy. (Think 10 feet to a manky bolt or tiny, bad nut to begin the second pitch, then 20 more feet to the next piece.)
Regular Screamers are great for general use and substiture well for quickdraws. I like to carry two of them on trad/alpine routes. For ice climbing, I carry about four as quickdraws, plus an Ice Scream or two. That has the same energy absorbing characteristics, but lets you do the tie-off thing. I set it up as a quick draw, but clip the bottom biner into the top one so it won't hang too low off my harness. I save them for last, so I'll have them available in case a screw bottoms out. If not, I just use them as a standard quick draw.
OLD-SCHOOL EDIT: I also like the wild lycra sheaths from the 80's/90's. I feel like they help to keep the dirt and grit out of the webbing. Yates doesn't use them anymore, so I just recycle my old lycra sheaths when I get new screamers. I don't know if John Yates would recommend this or not. There might be some reason why he doesn't use lycra anymore. (Besides the whole style thing - rock climbing and lycra got divorced in 1993.)
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Holdplease2
Big Wall climber
Yosemite area
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Feb 14, 2007 - 07:58pm PT
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Don't miss the Mammut "Shock Absorbers." They are made from spectra and are therefore far lighter than the Yates regular or shorty screamer. They are bartacked, rather than long stitches (hard to describe) so they "shudder" as they blow out.
I only carry the Mammut now as decreased weight and bulk make a difference if you want to carry 15 of the things. Rather than use the Zipper screamer, I'll just put two regular screamers in sequence if things are that grim. This way I don't have to drag some specialized screamer around.
Though the scream aids blow out at lower forces they also break at lower forces, so keep that in mind. Don't get lazy and start girth hitching these to nuts/heads or whatever. The 1/2 inch webbing will cut through on the wire before the thing even begins to activate. (NOT that I know... ;) ) Biners biners biners!
You can use the scream aids as tie-offs for pins, which is nice. But it better be a darn bad pin to make it worth it. If the pin is totally good, then you want your normal tie-off (Strong as can be) not a screamer that is going to blow out at 175 pounds and break just because you wanted to use it to tie off when the pin would have held 1000 pounds.
The best thing on the yates web site is talking about how you can use screamers in sequence to extend the time over which the screamers activate, further reducing your peak load when you do finally reach it. You can also use them in paralell to activate two simulataneously at double the load of a single screamer.
Tons of great info on the Yates site.
Hope this helps,
-Kate.
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crunch
Social climber
CO
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Feb 14, 2007 - 08:10pm PT
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The Screamers with the tie off loops sound convenient, but are not worth buying. The tie-off loop goes the way of all tie offs and rapidly gets cut/frayed, and once it's begun to fray you kinda wonder if the loop might just break if you fall. One more thing to worry about when you are already full of fear. Better to use a real tie-off (or two) and add a regular Screamer underneath.
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'Pass the Pitons' Pete
Big Wall climber
like Oakville, Ontario, Canada, eh?
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Feb 14, 2007 - 08:17pm PT
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One of the more impressive things about Yates Screamers is how uniformly they blow because of how well done the stitching is. Compare that to the bumpy deployment of the bar-tacked Mammut ones. Every "bump" is extra force, right?
Check out the smoothness of the Screamer activation chart. Apologies for hotlinking an image slightly wider than 700 pixels.
One thing I no longer do is girth hitch Yates Scream-Aids directly to heads - I now use a crab. Kate clued me into that one, and she can tell you why......
Yates Gear rocks! Their fall arrestors are second to none. You can click here to [url="http://www.yatesgear.com/climbing/screamer/index.htm#1"]read more about Yates Screamers.[/url]
Highly recommended by Dr. Piton!
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Holdplease2
Big Wall climber
Yosemite area
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Feb 14, 2007 - 08:33pm PT
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Pete, I think ewe'll find the Mammut aren't so baaaaaad, after all.
The bar tack blowing doesn't increase the force that the thing blows out at...each bar tack goes at something like 350-400 lbs at its individual peak.
Its just that there are micro-gaps between the tacks ripping out. Yates did it this way for a long time. If I said much more than that, I'd have to put on my Tall Boots, tho, as Im no physicist and would be talking sh#t from here on. :)
I also agree with crunch...how many tie offs do you clip and ruin during a wall? Tons. No big deal, though, as they're like 20 cents each. But you screw up the tie-off on a screamer and its 12 bucks you've screwed up.
-Kate.
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tomtom
Social climber
Seattle, Wa
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Feb 14, 2007 - 08:36pm PT
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The advantage of shorty screamers is that they are less likely to catch on a crampon when hanging from the back of your harness.
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LuckyPink
climber
the last bivy
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Feb 14, 2007 - 09:07pm PT
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personally I think everyone should do their own screaming...
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Russ Walling
Social climber
Out on the sand, Man.....
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Feb 14, 2007 - 09:38pm PT
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The bar tack ones that Kate might be talking about (where the bartack goes across the webbing instead of long ways down the webbing) will give you a very exciting gate flutter on a carabiner during load.... if you hit the end of the screamer while the gate is open..... oh well... broken biner. I believe that is why Yates and WildThings quit making them that way. YMMV
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rhyang
Ice climber
SJC
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Feb 14, 2007 - 09:57pm PT
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Shorty screamers are also more compact for 'alpine' stuff.
I have a partner who has some of the ice screamers and I hate them - they are so long that if racked from the harness you tend to trip on them. Annoying. Tying off ice screws is just not something I do.
Zipper screamers are meant for the first 1 or 2 placements off the belay, and absorb more force. Personally I have two of them. The rest are regular and shorties.
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Holdplease2
Big Wall climber
Yosemite area
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Feb 14, 2007 - 10:00pm PT
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Hey Russ:
Good point...Do you think that gate flutter thing is an issue with wire gates, as well as regular gates?
-Kate.
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Russ Walling
Social climber
Out on the sand, Man.....
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Feb 14, 2007 - 10:07pm PT
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Wire gates are supposed to reduce or eliminate it somehow... less mass plus more spring strength??? Anyway, if you get a regular biner and bang it against your other hand you can hear the gate slapping. With a wire gate, I do not think you get this slapping. So at a minimum, I would suggest using the wiregates on any of those load limiting things... or lockers to be sure.
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'Pass the Pitons' Pete
Big Wall climber
like Oakville, Ontario, Canada, eh?
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Feb 14, 2007 - 10:28pm PT
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Kate,
I wooldn't have guessed such a thang. My baaaaaaaaaad....
Just like wellies outperform leather in certain sit-ewe-ations, so do wire gates outperform regular gates, especially when thangs are a rattlin' like a barnyard gate left open in the wind. A feller [or gal, by tarny!] can't go wrong with'n a whar gate on th'end of a Screamer, no sir.
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P.Kingsbury
Trad climber
Bozeman
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Nov 12, 2007 - 01:09pm PT
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(old thread bump)
are the mammuts so much better that they can charge double for a screamer that yates has been making consistantly for years???
30 bucks seems like alot for a screamer (or is mgear just have a misprint??)...especially when you can score a yates for 12 bucks...
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tradmanclimbs
Ice climber
Pomfert VT
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Nov 12, 2007 - 01:20pm PT
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Ice screamers SUCK!!! they are too long, catch on sh#t. and heavy. Tying off screws dosen't work anyways, the nylon just cuts on the hanger. its a waste of energy to mess with a placement that bad in a situation where you are going to have to climb without falling anyways. I carry 6 reg screamers and 2 zipper screamers. The mamuts look sexy and light but have not seen the load specs on them and hate the price.
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rgold
Trad climber
Poughkeepsie, NY
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Nov 12, 2007 - 01:49pm PT
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The potential for gate flutter is still present even in the Yates version: Look at the 0.1 second interval in the graph with tension varying from 200 to 500 lbs or so. The situation, will, of course, be much worse for the bar-tacks, with the tension plunging to near 0 before climbing back up to the next bar tack's breaking strength, so I think the Yates units are much better.
The activation level is low enough not to break any biners, even with the gate vibrated open, during screamer deployment. The rub happens when the screamer fully deploys and the job of fall energy absorbtion passes back to rope stretch. If the fall is a long one, the tension will climb back up, possibly to gate-open failure levels, and the vibration may have left you with an open or partially open gate.
The ideal solution, at least if you aren't aren't carrying a truckload of screamers, is to equip each screamer with Mal's (i.e. Trango's) nifty light lockers. If alot of screamers are going to be deployed, perhaps having some with lockers clipped to the more reliable pieces is the best solution, with wire gates on the others if possible.
PS: The Yates site is is not entirely clear about Screamer functionality. Don't expect them to help that much for long falls. Their effect is primarily useful for short falls on crappy gear.
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tradmanclimbs
Ice climber
Pomfert VT
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Nov 12, 2007 - 02:11pm PT
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We just use em as ice quickdraws. They cant hurt INMOP. Lockers not an option. You need em fast and dirty. Wiregates, Strong body and a delosional mind are all that is required.
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TKingsbury
Trad climber
MT
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Dec 11, 2007 - 12:32pm PT
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Screamer nest or not, I wouldn't wanna fall from here!
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Holdplease2
Big Wall climber
Yosemite area
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Dec 11, 2007 - 12:35pm PT
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Specially not with that rope around the leg. Ouch!
-Kate.
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TKingsbury
Trad climber
MT
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Dec 11, 2007 - 12:38pm PT
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His leg/rope position is actually optimal, not wrapped nor between the legs, which would cause a flip.
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ec
climber
ca
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Dec 11, 2007 - 12:50pm PT
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"The bar tack ones that Kate might be talking about (where the bartack goes across the webbing instead of long ways down the webbing) will give you a very exciting gate flutter on a carabiner during load.... if you hit the end of the screamer while the gate is open..... oh well... broken biner. I believe that is why Yates and WildThings quit making them that way. YMMV" - Russ
If I remember correctly, there was a lawsuit filed against Wild Things over the use of the bar tacks. The accident occurred on an ice climb, the leader fell (unusual for ice IMHO) and the carabiner supposedly broke due to the gate flutter caused by the loading and unloading of the bar tacks ripping. The leader ended up breaking both ankles. When I worked at Sunrise Mountain Sports, some guy discreetly ordered bought at least 40 of them. I later found out that he was an investigator on this and was testing them concerning this accident.
 ec
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ec
climber
ca
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Dec 11, 2007 - 12:55pm PT
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rgold,
The still present flutter on the Yates screamers is apparently minimized compared to the former design and not an issue.
The longer the fall, the more rope you're going to have to absorb the energy of the fall...You're mostly correct, for 'short falls' on crappy gear. A long fall on crappy gear, either way, you're on your own, if you think about it...
ec
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Holdplease2
Big Wall climber
Yosemite area
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Dec 11, 2007 - 12:56pm PT
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Hmmm....OK, then,
So holding the rope behind your heel off to one side is better than climbing straight above it?
I could be wrong, but it looks to me like if he dropped straight down in a fall right now, the rope could end up behind his left leg and pointing up from the back out through the front his crotch, giving him rope burn and flipping him upside down, resulting in a helmet test.
OTOH, If the rope was dropping straight down between his legs, it would simply rotate at and point straight up in the fall, which is what you want it do do, right?
-Kate.
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P.Kingsbury
Trad climber
Bozeman
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Dec 11, 2007 - 01:04pm PT
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me on the route....
the picture makes the route look less steep than it is...(and i don't know if the gear would hold anyways...)
by keeping the rope in front of my body (and leg) if i slipped my feet would drop down and the rope would still be in front of me, making for a regular fall (edit...i would be falling to my right, not left)
if the rope was between my legs (the rope would then be behind my leg and body), as you suggested, if i slipped the rope would most certainly go against my calf and flip me for sure.
i have learned my lesson before and hope to not do it again, since i take wingers some what often.
thanks for your input though
but are mammuts really worth paying over double for??
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TradIsGood
Recently unshackled climber
the Gunks end of the country
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Dec 11, 2007 - 01:26pm PT
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I am in the "depends on how he falls camp." To me, it looks like his left hand is the more solid of the two. If the right foot slips and he catches with his left hand briefly, his CG may swing slightly left and his whole body may rotate clockwise, which could send the left ankle further under the rope - that would not be good, especially compared to having rope in front of leg. It is somewhat likely the same thing but without as much extension occurs on a left foot slip, but a barn door might save him if that happened?
Of course, it is hard to know exactly what line is straight down in this picture.
But having the rope between the legs does raise the issue mentioned. It is certainly preferable for the foot to stay below the rope. Which it nearly is now.
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Holdplease2
Big Wall climber
Yosemite area
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Dec 11, 2007 - 01:30pm PT
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OK, that makes sense. Its hard to tell that from the pic about the angle, it almost looks overhanging. Time and a place for everything, right?
I solve my rope position problems by refusing to climb above my gear. Less thought, safer all round. ;)
Regarding the screamers: I got a dealio on the Mammuts, so they ended up costing about the same as the Yates. I do like that they are less bulky, which is worth something to me, but how much depends on my disposable income at the time. Sometimes that number is high, sometimes its low.
Its probably mostly matter of taste, which some people are willing to pay for while others aren't. However, I will say that Yates has far more extensive testing data on their web site, and moved away from bar tacks.
According to the Mammut web site, their device activates slightly over 2.5 kn and the yates screamer activates at under 2 kn. Something to think about. CORRECTION EDIT: Read the wrong...Yates activates at >2kn. But they do have the scream aid option.
-Kate.
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Holdplease2
Big Wall climber
Yosemite area
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Dec 11, 2007 - 01:39pm PT
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* Standard SCREAMER, SHORTY, ICE-SCREAMS: Activation: >2kN. Reduction in system peak loading 3-4kN. Runner Strength: 26kN.
* ZIPPER Screamer: Activation: >2kN. Reduction in system peak loading 4-8kN. Runner Strength:26kN. (KR - Because it is longer)
* SCREM AIDS: Activation:>1.5kN. Reduction in system peak loading 1.5-2kN. Runner Strength: 7kN. "use on extremely marginal aid placements only"
Just as FYI. From the Yates web site. Mammut should make more info available on theirs, IMO.
-Kate.
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TKingsbury
Trad climber
MT
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Dec 11, 2007 - 01:51pm PT
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good info. Thanks Kate
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rgold
Trad climber
Poughkeepsie, NY
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Dec 11, 2007 - 04:12pm PT
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ec wrote: "The longer the fall, the more rope you're going to have to absorb the energy of the fall...You're mostly correct, for 'short falls' on crappy gear. A long fall on crappy gear, either way, you're on your own, if you think about it..."
I'm happy to share the dubious distinction of being "mostly correct" with you! Allow me to attempt a recovery by being a bit more precise:
Suppose you have a long factor 0.5 fall and a short factor 0.5 fall. At least in theory, without a Screamer, both falls will result in the same peak load at the protection, even though (or precisely because) "the longer the fall, the more rope you're going to have to absorb the energy of the fall." If a Screamer is employed in both situations, it may reduce the short factor 0.5 fall peak load significantly, but it will have little effect on the long factor 0.5 fall peak load.
So even though the two falls have the same "severity," as measured by peak load to the protection, the Screamer only helps much on the short fall. The explanation for this does not involve the fact that there is more rope available for arresting the longer fall.
We do agree, as does everyone, I suppose, on the creek you're up with a long fall on crappy gear.
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Majid_S
Mountain climber
Bay Area
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Dec 11, 2007 - 04:56pm PT
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I have few images of yates in action which may change your mind from buying them
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John Mac
Trad climber
Littleton, CO
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Dec 11, 2007 - 05:06pm PT
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Please post them up!
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flamer
Trad climber
denver
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Dec 11, 2007 - 07:27pm PT
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I used to be completely sold on screamers. The I started talking to some folks who tested them independantly...now I'm not so sure.
A lot of what they said was along the lines of what rgold is talking about.
rgold knowing(and understanding!) much more about the physics of it then I.
I've heard a couple of other things about them....the length a fully deployed screamer adds to the fall coupled with the "spike" in peak force (return?) once it is fully deployed making them not effective...I'd love to hear what rgold has to say about this.
Also I hear rumors that the violent vibrations from screamer deployment can cause certain types of gear to "wiggle" out of the rock?? Can anyone elaborate on this?
josh
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rgold
Trad climber
Poughkeepsie, NY
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Dec 12, 2007 - 12:54pm PT
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Josh,
My gut feeling is that Screamers and their imitations are over-rated. I hesitate to say even this much because so many people are devoted to them and insist that they took such and such a fall that was held by a screamer looped over a toothpick and this canape rig would never have held otherwise. But none of these stories comes with a repeat of the test to see whether, in the same circumstances, the olive and toothpick might have worked all by itself, so none of the testimony I've read seems to have any substance. Still, I expect some serious flammage for even suggesting that if it isn't quite true that emperor has no clothes, he is probably at best rather scantily clad.
I'd love to see some independent tests. Without such confirmation, I find it hard believe the claim on the Screamer site that "standard Screamer and Shorty Screamer reduce peak forces on protection anchors by 3-4kN." No qualifications here about the reduced effect as the length of the fall increases. Nor does it help that Yates has admitted that his Screamer numbers are better than one should expect and has suggested some principles that don't make any sense to me to explain the discrepancy.
I too have heard, from time to time, about people making their own tests of Screamers and concluding that their effect in reducing peak loads is quite limited. But these tests tended to be home-made affairs with very few trials, and it wouldn't be right to base conclusions on them. Whenever I try to calculate the Screamer reduction effect theoretically, I too come up with very modest results. But theoretical calculations have their own limitations and cannot be considered conclusive either.
Here is a very rough but still illustrative way to think about their effect. Let's use a 180 lb climber for reference. Screamers activate at 550 lbf and elongate two feet, so are capable of absorbing about 1100 ft-lbs of fall energy. But they also add four feet to the fall distance, meaning they introduce an extra 180 X 4 = 720 ft-lbs of fall energy that will have to be absorbed by the system. Consequently, their net effect is to remove 380 ft-lbs of the fall energy the rope would have had to absorb if there had been no Screamer, and 380 ft-lbs is the energy that needs to be absorbed if our 180 lb climber falls a bit more than two feet. So very roughly speaking, the effect of a Screamer for a 180 lb climber is to produce the peak impact on the pro that would have occurred if the fall had been two feet shorter.
Shortening a three-foot fall to one foot will obviously confer a significant benefit, and this is where Screamers can be expected to shine. But shortening a twelve foot fall to ten feet is not going to make much difference, and you can see where this is heading after that. Of course, with bad pro, one might argue that any reduction in peak load, no matter how small, is a benefit. We often place bad pro with an argument like this in mind anyway, so why not increase our chances a bit more? Sounds reasonable to me, my only point is, just don't expect too much.
As for the other objections, I don't believe in the spike effect (but I guess I don't even know what that means) and I find the vibration extraction of gear very dubious at best.
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rgold
Trad climber
Poughkeepsie, NY
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Dec 12, 2007 - 04:15pm PT
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Del, thanks for the reference, I hadn't seen it. It does seem to confirm the idea that Screamers don't reduce peak loads by much. I wish I could read Italian...
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morse
Trad climber
CT
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Dec 12, 2007 - 06:00pm PT
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Russ is right about the whole carabiner gate whiplash deal that is caused by horizontal bartacks.
I was photographing New England climber Pat Hackett who was tearing up the R-rated testpieces at Ragged Mountain, Connecticut, one day.
At the top crux of RAGGED EDGE 5.10d R, he was climbing above a small RP nut (#2 or #3) clipped with a Wild Things AIR VOYAGER. Right at the hardest move, he fell.
There was a noise like a long, loud fart, but the nut held!
But then we checked out the bottom carabiner on the Air Voyager (it was an old oval SMC or Eiger biner). What happened is that the vibration caused the gate to swing open while the carabiner stretched from the force of the fall.
When the fall stopped, the gate of the carabiner was trapped on the outside of the oval!
Pat went right back up on the climb, reached his high point, clipped in a second sling to the RP and sent this proud route on his next go.
Later, three of us were standing on top trying to stretch the carabiner and pop the gate back in. It didn't work, but at least there's a memorable souvenir from the climb.
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Melissa
Gym climber
berkeley, ca
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Dec 12, 2007 - 06:19pm PT
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Why aren't dynamic runners (like ropes) more componplace? In order to get something to stretch enough to matter, over such a short distance, does it loose too much stregth?
Anyone every monkey around w/ draws made of tight metal springs?
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John Mac
Trad climber
Littleton, CO
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Dec 12, 2007 - 07:05pm PT
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I use Trango Superfly lockers (Great Product!) on my Yates screamers and incorporate them into my anchor when soloing and also the first few pieces to limit the impact on the anchor. Other than that I don't worry too much about it once I get a decent amount of rope since I think the rope will take care of it.
Lockers are the way to go and the Trango Locker don't weigh much more than a standard biner. I brought 20 of them one day at Bentgate and they thought I was a real looney!
http://www.trango.com/prod.php?id=112
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flamer
Trad climber
denver
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Dec 13, 2007 - 05:33pm PT
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rgold,
Thanks for your reply.
The tests I was talking about were done by Rigging for rescue.
They were done in a very controlled environment.
What they came up with was similiar to what you discussed. However they talked about a "spike" effect that occurred when the load limiter came to the "end" of it's deployment.
They were using a dynmator(sp?) attached to a computer program so they could go back and examine the force's over time. What they said was when you look at the force's over time you could see the force that activated the load limiter, then you'd see the force's descrease(or slow down?) has the limiter extended, then when it came to the end of the limiter you'd see the force "spike" back up to near the original impact force. How this all relate's in the grand scheme of physic's is beyond me. My lay man's interpretation is that instead of "impacting" the marginal piece once, you instead "impact" it twice.
The vibration "wiggling" out gear thing was fairly specific. It wasn't RP's or cams(although it could cause cams to walk), but fixed pins that apparently could be a problem. Which does make some sense in my mind. Think about a marginal pin with only a couple of limited points of contact, maybe throw in alittle leverage...wiggle, wiggle....PING???
Who knows?
josh
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Russ Walling
Social climber
Out on the sand.... man.....
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Dec 13, 2007 - 05:49pm PT
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flamer writes: My lay man's interpretation is that instead of "impacting" the marginal piece once, you instead "impact" it twice.
This is just not true. The impact force to activate the screamer (or whatever brand device) is miles below the peak force that would have been on the piece had there been no screamer.
As the screamer deploys, as I understand it, energy is absorbed by the increased "time" and the increased "distance" and a braking effect from the resistance in the stitches. In an ideal situation the screamer would be long enough to never hit the end of the ripping stitches. Usually this is not the case, and there will be a "spike" when the screamer is fully deployed and there are no more stitches to rip. This final load should be below what the piece would have experienced had there been no screamer, this due to the additional "time" and "distance" and the braking effect the stitches have had on the load, and the elongation of the rope over that time.
as an example: say you have a screamer that starts to blow stitches at 500lbs. You ping off onto this screamer, and if it starts to blow, the 500 lbs limit has been reached until you either hit the end of the screamer, or you slow down enough to put your load back under 500lbs. If you dropped a 1 million pound weight onto a 500lb screamer attached to a #2 copperhead fixed at the top of ElCap, and the screamer was 3000ft long when fully deployed, the piece would hold, and the weight would slam into the talus.
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rgold
Trad climber
Poughkeepsie, NY
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Dec 13, 2007 - 06:57pm PT
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I agree with Russ; there's nothing you'd call a double impact. I think the term "spike" is misleading too. If you graph the load on protection over time, what I believe you see is a curve that rises until the screamer activation level is reached (the rope is stretching during this portion), then basically (or ideally) a horizontal line (i.e. load to pro remains constant at screamer activation level) while screamer is deploying, and then essentially the continuation of the original loading curve up until the peak load is reached.
I really do mean the continuation of the original loading curve, because while the screamer is extending the rope tension remains constant at the activation level, after which it continues to rise just as it would have if there were no horizontal interlude. (I think calling this a "spike," considering that we would have seen essentially the same curve had their been no screamer, is what is misleading.) The difference is that, since the screamer has absorbed some fall energy (not all that much, as I have argued), the load curve for the rope peaks at a lower level. I've suggested that the eventual peak in the curve will not, except perhaps for some very short falls, be much lower than if the screamer hadn't been used, and this seems to be confirmed by the tests that have come to light so far.
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Melissa
Gym climber
berkeley, ca
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Dec 13, 2007 - 09:01pm PT
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Maybe the physics gurus and wall experts already know about this, but I did a little googling on load-limiters and learned some interesting bits about seatbelts:
First, many seatbelts use rip-away stitching too as did most of the industrial load-limiting 'I don't want to deck off this scaffolding' lanyards that I saw. Many of the latter were made of elastic material, but I recon in those cases, the main load concern is the person, not the anchor. They were rated to strengths that would be helpful in catching climbing falls, although I don't know if recoil might do more harm than good.
Some also use a deformable metal bar that twists and bends to minimize the static jolt that happens when the stitches are all deployed. It would be interesting to see a biner with a sort of false bottom that bends when loaded, but w/ a real bottom that would prevent the whole works from breaking. I'm guessing it would be a tall order to produce structurally.
I also looked into load limiting knots. The only discussions I could find talked about how it lowered the strength of the material, but I figured in a dicey aid fall, you'd worry about your peice ripping or breaking long before you'd worry about using 7 mm Perlon at 30% strength. Do any of you know of which knots are most often use this way or of any data for impact absorbed by knot slippage?
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rgold
Trad climber
Poughkeepsie, NY
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Dec 13, 2007 - 10:02pm PT
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Melissa, it seems that ordinary tie-in knots account for a significant amount of energy absorption:
"We were able to make accurate measurements of the system stiffness and show that knots play an important role in system stiffness. The figure-8 follow through knot absorbs an equivalent of nearly 1.5 m (5 feet) of rope for the first impact force. After that, the knot is "hardened" and has less absorptive ability. Some climbers have theorized this and make it a general practice to retie their knot after every fall. Although not of practical use on bolted sport routes, this could have major consequences when falling on questionable anchor points."
From Measurement of Dynamic Rope System Stiffness in a Sequential Failure for Lead Climbng Falls, J. Marc Beverly and Stephen W. Attaway.
Google gives the following link:
http://www.amga.com/resources/various/Sequential_Failure_Paper.pdf
I don't use a figure-8 myself but have gone back to a double bowline rather than a single bowline on the assumption that you'd get more tightening effect from the double bowline.
I'm also reminded of a book from my now quite distant days of youth, On Climbing by Charles Evans. There he recommended something called the Tarbuck Knot, which was meant to be an energy absorber at a time when not all ropes were nylon. This knot looked pretty much like a loop tied with a prussik; one sees similar things nowadays in knot books for tent guyline tightening. The knot contracted under the tension caused by the prussik loop part. That book had some pretty wacky stuff in it. It'd be a hoot if the Tarbuck Knot was actually worthwhile...
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Melissa
Gym climber
berkeley, ca
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Dec 14, 2007 - 08:42pm PT
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rgold...Thanks for the knot reference. I'll try to post a pic of the one that J devised.
Does anyone else have any info/input on ripstitch alternatives?
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dirtineye
Trad climber
the south
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Dec 14, 2007 - 11:13pm PT
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OK the flat spot in the curve would be something like a local minima, wouldn't it? Not a spike but almost a dip, but not quite.
Has this been covered: as the screamer extends (and once extended it's not dynamic like the rope is) you lengthen the fall (by the length of the extended screamer) but the rope out remains the same.
That load limiting tent knot thing might be scary. Rope rubbing on rope very fast, can that be a good thing?
If this doesn't make any sense I plead drain bamage
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rgold
Trad climber
Poughkeepsie, NY
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Dec 15, 2007 - 12:01am PT
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"OK the flat spot in the curve would be something like a local minima, wouldn't it? Not a spike but almost a dip, but not quite."
The "flat spot" is...flat, i.e. a section of the curve that is horizontal, meaning that during that time (the time while the screamer is deploying) the load to the protection is constant. However, the spike Josh was referring to is the portion of the curve after the level section. I argued that that portion of the curve doesn't deserve to be called a spike, since it is very little different from what would have seen without the Screamer, and in fact doesn't go up quite as high.
"Has this been covered: as the screamer extends (and once extended it's not dynamic like the rope is) you lengthen the fall (by the length of the extended screamer) but the rope out remains the same."
I did mention this. In fact, the fall is lengthened by twice the extension of the screamer. Call that extension s. The pulley point drops s units, and if you fix your attention on the pulley point and ignore the fact that it is dropping, what you see is s units of rope feeding through the pulley. So the net loss of altitude for the poor leader is 2s.
"That load limiting tent knot thing might be scary. Rope rubbing on rope very fast, can that be a good thing?"
Righto. I'm not aware of the Tarbuck Knot finding favor anywhere but on Charles Evans' waist loop. But in any case, when knot tightening happens, there must be rope rubbing against rope. Not too much, one surmises. The Tarbuck Knot might be a lot worse. Personally, I am not planning to find out.
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dirtineye
Trad climber
the south
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Dec 15, 2007 - 04:37am PT
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Crap, I ALWAYS forget about the 2s.
So, what does the area under that curve mean? Is the area under the curve with screamer equal to the area under the curve without screamer?
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flamer
Trad climber
denver
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Dec 15, 2007 - 08:30am PT
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Wow i can't believe i could have been so dumb!
As russ and rgold point out my "laymans" interpretion was way off.
I don't know what I was thinking! As I read it again I can think is DUH!
josh
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Tom
Big Wall climber
San Luis Obispo CA
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Dec 15, 2007 - 12:11pm PT
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Here is a translation of the Italian screamer and rope dissipater testing.
[url="http://home.pacbell.net/takasper/ital_screamer_test.htm" target="new"]Italian Shock-Absorber Testing[/url]
The gist of the results is screamers are worthless for reducing the forces on an anchor.
EDIT: read at your own risk. I translated the article myself.
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rgold
Trad climber
Poughkeepsie, NY
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Dec 15, 2007 - 12:47pm PT
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"So, what does the area under that curve mean? Is the area under the curve with screamer equal to the area under the curve without screamer?"
The area under the curve, the integral of f dt, is called the impulse. Since f is the derivative of momentum, the impulse is equal, by the fundamental theorem of calculus, to the net change in momentum. Momentum at the moment the rope comes into play is mv, with v the climber's velocity at that moment. Momentum at the moment when the fall has been arrested is 0. So the net change in momentum is always mv, regardless of the way the force on the pro varies to arrest the fall. It follows from this that the area under the curve with the screamer is equal to the area under the curve without the screamer.
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Scared Silly
Trad climber
UT
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Dec 15, 2007 - 12:55pm PT
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What is difference between someone who falls 100 feet hitting the ground and someone who falls 10 feet hitting the ground?
The one who falls a 100 feet screams and then goes splat.
The one who falls 10 feet goes splat and the screams.
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rgold
Trad climber
Poughkeepsie, NY
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Dec 15, 2007 - 01:03pm PT
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Tom, thanks for the link to the translation!
It seems as if the predictions made from fundamental principles held true in the Italian tests. Note that their conclusions do indicate that Screamers may provide some value for short falls, which is again what one would expect, so their utility for aid climbing and very short leader falls within a few feet of the pro should not be dismissed. By the same token, their use on pro for moderately long runouts, a typical practice in ice climbing, I think, is probably illusory.
One does wonder why, with a live dynamic belayer, Screamers seem in some cases to perform worse than expected. A guess is that, in some cases, the Screamer activation serves to reduce the amount of rope pulled through the belay device, with the result the load at the top piece is ends up being slightly higher than without the Screamer.
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dirtineye
Trad climber
the south
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Dec 15, 2007 - 01:06pm PT
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Crap RG, I used to know that. Too much chemo, too much time passed.
I guess somewhere in the dark recesses the idea that those areas would be equal was still in there.
Thanks for the good explanation.
Impulse and Jerk (3rd Derivative) used to be two of my favorite things in classical mechanics. Maybe I'll go stare at the pages of Fowles for a while, and pretend I can still understand some of it.
Hey as far as the effect of a dynamic rope, I'm guessing that the dynamic quality widens and lowers the height that same curve, and that the dynamic properties are aiming for critical damping, ya think?
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Tom
Big Wall climber
San Luis Obispo CA
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Dec 16, 2007 - 06:12am PT
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I think rgold meant a dynamic belay in the sense that the rope slips. The Italian test data shows the extent of this slippage. They also ran "static" tests, with the belayer end of the rope securely tied off.
When the load without the rope dissipater was higher, it was probably due to operator error: the hand holding the munter hitch (1/2 barc; mezzo barcaiolo) wasn't consistent from drop to drop.
As far as critical damping goes, I probably depends on how much rock-rash the falling climber suffers.
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P.Kingsbury
Trad climber
Bozeman
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Dec 16, 2007 - 01:18pm PT
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So I'm out doing a little aid soloing the other day...up an overhanging rurp/ head seam. About 45 feet up the seam ends and my last placement is a love tapped cam hook, 3 feet above a beak, that is above a pretty good tipped baby angle.
I know that I'm going to drill soon since the features are ending, but i see one good edge that I can possibly hook off of. The edge seems good and it holds some small bounces.
I commit.
As soon as i start to drill from the hook though, I am instantly air born. Popping the hooked feature completely off and ripping the cam hook; but thankfully the beak held! The fall was only about 15 feet (eight or so feet of rope out above the beak) (all air), falling on to my cinch device. The screamer set-up at the belay only ripped about 1 stitch, and pretty much still looks new.
oh yeah none of the 16 or so pieces had screamers on them, just the belay.
My question is, me having almost 50 feet of rope out, weighing 135 plus a relatively large aid rack, and falling almost 1/3 of the pitch is not enough energy to activate a screamer?
I guess the bonus is that i still have an unactivated screamer...
(standard red yates)
The route did get finished though, 6 hours car to car in 20 degrees
edit: link to mproject route description: http://mountainproject.com/v/_in_progress/montana/gallatin_canyon/106078508
-Patrick
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rgold
Trad climber
Poughkeepsie, NY
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Dec 16, 2007 - 02:04pm PT
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"My question is, me having almost 50 feet of rope out, weighing 135 plus a relatively large aid rack, and falling almost 1/3 of the pitch is not enough energy to activate a screamer?
Not necessarily, if there is enough friction with the rope running through those 16 pieces to reduce the eventual load to the belay anchor to approximately the screamer activation level. If the screamer has been on the top piece that held you, I think you'd have seen substantial extension.
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