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winkwinklambonini
Feb 24, 2006, 10:56 PM
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I do not own doubles, nor a scale, but I'm wondering how they stack up.
I do have math though. Given a constant weight per area of a cross section of a rope:
area of 8mm double:50.24mmsquared
x2=100.48
area of 10mm single:78.5mmsquared
area of 6mm tag:28.26mmsquared
add them and you get:106.78
So if they all have the same length the single/tag combo has more volume and maybe weight?
If anyone has doubles or single or 60m tag line weight it,
I'd be interested to know.
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euroford
Feb 24, 2006, 11:56 PM
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go look up some ropes, they will have the weight per meter listed, your math will be more realistic that way.
(shit its hard to type right off the hangboard)
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sspssp
Feb 25, 2006, 12:34 AM
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The diameter the manufacturers list are pretty bogus. And one company used to (maybe still does) list the diameter of the "core" without the sheath.
Even the weight/meter is "tweaked." It is my understanding that the weight per meter is the weight of a meter rope after it has been stretched out by hanging some weight (35KG?) off of it. So if you took the weight per meter and multiplied it by 60m you still wouldn't get the real weight of the rope. The rope would weigh more (and stretchier ropes will show up in the catalogue as lighter than less stretchy).
Even simple things like the weight and sizes of cams are often significantly wrong.
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delcross
Feb 25, 2006, 1:02 AM
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slacklinejoe
Feb 25, 2006, 1:34 AM
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Go with grams / meter * advertised lenght it'll be close enough for comparisons.
Yes, weight / meter is modified, but rope length is sometimes subjective to the same type of measurements. Measure your rope under no stress and for many companies, it'll be shorter than advertised. Rope shrinkage occurs to complicate matters even more though, then there are companies like Mammut that intentionally under rate their rope length by something like 5% to account for shrinkage.
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kricir
Feb 25, 2006, 2:23 AM
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there is a section in Mark Twight’s book on this exact subject. A single lead rope with a skinny tag (7 mm) line is the lightest way to go.
twins are nice though, gives you redundancy in case one rope is cut, and let me say from experience, a 60m piece of 7 mm can be a damn fiddly thing to manage.
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winkwinklambonini
Feb 25, 2006, 3:03 AM
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I know somebody's got a scale in thier bathroom, with all the variables in length and diameter etc., it's easiest to just weight what ever you got, and post it. I think it would be interesting.........
I have a supersafe and a 7mm line that's about 15 feet shorter, I'll try to find a scale somewhere.......
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sspssp
Feb 25, 2006, 5:47 PM
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In reply to: there is a section in Mark Twight’s book on this exact subject. A single lead rope with a skinny tag (7 mm) line is the lightest way to go. twins are nice though, gives you redundancy in case one rope is cut, and let me say from experience, a 60m piece of 7 mm can be a damn fiddly thing to manage.
Well, yea a 60m piece of 7 mm is damn fiddly. But twins or doubles are even more fiddly.
There are always tradeoffs with weight and ease of use. If I don't think I am going to have to do a double rope rap, but want something "just in case", I take a 6 mm pulll line. If I expect to rap, I take a 8mm dynamic line. It is only a little heavier than 7mm, is easier to handle. And in a pinch, I would be willing to lead on it (even though it is not rated a single).
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iamthewallress
Feb 25, 2006, 7:04 PM
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In reply to: Given a constant weight per area of a cross section of a rope:
This isn't a great assumption for actually using them b/c you need to consider the drag to get a real feel for the weight you'll be tugging along on route. If the route winds like crazy, you can reduce drag using doubles, but if you're clipping them as twins, you can end up w/ a lot more drag than w/ a single.
A couple other things to think about (and the reason why I prefer twins to trailing a line) are that you effectively only need to stack one rope at the end of the pitch when you're using twins vs. pulling up 30-60m of trail line. Also, I don't need to worry about the trail line hanging up off route if I'm running twins.
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jakedatc
Feb 25, 2006, 8:20 PM
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Could also have the 2nd carry a coiled tag line in a small pack if you're only using it for raps. no stacking. no drag or getting stuck trailing it
could someone post or link the correct way to rig a single line rap with a small diameter pull line? pros/cons compared to a double rope rap.
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iamthewallress
Feb 25, 2006, 8:37 PM
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In reply to: Could also have the 2nd carry a coiled tag line in a small pack if you're only using it for raps. no stacking. no drag or getting stuck trailing it could someone post or link the correct way to rig a single line rap with a small diameter pull line? pros/cons compared to a double rope rap.
Then someone has to climb w/ a pack...and you need to change out the pack when you change leads. For me this has been a pain not only b/c I don't like the encumberance of a pack when I'm climbing, but b/c the pack needs to be readjusted for each person and dinking around w/ it takes as much time and energy as stacking an 8 mil.
To rig a rap w/ a small retreival cord bring small links and jam the knot against the links. You can back it up w/ a bight w/ a biner clipped through it and around the lead line.
The BIG FAT CON to this (if you're just using perlon) is that if it hangs up on the pull, you do not have any lead line in your paw w/ which to start releading the pitch inchworm style. I'd rather use at minimum a dynamic twin and rap in the usual way for this reason.
Also, it's good to experiment with small retreival cords at the crag first. In my (thankfully) limited experience w/ them they don't pull as well as bigger ropes and have a way of kinking up and jamming in all kinds of little constrictions that don't invite the big rope in.
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jakedatc
Feb 25, 2006, 9:01 PM
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Alright. pack i guess would be more beneficial on say full on slab where dragging the rope would leave you open to snag on things.
for double raps how much of a difference in diameter (both dynamic) is still ok? say 9.5 lead rope + 8.4/8.8mm half rope
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iamthewallress
Feb 25, 2006, 9:06 PM
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In reply to: for double raps how much of a difference in diameter (both dynamic) is still ok? say 9.5 lead rope + 8.4/8.8mm half rope
If you tie your knot tightly, pay attention to the way that you're feeding it through your device, and keep an eye on your ends, the difference doesn't really matter. I normally use a 9.7 w/ an 8.1 and I've never had the knot creep.
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winkwinklambonini
Feb 28, 2006, 11:36 PM
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Ok, even though everyone is off topic........
My spiffy new Mammut Infinity 60m 9.5mm:
8.2lbs
60m 7mm chord:
4.5lbs,
for a grand total of 12.7lbs.
Does anyone have doubles and willing to weight them?
I understand what someone said about drag, and althought it's a valid point, I'm not willing to give up the simplicity of one rope(which makes my interest in comparing them pointless....oh well). Especially since we usually carry the cord in a camelbackpack with the follower, and especially since we lead in blocks. Btw, I've tried the tech. where the pull cord is attached to the eight on a bight which in turn is clipped to the standing end with an even thinner line, and it does cause problems. We do the EDK between the 7 and 10+-, dressed to impress.
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yetanotherdave
Mar 1, 2006, 3:43 PM
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On my scale, my 60M 8mm mammut doubles are approx. 6 pounds each.
The MEC website claims 41 g/M, which gives 5.4 pounds (note that my scale isn't the world's most accurate).
The 7.5mm twins are listed as 39g/M, or 5.1 pounds per 60M rope.
So even with winkwinklambonini's skinny single, you'd save just under 1 pound with doubles, and almost 2 with twins. When was Twight's book written? Ropes have gotten a lot better in the last few years...
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mr8615
Mar 1, 2006, 4:01 PM
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I usually trail a 8mm static line when aiding, and make a butterfly coil backpack out of it when climbing multipitch trad that requires double rope raps. I've done plenty of leading with the line on my back and I don't even notice that it's there. I guess it would suck in a squeeze chimney, but other than that, it's super light and doesn't bother me one bit. Plus I feel way more solid rapping on an 8mm w/ a reversino and two biners than on a 7mm when simul-rapping. To connect the two, I just tie a figure 8 on the lead line and follow through the opposite way w/ the 8mil line, leavin plenty of tail. I'm not at home, and dont' have a scale, so I won't be weighing them.
Mark
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qtm
Mar 2, 2006, 3:11 AM
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In reply to: Ok, even though everyone is off topic........ My spiffy new Mammut Infinity 60m 9.5mm: 8.2lbs 60m 7mm chord: 4.5lbs, for a grand total of 12.7lbs.
My 60m 8.5mm Mammut Genesis come in at about 12.5lb; it could be +/- .25lbs since the scale only measures in .5lb increments.
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winkwinklambonini
Mar 2, 2006, 11:47 PM
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So they're about the same, good to know. Thanks 8^)
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