rcwild
04-11-2004, 09:31 PM
Submitted by Charly Oliver
When I worked at BlueWater, I would see ropes returned for sheath damage due to abrasion on a fairly regular basis. Invariably it was a brand new rope who's owner returned it complaining "the sheath just blew up!"
When a rope is under tension, it is surprisingly easy to damage the sheath, or in extreme cases actually cut entirely through the rope. This damage generally occurs when the rope (under tension) is dragged sideways across a sharp edge or an abrasive surface. Modern kernmantle rope design attempts to address this by building a sheath (kern) around the core (mantle) of the rope to protect it from damage.
The sheath of a modern kernmantle rope is relatively thin compared to the overall diameter of the rope. Say, 1mm of the 8mm total diameter. Smaller diameter ropes of course, have thinner sheaths than the larger diameters. Some ropes (BWII and Millet Canyon 2 are two examples) even have sheaths that comprise as much as 40% of the total amount of fiber in the rope.
Small diameter ropes are very attractive because they have the distinct advantage of being both lighter in weight and more compact in size. Their smaller overall size and correspondingly thinner sheaths allow these ropes to be more easily damaged than larger diameter ropes. Hence, (I got this word from Joey) these ropes are more suitable for use by experienced people in more remote situations where weight and overall size (bulk) are a consideration. Using a smaller, lighter rope trades off a certain measure of safety. This "traded off" measure of safety can be overcome by knowledge and experience.
Larger diameter ropes have an additional safety margin built in by virtue of the fact that they physically contain more material. The more nylon there is in a rope the more abrasion resistant it will be. Additionally, the thicker the sheath the more abrasion it will take to abrade through to the core. These ropes however, are much heavier and take up considerably more space in a pack. The trade off you make for safety here is weight and bulk.
All that said, I am a huge fan of skinny, light weight ropes. I rely on knowledge and experience to increase my "safety margin". This is also why I encourage first time rope buyers to purchase fat ropes. This gives them a rope able to withstand the inevitable accidental abuse (a first rope can not avoid) on which they can "learn". As a person gains more experience and learns how to identify situations and actions that can potentially damage a rope, they can then consider using smaller diameter ropes to lessen the weight/bulk package in their pack. People who do not understand the myriad dynamics behind rope damage will continue to "blow up" their ropes until they learn how to identify and avoid these potentially damaging situations.
There are now a number of awesome small diameter ropes available which run the gambit from not addressing the added safety issue that fat ropes provide at all, to using special high strength/high abrasion fibers to increase these safety margins. Please note, these ropes are designed to be used only by experienced people. They should not be considered for "first time" rope purchases.
Small diameter 100% nylon ropes cut more easily than large diameter ropes so an extra level of understanding and experience is recommended to use these ropes safely. These ropes do however, have a distinct advantage in that they are able to stretch and so absorb the shock of an accidental dynamic loading. Something to think about when faced with having to use a less than bombproof anchor.
The use of special fibers (Spectra or Dyneema) to increase strength is one way to increase the safety margin of a small diameter rope. Just using high strength, cut resistant fibers however, is not the answer. Ropes made of these special fibers should be used with caution because these fibers don't stretch (read absorb energy). By using these ropes you have plenty of overall strength and abrasion resistance but run the risk of of possible anchor failure under accidental dynamic loading. Again, something to think about when faced with having to use a less than bombproof anchor.
Moving side to side while rappelling will almost always abrade the sheath of the rope some. If you are careful, you can keep this abrasion to a minimum. There are numerous techniques and equipment specifically designed to address this situation and quite a bit of gear not specifically designed for this purpose but which works quite well.
A thorough understanding of equipment limitations and the techniques and gear designed to address these limitations is essential to making the choice to use small diameter ropes. Likewise, this same understanding can be be applied to larger diameter ropes to lengthen their useful life.
There are a lot of rope choices out there and it's easy to pick a rope that may not be suitable to you needs. I hope the group finds this discussion at least informative and hopefully useful.
When I worked at BlueWater, I would see ropes returned for sheath damage due to abrasion on a fairly regular basis. Invariably it was a brand new rope who's owner returned it complaining "the sheath just blew up!"
When a rope is under tension, it is surprisingly easy to damage the sheath, or in extreme cases actually cut entirely through the rope. This damage generally occurs when the rope (under tension) is dragged sideways across a sharp edge or an abrasive surface. Modern kernmantle rope design attempts to address this by building a sheath (kern) around the core (mantle) of the rope to protect it from damage.
The sheath of a modern kernmantle rope is relatively thin compared to the overall diameter of the rope. Say, 1mm of the 8mm total diameter. Smaller diameter ropes of course, have thinner sheaths than the larger diameters. Some ropes (BWII and Millet Canyon 2 are two examples) even have sheaths that comprise as much as 40% of the total amount of fiber in the rope.
Small diameter ropes are very attractive because they have the distinct advantage of being both lighter in weight and more compact in size. Their smaller overall size and correspondingly thinner sheaths allow these ropes to be more easily damaged than larger diameter ropes. Hence, (I got this word from Joey) these ropes are more suitable for use by experienced people in more remote situations where weight and overall size (bulk) are a consideration. Using a smaller, lighter rope trades off a certain measure of safety. This "traded off" measure of safety can be overcome by knowledge and experience.
Larger diameter ropes have an additional safety margin built in by virtue of the fact that they physically contain more material. The more nylon there is in a rope the more abrasion resistant it will be. Additionally, the thicker the sheath the more abrasion it will take to abrade through to the core. These ropes however, are much heavier and take up considerably more space in a pack. The trade off you make for safety here is weight and bulk.
All that said, I am a huge fan of skinny, light weight ropes. I rely on knowledge and experience to increase my "safety margin". This is also why I encourage first time rope buyers to purchase fat ropes. This gives them a rope able to withstand the inevitable accidental abuse (a first rope can not avoid) on which they can "learn". As a person gains more experience and learns how to identify situations and actions that can potentially damage a rope, they can then consider using smaller diameter ropes to lessen the weight/bulk package in their pack. People who do not understand the myriad dynamics behind rope damage will continue to "blow up" their ropes until they learn how to identify and avoid these potentially damaging situations.
There are now a number of awesome small diameter ropes available which run the gambit from not addressing the added safety issue that fat ropes provide at all, to using special high strength/high abrasion fibers to increase these safety margins. Please note, these ropes are designed to be used only by experienced people. They should not be considered for "first time" rope purchases.
Small diameter 100% nylon ropes cut more easily than large diameter ropes so an extra level of understanding and experience is recommended to use these ropes safely. These ropes do however, have a distinct advantage in that they are able to stretch and so absorb the shock of an accidental dynamic loading. Something to think about when faced with having to use a less than bombproof anchor.
The use of special fibers (Spectra or Dyneema) to increase strength is one way to increase the safety margin of a small diameter rope. Just using high strength, cut resistant fibers however, is not the answer. Ropes made of these special fibers should be used with caution because these fibers don't stretch (read absorb energy). By using these ropes you have plenty of overall strength and abrasion resistance but run the risk of of possible anchor failure under accidental dynamic loading. Again, something to think about when faced with having to use a less than bombproof anchor.
Moving side to side while rappelling will almost always abrade the sheath of the rope some. If you are careful, you can keep this abrasion to a minimum. There are numerous techniques and equipment specifically designed to address this situation and quite a bit of gear not specifically designed for this purpose but which works quite well.
A thorough understanding of equipment limitations and the techniques and gear designed to address these limitations is essential to making the choice to use small diameter ropes. Likewise, this same understanding can be be applied to larger diameter ropes to lengthen their useful life.
There are a lot of rope choices out there and it's easy to pick a rope that may not be suitable to you needs. I hope the group finds this discussion at least informative and hopefully useful.