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92 lines
4.7 KiB
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<title>Cambridge Underground 1981: Slipping Ascenders</title>
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<link rel="ToC" href="../../../jnl/1981/index.htm" title="CU 1981 Contents page">
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<link rel="stylesheet" type="text/css" href="../../css/main2.css" />
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<center><font size=-1>Cambridge Underground 1981 p 22</font>
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<h2>SLIPPING ASCENDERS</h2>
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<p>Ben van Millingen</center>
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<p>On expeditions to Austria in the last two years several types of ascenders
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in different prusik systems were used. Pitches of varying lengths were
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climbed in muddy, icy, wet, and dry conditions. The most popular prusiking
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system used was the Frog, as its ease of handling was suitable on the pitches
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encountered in Austria which tend to be long and split by rebelays. This
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system in turn favoured the "Jumar" type ascenders rather than Ropewalkers.
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<p>In Austria, caves under exploration were left rigged during the whole
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expedition, being used by at least two people each day for two weeks. Some
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ropes rigged in muddy areas of the cave became mud-coated straight away, but
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after two weeks mud had spread onto nearly all the ropes, even in clean areas
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of the cave. Mud was often transfered from dirty racks, but also just by
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clothing rubbing against the ropes. The Fiesta Run in Eislufthöhle was
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particularly bad - a sloping pitch with the rope being lost in the mud lying
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on the wall. Similarly one arrived at the top of the big pitch in
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Stellerweghöhle as if one had just walked through a ploughed field.
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Often the seemingly dry, dusty mud was the worst for producing a fine coating
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of lubricant on the ropes. Under these conditions the difference between
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ascenders showed most strongly.
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<p>Jumars performed very well with almost no slippage, as did Petzls; by far
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the worst were CMI's. Though they were little used, the most certain ascender
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for use on muddy pitches were Ropewalkers, where the cam bites the rope by
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direct application of the climber's weight. On muddy ropes CMI's frequently
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slipped, providing an agonising ascent only made possible by fingering the
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cams into position at each step. Usually only one ascender slipped at a time,
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but occasionally the second slipped when shock loaded by the fall from the
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first.
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<p>Jumar type ascenders rely on spring loading to close the cam and thus grip
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the rope. The spring may not have the force required to grip on a very muddy
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rope, particularly if the cam teeth are also muddied. CMI's seemed especially
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vulnerable to clogging with mud. Even if ascenders were cleaned at the bottom
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of a pitch the cam was clogged with mud by the top.
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<p>The spring in CMI's is much weaker than that of a Jumar, and so does not
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provide sufficient force on a muddy rope to clamp it. Three springs distorted
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so badly that the cam was able to flap loosely in the frame rendering them
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useless. The cause of this might have been mud getting in behind the cam
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where it is pressed by the thumb each time the cam is opened. Furthermore the
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pin on which the cam pivots is held in place by a small circlip which does
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not look up to the task. This should never be used again once removed, as it
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is very easy to deform permanently.
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<p>Though no serious accidents were experienced because of the failure of
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CMI's; several people had falls which must have badly shock loaded both ropes
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and bolts at the head of pitches. From these experiences I do not feel that
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the design of CMI's is up to the conditions found underground.
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<p><hr>
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<!-- LINKS -->
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<img alt=">" src="../../../icons/lists/0.png">
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<a href="../../../jnl/1981/index.htm">Table of Contents</a>
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for Cambridge Underground 1981<br>
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<img alt=">" src="../../../icons/lists/0.png">
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<b>1980 Expedition info</b>:<br>
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<img alt="--->" src="../../../icons/lists/1.png">
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<a href="log.htm">Logbook</a><br>
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<!-- <img alt="--->" src="../../../icons/lists/1.png">
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<a href="bcracc.htm">BCRA Caves & Caving Report</a><br> -->
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<img alt="--->" src="../../../icons/lists/1.png">
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Stellerweghöhle - <a href="descnt.htm">from Descent 49</a><br>
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<img alt="--->" src="../../../icons/lists/1.png">
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Austria 1980 - from <a href="npcpub.htm">NPC Newsletter</a><br>
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<img alt="--->" src="../../../icons/lists/1.png">
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<a href="song.htm">Another Kick in the Balls</a> (expedition song)<br>
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<img alt=">" src="../../../icons/lists/0.png">
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<a href="../../pubs.htm#pubs1980">Index</a> to all publications<br>
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<a href="../../index.htm">Back to Expeditions intro page</a><br>
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<a href="../../../jnl/index.htm">Index</a> to Cambridge Underground<br>
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<A HREF="../../index.htm">Back to CUCC top page</a><br>
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