26 February 2012

Do ropes need to rest between falls?

Black Diamond carried out some tests to find out if letting your rope rest between falls would help to reduce the peak forces experienced in a fall. They did tests where the rope was left to rest for 30 mins, 2 hours and 24 hours. They also checked to see if loosening the knot after a fall helped to reduce peak forces.

The graph shows successive falls from 1-10, with peak force on the vertical axis (using antique lbf as units, 1000 lbf = roughly 4.4 kN).

Their conclusions were:

"As expected, progressive drops resulted in increasing forces

The largest increase was from the 1st to the 2nd drop as expected

 Loosening the knot after each fall reduced the load a bit, but not much

Letting the rope rest 30 min between drops had a bigger effect at lowering loads than loosening the knot, but still not much

Allowing the rope to rest for 2 hours and 24 hours had an even greater effect at reducing the loads on the 2nd drop, as expected

Allowing the rope to rest 24 hours still resulted in a 2nd drop load of 11% greater than the first drop"

19 February 2012

Thread slings through wires rather than larks footing to improve runner strength

DMM carried out some tests comparing the strength of using a larks foot versus simply threading (ie 'basket hitch') a sling through a wire. This is often done when you can't clip a carabiner directly to the wire because it would end up with the carabiner being loaded over an edge. The results showed that threading a sling through a wire is always stronger than using a larks foot (ranging from 1kN to 5kN stronger roughly).

12 February 2012

Homemade offwidth super-size cam

Jeremy11 from the rockclimbing.com forums has created a very cool homemade cam for offwidth cracks. The cam is bigger than the biggest camalot (camalot size 6, range: 114-195 mm, weight: 650g) weighing in at around 850g with a range of very roughly 130-210 mm. He used an oversized solid aluminium axle - the original intent was to minimize weight but it turned out that over-sized aluminium axle was heavier than the steel alternative that he had considered.

The homemade cam side by side with other big cams. Image from rockclimbing.com forums

He tested prototypes of the cam and they held over 14kN - pull tested using a jeep!