Blake's Hitch Drop Test DRT, SRT
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- Опубликовано: 9 сен 2024
- This test examined the Blake's Hitch, a common friction hitch in modern day tree climbing. We used a DRT split tail, with New England Ropes Safety Blue and Hi-Vee, as well as a bolted 180lb rock. This test simulates a fall of a climber who was not properly tending the friction hitch.
A good experiment is worth more than a week of talking and theorizing!
But it's a lot more work, and you can't do it while tossing back a cold one, which is why most folks opt for the talking and theorizing. :-)
Excellent work!!
This is a very thoughtful experiment. Coming from the climbing community, we would never climb on a prusik like the Blake's knot, it is strictly for ascending, but arborists do it all the time. They trade off a weak point in the system to make their lines more easily and quickly adjustable. The whole point is to limit any fall to only a foot or so, but if climbing above the last point of attachment, distance is doubled. This is worth thinking about when scrambling about the canopy, since it wouldn't take much of a fall to duplicate what is shown here. Heavy rope is worthless if the weakness is in the prusik line.That said, I believe most guys use heavier line for the Blake's hitch, and sometimes double up a variant prusik knot onto either side of a pulley.
Yes, we have tested the prusik. I think the videos are around somewhere, but the general result is that you don't want to fall on a prusik. In long slow pull tests the prusik slid. In drop tests it didn't. If I recall correctly the prusik snapped at the knot under tests with fairly low fall factors. Ascenders, on the other hand stayed attached, but de-sheathed the rope.
@thwackaddict Sure thing. The setup was a split tail double rope over a bare branch (or pulley block) with a blake's hitch as the friction knot. During some past tests we saw the blake's hitch slide under very high impact forces. We did this test to more closely resemble a real situation - where an inexperienced person climbs without tending the slack in the line. Fall factor = Distance of fall / length of rope being fallen on.
@joshuarugg Yeah - I think we were anticipating that the friction part would slide. Certainly some other type of termination would have been stronger.
We don't really use a bowline for a termination knot for people or otherwise. We just figured that the Blake's hitch would fail before the termination knot. I think Morgan just tied it on there by chance. Cornell Tree Climbing is located in Ithaca, NY.
Cornell--great stuff. We can all learn a lot from your efforts. However, your "fall factor" needs some kind of standardization: a factor of 1.0 at 1 foot is very different than at 100 feet!
Get these guys some dynamometers!
i find it interesting that you guys used a bowline for a termination on that last bit. arborists are not allowed to tie in with a bowline becuase of possible sideloading the carabiners gate. maybe if it had been a tripple scaffold knot, it woulda held.
Great testing. Really demonstrated the integrity of the blake's hitch. Have you performed similar testing on triple wrapped prussic? We use the prussic in the fire service, but I've never seen it put to the test. Good stuff.
HowNot2 has done that
@thwackaddict I'm fairly sure that the cord was 5/16. It was definitely around just one strand of the climbing rope. I can't say for sure what a prussik would hold with this cord, as it may have cut at the gate of the carabiner. In general terms two strands are certainly better than one, but even still, this impact is pretty high. Previous factor 1 tests with regular utility cord snapped a three wrap prussik...
I looked closely at the diameter of the small blue cord, as I want to try 9mm hitch cord (compatible with ropes 11 to 13mm). I’m interpreting the diameter as 8mm, per my own eye, Samson’s ultra tec spec, and the 5/16in spec written up at the end of the video. Great work CornellTreeClimbing!
Seen this 1st time 0N 05-01-2107 really appreciate your video, ISA 10168AT
nice work!
180 lb = 81,6 kg for the metric guys.
@krackanz Oh, sure - We're pretty good with the numbers. We just like to break stuff!
where about are you from?
you have different rules to the uk, we can tie in with a bowline :)
Is that a Mazda 323 in the background or a Civic?
1991 Civic...good eye
What mm cord was the blakes hitch? Thanks and great video
it's been so long, i forgot...but it was pretty thin.
The orange is 1/2inch (12.7mm), the blue is 5/16inch (8mm).
this is why i only use my 9mm cords with blakes for foot loops, always staying on the mainline, becouse im 240lbs
Are y’all reset/redressing the Blake’s after each drop?
Good question...I don't recall. It was so long ago...
Yes you did it was noted at the end of video
a little common sense goes a long way