With regard to the link to the Black diamond test report:
The underlying intent of the testing was to determine the effect of a permanent marker pen (eg 'Sharpie pen') on a synthetic human rated climbing rope (EN892).
In my view, knot geometry was secondary in the testers mind - so not much attention was paid to precisely how each knot was tied (the F8 knots are there simply to provide a convenient attachment point).
The test articles did not point to any measurable effect caused by a permanent marker pen.
Criticisms of the Black Diamond testing:1. The test sample size was relatively small - and there has been no peer reviewed follow up testing by other testers to confirm or refute the results.
2. It was not reported as to the
duration that test articles were exposed to the sharpie marker pen.. eg was it 5 minutes? Was it 1 hour? Were ropes marked and then left for 24 hours or longer (eg a week)? Who knows?
3. No MSDS (or just 'SDS') info on the formulation of the sharpie pen was provided! In other words, we have absolutely no idea what the chemical constituents were in the 'sharpie' pen.
They could have at least done a litmus paper pH test - litmus paper would at least provide some clue on the pH of the sharpie pen. (A PH of 7 is neutral.. a pH less than 7 is acidic). The pH scale runs from 0-14. Note: It is well understood that
acids have an immediate destructive affect on human rated synthetic ropes (eg EN892 rope).
Given the cheap cost and easily obtainable status of
litmus paper - I am somewhat astounded that Black diamond did not check the pH of the 'sharpie' pen. You can even purchase digital pH test devices for less than $30 USD.
...
With regard to the reported positions where the knots yielded to load - the tester simply stated
As expected, the ropes always broke at the knot
The test configuration was a mirror (dual) test article - ie, same knot tied at each end of the rope.
It was reported that the test article that failed was the "bottom knot".
What does "bottom knot: actually mean?
We can only take a guess because (as is usual with these types of tests) - specificity is lacking.
Lets say we speculate and 'assume' the break occurred at the knot fixed to the stationary pin.
In most tensile testing machines, there will be a stationary (fixed) end and a moving end where the force generating machine is located.
I have noted before that it is rare for a tester to declare which knot and at which end broke first.
I have also pointed out that no one appears to have carried out extensive testing to look into this issue - ie which knot yields first - or is it random - or is it indeed affected by the test configuration where one end is fixed and the other end is 'moving'.
NOTE:Those of you who now wish to interject and
shout loudly that reference frames and Newtons laws point to both ends actually moving from the perspective of the knot specimen (even though one end of the test rig is fixed) can take a nice slow calming breath.
Yes - from one point of view within a moving reference frame - both pins on the test machine are 'moving'.
Please remain seated and remain calm
Please read very carefully before replying to this post:All I am suggesting is that someone needs to conduct peer reviewed lab testing to rule out any test rig bias.
What if there is indeed a measurable bias caused by having a test rig that employs a fixed pin on one side and a moving pin on the opposite side?
Right now, I am confident enough to state that we are
not 100% certain that such a test rig induced bias.
And further food for thought...
Could any experimental bias be introduced due to the spacial orientation of the test rig?
That is, a
vertically oriented test rig versus a
horizontally oriented test rig? Could gravity cause some slight bias in a test rig that is
vertically oriented?
...
As to the precise geometry of the hand tied test knots - this is another matter.
Upon closer analysis of a blown up image (which pixelates) it does appear that there is variation in the way the F8 knots are tied.
#1047 F8 can be tied in different geometries - predominantly in where the SPart is positioned.
In my view, the orientation/position of the SPart segment has no statistically significant impact on MBS yield.
However, it does affect the jamming threshold.That is, the position/orientation of the SPart segment plays a role in how the knot responds to load - and one way yields greater resistance to jamming.
I therefore respectfully disagree with Dan Lehman that the position/orientation of the SPart segment should be described as (quote) "strong Vs weak form" (unquote).
Rather, it is best described as; "jam resistant Vs vulnerable to jamming".
The j#1047 F8 is more
vulnerable to jamming when the SPart segment lies 'on top of' adjacent segments so it is located closest to the fixed eye of the knot.
