I'll go out on a limb and state that this additional test is pointless. Newton's laws have been pretty well tested, so we can categorically state that the force exerted by your hoist at one end is equal and opposite to the force exerted by the tree on the other end. It is about as useful as doing the tests under different phases of the moon.
I have to agree with you Harold, However, we have an unresolved situation, the knots always jam on one side of the test rig. Do you have any ideas what might explain this or can you suggest a test to identify the cause?
Reading through the thread, I noted 4 cases of jamming. I might have missed something, but if it was 4, then if there is a 50-50 probability in each case, it would be like flipping a coin 4 times and getting heads each time. That is 1 chance in 16, which is not entirely incredible.
In my case, the collar of the end-to-end joining knot always jammed on the side facing the force generating machine.
This occurred in 100% of the tests.
I used EN564 cordage and EN1891 type A ropes.
In terms of jamming, I modeled my definition as follows:
Initial/threshold jamming; and
Maximal jamming.
With initial/threshold jamming, it is not possible to untie the structure by hand. Tools are required.
With maximal jamming, not even tools will not loosen the knot structure.
I did not reach maximal jamming - because the peak load I achieved was 12kN.
I speculate that maximal jamming will occur beyond 15kN (in EN certified ropes).