Knot test report:
#1053 Butterfly
Tester: Andy Schmitz (aka 'knot rigger')
Test date: April 2015
Link to test report:
http://tinyurl.com/ohlsd43Original link to post in IGKT forum:
https://igkt.net/sm/index.php?topic=5290.0 (under the name 'knot rigger')
This is an old post from IGKT - which I thought should be shifted to a more appropriate location (ie in Knot test reports!).
This is of interest to me - because I am in the process of writing a technical paper on #1053 Butterfly along with some other
BTL eye knots (bi-axially through loadable).
...
COMMENTARY:This may seem a little harsh - but I am of the view that Andy Schmitz made some technical errors.
1. Andy referred to the #1053 Butterfly as being either 'left handed' or 'right handed'.
This descriptor can be problematic.
Andy is referring to the twist method of tying the knot - where the twist can be in the 'S' direction or the 'Z' direction.
The problem is that
regardless of the chosen tying method, #1053 Butterfly is geometrically constructed from an 'S' overhand knot and a 'Z' overhand knot.
The geometry is always S/Z (or Z/S). It can
never be S/S or Z/Z.
And so describing a #1053 Butterfly as being 'left-handed' or 'right-handed' makes no sense (because it consists of a left-handed knot and a right handed knot).
2. What changes (according to chosen tying method) is the position of the
riding segment (which is visible from the overlapping side of the knot).
The riding segment can exist on either the 'S' side or the 'Z' side.
To create a riding segment on the 'Z' side - the initial twist tying method must be in the 'S' direction.
Therefore: A riding segment on the 'Z' side is created from a 'S' twist tying method (so called 'twirly flop').
A riding segment on the 'S' side is created by 'Z' twist tying method (ie a twirly flop in the 'Z' direction).
3. The underlying premise of Andy's test is to investigate if one side of a #1053 Butterfly is 'stronger' than the other.
Andy's test configuration (in my view) is incorrect - and does not prove if such a condition exists.
4. The test configuration employed by Andy was '
eye loading'.
When loading the
eye of a Butterfly, the direction of load will either be in the 'S' direction or the 'Z' direction. When loading the eye of a Butterfly, it is required that one SPart is chosen to be anchored.
In theory, there should be no statistically significant difference in MBS yield in either direction.
5. In order to investigate Andy's purported 'strong' v 'weak' side - the #1053 Butterfly would need to be subjected to a
BTL loading profile (bi-axial through loading - from Spart-to-SPart).
In addition, to remove variables from such a test configuration, each SPart would need to be terminated with a
tensionless hitch (#2047). The knot would then by pulled until the MBS yield point was reached - and then determine the point from where failure propagated.
SUMMARY:Andy's test was configured as 'eye loading'.
This test configuration did not prove if there was a 'strong' side or a 'weak' side.
The test configuration was incorrectly designed for investigating if one side of a Butterfly is 'stronger' than the opposite side.
To confirm (or refute) if a 'strong' or 'weak' side actually exists, the #1053 Butterfly must be subjected a 'BTL' loading profile (in a BTL profile, the eye is isolated from load).
EDIT NOTE:I have attached photos from Andy's original test report (I enhanced and tidied up the images - they were originally very dark and hard to discern any detail).
