I destroyed some more 3D printed parts in the guise of science today. This time I put a spring balance between the hand winch and the kite line to measure the line tension that would break a line hook with kite line wrapped around it. I had one camera recording the fate of the hook, and another recording the tension being applied to the balance. The video quality is marginal, but the answer is that it takes between 19 and 31 kilograms of pull to break a 3D printed line hook. That’s 42 to 68 pounds of pull.
It is possible for a kite to generate that much pull, but it is not going to happen to Public Lab mappers and KAPers very often. A big kite in a 20 mph (32 km/h) wind will pull so hard that most kite photographers will go home. Such a wind could generate about 15 kg ( 33 pounds) of pull which will make your arms tired really soon. But last month some mappers flew a kite and camera at Far Rockaway in Queens, NY while JFK airport recorded 40 mph (64 km/h) gusts 4 miles away. A gust much lower than that could generate enough pull to break one of the 3D printed line hooks (if the kite didn't break first).
So I have discontinued the 3D printed hooks and replaced them with stainless steel fishing tackle. The new KAP’n Hook is a 3 inch long line hook used in fishing and to attach duck decoys to underwater lines. I modified them to save weight (removed a swivel) and to work better with kite line (narrowed the gap).
These are much quicker to attach to or detach from a kite line because the line is not wrapped around the clip. The clip just clamps down on the line. Because the line does not wrap around the clip, line tension cannot damage the clip (of course, this suggests that I could design a 3D printed version of this).
These clips are now included with the Picavet Kit and the Picavet Hardware kit at the KAPtery, where you can also buy then by the pair.