Duplicate from outhaul thread . . .
ok, velcro . . .
This is "genuine Velcro brand, made in USA", I bought at WM, which is not a 3m product, and appears to be weaker than the 3m product. So, first lesson is that there are differences in strength between the various hook and loop products.
I pulled between two shackles.
A straight line shear pull (eg no loops) I got 7.5 psi
A "2-wrap" I got 45 psi (6X the straight line - I 'expected' a bit more than 4x, and got +2x more)
A "3 wrap" I got 70 psi (9.3x the straight line - I 'expected' a bit more than 6x, and got +3.3x more)
So, it would appear there is a lot of advantage to the first loop, probably because it puts a compression friction loading on the velcro, and then significant but diminishing returns to further loops.
Extrapolating a bit - A 6' webbing piece made into a 3-wrap loop, of the 3m tape, should then be 72 sq in x 14psi x 9.3 = 9400lbs (if the 14psi spec is correct - I have some on order to test/confirm).
If I have this right . . . . That's pretty damn strong, dyneema soft shackle country - surprised these are not used in more applications.
As thinwater mentioned the failure mode is also nice . . . a very slow creep, rather than just letting go.