i use an a 7' leash in surf and never had a problem.
it's one that doesn't stretch though, the board will get dragged away from me by a wave, my leg will get a tug. then the board just stays that far away from me until i want to get it back.
i should get a helmet though, as a friends have had their heads bashed when getting tumbled.
I think that you may have been lucky, that your leg has not been yanked out of joint!
I base this opinion (right or wrong) on this comment, expressed a few years ago, on this forum:
"I haven’t tested the conventional surfboard leash, but have tested the ½ inch single thickness, nylon webbing strap that comes with the Oceanic Reel leash for its ability to store up this “potential energy”…and the results were scary…I would like to know how the plastic tubing of the conventional surfboard leash compares to the ½ inch webbing.
Here are some facts:
(1) When I applied 85 pounds of force (with my weight machine) to a 44 inch length of the ½ inch webbing, the webbing stretched about 4 inches (11% of its length). When the webbing was under tension and I applied about 100 pounds more of force to the suspended weights, it made the 85 pounds of weights on the machine…bounce up and down about an inch.
(2) This ½ webbing has a rated strength of 1000 pounds. Like most strength ratings, this is probably an under-rating of the true strength.
(3) The webbing is about 4 times as long as my test sample, so I think that it is reasonable to assume that the full length of the webbing can be loaded up with at least 4 times 85 pounds of force or 260 pounds of force…and I would guess that the full potential load and resulting force of the leash would be 3 times that amount of force.
(4) Without doing the math to determine the momentum with which an 8 pound kiteboard has the potential to slam into the kiter’s body, I would conclude from the damage seen in those pictures that it is something to be feared and respected.
(5) The fact that many kiters have actually broken the webbing on the reel leash indicates that the situation actually occurs, whereby the webbing is loaded up with more than 1000 pounds of force. The expected deterioration with time may allow the leash to break at less that this force, so this should be considered also.
(6) When these leashes break, most often the conclusion of the kiter, and the resultant complaint from kiter is: “the problem with the leash is that is not STRONG enough’…Why don’t kiters conclude that the breaking of the leash was a good thing?
Answer: Kiters don’t wear the reel leash on their ankle or wrist, or I think that they would conclude that it was good that the leash broke, when it did. Instead the leash is attached to the harness, and the harness is attached to the kite… and the source of the force on the leash is the power supplied by the kite. The kiter’s role in this system of lines and power supply can be viewed as simply …”ballast”… so the kiter never feels the extreme forces from the resistance of the board loading up due to the action of it “tombstoneing” or “fish-luring” of the board in the water."
So....based on the above information, I would comment that , if your leash was attached to your ankle, and not to the spreader bar or harness, then, during your incident of being dragged through the water... that your body was not acting in the manner of "ballast, just along for the ride", but instead, was functioning as part of the "leash", and as such, could have experienced a much greater force, which I would imagine, could have dislocated your leg.
What do you (and others) think about this analysis of the "chain of force... from kite lines to the resistance of the board"? And of its application to determining the safest place to connect the board leash to the rider.
From this picture, you can see that the "chain of force" goes through the harness, and that the kiter is "just along for the ride, as balast".