Okay, another entry from my collection of different flippers; this is the Farralon Fara-Fins. They are iconic due to the leg brace, which no other fin has tried. Here's my pair, after a modification.
Fara-Fin Repair finished by
John Ratliff, on Flickr
Note that they also needed some suturing too, and an application of ShoeGoo over the suturing.
Now, I mentioned a modification. I bought these when they first came out, and rapidly discarded and sold them when I found that they would not let my foot get into a proper, pointed toe orientation to allow the fins to actually propel me. So years later, I got a pair off E-Bay that were broken, and endeavored to put them back together. In the pool after my suturing was a success, they again disappointed me. So I looked closely at the brace, and determined that I could use a grinder to grind down the limits on the brace's movable connection to the fin itself.
Fara-Fin Mod-2 by
John Ratliff, on Flickr
Note the difference in the amount of travel of the foot pocket/blade on the modified set of Fara-Fins.
The leg brace could be adapted to the person's foot too, by changing the "positive locking dial adjustment" on the brace.
Fara-fin 003 by
John Ratliff, on Flickr
Note, though, how the angle was not adjustable.
The fact that the angle could not be adjusted doomed this aspect of the fin. But the Fara-Fin continued without the leg brace, a mistake in my opinion, since once I got that blade angle adjustment correct, it became the best propulsive fin set I have ever used.
Sea Turtle-Dolphin Swimming by
John Ratliff, on Flickr
Now, with the leg brace angle set correctly, I could do a very powerful flutter kick or dolphin kick. Here I'm using it with my hammerhead unit and a dolphin kick. Note that the angle is such that the blade is actually at 90 degrees to the desired direction of travel, thus producing extremely effective propulsive motion.
I used this in a video (which I may post later) when I was working in very heavy currents in the Clackamas River trying to get video of Pacific lampreys spawning a few years back. With the leg brace, there is a lot more involvement of the thigh muscles than the calf, and of course, the thigh muscles are much larger and stronger than the calf muscle. Here's what I wrote on ScubaBoard about these experiments in 2017:
We here on the Vintage Scuba Community Furum also have a very good thread on these fins:
vintagescuba.proboards.com/thread/3155/farallon-finsJohn