Maybe the muscle movements are more natural and comfortable. Swimming with high power foot fins is probably as fast as this, but it gets very tiring real fast.
Tiring is good though, it means you can reach a maximum of energy expenditure. There’s a trade off with how big to make the fins though, similar to gears on a bike. Too small and you get bigger losses, I assume.
Also depends a lot what you optimize for. For underwater swimming, especially scuba, you want to optimize for saving air, meaning minimize the total energy expenditure and keeping heart rate low (the mammalian dive reflex helps here too). In water, that means moving very slowly and with longer strokes, for the same reason container ships move slowly to conserve fuel. It looks really inefficient to pedal fast because all that water around your knees needs to be pushed back and forth for no gain.
From the videos, not much IMO. Presumably the guys doing it in the videos have a fair amount of experience with it, and it looks... awkward.
Flippers have a great deal of fine control in all axis, and this doesn't look like it does. I'm a pretty fair diver, but when you see guys who dive all the time, they look like they were born with those flippers.
And free divers? I can't imagine them giving up their fins. They take advantage of the really long and strong muscles in the legs.
I live near a fairly dangerous ocean in SF where I’ve gone bodyboarding with a wetsuit and fins. I’m concerned that, if caught in a current, fins are not enough to propel me out of it.
This would. The extra power and ease of propulsion could make all the difference.
I guess the logistics of the thing make all the difference here. Is this something you can detach from a surfboard and equip while being carried out in choppy waters? Could be either really useful or useless depending on that answer
Your comment kind of implies that a strong swimmer with a surfboard and the right knowledge will pretty much never be in a situation where a riptide/undertow/current/whatever you call it carries them out too far to swim back. Is that true? (It might be, I just know very little about surfing)
Well informed local ocean | river mouth swimmers are gemnerally aware of the currents and tend to know how far out they carry and where one can get to the side to make their way back.
That said, currents are strong, people have bad days, they can panic, water can be cold .. far colder further out than might be expected and that can weaken the body.
Surfing is a whole other ball of wax; dedicated surf spots might be well offshore and require a boat or a jet ski to even reach, if those get crunched by a slab or fail there might be a whole lot of swimming to get back to shore, assumming the surf didn't get you.
This article about my beach makes it sound like, if the waves are big enough, all bets are off. Note: it's about a surfer who died, but I'm focusing on the comments of the surfers they interviewed.
