Split Fin Bashing?

[Lorenzoid]

If split fins have a superior mechanical advantage, I wonder why more fish don't have split fins. It seems to me that it would have been a pretty good evolutionary advantage to be faster and use less energy than predators or prey.

Maybe I missed it, but I don't think anyone has said split fins provide more speed for less energy. They don't violate the laws of physics. The way I think of how split fins work, they can provide more speed but only at the cost of requiring more kicks and therefore more energy.

 

[Steve_C]

If split fins have a superior mechanical advantage, I wonder why more fish don't have split fins. It seems to me that it would have been a pretty good evolutionary advantage to be faster and use less energy than predators or prey.

Actually ambush predators like cudas, and reef fish that need to suddenly get away from a cuda have a fairly full fin but the fish that swim all the time tend to be fairly split like the tunas and some mackerals..

 

[nimoh]

Maybe I missed it, but I don't think anyone has said split fins provide more speed for less energy. They don't violate the laws of physics. The way I think of how split fins work, they can provide more speed but only at the cost of requiring more kicks and therefore more energy.

Faster while using less energy doesn't violate the laws of physics, the auto industry has been doing this for years. However, removing the "less energy" from my post doesn't really change it:

...It seems to me that it would have been a pretty good evolutionary advantage to be faster than predators or prey.

---------- Post added May 16th, 2014 at 02:33 PM ----------

Actually ambush predators like cudas, and reef fish that need to suddenly get away from a cuda have a fairly full fin but the fish that swim all the time tend to be fairly split like the tunas and some mackerals..

come on, that's clearly a force fin

...but good call. It's just a thought that popped into my head while reading through this thread. It could very well be completely irrelevant since fish don't have knees

 

[boulderjohn]

I have never owned splits, but I used to teach for a shop that had an on-site pool with a room full of rental equipment. I used a large variety of fins while I was teaching, including splits, just so I could get to know what they felt like. I also had an unusual experience in which circumstances forced me to use a student's oversized Atomic splits.

The main idea I want to add to this thread is that if you say you tried split fins once and know what they are like, you are wrong. You only know what that model of split fin is like. There is a world of difference among the various models. Some are so soft and floppy that I felt like I didn't even have a fin on when I wore them, but others are not nearly that bad. Depending mostly on the degree of floppiness, you can do all the kicks associated with technical diving with them, but I also agree that you can't do them as well.

About the back kick....

There are two very different ways to do a back kick that I know of, and the appropriateness of the fin depends a lot upon how you do it. I used to use a method that depended a whole lot upon the stiffness of the blade for propulsion, and I still have to use that method with certain models of fin. When instructing, I used to use a certain model of blade fin from the rental gear for the most part, and after working with an individual student in a group, I would back kick into position to face the whole group again. Our shop ditched all those fins one day and replaced them with another model of paddle fin. It took me at least twice as many kicks to cover the same ground--they were too soft and floppy. Thus, it is not only splits that can have this problem. On the other hand, I mentioned that I was once forced by a strange situation to wear someone else's oversized Atomic splits while teaching a class. They were literally falling off my feet as I used them. Still, when I backed up with them, I could do it surprisingly well, better by far than I could with the floppy paddle fins.

The second method of back kicking, the one I usually use now, relies upon the fin's side wall for propulsion. I have not tried this method with any split fins, but I would imagine a split fin with a wide side wall would do OK.

 

[nimoh]

The second method of back kicking, the one I usually use now, relies upon the fin's side wall for propulsion. I have not tried this method with any split fins, but I would imagine a split fin with a wide side wall would do OK.

I have tried this, and the problem I found was that the trailing half of the split fin catches, causing lift such that the fin doesn't track straight.

 

[freewillie]

In several posts recently I have seen several disparaging remarks about split fins. I did a quick search but there are no posts that give any reasoned response as to why. So here the question. Why do you consider split fins to be so useless?


FYI I dive in cold waters 7 degrees – 18 Celsius, but not often in any significant currents, mostly in surge and low viz conditions.

You are posting on a website asking questions to a group that in general are scuba fanatics (myself included.) If you see the tag lines most of the people who have responded are either very experienced with over 100 dives, are instructors, dive tech or caves, or all of the choices. I am a self admitted scubaholic but my diving is purely recreation. Mostly local shore dives and vacation. I don't dive double, anything even close to tech, will likely never dive caves or overhead environments, and in the ocean and on vacation never worry about silt like in quarries. For my diving and where I dive my split fins are just fine.

Split fins primarily cater to the recreational diver because they are easier to dive with less strain on ankles and knees, and are more forgiving when using poor kicking technique. They specifically by design are best and most efficient when using a standard flutter kick. For all those who complain that they are not good for frog kicks, helicopter kicks (which I still don't really know what type of kick technique that is), and back kicks how many times do you see vacation divers use those kicks? For the record I've done frog kicks and been in moderate current on drift dives and my splits did just fine.

When asking questions in a forum where most of the divers have special training and special needs their answers will generally reflect their experience and preferences. I don't even think the average LDS pushes them simply because they are more expensive than some paddle fins. I think it's more of if you sell something to the general population and have to please more people than less you want them in something the majority of people will find easier to dive. For the most part that would be a split fin. Doesn't cater to everyone but on average most will prefer them to standard paddles because they are more forgiving of poor technique, cause less strain on ankles and knees, are less likely to have issues with cramping than paddles.

If for no other reason I have a pair of splits that I like, they do well for the types of diving that I do, and I'm not going to have another argument with my non-diving wife why I need to replace them just because someone said I need to be able to do frog kicks, other specialty kicks, or any other type of diving I just don't do.

 

[fiziks]

During a DEMA show in Orlando, a dive shop owner friend of mine got us tickets to dive Disney's The Living Seas. In order to help maintain a stable environment for the fish diver must wear the equipment Disney provides. When I dove it they used split fins. I tried doing the frog kick, the modified frog kick, the modified flutter kick, shuffle kicks, helicopter turns and backward kicks and the performance of split fins was sub-par compared to ScubaPro Jets. I couldn't backward kick which I can do without fins as well as when wearing paddle fins. I know a girl cave diver who wears splits and can backward kick, but her kick isn't at all pretty as she seemingly forces the fins to obey and reverse.

Disney's use of split fins probably has more to do with who was willing to provide free equipment and pay the most to advertise themselves as the "Proud Sponsor of the Disney Living Seas Exhibit" than any benefit they though they would get "maintaining a stable environment". The issue for Disney is that they don't know where YOUR equipment has been and what sort of contaminants your equipment might carry. They assume you bathe on a regular basis, but not everyone is as meticulous about their equipment as they are about their own personal hygiene. They don't know what sort of parasitic bacteria your gear might be carrying.

---------- Post added May 16th, 2014 at 03:58 PM ----------

Maybe I missed it, but I don't think anyone has said split fins provide more speed for less energy. They don't violate the laws of physics. The way I think of how split fins work, they can provide more speed but only at the cost of requiring more kicks and therefore more energy.

I have used split fins. I have used a couple different models. Basically what I found was that they do require more kicks, but those kicks require less effort. The amount of energy to go from point A to point B in the same amount of time is about the same. I found that I could do timed laps in split fins almost as fast as I could with my Plana Avantis (but not as fast as my long fins), I just had to kick a lot faster, and I used about the same amount of energy. So I don't think they are violating any laws of physics.

BTW, when I took my GUE Fundamentals class, the instructor said it was impossible to do some of the skills with my Plana Avantis. She admitted afterwards that she was wrong, and I passed (Side note, some parts of the Fundamentals course were a bit humbling and I did learn some things - overall, a valuable experience, even for someone as experienced as I thought I was at the time). And the one guy who used split fins WAS able to do all the kicks except kicking backwards. The instructor loaned him a set of jet fins and he was able to kick backwards very well. He switched to jet fins immediately following the class. Me, I've had the same pair of Avanti's for 17 years now.

The other issue I'd like to address has to do with the silting issue. We tried a test in our local silty watering hole. I'm not going to claim that a flutter kick with paddle fins doesn't kick up silt, but we performed a test with divers passing over a silty area about six feet off the bottom. With jet fins and my Avanti's, you'd occasionally see a tuft of silt pop up beneath a down stroke. With the split fins and the increased number of kicks to cover the same distance, there was a virtual silt-smoke trail on the bottom behind the diver.

But I would not bash anyone who wanted to dive with them. Some people just don't have the legs for a good paddle fin. And i admit, mine do cause me to cramp up every once and a while.

 

[fjpatrum]

You're right. You can move your legs and feet in the motion of a frog and helicopter turn while in split fins. However, the absolute lack of any kind of propulsion, control, or results for your effort make them utterly useless AT those kicks. So, you can "do" a frog kick in splits.....but the splits won't "do" a frog kick in that you get nothing useful for your effort. For that reason, I believe that saying "splits can't do frog" is an accurate statement for the VAST majority of split fins.

"Utterly useless" is not how I would describe forward motion while diving when that was my intent. Was it as easy to do frog kicks in splits as it is in paddles? No. Was it utterly useless? Definitely no. I have experience with only one set of split fins and didn't have the bias that I think some people have. (I didn't know they weren't supposed to be able to do frog kicks and helicopters and somehow they worked for me.) Like I said, not as efficient as paddles for those kicks, but it is certainly possible and far from useless.

All that said, I prefer my snorkeling full foot paddle fins to my splits but I can't wear wetsuit booties or dive dry with my full-foot fins.

You use what's appropriate for you on a given dive. If that means splits, so be it. If not, that's fine too. I'm considering trying out some free-dive fins and jets too, if I can ever find any at a price I find reasonable.

 

[boulderjohn]

I have tried this, and the problem I found was that the trailing half of the split fin catches, causing lift such that the fin doesn't track straight.

That makes a lot of sense.

 

[rongoodman]

helicopter kicks (which I still don't really know what type of kick technique that is)do.

If you do a forward frog kick with one foot and a back kick with the other, you will spin in place, like a pedal turn in a helicopter.