Pervasive Fallacy about Split Fins

[Temple of Doom]

How would you account for all the variables; profile, current, tide, temp, training, skill, nutrition, pms, cheating spouse (task overload?), yada yada yada.

Do you really think all those variables really matter as to whether one fin is more efficient than another?

No, they don't. However, they certainly matter when determining which is more efficient than the other. If you don't see that you don't understand the basic principles of scientific research.

Maybe you could explain your point. When you design a test that effectively equalizes pms, temperature, training, skill, etc, between the two fin types, if you design a test where the only variable between two runs is the fin, then all that no longer matters.

 

[Temple of Doom]

A note about energy: Different fins aren't going to change the energy output of your body. You're going to put out the same energy whether you're wearing splits or paddles. It's the efficiency of the fins turning your body's energy into thrust that translates into faster or slower fins. If the same diver under the same conditions can swim 65 feet faster in splits than paddles, it's because the splits are more efficient at translating that divers energy into thrust.

Sorry, this is just plain inaccurate about energy expended.

The work performed is force x distance. So, when I move my leg, the work performed is the force I am pushing with multiplied by the distance I am moving it.

When I use paddle fins, I feel them 'bite' against the water. There is more force.

When I tried split fins, it felt like I had no fins at all. They didn't 'bite' the water. My leg moved the same distance, but there was less force.

Thus there was more energy expended using the paddle fin. W = F x d.

So a kick with the paddle fin requires more work. Your body is expending more energy.

You're absolutely right that a kick with paddle fins requries more work, and thus requires more energy to do it.

You almost finish that thought to prove my point. I'll take up where you left off:

As you said, the paddle requires more work and less times. And that the split fin requires less work, but more times. Can you see where I'm going now? They balance each other out.

Do you honestly believe that the energy output of your body is changing depending on the fin you're using? Are your legs able to metabolize sugars any more because you have a different piece of plastic/rubber on the end of your feet?

Of course not.

When swimming your hardest (or swimming at your max sustainable rate), your body is outputting a certain amount of energy. Whether you're in bare feet, paddles, or splits will change the velocity and effort of each kick, but the energy coming out of your body is the same.

The harder/less or faster/more ratio of fins doesn't really matter, it's their efficiency. How much of your body's energy is turned into thrust. One could easily tweak split fins to be as efficient as padles (I think adding some generators to charge your light and reduce the efficiency down to paddles would work nicely ). If you did that you would find that both fins would have the same thrust and speed through the water.

 

[Soggy]

If you can move against still water at 4.0kt in split fins and 3.0kt in paddles, then in a 3.5kt current you're going backwards in paddles and forward in split fins.

You can't...I would bet that no one here can swim faster than 1-1.5knots, and only full tilt for a few seconds. Scooters run at about 2 knots.

 

[Wolverine]

Don, I think I'll do that. We have a MEGA Dive-O-Rama coming up here in 2 weeks at Puerto Galera and I'm going to rent a pair. I take pictures and dive pretty slow. I also frog kick almost all the time to keep the sand where it should be, on the bottom, so it will be interesting to see how they work for my style of diving.

Dennis, you can borrow mine.. I am going to get a pair before the Mega DOR. Will be bringing it down to have a go. I still love my quasi-paddles (Volo-Power) but I won't mind trying out a split.

BTW, I have used SP Jets, Mares Planar Avanti, Planar Avanti Quarttro.

 

[EANx.2000]

I have the Tusa Imprex paddles and...the tusa x-pert zoom split fins...I can't tell a extraordinary difference...I think I am going to have to wear the paddle on one leg and the zoom split on the other while in my pool at home and try to see if i can tell any large noticeable difference between the two...this is what I have found that the manufactures say....or this is what "They" say

When using the standard, flat fin, propulsion is inhibited solely by fault of design. When the leg is completely extended, there remains an angle of 27 degrees between the heel of the foot and the calf of the leg. This 27-degree angle causes 10% of the propulsion that is produced by the kicking motion to be lost. Because the fin is angled below the body, during the kick phase, the body is pushed up and forward, instead of straight ahead. With a normal flat fin, 10% of the diver exertion to propel him forward is lost by battling this upward force. With the TUSA X-PERTZOOM FIN, that 27-degree angle has been incorporated into the fin. This means that when the leg is fully extended, even though the angle exists between the foot and calf, the fin ends up parallel to the leg. This means that 100% of the energy expended during the kicking phase is directed toward the propulsion of the diver.


AND

[FONT=Verdana,Arial,Helvetica,sans-serif]The Propelling Power
Traditional fins only use repulsive force to create propulsion. This normally means that in order to create strong propulsion, maximum effort is required, resulting in muscle fatigue not only for beginners, women, and middle-aged divers, but professionals as well. Added to which, the body moves left and right in reaction to the kicking needed to move forward, thus reducing propulsion. The SF-8 and FF-9 have blades that are split down the middle, so they take the shape shown in the diagram when kicked under water. This special blade shape creates propulsion (lift) by generating a pressure differential above and below the blade, in addition to the repulsive force created by kicking. The SF-8 and FF-9 are fins that allow all divers to create propulsion using only a small bent-knee kick, with a light rhythm.[/FONT]

A light kick reduces water resistance and creates less turbulence.
Traditional fins required fin-work with large strokes in order to create propulsion, since they depended solely on repulsive force. The SF-8 and FF-9 obtain propulsion not only from repulsive force but also from lift, so it works ideally with a light, rhythmic kick. In other words, a small "bent-knee kick" will bring out this fin's best performance. This makes possible a light kick which creates less burden on the legs than with traditional fins. A light kick with small strokes reduces the diver's fatigue and the amount of air consumed. Also, small strokes reduce the resistance of the water on the entire body moving forward and also create less turbulence, so propulsion is smoother.

 

[MXGratefulDiver]

You can't...I would bet that no one here can swim faster than 1-1.5knots, and only full tilt for a few seconds. Scooters run at about 2 knots.

I was wondering if somebody was gonna pick up on that ... I didn't want to interrupt all the fun these folks are having justifying their chosen pieces of plastic ...

... Bob (Grateful Diver)

 

[Charlie99]

When I tried split fins, it felt like I had no fins at all. They didn't 'bite' the water. My leg moved the same distance, but there was less force.

Thus there was more energy expended using the paddle fin. W = F x d.

So a kick with the paddle fin requires more work. Your body is expending more energy.

Did you look down at the ground and see how fast you were going though. When I first tried Apollo BioFins I had that same impression that they weren't biting into the water. Then I looked down at the bottom and realized I was zipping along.

While I may have felt like they weren't grabbing hold of the water properly and it felt like I'd had forgot to put on my fins, in fact I was swimming much faster than normal. Very strange feeling.

Accelerating from standstill was also a bit strange. It reminded me of spinning the tires on a car while getting going on ice.

Throughout the dive I had to consciously slow down because I was leaving my buddy behind. Overall, the split fins performed wonderfully, but they just felt WEIRD. So I kept my old fins.

BTW, my experience with Jetfins was very similar. While they obviously have more bite and instant acceleration than do splits, compared to my old original USD Blades fins, the jetfins are tiny. I found that I had to wave my whole leg around to frog kick, rather than doing a sculling style frog kick using mostly my ankles while keeping my legs extended backwards in a streamlined form. Since I've found 3 jetfins/IDT jet clones while diving, I still have a pair of XL's and have done about 2 dozen dives with them to give them a fair chance. Blades still beat them hands down.

At least one other diver has come to the same conclusion. Atomic Split Fins vs. ScubaPro Jetfins -- and the winner is AQUALUNG BLADES!

What happened is that Blades were the first fins I used. After getting tired of flutter kicking, I would change kicking style for a while to change which leg muscles were used. I just gradually evolved into a frog kick long before I had ever heard the term. I'm used to those fins and any other fin feels weird and awkward.

OTOH, a diver that started out with split fins would probably reject paddle fins as very inefficient, way too hard on the muscles and knees, and probably thinks anybody that doesn't use split is an aging dinosaur.

While it makes for some interesting arguments on SB, in the end each diver simply makes his choice.

 

[Soggy]

I was wondering if somebody was gonna pick up on that ... I didn't want to interrupt all the fun these folks are having justifying their chosen pieces of plastic ...

... Bob (Grateful Diver)

Heh....It's one of those pet peeves of mine...I've heard a few too many stories about people diving in "4 knot currents." A 4 knot current will, quite literally, rip your mask off your face. Heck, a scooter on full blast can dislodge your mask if you get outside of the slipstream and that's only about 2-2.5 knots if you're really good at it!

To put it into perspective for those that don't understand it, the Oriskany is just over 800 ft long. 4 knots is ~400 feet per minute. Does anyone think they could swim the length of the Oriskany in 2 minutes?

 

[Splitlip]

You can't...I would bet that no one here can swim faster than 1-1.5knots, and only full tilt for a few seconds.

I disagree. 1ft per second equals .6Kt. How many seconds would it take to swim the length of a 25 yard pool at 1Kt?

 

[dschulte]

...Do you honestly believe that the energy output of your body is changing depending on the fin you're using? Are your legs able to metabolize sugars any more because you have a different piece of plastic/rubber on the end of your feet?

Of course not...

Yeah, it is called resistance. I am not sure if you have tried different fins to see for your self the difference, but try this at home. Take a piece of 8.5 X 11 paper in one hand and wave it back and forth in front of you. Now take a piece the size of your car and wave it back and forth. The air resistance from the surface area will increase the work load on your arm. This is the same for fins, wetsuit vs. dry suit and dive profile. The way the fin moves through the water contributes directly to the energy expended. You can move your arm in a waving motion a lot longer when your hand is empty then when you are holding something large and flat. My suggestion to you would be to get a pair of Turtle fins, Twin jets and something like a Kinesis. Try them out in a controlled environment and see for yourself how design impacts performance and diver fatigue. After you tackle that you can look at profile and exposure suit differences.
:monkeydan