Pervasive Fallacy about Split Fins

[Diver Dennis]

Quote:
Originally Posted by Diver Dennis
Isn't the whole idea that you are trying to move forward relative to the bottom, not the water? Let's say you are traveling north along a reef at .5 knots. If there is a current against you going 1 knot and your energy output is the same, you would be going backwards at .5 knots. Correct?

Of course. But you're not moving against the ground, you're moving against the water.

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.

Ahhh. You didn't say this was based on the theory that splits are faster and more efficient. Are there tests that give credence to that theory?

Actually to say you have forward motion, I think you have to use a stationary object to measure it.

 

[Temple of Doom]

If ya want to get back to the shore or where the up line is, ya are !!!

the K

I understand you're joking, but for those for whom this is still in doubt: You want to move relative to the ground, but the only thing you're actually moving against is the water (unless you're using one of your 3 octo's as a hook to drag yourself along).

Ahhh. You didn't say this was based on the theory that splits are faster and more efficient. Are there tests that give credence to that theory?

Actually to say you have forward motion, I think you have to use a stationary object to measure it.

Split fins win every time they are scientifically measured against paddle fins in both max speed and max thrust (obviously in water one correlates to the other, all things being equal).

You're right, I should have said you're moving forward at 4kts relative to the water, you're moving at 0.5kts relative to the ground, and yes you're moving at about 29km/s relative to the sun.

Since what's important in determining net velocity relative to the ground, you have to add the water's velocity relative to the ground (-4.0kts) and your velocity relative to the water (3.0kts). That gives you a -1.0kt velocity relative to the ground, but you can just as easily calculate both as relative velocities to a lobster you're chasing:

Lobster is moving N at 1.0kt relative to the ground. Current is moving south at 1kt relative to the ground. Water is therefore moving at 2.0 kt South relative to the Lobster. If you're moving at 3.0kt North relative to the water, then you're moving at 1.0kt North relative to the lobster...

Craig

 

[The Kraken]

But see there, the whole argument is that some believe that blade type fins are more efficient at making way into a current than split fins are.

It's about going from point "A" to point "B" in the most efficient manner, even regardless of a current.

Following the same hypothesis, one could argue that one could go from point "A" to point "B" faster with blade fins because they're more efficient (no current incurred). The increased forward velocity equates to the current, if you would.

But then others come back and make an argument, ableit somewhat flawed, that it all equals out because it takes less energy to move the split fin through the water than it does the blade fin. But then one must make more kick cycles to match the result of "X" number of kick cycles with the blade fin.

I really don't care.

Do love to watch the arguments, however.

the K

 

[Temple of Doom]

Following the same hypothesis, one could argue that one could go from point "A" to point "B" faster with blade fins because they're more efficient (no current incurred). The increased forward velocity equates to the current, if you would.

But then others come back and make an argument, ableit somewhat flawed, that it all equals out because it takes less energy to move the split fin through the water than it does the blade fin. But then one must make more kick cycles to match the result of "X" number of kick cycles with the blade fin.

See the only thing I'd want people to understand is that if you believe the test results that show people consistently swimming faster with split fins than with padles, with *everything* else being equal, then you have to accept that they are the more efficient fin. They may not be for every diver, or whilst using every kicking style, but everybody who's run tests has found that the fastest split-fin kick is faster than the fastest paddle kick (all things, including energy expended, being equal).

Basically, I'm ok with people not liking split fins, there's lots of reasons not to. What I don't like is if the reason is the one in the OP, because it's just a myth.
Craig

 

[MikeFerrara]

Split fins win every time they are scientifically measured against paddle fins in both max speed and max thrust (obviously in water one correlates to the other, all things being equal).



Craig

The problem is that they don't test the fins as they are often used in diving. Those doing he testing never seem to know very much about diving.

In my diving what's most important is max amount of motion with minimal moevement. In other words I'm more interested in how far/fast I can move with a SINGLE kick.

I primarily use a frog kick both forward and reverse and use a combintaion for turning or stopping. I can more precisely maneuver and move further with a single flip of a fin with paddle fins.

Note that a frog kick, reverse kick, turns ect use the fin exactly as we use boat oars (paddles). Next time you go out in a canoe, try using paddles with splits in them and let me know how they work for you.

 

[Temple of Doom]

In my diving what's most important is max amount of motion with minimal moevement. In other words I'm more interested in how far/fast I can move with a SINGLE kick.

And that's a terrific reason to not prefer splits! You may exert a little more energy, but it's quicker, and you prefer that.

 

[Garrobo]

Do the SEALS use split fins? Therein lies the answer.

 

[MikeFerrara]

Are there any pilots out there that can see that the splits on the fins are to increase the efficiency of the fin, in the same way the slots in slotted flaps do for flaps on aircraft? .. notice the slots in a jet fin, do they look familiar?
... air or water, the same effects apply


(unless their pink )

But we don't use fins the way a plane does. As I mentioned in my last post, many finning techniques (the most useful ones) use a fin the same way that we use a boat paddle...and that doesn't work if the paddle is split.

The split fin manufacturers are fond of pointing out that fish often have split tails...but I don't have a tail. I have feet. Watch a fish and note which fins they use for tight manuevering. Those fins are usually NOT split and they are, again, used to "paddle" and they are shaped like paddles.

unfortunately, most divers aren't really taught how to use fins so they don't know the difference.

 

[in_cavediver]

I belive there is quite a bit of truth to the split fin efficiency problem mentioned above. I don't have the 'objective' scientific test only gereralized observation.

Ask yourself this, why is it that Cave divers and Tec Divers use Paddles? This is the same group of divers who have brought to octo, bcd, spg, single hose regs and other fundemental pieces of dive gear to the rec side. Why wouldn't they also lead the way in a more effecient fin design?

Personally, I don't care what people use so long as they don't silt the place up (which mostly they do).

 

[The Kraken]

"Originally Posted by MikeFerrara
In my diving what's most important is max amount of motion with minimal moevement. In other words I'm more interested in how far/fast I can move with a SINGLE kick."

Of course one must consider the amount of energy required to effect said result . . .

Resistance / Force / Distance

Resistance is the constant, the remaining two are the variables generated by the two different types of fins.

One of the problems in this eternal argument is that so often an additional variable of different kick types is thrown into the matrix.

Really, about the only way this argument could be settled, and it would be next to impossible, is to establish a control group that would test the two types of fins, with their respective most efficient kick styles, and measure the caloric usage required to swim a given distance in a controlled environment.

After all, doesn't it all come back to the amount of gas one has to use to overcome the resistance of the water during a dive? And the amount of gas used is in proportion to the energy required to move a body through a distance.

Oh well, life and kick cycles go on . . . .

the K