Split fin hate?

[BoltSnap]

Oh, I forgot to mention: I used my Scubapro Hydros Pro BC, SP Everflex 3mm wetsuit, 3mm Bare hood, Bare Tropical gloves, SP MK19/G260/S600, BigBlue 8000 Lumen lights, Ratio iX3M Tech+ computer with transmitter, D Mask with SP Snorkel in addition to my SP SuperNovas.

OMG, OMG, OMG, I forgot to mention that I saw a trumpet fish for the FIRST time ever in Libya in 3 meters when I was very close to the exit point. It must be the fins

 

[boulderjohn]

I'm definitely no expert on this, so I might be wrong, but this seems counter-intuitive. Why would something soft and flexible create resistance when dragged through the water? I would think that a flexible material would follow the path of least resistance, not bend "into" resistance. I always thought the problem with split fins were lack of direct push, not too much resistance...

jborg gave one example. Another example is the back kick. On the recovery stroke, you have to push the fin tips backward, like shoving a knife into a loaf of bread. A floppy fin will bend 90°, putting on the brakes to stop all momentum from the power stroke.

 

[steinbil]

jborg gave one example. Another example is the back kick. On the recovery stroke, you have to push the fin tips backward, like shoving a knife into a loaf of bread. A floppy fin will bend 90°, putting on the brakes to stop all momentum from the power stroke.

Good points. For some reason I was hung up on the pulling recovery motion of the frog kick. I can see that the sideways and pushing movements would be awkward.

 

[NW Dive Dawg]

Folks who don't like split fins should not dive with split fins.

Folks who don't want to dive with others who use split fins should not dive with others who use split fins.

Folks should not create silt outs or environmental damage regardless of their personal fin choice.

Beyond that, folks should dive with whatever fins they want to dive with!

 

[BoltSnap]

Folks who don't like split fins should not dive with split fins.

Folks who don't want to dive with others who use split fins should not dive with others who use split fins.

Folks should not create silt outs or environmental damage regardless of their personal fin choice.

Beyond that, folks should dive with whatever fins they want to dive with!

But life is no fun and has no meaning for some folks here if they don't judge and condemn others.

 

[davehicks]

I dive in a very silty region where it takes very little to stir things up. My observations of causes have very little to do with fin design. Here is what I see:

• Vertical to 45deg body position. Due to poor or non-existent trim the diver is kicking straight down into the silt or kicking the bottom.
• Poor Buoyancy. The diver is negatively buoyant and as a result is constantly kicking, even when they are not moving much and observing/photographing something.
• Hand Movements. Along with kicking, the diver is compensating for their poor buoyancy by using hand movements and stirs up the bottom.

Vortexes from split fins seem like a minor and frankly mostly made-up excuse to explain away the three major skills issues above. Any fin design is going to have some sort of "vortex" or pressure wave just from moving through the water. Even if one fin design is worse than others, this pales in comparison to the poor skills causes.

 

[John C. Ratliff]

I have been studying the effects of fin design for decades. I took these photos of a modified Voit Viking set of fins in 1970, and it shows the effects of the vortices from the fin on the bottom with a hard "flutter" kick. It also shows how this "scoop" design that I pioneered and still use causes the fins normally "dead" area just under the toes is translated into forces that propel. I'll talk about the split design in my next post, but this gives a good idea of a more effective design for fin propulsion. The afore-mentioned Mares fins that BoulderJohn doesn't like actually don't have enough "scoop" built into them to be more effective. The strings on the fins are designed to show water flow off the fins; note that with this design, the flow is straight backwards.

SeaRat

 

[BlueTrin]

With all these posts about split fins, I really want to try a pair now …

 

[John C. Ratliff]

In 2010 I did a series of experiments in a 25 yard pool to determine the differences in propulsion of tree different designs on the same Plana Plus fins. The basic fin shape was the same for each swim. But one was the original flat blade, one for the "split fin" design, and one for my "scoop fin" design. The results of this experiment are shown in the following table. I used as close to the same kick on all the trials. As you can see, swimming 50 yards using the flat blades resulted in a 30.8 strokes in 43 seconds. The split design resulted in an average of 30.2 strokes in 43 seconds, indicating that the split fin has an advantage over a flat blade. The scoop fin design had 29 strokes in 40 seconds, showing an increased efficiency of stroke over the other two designs.

Over a mile swim, that would be 1084 strokes for the flat blade, in 25.2 minutes. For the split blade, that would be 1063 strokes for a time of 25.2 minutes (time was the same). For the "scoop blade" configuration, the mile swim would result in 1021 strokes for a 23.5 minute per mile swim, showing a significant improvement over the other two designs.

I'm also including an image of my Plana Avanti fin with my modified Plane "Scoop Fin" design. I am still using this design in my river diving adventures.

SeaRat

 

[Gone for diving]

Do you notice a difference in how they kick? I assume so...

Scoop design, does it frog kick well?

What material do you use for the scoop?