That may be the reputation, but I'm not sure that it is true. All flexible fins will have a sweet spot, but my test didn't indicate any tragic drop in performance when I was kicking them like mad. I'm not sure they are any more sensitive to that than other fins.
Diving Performance - Beyond Drag (article Series And Discussion)
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That may be the reputation, but I'm not sure that it is true. All flexible fins will have a sweet spot, but my test didn't indicate any tragic drop in performance when I was kicking them like mad. I'm not sure they are any more sensitive to that than other fins.
Eric Sedletzky
Contributor
I used Apollo Biofins and Scubapro splits once in the ocean and Biofins once again in a pool. I could never get them to do much of anything, felt like two loose noodles on each foot. When I used them out in the ocean we were kayak diving and I rented a pair of each to see what all the hype was about. It almost got dangerous when I had to get back to my kayak against a slight current and some surge. They were almost useless. This was with Biofins, the SP's were a little better but not much. Certainly not good enough to buy either. I found that the kick was way easier but I had to do three times the amount of kick cycles to get the same result as regular fins, and even then the top performance with me trying everything was mediocre compared to the pisitive power hook up of a solid freediving fin or even a jetfin for that matter. I told this to the shop where I rented them and their response was that I didn't know how to kick fins properly, which I found offensive since I am a freediver and have used many fins over the years with no problems. I boiled it down to dive shop arrogance and their addiction to highest profits.
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I got 17 fin strokes with the Biofin and 16 with the Rockets to cross my 20 meter pool (more kicks, but not 3 times more). That was using a larger amplitude whip like fin kick with the Biofins though. I think this is probably the best way to use that kind of fin, so you could say that I had optimized the run to make the Biofin look as good as possible.
By the way, I didn't buy the Biofins, I inherited them from someone who quit diving from old age and lack of interest. I've only used them a few times now, and only in the pool. I've never had them in OW.
By the way, I didn't buy the Biofins, I inherited them from someone who quit diving from old age and lack of interest. I've only used them a few times now, and only in the pool. I've never had them in OW.
Okay folks. I did more swimming tests, this time using my DiveRite Transpack 2 and no BC wing. I have a 48" hose on my single regulator with the hose routed in a low drag configuration. It's the kit shown in part 4 of the article: Diving Performance, Beyond Drag - Part 4 – DeeperBlue.com under "Equipment Considerations".
Normalizing the data to that of a freediver swimming with arms at the side, here is how the drag coefficients (Cd)s breaks down:
Cd Freediver = 1.0
Cd Diver with Al80 in experimental streamlined kit = 1.15
Cd Diver with Al80 in DR Harness with no BC = 1.6
Cd Diver with Al80 in OMS BP/Wing = 2.0
As a kit and compared to the OMS BP/Wing:
Ditching the wing cuts the drag of the scuba kit by 40%.
The streamlined kit cuts the drag of the scuba kit by 85%
For the whole diver system:
Ditching the BCD wing saves 20% in total diver drag.
Using the experimental streamlined kit saves over 40% in total diver drag.
Streamlining gear works and can make a really big difference in the overall diver's performance, level of relaxation and efficiency of air use.
Normalizing the data to that of a freediver swimming with arms at the side, here is how the drag coefficients (Cd)s breaks down:
Cd Freediver = 1.0
Cd Diver with Al80 in experimental streamlined kit = 1.15
Cd Diver with Al80 in DR Harness with no BC = 1.6
Cd Diver with Al80 in OMS BP/Wing = 2.0
As a kit and compared to the OMS BP/Wing:
Ditching the wing cuts the drag of the scuba kit by 40%.
The streamlined kit cuts the drag of the scuba kit by 85%
For the whole diver system:
Ditching the BCD wing saves 20% in total diver drag.
Using the experimental streamlined kit saves over 40% in total diver drag.
Streamlining gear works and can make a really big difference in the overall diver's performance, level of relaxation and efficiency of air use.
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I came across an article that, I think, adds some support to the swimming performance goals I had set in my articles.
If navy frogmen can only average 1.2 knots, I think my assumption that average recreational divers can maintain 1 knot is a reasonable assumption.
Also, my assumption that achieving the ability to cruise efficiently at 3 knots is where the knee in the curve resides on swimming speed vs. benefit to the diver, is likely more realistic than the assumptions some others have expressed that 1 knot is already beyond what is appropriate or needed by divers.
FYI: These quotes came from this article: Drift Diving - Going with the Flow – DeeperBlue.com
"A number of years ago, Navy frogman were tested to determine the maximum sustainable current they could endure. They were to swim to maintain their position. A current of just 1.2 knots was the average these professionals were able to deal with....
When the current is between 2 and 3 knots it is generally called a strong current.... In a strong current the diver has given up almost all directional control of the dive. They are not able to turn into the current and fin to stay in one place to watch something....
A current of up to 3 knots is generally the strongest currents that all but the most experienced diver will dive."
When the current is between 2 and 3 knots it is generally called a strong current.... In a strong current the diver has given up almost all directional control of the dive. They are not able to turn into the current and fin to stay in one place to watch something....
A current of up to 3 knots is generally the strongest currents that all but the most experienced diver will dive."
If navy frogmen can only average 1.2 knots, I think my assumption that average recreational divers can maintain 1 knot is a reasonable assumption.
Also, my assumption that achieving the ability to cruise efficiently at 3 knots is where the knee in the curve resides on swimming speed vs. benefit to the diver, is likely more realistic than the assumptions some others have expressed that 1 knot is already beyond what is appropriate or needed by divers.
FYI: These quotes came from this article: Drift Diving - Going with the Flow – DeeperBlue.com
undrwater
Contributor
Something I've learned from this and other threads is there is something important called "kick shape". It appears that different fins will work more efficiently with its own unique shape. In other words; the biofin will likely require a different shape than a typical freediving fin. This may be why Eric experienced some trouble using his freediving shape with a biofin.
Learning the appropriate shape may be intuitive for some fins (or divers), but maybe much less intuitive for others. Currently I'm using the F1's for most of my diving (I also have biofins), and I can't get a flutter to work well for me in those fins, though I'm sure others have success using some kind of kick shape. The F1's for me seem to WANT to be frog kicked (I'll bet mine looks ugly, but it gets me where I want to go).
My point here being that someone may recommend a set of fins, but the kick shape to maximize efficiency for that fin does not come with the price of the fin. It's not so easy finding someone who can teach you the proper kick shape for a particular fin, and I'm going to assume learning comes over many, many dives.
I want to learn how to frog, helicopter, back, flutter kick efficiently, but I don't want to take a full course such as tech or GUE. I'd like to see some fin clinics with reasonable prices show up in my area. I've talked to some GUE folks about modularizing some of their skills classes, but I guess that's kind of outside their vision.
Learning the appropriate shape may be intuitive for some fins (or divers), but maybe much less intuitive for others. Currently I'm using the F1's for most of my diving (I also have biofins), and I can't get a flutter to work well for me in those fins, though I'm sure others have success using some kind of kick shape. The F1's for me seem to WANT to be frog kicked (I'll bet mine looks ugly, but it gets me where I want to go).
My point here being that someone may recommend a set of fins, but the kick shape to maximize efficiency for that fin does not come with the price of the fin. It's not so easy finding someone who can teach you the proper kick shape for a particular fin, and I'm going to assume learning comes over many, many dives.
I want to learn how to frog, helicopter, back, flutter kick efficiently, but I don't want to take a full course such as tech or GUE. I'd like to see some fin clinics with reasonable prices show up in my area. I've talked to some GUE folks about modularizing some of their skills classes, but I guess that's kind of outside their vision.
Divers need to recognize that the parameters which make a fin good for flutter kicking are very different from the parameters that make it good for frog kicking. Most scuba fins are not good at flutter. They are too stiff at the end and are usually too short to be able to efficiently convert the energy of a flutter kick into thrust.
I think this is why so many divers have become drawn to the frog kick. With a bad fin design, a flutter kick is going to just waste energy throwing bombs of water at the bottom instead of throwing the water back to push you forward. Obviously, this is undesirable.
Showing a great deal of adaptation, many divers changed how they use the fins to get some acceptable performance out of them. They learned to frog kick them. It's not a natural choreography of motion for the human body to do, but the body can be trained to do it with a bit of effort. Instead of pursuing fins that can efficiently convert the energy of a natural flutter kick into thrust, the work around solution has become so entrenched that many divers now actively seek out fins that are bad at flutter,in favor of having a fin that is good at frog.
Divers have proved themselves to be far more competent than the fin manufacturers and have learned to make the most of what was readily available. Meanwhile, the manufacturers have basically gotten stupid and lazy. They have stopped innovating for better solutions and are stuck on using 70s technology while trying to make it look about 40 years more modern.
My problem with the frog kick is that it is power limited and unstreamlined in the water, and this restricts the swimming performance that I can achieve using it. When I use good fins, the benefits of the frog kick vanish. With good fins, the frog kick naturally evolves into a dolphin kick and it is more efficient and comfortable than the weird ankle twisting motions of the frog kick. More motion; Less effort; Easier to learn... What's not to like?
I think this is why so many divers have become drawn to the frog kick. With a bad fin design, a flutter kick is going to just waste energy throwing bombs of water at the bottom instead of throwing the water back to push you forward. Obviously, this is undesirable.
Showing a great deal of adaptation, many divers changed how they use the fins to get some acceptable performance out of them. They learned to frog kick them. It's not a natural choreography of motion for the human body to do, but the body can be trained to do it with a bit of effort. Instead of pursuing fins that can efficiently convert the energy of a natural flutter kick into thrust, the work around solution has become so entrenched that many divers now actively seek out fins that are bad at flutter,in favor of having a fin that is good at frog.
Divers have proved themselves to be far more competent than the fin manufacturers and have learned to make the most of what was readily available. Meanwhile, the manufacturers have basically gotten stupid and lazy. They have stopped innovating for better solutions and are stuck on using 70s technology while trying to make it look about 40 years more modern.
My problem with the frog kick is that it is power limited and unstreamlined in the water, and this restricts the swimming performance that I can achieve using it. When I use good fins, the benefits of the frog kick vanish. With good fins, the frog kick naturally evolves into a dolphin kick and it is more efficient and comfortable than the weird ankle twisting motions of the frog kick. More motion; Less effort; Easier to learn... What's not to like?
undrwater
Contributor
How non-silting is the dolphin when you're inches from a silting bottom?
I'd love to learn the dolphin kick too!
I'd love to learn the dolphin kick too!
When we move through the water, it sticks to us and we literally drag it along with us; hence the hydrodynamic use of the word "drag". Per Newton's third law, we are going to have to take a mass of water and throw it back, opposite our direction of travel, and with as much momentum to overcome that which we are dragging along with us.
The more drag we have, the more we disturb the water as we move through it, and the more we must disturb the water to overcome the drag. Silt gets mixed into the water from these disturbances. This basic concept is why divers that deal with silt should be fundamentally concerned with hydrodynamics. With good hydrodynamics, we could glide over the silt without disturbing it, because we are barely disturbing the water above it.
Personally, I believe that the whole diver system needs to be addressed. Hydrodynamics is not just a fin design consideration.
Regarding the questions above on the dolphin kick and silting, the answer is that it depends on the fin and technique used. If the fin only throws the water back, it can be within inches of the bottom and be fine. The problem arises when the water gets thrown down toward the bottom. This is what happens when the fin is too short and stiff to rotate the vortices to aim the water back and the fin directs it down and back instead and disturbing silt.
I'll need to spend more time diving in areas with silt to be able provide a good and credible answer for the fins I made. I know that they are pretty efficient and from observing debris on the bottom of the pool, it looks like the reverse dolphin kick has very benign silting properties with these fins. If the silt is the driving concern, a diver can still bend the knees some to raise the fins further from the bottom same as they do with the frog kick. I know I'm in a position of bias on this topic, but I think the super soft tip fins I made naturally have less off axis waste momentum than stiff fins that are frog kicked to get the off axis waste momentum to cancel and redirect. The soft flexible fin tip makes for an easier and more direct method of getting the water moving the right direction.
The more drag we have, the more we disturb the water as we move through it, and the more we must disturb the water to overcome the drag. Silt gets mixed into the water from these disturbances. This basic concept is why divers that deal with silt should be fundamentally concerned with hydrodynamics. With good hydrodynamics, we could glide over the silt without disturbing it, because we are barely disturbing the water above it.
Personally, I believe that the whole diver system needs to be addressed. Hydrodynamics is not just a fin design consideration.
Regarding the questions above on the dolphin kick and silting, the answer is that it depends on the fin and technique used. If the fin only throws the water back, it can be within inches of the bottom and be fine. The problem arises when the water gets thrown down toward the bottom. This is what happens when the fin is too short and stiff to rotate the vortices to aim the water back and the fin directs it down and back instead and disturbing silt.
I'll need to spend more time diving in areas with silt to be able provide a good and credible answer for the fins I made. I know that they are pretty efficient and from observing debris on the bottom of the pool, it looks like the reverse dolphin kick has very benign silting properties with these fins. If the silt is the driving concern, a diver can still bend the knees some to raise the fins further from the bottom same as they do with the frog kick. I know I'm in a position of bias on this topic, but I think the super soft tip fins I made naturally have less off axis waste momentum than stiff fins that are frog kicked to get the off axis waste momentum to cancel and redirect. The soft flexible fin tip makes for an easier and more direct method of getting the water moving the right direction.
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