Flying Underwater, A Blast From The Past

[ricki]

I was wearing regular free diving gear including fins, in the Aqueon. I would be on my back dolphin kicking along looking slightly forward. For best speed I should have been looking at the surface. I just picked up my first set of nose plugs recently, need to give them a go.

I have been looming near the bottom when I go all out inverted recently with the Aqueon. Don't want to hammer into a hard bottom at speed, ouch! Need more practice to get back into it.

I recall Martin Stepanek saying something about maximizing speed with monofins in an inverted position as well. What have others experienced like this? He found cetaceans in particular could be brought in closer at times doing this.

[trux]

When you spoke about swimming in inverted position with the Aqueon, I first thought that you swam feet first, which would be pretty cool, interesting, and possibly it could have some advantages. And unlike with a monofin, I think it could be indeed possible with such (or similar) device.

It is true that swimming on the surface with fins is more efficient on your back, and I often do it when needing to cross bigger distance quickly. However, once you are under the surface, there is no difference - you can swim in any direction and in any position, and there won't be any significant difference. It could bring you some advantage only if the Aqueon was quite positively or negatively buoyant, allowing so some asymmetric gravitation effect. Even that is quite questionable though. And as long as it is approximately neutrally buoyant, the position cannot have practically any influence on the efficiency or speed. And while at a monofin, theoretically there could be a very tiny difference when swimming underwater close to the surface (moving the water against or above the surface, hence having asymmetric gravitation effect), at Aqueon due to the two hydrofoils moving in opposite directions (when the front moves down, the back goes up, and vice versa, as far as I see), any such difference would be eliminated. If you feel that you move faster when on your back, on my mind, it is just a psychological effect - either you just think you move faster when watching the surface, or maybe you even move faster, but not because of physical conditions, but rather because of the psychological ones (you think you should move faster, hence you do so - that's a quite common effect in human psychology).

[Bill]

'two hydrofoils moving in opposite directions '

Not sure if it is important or even true but it feels very different. The rear foil always points at the centre of the front foil. The front foil is free to swivel restricted of course by the bungee which can be adjusted for 'fin stiffness'. If my long term memory can be trusted, it feels like your feet are anchored in place and your body hardly bends. This can't be because when the front foil starts up the rear must go the same direction but the delay forces the undulation with no input from the swimmer. It becomes obvious when you try to wear fins too. The efficiency seems to go way down.

[cdavis]

Ricki,

Check your pms

Connor

[ricki]

Originally Posted by trux

When you spoke about swimming in inverted position with the Aqueon, I first thought that you swam feet first, which would be pretty cool, interesting, and possibly it could have some advantages. And unlike with a monofin, I think it could be indeed possible with such (or similar) device.

This is possible, although I have yet to do it. Perhaps this weekend if things work out in deep water. It is that simple mod Bill and I were discussing.

Originally Posted by trux

It is true that swimming on the surface with fins is more efficient on your back, and I often do it when needing to cross bigger distance quickly. However, once you are under the surface, there is no difference - you can swim in any direction and in any position, and there won't be any significant difference. It could bring you some advantage only if the Aqueon was quite positively or negatively buoyant, allowing so some asymmetric gravitation effect. Even that is quite questionable though. And as long as it is approximately neutrally buoyant, the position cannot have practically any influence on the efficiency or speed. And while at a monofin, theoretically there could be a very tiny difference when swimming underwater close to the surface (moving the water against or above the surface, hence having asymmetric gravitation effect), at Aqueon due to the two hydrofoils moving in opposite directions (when the front moves down, the back goes up, and vice versa, as far as I see), any such difference would be eliminated. If you feel that you move faster when on your back, on my mind, it is just a psychological effect - either you just think you move faster when watching the surface, or maybe you even move faster, but not because of physical conditions, but rather because of the psychological ones (you think you should move faster, hence you do so - that's a quite common effect in human psychology).

Thank you for your thoughts on this. The added speed could have been only a perception but a strong one all the same. Your point about the proximity of the surface might add to the impression. The Aqueon is slightly positive say around a couple of pounds. The aft foil acts like a stabilizer on an airplane and is asymmetrical in section unlike the two forward foils which are symmetrical. My impression from many years back was that the advantage was more a function of physiology as opposed to the mechanics of the Aqueon. I need to reacquire some control while using it inverted for some comparative speed trials, inverted vs. not. I'll pass along what I find out, deceptive appearance of fast moving surface vs. actual faster movement.

[ricki]

Originally Posted by Bill

'two hydrofoils moving in opposite directions '

Not sure if it is important or even true but it feels very different. The rear foil always points at the centre of the front foil. The front foil is free to swivel restricted of course by the bungee which can be adjusted for 'fin stiffness'. If my long term memory can be trusted, it feels like your feet are anchored in place and your body hardly bends. This can't be because when the front foil starts up the rear must go the same direction but the delay forces the undulation with no input from the swimmer. It becomes obvious when you try to wear fins too. The efficiency seems to go way down.

Your body moves sparingly above the waist particularly once you are up to minimum cruising speed with the Aqueon. Your legs move slightly with the majority of the displacement being described by the kneel and foils. The effective kneel or moment arm length is adjustable, slightly, on the current unit with two "settings" based upon where you bolt the leg mounting assembly. It would be nice to have an incremental moment arm adjustment on a newer version. This would help to adjust stroke period and effective amplitude for different physiques and characteristics for a given session.

[ricki]

Originally Posted by cdavis

Ricki,

Check your pms

Connor

Just got back and will respond to your PM's soon. Had some interesting shallow water sessions with it. There is some still and video imagery inside and around the Wreck of the Sapona that is pretty intriguing, stay tuned for that.

Unfortunately, I missed out on a deep water session with the Aqueon. Spent too much time looking for a purported sinkhole with an intact roof that was described in the '70's off Cat Cay. I think the horizontal access crevice, perhaps two feet high may have been closed off by sand in filling in the hurricanes. Did have a chance to drop down to the rampart of the Wall around the "Graveyard" a couple of times quickly on the way back to the dock in Bimini using fins. If I had more time out there it would have been fun to rig the device for vertical descent and see how fast it might take you down, oh and up again too after resetting it!

[cdavis]

On the inverted question, competitive freestyle swimmers have discovered that they are faster underwater, dolphin kicking, inverted. Once this became widespread, the rules were changed to require that swimmers surface not more than 15 feet from the wall after the turn, otherwise, short distance freestyle events would have turned into underwater dolphin kick only.

I don't know how this will apply to the aqueon, but it will be interesting to find out.

[cdavis]

Looking at the videos, it appears that virtually all of the propulsion results from bending the knee. Is that correct? If so, that is a pretty extreme concentration of effort on a few muscle groups, seems like you would get tired quickly. The lactic burn on a long dive should be prohibitive. If all you are using are knee muscles and the gadget is so efficient that you don't get tired, this would have to be the best way to depth ever.

Connor

[ricki]

Interesting observations about dolphin kicking competitive swimmers. You would think body orientation during the kick wouldn't be that significant but it certainly feels that way.

There is more full body involvement in the stroke just as in dolphin kicking with fins. Propulsion is reliant upon far more muscles than those connected to the knee. I am still getting used to and tuning the Aqueon myself and as a result am still improving performance. Given our coastal characteristics in SE Florida, deeper water is a ways offshore. Most of my recent time has been nearer to shore. Hope to hook up with a boat this weekend, here or perhaps out of town to take a better look at deeper water performance.

[Aquagenic]

Actually, from a biomechanics perspective you are removing a link in the kinetic chain. You would no longer need to stabilize the ankle which greatly increases over all muscular efficiency (eliminating the use of 12 muscles of the lower leg and numerous foot muscles) not to mention it would prevent foot cramping and pocket trouble.

Further, restricted motion of the knee, rather than deep bending, is much easier on the quads and hams. Also, it seems from the video that the hip is held in a much more neutral position throughout the stroke than with monofinning.

Finally, by bringing the anchor point of the device closer to the core the body's muscles can exert much more force per effort. Ever try to hold a 2x4 from an end at arms length? Same concept, it's much easier for your body to exert force onto something if it's closer to the core.

Not sure if they were considered in the making of this thing, but the biomechanics make a lot more sense. I'm definitely a fan and would love to see this thing in production again.

~JMP

[trux]

Originally Posted by cdavis

On the inverted question, competitive freestyle swimmers have discovered that they are faster underwater, dolphin kicking, inverted. Once this became widespread, the rules were changed to require that swimmers surface not more than 15 feet from the wall after the turn, otherwise, short distance freestyle events would have turned into underwater dolphin kick only.

Originally Posted by ricki

Interesting observations about dolphin kicking competitive swimmers. You would think body orientation during the kick wouldn't be that significant but it certainly feels that way.

It is not really the body position that makes the difference - that is pretty unimportant in the quasi-weightless environment. It is the proximity of a material threshold (surface, wall, pool bottom) that is important. When a fin moves against a barrier (as I wrote: surface, wall, or a pool bottom), the water pushed away with the fin, unlike in free space in deep water, is restricted fro two sides, and hence instead of being pushed away in an angle close to 90°, is rather forced backward, and propulses so the swimmer similarly like a burning fuel in a rocket reactor. Well, the matter is little bit more complicated, because the positive propulsion effect is reduced by higher turbulences, friction, and suction effect, but generally swimming close (in optimal distance) to any surface while propulsing against it, gives an advantage against swimming in a free space.

Now, once you realize the opposing surface gives you an advantage, swimming face to it is indeed better for two reasons:

1. You can much better control your distance to the surface/bottom/wall when looking at it, and keeping it so optimal, avoiding touching the surface, or getting too close which increases suction effects and turbulences.
2. Due to the physiology, I believe the forward kick is little bit stronger and faster than the reverse kick. Hence when you swim face to any surface, you use the stronger part of the kick to push water against the surface which gives more propulsion than the reverse kick moving water into free space.

However, although this is valid for swimming with conventional fins and monofins, I believe that due to the use of the hydrofoils, and due to their position, the propulsion is more symmetric with the Aqueon, hence I would not expect the same advantage as at fin swimmers. On the other hand, it is true that the pair of Aqueon hydrofoils that is under the breast is much closer to the surface if you swim face to it than vice versa, so maybe finally it could give some extra speed (though I wouldn't expect any important difference).

Still, for real diving (I mean being deep), the body position is absolutely unimportant (unless you can sink or swim along some wall).

If you are interested about fluid mechanics and biomechanics related to swimming and fin swimming, there are some documents in my Freediving Media Base: documents hydrodynamics @ APNEA.cz In this case, I especially recommend the one titled Swimming Biomechanics - it includes several studies of monofin swimmers and also many other references for those who are really interested in that matter.

[ricki]

I am finding spending more time with the Aqueon to enhance performance is important. I remember just putting the thing on and taking off as a kid. Still, if you are trying to hit maximum speed and evaluate on deeper dives more time in the saddle and tuning of the device helps.

I took it down to Key Largo this weekend for some free diving on the wreck of the Spiegal Grove. I started on it immediately but would have benefited from some warmup time with fins alone or with a dive scooter I brought along. The scooter diving was interesting with possible decompression issues that I raised HERE Next time I'll get that sequence right. Anyway, once you are inverted and descending it is straight forward enough. I cut the dives off at 80 ft. with the Aqueon. I am still evaluating the best speed and amplitude of kick for extended depth vs. air consumption. The current was light fortunately but visibility wasn't as good as I had hoped.

I setup the mod for feet first descent (inverting the foils and securing them to the line and spring) but discovered a serious problem with the eyehooks it was suggested that I use. They hit the axle the foils ride upon without sufficient embedment to probably stay put so I didn't get to try that approach. I need to work something up externally on the foils that will allow reliable, quick and easy inversion and righting at depth for ascent. I'm thinking something with line and hooks. Will update on that once I work it out.

I also tried inverted swimming a few times at max speed and really didn't notice that much difference, this time. The jury is still out with me until I have more time on this thing and get it tuned just right and am using the right type of kick for max speed. I am still trying to figure out the balance between kick amplitude and frequency or speed vs. distance/air consumption. You can actually move quite fast with fairly good efficiency with a small amplitude, rapid kick as opposed to a more larger amplitude, powerful kick.

[wet]

Originally Posted by ricki

... I also tried inverted swimming a few times at max speed and really didn't notice that much difference, this time. The jury is still out with me until I have more time on this thing and get it tuned just right and am using the right type of kick for max speed. I am still trying to figure out the balance between kick amplitude and frequency or speed vs. distance/air consumption. You can actually move quite fast with fairly good efficiency with a small amplitude, rapid kick as opposed to a more larger amplitude, powerful kick.

I'm thinking that the faster the speed through water, the smaller the arc of the tail/fin/foil on each stroke. As speed increases, arc decreases, and the muscular output becomes more like a rhythmic beat. Hard to explain this, higher amplitude = smaller arc = more automatic like heartbeat = far more efficient per axial distance per O2 consumed; as opposed to eel-like swimming, where the arc may be 1/2 as long as the body (?).

My point being, maximize hydrodynamics and minimize arc of stroke at high speed in order to conserve oxygen. Like a speeding dolphin with the tail just barely flicking. At high speeds, you are literally pushing a wall of water out of your way, so hydrodynamic streamlining is absolutely essential, otherwise you're burning O2 just swishing.

High speed apnea swimming = DANGEROUS, be very careful, the more successful (faster), the higher the risk. IMO, requires a buddy on a scooter closely accompanying the diver. Oxygen consumption rate is critical.
That's not even considering all the other normal free-diving risks and distractions. Safe diving.

[ricki]

Interesting points and they make sense. I've been looking at caudal fins since I reacquired an Aqueon. Wondering if a thinner foil section might perform for faster, easier oscillations with lower air consumption. Say something like a tuna fin or maybe that of some marine creature with a fin beat rate that might be comfortably approximated by a human.

The current foils are fairly thick and shove a fair amount of added mass as you point out. There is the tradeoff between lift, drag and added mass vs. energy input and air consumption. I have no doubt Cal did a lot of development in these areas years back. Still, the candidate design was to have wooden foils which have to have a minimum sectional area to be strong enough to perform. Wonder what would be experienced with thinner, lighter foils of varying aspect ratios.

The spring supposedly aids performance until sufficient speed is achieved, I suspect until the vortical streets shed by the foils promote oscillation. I am not totally convinced though and wonder if some benefit is provided even at higher speeds. I was thinking of some form of spring tensioning, better still a spring replacement, that could be tensioned on the fly.

You are right, going full out in apnea is a hazardous activity. A minder closely paralleling your movement is a reasonable precaution.



A photo of the Aqueon on the Wreck of the Sapona off Bimini in the Bahamas. Shot a fair amount of still and video of the Aqueon within and around the Sapona. Hope to get things processed and uploaded soon.