Hydrodynamics - Monofin and legkick

[baiyoke]

Not sure if this should be in training-, equipment- or science-forum, so I put it here...

There's something that has been on my mind about the Monofin design (oldschool finswimming-like) and also about the monofin technique. The two things kind of add up...


About the technique:
Many people talk about the proper dolphin-kick. But lately Goran did a WR with something that looks more like kick-glide, with knees bend (actually more like kick-glide-short, kick-glide-long it looks like, but nevermind). Bending the knees is something that works for me also. When I do that it kind of feels like I'm pushing off from the poolside, it feels good and powerfull, but I'm totally bending my knees, and that is something that many people associate with "poor form" or "to stiff blade".

(On a side-note: I don't have anyone at the moment to guide me, because I'm the local instructor for a small dedicated group (really basic level), so I'm kind of just trying to do what feels nice/efficient. I've been monofinning a month, and before that bi-finning 3 months. And right now bending the Knees feels efficient. Doing dolphin-style swimming doesn't. I know it might be because of poor technique... I have to add that I'm very stocky physically, short big muscular legs, so perhaps that is the reason I don't feel like a "dolphin" when kicking. But perhaps not, dolphins can look pretty stocky/muscular too, allthough gracefull. I'm doing 112m PB DYN, so I'm thinking maybe that style just fits me... But I'll make another thread to get advise on that.)



About the design of finswimming-style monofins:
To me it looks like a bad idea to have such a big surface-area close to the feet. Becausee the feet moves up-and-down, so it must create a lot of VERTICAL drag near the feet, since it's only the last part og the blade that really gets a good angle. At least on the down-stroke.

On whales/dolphins the tale seems flexible enough to let the thrust/power inducing part/the "fluke" (File:Baleen parts.png - Wikipedia, the free encyclopedia
), be in a better angle for most of the movement.

For humans the shin and feet are not that flexible, at least not on the down-stroke... on the up-stroke the feet can bend and create a good angle.

So, I'm thinking, the monofin should/could be extended with two nice round hydrodynamic flexible parts, sort of imitating two "tales" or "peduncles", one for each leg. That way the up-and-down moving feet would not create (much) vertical drag, and the flexible parts would make the blade/fluke be in a better angle to create thrust.

But then I was thinking; perhaps that is why the movement with the "push-kick" kneebending technique feels good. Because the feet can create an angle going up, and the knees can create an angle going down. That way you get a better angle with the existing "finswimming-style" monofins. the chin and feet imitates the flexible tale/peduncle.


Does it make sense? Can you follow my thoughts?


1) The finswimming-style monofin looks like its moving too much water up-and-down near the feet (fast, but not O2 efficient).

2) Bending the knees might actually be a good idea BECAUSE of that design.

What do you think?

 

[cdavis]

You are thinking about some of the same things Ron Smith has been working with in developing his Dol-fin products. They use a horizontal blade, like a airplane wing which is set about 10 inches behind the feet. The blade pivots to allow the best angle of attack for up and down stroke. Below is a thread you might like to read through. Pages 1-20 are early models, 20-last are more recent models.

http://forums.deeperblue.com/monofins/85969-extreme-dolfinism-20.html

Connor

 

[Mullins]

If you look at a video of a hyper fin, they bend mostly at the footpockets. So the whole blade is at a decent angle.

Swimming with knee-bend in DYN seems to work fine, since we're not going fast enough for drag to be a big issue. Bit different if you're going fast in CWT but most people get very leggy there too, because without full lungs their midsection has a lot less support which means more abdominal effort... which you don't really want at depth. So it's a compromise.

 

[baiyoke]

You are thinking about some of the same things Ron Smith has been working with in developing his Dol-fin products. They use a horizontal blade, like a airplane wing which is set about 10 inches behind the feet. The blade pivots to allow the best angle of attack for up and down stroke. Below is a thread you might like to read through. Pages 1-20 are early models, 20-last are more recent models.

http://forums.deeperblue.com/monofins/85969-extreme-dolfinism-20.html

Connor

Thanks cdavis. I know the thread and have read some of it, but not all the posts. Just some here and there. I think I will read it more thoroughly

Dol-fin Orca is another solution, to the same "problem" as I se it. But I can't help thinking it creates a lot of drag around the feet, the way the footpocket is made, and the legs sticks into it. It doesn't look powerfull in videos, but then again, it doesn't necessarily have to. Does anyone know the longest DYN performance of the Dol-fin (Orca)?

In its own way it's actually quite nice looking once you get used to looking at it, and I think he's on to something.

But as mentioned in my post above, I'm thinking more about a solution where the footpocket is split up in two, and looks more like long hyper-fin footpockets.

 

[baiyoke]

If you look at a video of a hyper fin, they bend mostly at the footpockets. So the whole blade is at a decent angle.

Swimming with knee-bend in DYN seems to work fine, since we're not going fast enough for drag to be a big issue. Bit different if you're going fast in CWT but most people get very leggy there too, because without full lungs their midsection has a lot less support which means more abdominal effort... which you don't really want at depth. So it's a compromise.

I didn't know they bend so much near the foot. Nice.

But I did notice that the fotpockets are attached further out, wich is nice. But I wonder if it could be even longer/further away from blade...

 

[Mullins]

They probably could - the thing is the mono manufacturers are all constrained by the CMAS regulations for fin dimensions. We presumably aren't a big enough market to be worth experimenting with longer/wider fins.

 

[efattah]

Does anyone know the longest DYN performance of the Dol-fin (Orca)?

I think it was 226m by Natalia Molchanova.

 

[trux]

Yes, Molchanova, but not 226m, it was 217m on the Team World Championship in Okinawa 2010. Her world record of 225m was done before that with a regular monofin.

 

[baiyoke]

217m!! That seems very promising for a new design paradigm of monofins... And deserves some respect regarding the projects outcome at this point I think.

Perhaps she could have gone further on an individual record attempt...

Any more thoughts about the "knee bending technique" and its possible relation to the monofin design? Do you bend your knees?

 

[trux]

I think it is important to note, that Natalia tried the fin for the very first time just a few days before the final swim, already on the championship, and did not train with it more than just very few hours.

 

[efattah]

Natalia told me she did only ONE dynamic to 100m with the Orca before the 217m swim.

 

[trux]

Incredible! Does she in fact own one DOL-fin now, or did it stay at the single attempt with the borrowed fin?

 

[efattah]

Natalia was 'borrowing' the Orca, last I heard she still had it.

 

[baiyoke]

Bit different if you're going fast in CWT but most people get very leggy there too, because without full lungs their midsection has a lot less support which means more abdominal effort... which you don't really want at depth. So it's a compromise.

That kind of implie something I haven't come upon in freediving training: It must be important to build a strong abdominal corset of muscles, especially the muscles going across the stomach diagonally/oblique/twisting....

 

[baiyoke]

I just read an article wich shows what I kind of knew allready: Hydrodynamics is a very complex matter he he...

Delphine Mystery
While planning our machines, we availed ourselves of the long trail of theoretical
experimental and biological studies of how fish swim. In 1936 the British zoologist
James Gray created a stir by calculating the power that a dolphin would need to
move at 20 knots, as some were reported to do. Gray assumed that the resistance
of the moving dolphin was the same as that of a rigid model and estimated the
power that the muscles of the dolphin could deliver. His conclusion, known as
Gray’s paradox, was that the dolphin was too weak, by a factor of about seven, to
attain such speeds. The inescapable implication is that there are flow mechanisms
at work around the body of the moving dolphin that lower its drag by a factor of
seven.

http://web.mit.edu/towtank/www/Papers/efficient-swimming.pdf

Damn!..

That kind of suggest that maybe moving more like a dolphin or fish might be the "better" method... Contrary to bending the knees... hmmm...

The control of vortices offers a novel solution. The idea is to produce favorable
pressure gradients and then control them to optimize the response. Specifically,
pitching and heaving a foil to a maximum angle and then back again produces a
strong, sudden force, ideally suited to maneuvering and a fast start. The motion
gives rise to a large initial vortex, followed quickly by another one spinning in the
opposite direction. Sudden forward thrust, as well as a lateral force, results when
the second vortex is briefly trapped between the first one and the surface of the foil.

This maneuver is exactly what a fast-starting agile fish does with its tail. Just before
shooting off in some direction, its body flexes sharply, with the forward half of the
body oriented at 60 to 120 degrees with respect to the ultimate direction of motion.
Such orientation is necessary for the fish to compensate for the lateral force that
accompanies the thrust.

So there might be some benefit from flapping continouesly instead of kick-glide... hmmm...

Interestingly they think about using flaps to move ships:

Ships and submarines,
on the other hand, exert no control over the flow around their hulls and move at a
slow pace, their very large wakes with uncontrolled vortices creating enormous drag
forces.

These findings, along with those concerning the Strouhal number, suggest that a
properly designed foil could be a very attractive propulsor for ships, motor yachts
and underwater vehicles. Given its natural advantages and the fact that
development of the proper motors and gears is well within today’s technological
capabilities, this foil might be the first fish-inspired technological application. The
use of an even number of countermoving foils, properly positioned, could minimize
unpleasant swaying or vibration. Of course, future shipbuilders would also have to
address structural reliability, the hydrodynamic shapes of sterns and other
variables.

 

[Azrael3000]

'Gray's Paradox' Solved: Researchers Discover Secret Of Speedy Dolphins here is a bit a contradictory view on the matter. I haven't read the scientific paper yet, but according to the article, dolphins are simply really strong. Well I guess that's not the only answer but it's suggested that it is a significant part.

 

[baiyoke]

Nice Azrael. That makes sence to me. It sounded strange that it should be a 6 times diffence in a streamlined creature like the dolphin.

I don't know much about hydrodynamics, but I do know a little about training and muscles, and those dolphin tails look pretty buff. If its all muscles underneath, I'm not surprised they do 20 knots.

And I also think that the dolphins ability to "dance" indicates a lot of power

 

[baiyoke]

Just read another thread about the subject, old one, but good one, maybe someone is interested in reading it too: http://forums.deeperblue.com/static-dynamic/80273-monofin-technique-dynamic.html

I especially like post number 24, because its similar to what I experience when trying to be (too) technical (allthough it's also fun to play with):

Hi all- Very interesting thread. Very technically advanced, I'd like to throw in a another angle...
I have been working on my mono DYN technique for a while and kinda have the Elisabeth style going quite well. Then I did a dive a few weeks ago at the Nordic Deep comp in Sweden, funny enough with Elisabeth in the lane next to me
I'd had a week of competing with daily maxes and DYN was an extra at the end, I decided to really just
focus on relaxing and not even think of technique, distance or anything technical.
Well, I had my coach the judges and the girls diving with me baffled! It was the longest dive I'd ever done, around 3 minutes. My technique was terrible... but I did a new PB of 150 and came up so strong my coach reckoned I could've done quite a bit more... and this fascinates me.
Seriously my technique was atrocious... moving arms up and down, bent knees, looked like an untalented beginner! So how much is feeling good and relaxed and how much is technique and equipment? 50 50? 40 60?

And from this my tip for those not pushing world records is to work as hard at feeling goooooood underwater as you do on technique.

But there's some other really good explanations there, including Laminars post number 9.

Anyway, I just played around looking at some videos of Goran, Elisabeth and Mullins, and did a screenshot. To see the degree of knee-bend, and to see the degree of hyperfin-bend (Gorans). The hyperfin really bends A LOT near the feet like you said Mullins!!! Especially with Gorans strong kick. WOW! It looks almost vertical it seems

I also looked frame-by-frame at the degree of knees bend, when it is in outermost position. Just to see differences in style.

Goran bends A LOT with a nice powerfull kick...

Mullins bends much less with a rock-solid nice style kicking continuously (video from the thread I mentioned before, post 18)...

Elisabeth bends only a tiny bit doing 3 kicks and glide, first kick...

Interesting how different peoples technique is...

 

[baiyoke]

Damn, the pictures are there in preview, but disappears everytime I post. Perhaps someone can help...

Btw it's also interesting how much your fin "spoon" in this video Mullins:

[ame="http://www.youtube.com/watch?v=Ltkb-95RQrc&feature=player_embedded"]Hyperfin - YouTube[/ame]

 

[Mullins]

I've got a photo of it folding past 90 degrees on a CWT dive. I think it's on here somewhere.