Extreme Dolfinism G2

[divebike]

Stand with your weight back in line with the mid point of your heels, see how you go just lifting your own body weight, ah still trying, that's me not you

 

[baiyoke]

To be fair I don't know how strong the feet is going the other way - but we don't need a huge amount of force I think, at least not more than we got.

There are many variables to take into acount depending also on the tecnique we use, and what we do. Fx continoues kicking or kick-and-glide in dynamic. For dynamic we need to be fairly relaxed and efficient. For constant weight we need more power if negatively buoyant. For recreational diving or spearfishing things vary.

One advantage to using feet-movement actively could be better streamlining. However when moving feet the leverage is shorter, so the foil angle changes more... this is not good, but it does so anyway to a lesser extend. It's complicated...

-i also think that it might be possible to attach something to the legs... But is it better... And for what activity?

 

[cdavis]

Let me help you out some. The ankle flicks use both up and down strokes. See Efattah's vids; his toes come almost perpendicular to his legs. Works great with the Dolfin, very efficient, but isn't fast, not enough power is correct.

Lower drag in the fin is probably not as important as shape resistance, but its a game changer none the less. The difference in falling vertically with a dolfin vs bifins or a traditional mono is huge. That has to be mostly if not totally lower drag. That much difference has to affect overall efficiency and distance ability.

 

[cdavis]

Couple of other thoughts. Keeping the body straight does reduce drag, but it also reduces undulation and channeling of water to the fin, which reduces fin efficiency. For me, going slow, as you do in serial diving, and having a poorly undulating back, its worth it energeticaly to keep the body straight when going slow, feels much more efficient. Thats why ankles work so well for me. As the need for speed increases, undulation increases, and (for me) ankle flicks decrease. At full power, I'm just letting the ankles go along for the ride and trying to getting all my power from the core with as little leg bend as possible.

 

[divebike]

sorry revan ,might of hijacked your thread momentarily , still interested in your views on my original posts

 

[divebike]

Couple of other thoughts. Keeping the body straight does reduce drag, but it also reduces undulation and channeling of water to the fin, which reduces fin efficiency. For me, going slow, as you do in serial diving, and having a poorly undulating back, its worth it energeticaly to keep the body straight when going slow, feels much more efficient. Thats why ankles work so well for me. As the need for speed increases, undulation increases, and (for me) ankle flicks decrease. At full power, I'm just letting the ankles go along for the ride and trying to getting all my power from the core with as little leg bend as possible.

i'm not discounting the value of the ankles and feet in the current set up, it's more that maybe you could replace them in a way, to take the strain off them so they are not a limiting factor.

 

[Bill]

Thanks Ron.

 

[REVAN]

Wow, take a little time away, and suddenly the thread lights off! Lets see if I can answer a few of these...

In a practical sense how much does wetted area come into the equation , I firstly would look at shape resistance as generally being the most important factor, apart from thrust production.

Every little bit counts. As a rough approximation, I'd guess the surface area of a hyperfin is about 25% to 30% the area of the diver it is attached to. So, it is not insignificant, but then the parasitic drag is not the largest drag contributor for a diver either. The form drag is a larger component, so it is a 25% increase in something that is less than half of the total to begin with. I don't have good numbers to quote for the ratio between parasitic drag and form drag of a diver, so I cannot get much more specific than this right now.

Also is there a huge difference between the pilot or x20 and the orcas, this is not meant to be a slight on the orca models, as I see them as being of the highest performance monofins available for freediving, it's more of a case that by your words they seem to be substantially lesser, but looking at the designs I can't see it. I understand there is a market for the best even if it's only incrementally better. As of another interest have you ever tried to create a sprinters fin , I expect it to be larger and stiffer and or placed further back from the feet, the load on the feet is important I believe.

The difference between the X-20 and the Orca1 was maybe as much as 10% overall. They felt a little different also, but not a lot different. The Pilot and the Orca2 will feel quite a bit different. I have not done a detailed comparison of the overall performance difference between them, but since I think the Orca2 is performing better than the Orca1, and the Pilot was tuned with the intent of being bit more recreational and easy swimming than was the X-20, I'd expect there to be a larger difference between the new Orca vs. the new shoe model. There is also a bigger price difference as well. The X-20 was about a $900 fin, the new Orca is about $300 more than the X-20 and the Pilot is about $250 less than the X-20.

I hope this clarifies things for you. Oh, and no; I have not made any monofins for sprinting. My interest has always been freediving.

 

[cdavis]

Divebike: They aren't. at least no more than in a normal mono. Ankle is just much morel useful in a Dolfin when going slow.

It would be interesting to see what could be done with a Dolfin type foil in a sprint fin.

 

[REVAN]

The load on the ankles is of interest to me, there's no way the feet can create any significant power as I see it, there importance in most fin propulsion is the change in the arc distance and or angle control, with the way that the dolfins and lunocet designs work I wonder if a little more flex built into the designs and a more direct power transfer through the line of the shin bone to what would line up approximately with the midpoint of the heel wouldn't work better, this doesn't match in well with the design of bike shoes however.

I'm not sure what you mean here. These two things are contradictory, "...I wonder if a little more flex built into the designs and a more direct power transfer...". More direct power transfer is more rigid, less flex. If you want to try to explain your question again, I can try to answer again.

 

[Fondueset]

Interesting thread - I've not visited it in awhile. Dive bike - the power business with these fins is quite different from either bi-fins or hyperfins. In cruise mode you just don't get the same kind of feedback - if, like me, you are accustomed to hyperfins - you'll likely have a tendency to physically search for that feedback - overpowering the fin and losing efficiency. Relatively speaking There is very little felt load anywhere in the body - though obviously this increases with a wider blade. Upshot is it's about lift - not power. I'm still most relaxed when I can see something - a line or the bottom - and measure my speed by it's passage.

Using the ankles can be a way to do a minimal exertion/perceived movement cruise and a way to extend your undulation while reducing the drag of large body movements. I've really had to reprogram myself kinesthetically to properly exploit the Orca.

In terms of strength - these fins can be tuned to the individual by different blade widths - but even the wide-blade model I have places less stress on the ankles that my soft (Omer Ice)free diving bifins.

This video is with mostly ankles - in the beginning I got a little too close to the bottom and was worried about bashing up the fin and pool bottom, but you can see I eventually get going pretty well. It's not entirely ankles - but mostly.

 

[divebike]

I'm not sure what you mean here. These two things are contradictory, "...I wonder if a little more flex built into the designs and a more direct power transfer...". More direct power transfer is more rigid, less flex. If you want to try to explain your question again, I can try to answer again.

Lines of force are what i'm talking about in talking about the directness of the power input , there's a slight rotational aspect to the power input when going through the front of the foot, I meant the power to be sent directly through the line of the shin bone and a little more flex built into the design to take into account of the feet flexing adding less angle change then normal,

 

[REVAN]

Lines of force are what i'm talking about in talking about the directness of the power input , there's a slight rotational aspect to the power input going through front of the foot, I meant the power to be sent directly through the line of the shin bone and a little more flex built into the design to take into account of the feet flexing adding less angle change then normal,

Okay, I think you are talking about bypassing the feet and tieing into the lower leg for the force transfer, similar to how the aqueon/powerswim concepts connected. Is that right?

 

[divebike]

It's the main problem with the aqueon in terms of the power input, the overall average power input is downward with that invention, this is compensated for, probably unconsciously, by assuming a drag posture that negates this and having a rear wing that compensates for the rotational aspect of the designs power input, now the overall average power input is parallel with the body with the dolfin and lunocet but it's slightly off centre, just being picky really ,probably doesn't mean much.

 

[divebike]

Well when I say downward with the aqueon I mean midway between the 2 extremes of the angle of the bar that connects to the front wing, to the body, this is the net line of force

 

[baiyoke]

Lines of force are what i'm talking about in talking about the directness of the power input , there's a slight rotational aspect to the power input going through front of the foot, I meant the power to be sent directly through the line of the shin bone and a little more flex built into the design to take into account of the feet flexing adding less angle change then normal,

Adding flex will, like Ron said, Be the opposite og what we want. Because then it will flex from the start (the wrong way) and when it finally realeses it is again the wrong way at the end of the stroke...

What you talk about must be achieved differently. And probably can... But not easely. It is kind of an "opposite flex".

 

[baiyoke]

well, actually opposite is not right, "controlled realese" would be a better description...

 

[divebike]

I'm aiming for the flex to be the same as before , part of the wings angle changes are made by the feet, if I take these out of the equation and they were correct before then I need to add it back in somewhere else, i'm doing this by increasing flexibility of the wing connectors but only to put that part back the way it was ,but now I have the correct amount of flex as before but a better line of force

 

[divebike]

with all these designs mostly with the aqueon ,the power input creates a situation where you would swim in a circle, looping backwards if not for compensatory drag, and drag is a drag. Well with fins other then the aqueon this 1st statement I've realised isn't entirely right as you could vary your stroke also to stop this.

 

[baiyoke]

Interesting thread - I've not visited it in awhile. Dive bike - the power business with these fins is quite different from either bi-fins or hyperfins. In cruise mode you just don't get the same kind of feedback - if, like me, you are accustomed to hyperfins - you'll likely have a tendency to physically search for that feedback - overpowering the fin and losing efficiency. Relatively speaking There is very little felt load anywhere in the body - though obviously this increases with a wider blade. Upshot is it's about lift - not power. I'm still most relaxed when I can see something - a line or the bottom - and measure my speed by it's passage.

Using the ankles can be a way to do a minimal exertion/perceived movement cruise and a way to extend your undulation while reducing the drag of large body movements. I've really had to reprogram myself kinesthetically to properly exploit the Orca.

In terms of strength - these fins can be tuned to the individual by different blade widths - but even the wide-blade model I have places less stress on the ankles that my soft (Omer Ice)free diving bifins.

This video is with mostly ankles - in the beginning I got a little too close to the bottom and was worried about bashing up the fin and pool bottom, but you can see I eventually get going pretty well. It's not entirely ankles - but mostly.

That looks Nice. It is a 1,39 m/s dive... Wich for me would be quite fast. But it looks relaxed. How much force Are you putting into it?

Sorry divebike, I can't follow you there, not a clue about what you mean In the last posts. Doesn't seem right though...