Fins for Frog Kick

[dherbman]

If you can point to my erroneous statements, I'd appreciate it. I strive for accuracy in my understanding and welcome any correction. Other than that, I agree with you that quitting while you are behind is probably a good option.

 

[SparticleBrane]

Ask any caver about flutter vs. frog...

 

[dherbman]

That extra set of legs you have in your ava look like the way to go. You could flutter and frog at the same time.

You know what the cavers will say, but there's a lot of good reasons to use that kick outside of the cave and in the recreational realm. Of course, you already realize that.......

 

[alo100]

In that "perfectly trimed" frog kicking position where the lower leg is kept bent upward at the knee I'm wondering how much drag is created by the legs themselves? With the lower legs held upward, like two little sails against the water, they are out of the slipstream, if you will, and it seems they would create considerable drag.

Thank you for your explanation. I watched the video before, and I can see the "speed" just do not know how fast. So you're saying that as long as the knee bent and the fins are part of the sail and they produce thrust, it should be fine in terms of drag. Is that what you mean?

Same for the modified flutter, eh? Or flutter could be different?
See, for the modified frog, I can see that, having the knee bent, use the lower legs and the heels to make the particular movements is very effective. However, for the flutter, comparing to the orginal flutter style, with no knee bent, I think this old style is just as effective (comparing to the modified flutter). It's just my estimation, since you're using split, maybe you can tell if you'd prefer to use orginal flutter or the knee bent flutter. Or anybody is welcome to comment on this....

 

[alo100]

Not really. Stiff, short and constant is the most efficient method for splits. It doesn't take that much effort, but it has other disadvantages.

Unfortunately, this still produces a "V" of propulsion which directs force both upwards and downwards.

If you could see the force generated while viewing the flutter from the side, there would be a "V" that extended behind the diver.

Here's a short video that should illustrate this. This isn't a silty bottom, but you can still see the effect. Click on the image to follow the link to the video.

I'd try to share what I think of it, just try to, may not be able to give an explaination.
For the traditional flutter kick, I think the front kick (i.e. kick down towards bottom) is not as useful as the back kick, esp when the kicks involves a big angle. As all of you have discussed this previously, it push you forward but also up. When the angle is big, it's even worse, part of the component can push the water towards the front (diver's head). Well, exaggerated, cause the fins are elastic so it won't be that bad... So some of the fins resolved this by changing the fin angle, e.g. like what they did for the Tusa X-pert, so even when the user kick forward, the component pointing towards the front is minimized. For split fins, any split fins, as you have pointed out already, imagine we are following the diver, like in this picture, we can see ^ for front kick, and V for the back kick.

First, imagine it's a regular non-split fin. During front kick, imagine the kick is made as wide as possible, then imagine that the water being kicked is right in front of the fin like a soccer/football. Image also that we are all following this diver. When the shot is made the ball would go down (to the bottom of the sea) or even a bit towards the diver's head.
Now imagine the case of split, because it's a split, part of the water slipped through the slit, and squeezed towards me, which is good. Imagine 3-D, the fin is bent like the one in the picture. Break the ^ into 2 parts / and \. Imagine again that we are following the diver with the split fin, the / push the water towards right and towards me (we're following the diver, water squeezed through the slit mainly), the \ push the water towards left and towards me. The left and right components cancelled each other, the left over component is the water pushing towards me.

The back kick movement is similar but harder for me to tell, how about that?

 

[djanni]

As I understand it, the slip stream is shaped something like a cone that begins at the head and the fins stay within this cone.

Well sure there would be a cone effect.

While I'm not encumbered by a lot of knowledge about water dynamics it seems very logical that the diver would have to be going really fast for the cone to spread 18" to 24" within 3/4th's of a body length. I don't think a diver can generate that much spped. Also, it seems it would take a lot of speed for the cone to maintain itself during the kick cycle. I don't think a diver can generate that much speed.

As I think about it I don't think a diver can generate and/or maintain a significant enough cone. The divers legs would be are outside the slipstream and would cause significant drag.

Think about it? Doesn't it seem that way to you? So I guess I'm thinking that while a frog or mod flutter helps reduce silting there is a penelity to be paid for not being as streamlined as one could be.

 

[dherbman]

Think about it? Doesn't it seem that way to you? So I guess I'm thinking that while a frog or mod flutter helps reduce silting there is a penelity to be paid for not being as streamlined as one could be.

Check this pic out. Nice trim, nice form. You may be right that the fins are out of the slip stream at some point, but I don't think it's to the extent you believe. I'll shoot some video next time I'm in the pool and see how far out they actually get.

 

[SparticleBrane]

That extra set of legs you have in your ava look like the way to go. You could flutter and frog at the same time.

Haha yes I have double the frog-kicking power!
Actually that was taken when I was diving with a new student in the Keys on May. He and I were both slightly head down for whatever reason so you can't see him in the pic.