Venting for Drag.

[John C. Ratliff]

I've tried dolphin in the pool. Its fairly hight energy. I can try whip. Don't really have a cave handy to try whip in with fins.

How have you found it in caves?

I haven't dived caves since the 1970s; I'm in Oregon, and dive high current rivers. Try it and see.

SeaRat

 

[tbone1004]

@John C. Ratliff the end of your post was not something that sounded like you were going to finish your post. Sounded like you had another "chapter" to write, not that I cut you off.

whip kick is also a b!tch on your knees... That said, the whip kick does still have quite a bit of downward thrust and the feet do not remain above your body.

In terms of flutter kicking in a cave. In certain caves that is an option, and I have used it in VERY high flow caves to assist a scooter as recently as a month ago.

@MichaelMc I've used both, but more time on the pros. We have several pairs at school. I used them during our 1200m circuit since 400 of it is finning and they were much better than my jet fins at the time.

 

[John C. Ratliff]

@John C. Ratliff the end of your post was not something that sounded like you were going to finish your post. Sounded like you had another "chapter" to write, not that I cut you off.

whip kick is also a b!tch on your knees... That said, the whip kick does still have quite a bit of downward thrust and the feet do not remain above your body.

In terms of flutter kicking in a cave. In certain caves that is an option, and I have used it in VERY high flow caves to assist a scooter as recently as a month ago.

@MichaelMc I've used both, but more time on the pros. We have several pairs at school. I used them during our 1200m circuit since 400 of it is finning and they were much better than my jet fins at the time.

Okay, next time I'll simply say that I have to go and drive my wife, and will finish when I return.

Concerning the whip kick, it takes advantage of the disadvantage of the Force Fins, their folding on recovery. The recovery on the whip kick invites this fin, and then there is a kick backwards from a high point. I'm simply pointing out that there is this option. Whether you use it in a really hard kick, or in a finely-tuned kick, that is your option, but you might try it and see just how it works.

Now if you want to be experimental, take one of your flat fins, cut it up and make a pair of "scoop fins," per my photos above. I think you'll be really surprised about that.

The other thing to think about is that this is the Force Fin forum, and not a cave forum. A certain amount of decorum is required here, as this is a manufacturer's forum. I'm pointing out the advantages of the Force Fin. By the way, the hydrodynamics above is somewhat mis-represented. To get a better idea, read "Swimming into the 21st Century" book, especially the chapter titled "The Fluid Dynamics of Swimming Propulsion," which goes into some detail of how these dynamics work for swimming, and can be applied to fins for diving too. And, it would not hurt to look at the Force Fin patent (a link to which is in a previous post by me).

SeaRat

 

[Bob Evans]

Well I guess I get DEFENSIVE. May be I am no match to comments I don't get or am not smart enought to respond. John your cool and it has been a long time. Years ago I made a Frog Kicking fin for Captain Billy Deans.EXCELLERATING FORCE FIN – Force Fin As for the Military I work with, well it is a proud moment for me..anyways. We have been hit hard by People of Republic of CHINA now that those ......PATENTS have expired. In hind sight I wish I have bought a house in Hawaii for the money spent for all those PATENTS, around $500,00. Then to make and test each Force Fin model was around $ 60,00. The bottom line was when our "SPLIT FIN" got ripped off we did not have the half million to start a law suit with several other companies. So their you have it and we keep our doors open for those who have purchased our America Made products.

 

[Rooster59]

This thread seems like a 2AM argument at Flanagan's Ale House

 

[John C. Ratliff]

This thread seems like a 2AM argument at Flanagan's Ale House

No, it's not. It's a discussion on the fluid dynamics which causes diver propulsion, and some of the misconceptions by divers about that. Some of those misconceptions apply to the Force Fin. I started using mine again last summer, and was surprised at how well they performed in the current. Bob Evans talked just a bit about the Force Fin's performance in the water, but what I found is that the profile of the fin split the current's force, and did not affect the fin (I've had other fins pull off my feet in a strong current, including one of my scoop fins).

In Swimming into the 21st Century, Cecil M. Colwin discusses on page 61 "How a Starting Vortex Creates Circulation in the Form of a Bound Vortex." He discusses this in relationship to how these vortex's are formed:

...It is provable mathematically that because a flow does not contain a circulation at the start of a movement through it, it cannot contain a circulation at the end of the movement. This principle applies to lift propulsion in human swimming: The shed vortex at the end of each propulsive effort in that particular direction has ended.

From the preceding it can be seen that any lift-producing mechanism comprises the following three phases of vortex action:

1. The starting vortex
2. The bound vortex
3. The finishing vortex (also termed the shed, or free, vortex)

This is also true of fins, and especially the Force Fin. My scoop fins do the same too. But the Force Fin, with its very high degree of snap back, produces very good shed vortex's. This is propulsion! You can see these vortex's in the bubble formation from surface swimming. You can also see where the vortex goes (down, or backward). I have some video of this, but will need to do some work to get them onto YouTube and visible here (may take some time--I'm working on other things too).

Now, about my scoop fins, the Murdock patent covered it:

But if you wish to make some, feel free. It will take time and effort to do so, but it would be interesting to do it. Here's what my third try at it looked like in 1970:

You want the flexible membrane to be tight at the toes, but make a semi-circle at the tip of the fins. Any flexible waterproof fabric (neoprene-impregnated nylon or something similar) will work.

Or, you can buy some Force Fins and save yourself a lot of labor. Below you can see a screen shot of the shed vortex's of the Force Fin at the end of one whip kick stroke. Note that the bubbles are mostly behind me.

Force Fin Sted Vortex's by John Ratliff, on Flickr

Here you can see the bound vortex coming off the edge of the Force Fin using a flutter kick:

Force Fin Bound Vortex--flutter kick by John Ratliff, on Flickr

SeaRat

 

[Bob Evans]

No, it's not. It's a discussion on the fluid dynamics which causes diver propulsion, and some of the misconceptions by divers about that. Some of those misconceptions apply to the Force Fin. I started using mine again last summer, and was surprised at how well they performed in the current. Bob Evans talked just a bit about the Force Fin's performance in the water, but what I found is that the profile of the fin split the current's force, and did not affect the fin (I've had other fins pull off my feet in a strong current, including one of my scoop fins).

In Swimming into the 21st Century, Cecil M. Colwin discusses on page 61 "How a Starting Vortex Creates Circulation in the Form of a Bound Vortex." He discusses this in relationship to how these vortex's are formed:

This is also true of fins, and especially the Force Fin. My scoop fins do the same too. But the Force Fin, with its very high degree of snap back, produces very good shed vortex's. This is propulsion! You can see these vortex's in the bubble formation from surface swimming. You can also see where the vortex goes (down, or backward). I have some video of this, but will need to do some work to get them onto YouTube and visible here (may take some time--I'm working on other things too).

Now, about my scoop fins, the Murdock patent covered it:
View attachment 512259

But if you wish to make some, feel free. It will take time and effort to do so, but it would be interesting to do it. Here's what my third try at it looked like in 1970:
View attachment 512260
You want the flexible membrane to be tight at the toes, but make a semi-circle at the tip of the fins. Any flexible waterproof fabric (neoprene-impregnated nylon or something similar) will work.

Or, you can buy some Force Fins and save yourself a lot of labor. Below you can see a screen shot of the shed vortex's of the Force Fin at the end of one whip kick stroke. Note that the bubbles are mostly behind me.
View attachment 512261Force Fin Sted Vortex's by John Ratliff, on Flickr

Here you can see the bound vortex coming off the edge of the Force Fin using a flutter kick:
View attachment 512265Force Fin Bound Vortex--flutter kick by John Ratliff, on Flickr

SeaRat

John, Thank you. I was going to say some thing about Murdoch, who did it before Mares. Mares got around his patents with their double molding of two types of materials. Made some designs along the same concept with Fabric. The Fab Force Fin.

 

[Bob Evans]

John, working on a 40 year Force Fin Exhibit for 2020. Here is another example of a flexable Urethane blade I was developing for JMC Ocean Futures Dive Team, 19 years ago.

 

[Bob Evans]

John I found the fin blade like the one you made, but all in fabric. Susanne did the sewing and we pushed Poly-Urethane into the rib part. At one point filed Patents on the process of non-molding. The final mocel ended up like this with JMC checking our Connie Lyn Morgan SD-1 Fab Force, now almost 20 years ago. How times flies..

 

[Bob Evans]

The jet fin you show is a stepped/offset design with vents between the 2 surfaces to allow water to pass through on the back stroke to reduce drag/resistance. The spoiler on the aircraft wing you show is extending a surface out (at a very diffent angle than the rest of the wing) into the airflow over the wing to disrupt it and add drag to slow the plane - there is no venting, so really apples and oranges...

I'd also love to understand how you claim to have created a surface (a wing) that you move through the water without creating any drag?

I guess this post was over a year ago. You caught me off guard and did not how to respond at the time. But you were right about the spoiler and jet fin vents. I missed the point, maybe to much Titos. The vents spoil the water flow, create drag. I did experiment with vent like areas, Split fins and the OPS. Thank you for directing me to be more thoughtful. This might help you understand my direction of thought. Engineers – Force Fin