Dol-fin customization

[baiyoke]

Not really. The gap is a combination of just needing to fit the float around the shoe, combined with thinking there is a structural advantage to not having the two parts in contact with each other. The shoe if pretty rigid, but it does flex some. When it makes contact with the float, it will transfer loads to it that must then be carried through the fasteners that connect the floats to the frame. Maintaining a small gap adds confidence that those fasteners will not loosen or fail with time.

I just re-read your response, and I realize you are talking about the gap shoe-float.

What I ment was if the gap between the two shoes and between the two floats (the gap "between the feet") does it need to be open performancewise (or could a float fill out that space without any significant drag added)?

 

[REVAN]

I just re-read your response, and I realize you are talking about the gap shoe-float.

What I ment was if the gap between the two shoes and between the two floats (the gap "between the feet") does it need to be open performancewise (or could a float fill out that space without any significant drag added)?

The space between the shoes is not there for performance. It is just there to accommodate the different shoe sizes. It would make little, if any, difference if it were blocked by the floats. The DOL-Fin Orca is closed between the feet. However, it has the fairing which tapers down and is streamline to better slice through the water in the extension between the feet and the fin. This design for the X-20, by maintaining 2 separate extensions, will have 2 narrower float section to slice through the water on the kick cycle. If the space there, between the feet and the fin, were entirely blocked by float, that probably would make a difference as there would be a thick section with a lot of resistance to being stroked even without any fin attached to the structure.

 

[baiyoke]

Oh ya, the stroke would be harder... unless perhaps the float was very well rounded and "sharp" in the center... In light of that, perhaps your wooden floats could even be a bit more rounded I think, they seem a bit flat on top, or what do you think...?

Another question: If two short pvc water pipes were sealed in both ends with end caps (as on the picture), do you think it would stand pressure of 8-9-10 bar, given the round shape, and evenly applied pressure?

I'm just playing with the idea of seperating the buoyancy, and the streamlining wich could then be shaped around the pipes.

Balsa-wood seems by far to be the most buoyent... not taking physical beating into account, do you think it would stand the pressure at depth?

 

[REVAN]

Oh ya, the stroke would be harder... unless perhaps the float was very well rounded and "sharp" in the center... In light of that, perhaps your wooden floats could even be a bit more rounded I think, they seem a bit flat on top, or what do you think...?

Another question: If two short pvc water pipes were sealed in both ends with end caps (as on the picture), do you think it would stand pressure of 8-9-10 bar, given the round shape, and evenly applied pressure?

I'm just playing with the idea of seperating the buoyancy, and the streamlining wich could then be shaped around the pipes.

Balsa-wood seems by far to be the most buoyent... not taking physical beating into account, do you think it would stand the pressure at depth?

I have some schedule 40 PVC 3" here. It is rated to 280 PSI. As a float, it's design crush depth should be about 600ft or 180m. I'd expect the ultimate depth at rupture to be closer to 1200 ft, as I'm sure that it uses at least a factor 2 safety margin.

I'm not sure about the crush pressure of balsa, but I think it is too soft to use from an abrasion perspective.

Regarding my floats, a little more rounding would be nice for aesthetics and may help with streamlining as well. Keep in mind, the pictures I posted previously show a quick prototype I threw together to investigate the idea and are not meant to represent a final product.

 

[baiyoke]

Cool, thanks.

I forgot one question: Do you know the weight of the X-20 when submerged?

I can feel the weight on land, but when wearing it, my buoyancy does not seem to change as much as I would expect...

 

[REVAN]

Cool, thanks.

I forgot one question: Do you know the weight of the X-20 when submerged?

I can feel the weight on land, but when wearing it, my buoyancy does not seem to change as much as I would expect...

If I'm remembering correctly, it is about 1.2 to 1.4 pounds negative when in the water.

 

[cdavis]

I'm looking for an idea to replace my foam floats, maybe pvc? 1.2-1.4 lbs? Time to pull out the calculator and find a way to make the pipe streamlined enough.


scramble, scramble, find the tape measure, find the calculator (sound like I'm organized??, not), measure, think, think, think.

You know, I think this will work, 2 inch pipe should hide in the drag shadow and two 7 inch lengths should have about 1.5 lb if buoyancy, if my math is near right. Wire ties will suffice to attache them. Not pretty, but it should be simple.

Time to get me to the hardware store.

Connor

 

[baiyoke]

For the sake of inspiration:

Did some quick floats in 1 hour the other day. I needed some floatation because I was waering a sharkskin/swimsuit with no buoyancy... Not sure about the drag and performance, but I thought it was more important with correct overall streamlining/weighting so used them at the pool national championships

They are NOT pretty Foam inside, so only works for pool use... Only ads a little buoyancy, even though they are fairly big...

Now I'm thinking about a solution where buoyancy is added between the frame and the shoes... So that the shoes are attached on an "extension" part (wich would add some more lever also...

On the other hand: It is surely possible to make something that extends from the shoe and backwards, to make it really hydrodynamic.. Something looking like a fairing.

 

[cdavis]

I love new ideas, looks great! Much more streamlined than the capped pipe idea.

Do the floats have enough bouyancy to make the fin neutral?

 

[baiyoke]

Before making it, I even considered just taping on two empty waterbottles...

No, not yet neutral. Don't know how far from neutral it is, didn't have time to experiment, but it can't be a lot... might check it tomorrow, if I'll go to the pool...

The space between the shoes is not there for performance. It is just there to accommodate the different shoe sizes. It would make little, if any, difference if it were blocked by the floats. The DOL-Fin Orca is closed between the feet. However, it has the fairing which tapers down and is streamline to better slice through the water in the extension between the feet and the fin. This design for the X-20, by maintaining 2 separate extensions, will have 2 narrower float section to slice through the water on the kick cycle. If the space there, between the feet and the fin, were entirely blocked by float, that probably would make a difference as there would be a thick section with a lot of resistance to being stroked even without any fin attached to the structure.

Just re-read that also; so if I get you right there's no harm in putting flotation in the middle also... As long as it doesn't stick out towards the fin, and preferably is swallowtail-shaped (had to look up that word) http://flagspot.net/images/q/qs-su_n.gif

Making one big floatation device would make it much easier to get enough flotation, and to make a good attachment I think...

 

[baiyoke]

Cdavis -> to my surprise the fin was only 160 gram heavy! The fin is not as heavy in water as one would expect.

I don't have a weight I can bring, so took a small plastic bottle down one shoe, filled it until neutral, and then back home I put as much water in it, as the airspace that kept it floating, and measured this amount (minus the bottle).

At ½ meter it became sligtly negative. At 1½ meter air/foam will compress to 87% volume, so might be nescessary to adjust it to 1/0,87 x 100= 115% volume if using compressable material, and you use it for DYN. If using wood it shouldn't matter of course...

 

[REVAN]

baiyoke,

Are you still doing all surface swimming? If so, I am surprised that you are wanting to add flotation to the fin. In the past, I have found it more difficult to surface swim when my feet are too buoyant. My Orca presently has buoyancy in it making it close to neutral. On one occasion in a 3mm wetsuit and 10 pounds of neck weights, I had a long swim ahead of me. I removed 4 pounds of neck weight and clipped it around my ankles instead, which made the surface swimming much easier and more efficient for me. I had previously noticed Eric Fattah's Orca with added buoyancy was harder for me to surface swim with as well.

Two things that I thought would make the X-20 a better recreational monofin was it's negative buoyancy and the low mounted fin blade; two features that both help to keep the fin blade submerged when surface swimming. So, I'd think adding buoyancy would reduce the fin's efficacy for surface swimming.

Please talk some about your configuration and the differences in swimming performance relating to fin buoyancy so that I can better understand your issues and needs. It will be useful information to have for future DOL-Fin developments.

Also, if anyone else has things to say that would be useful considerations for future monofin developments, I'd like to hear from you.

REVAN

 

[baiyoke]

Hey Revan, I think you have me confused with someone else, I don't do surface swims...

Did some quick floats in 1 hour the other day. I needed some floatation because I was waering a sharkskin/swimsuit with no buoyancy... Not sure about the drag and performance, but I thought it was more important with correct overall streamlining/weighting so used them at the pool national championships

I have just changed the settings, so it's a little early to comment on performance. I found out I was doing really slow DYN dives, so tried to make it more DYN performance specific: The shoes are moved to the outmost position, and I've mounted the nr. 7 trimplates... Allthough slow dives are good for me I think, since I'm relatively short and muscular, and have a relatively good static time... Never the less I think this configuration is more streamlined for DYN... It seems also to demand a better technique...

 

[REVAN]

Hey Revan, I think you have me confused with someone else, I don't do surface swims...

You are right. As the customer list grows I have trouble keeping straight, who is who. Sorry about that.

 

[mikaellaine]

Can someone send a pic of the side profile of the DOL-fin? I just broke a Leaderfins monofin, and was wondering if I could use the footpockets from it and make a fin from plywood for it. Its not a wing, but is it close to a tail fin on an aeroplane? Thanks!

 

[REVAN]

Can someone send a pic of the side profile of the DOL-fin? I just broke a Leaderfins monofin, and was wondering if I could use the footpockets from it and make a fin from plywood for it. Its not a wing, but is it close to a tail fin on an aeroplane? Thanks!

This should do it for you:

 

[mikaellaine]

Thanks! The fin seems pretty thin... I'll have to design my own shape with thicker plywood..

 

[mattbigblue]

Last weekend I've tried DOL-Fin Orca, I must say I was positively surprised.
It seems rather easy to swim with it with really good power transfer. Would love to try X20 one day in a pool with my neckweight etc. cause this I tried just in a lake (surface swimming) after depth competition.

Anyway I think they have a great potential and they will meet somewhere in the middle with standard hyperfin. I saw Natalia Molchanova had in Belgrad quite short monofin with concave endning. Will see what future brings

 

[Kars]

Was that the fin I saw on the video doing her new WR?

 

[mattbigblue]

Was that the fin I saw on the video doing her new WR?

Yes, You can clearly see it on the newest WR video (together with noticable V-bending). I guess she draw conclusions from Orca-Fin and try some kind of hybrid (orca and traditional hyperfin). After Trying Orca, I would also like to test this kind of blade in normal monofin.