Dol-fin customization

[cdavis]

As Laminar pointed out in his x20 review, the Dol-fin is very susceptible to customization for the specific uses of a given diver. Below is my attempt. What about yours? What other ideas are out there? Let us know.

I usually dive with no wetsuit on my legs, maybe no wetsuit at all. I found the Dol-fin x18 to be oustanding in many ways, but the thing was tail heavy in those conditions. Sit still and your legs sink fast, dive straight down and the fin wants to fall faster than you do unless you keep stroking. Drifting was difficult because as soon as speed dropped, the tail sank. I could not get Ron's negative drift to work. I tried a neck weight and that helped, a lot, but did not solve all the problems.

Solution, add some flotation. A simple idea, but exactly how? After much thought, I made up a batch of pour foam, 4 lb density, shaped it into something approaching streamlined, attached it to the bottom of the shoes and covered the foam with an epoxy/glass cloth layer for chafe protection. This took more than a few tries to get it close to right. Pics below. The fin is now almost exactly neutral in fresh water. I regard this as a first attempt, any suggestions for improvement would be appreciated.

Performance: Works great. No drag that I can feel, although there probably is some. I can dive straight down now, float flat on the surface with almost no effort, surface swimming doesn't seem to be affected (one of my worries) and negative drifting is incredible!!! This is the most fun thing so far. This is a technique that I use a good bit with bifins. You get below the level of neutral buoyancy, flatten out and use your negative buoyancy to "fly" forward. The amount of forward progress with the Dol-fin for a given drop is far far more than bifins, really noticeable. I'm pretty sure that speed for a given slope is higher. That's hard to measure, but feels like it.

Today was the first time I had it in deep water, down to 90 ft. Careful inspection of the foam blocks showed no sign of compression damage, so the makers of the foam were telling the truth. According to them, it should be good to around 40 meters.

Over all, very pleased. Now, how do I make it better? suggestions?

Connor

 

[Mukiker]

Hi Connor,

interesting fin tunning!

Regarding surface swimming, you say it doesn't feel the change affects it. I am thinking if this change isn't actually useful for surface swimming. A better flotating fin may help one get to surface to take a breath.

Does it work this way?

Thanks.

 

[laminar]

Very cool! :martial

Are the foam blocks removable or permanent?

 

[cdavis]

Foam is removeable. There is a bolt through the frame and front of the foam and a screw through the bottom of the heel of the shoes. It took a while and a bunch of tries to find something that was strong enough to not come apart. Lots of force on the foam as the fin is stroked.

The amount of floatation is so small that it has minimal effect on how easy it is to surface, although making the fin exactly neutral leads to the need to add a pound or two in weight.

Laminar, have you done anything to yours?

Connor

 

[baiyoke]

Very nice work Cdavis...

 

[REVAN]

I've been very slow with regard to implementing flotation options.

I was going to focus on the Orca first, thinking it would be more easy to make since the float will be hidden and does not need to look nice. So far, I have not gotten a float made that I am happy with. The float in the Orca I took to the World Championships compressed during depth diving. By the time we got to the dynamic event, I found my fin did not quite float any more. So, I'm still looking for the right material to use.

My long-range plan for the X-20 is of similar concept to what CDavis has done here. But, if I am going to sell something to go with the fin, I'll need to find a way to make it look nice as well as adding buoyancy. So there will be the added issue of cosmetics that I've been ignoring with the Orca's float.

Ron

 

[cdavis]

Are you insinuating that my creation isn't pretty???? Hmm. . . . maybe you're on to something.

FYI, US Composites sells 2 part urethane pour foam up to 16 lb density, hard as stone, would mould perfect. 8 lb density is more like soft wood and has a compressive strength that should go to approx 160 m. The 8 lb stuff would probably need to be covered with an epoxy/cloth layer for abrasion resistance.

Connor

 

[REVAN]

Cdavis: You have inspired me to work through Christmas and build a prototype of the idea that has been sitting in my mind for the past 3 months. When the float I had in my WC Orca squeezed (a 3 pound/cubic foot foam). I started to think about using wood instead of foam. The heavier foams are very expensive whereas wood is both economical and environmentally friendly. Also it does not matter how it looks in the Orca because it is hidden under the fairing. Using wood has been my plan, but I had not built it yet as I have been busy with other business matters.

I then started to think about making something similar for the X-20. As I said earlier, the float in the X-20 will not be hidden, so how it looks will matter. The prototype shown here will functionally work. The question is how will customers like it as a product? Please let me know your thoughts on this design and if you like the idea of using a natural material like wood better than using synthetic materials like foam and fiberglass.

Prototype Flotation for X-20 | Facebook

 

[cdavis]

Yep, looks a lot better than mine. I don't think anybody will object to the cosmetics of how yours looks. Nice job!

Wood seems fine, as long as the wood used is strong enough. The thing to watch out for is how much abuse the float will take. It gets beat up much more than I expected. I'm beginning to think that even a fairly thick epoxy/glass layer in mine isn't enough for the trailing edge. Will the wood stand up to the punishment?? How is the float attached to the fin? needs to be strong as heck.

Streamlining: On the trailing edge, near the blade, the floats are asymetrical, a lot. Does this introduce any drag issues? the leading edge (under the shoes)is fairly blunt. Same question. I initially faired the floats to a sharp point on the leading edge, Bad idea, it got beat to pieces quickly. Getting beat up, the floats seem to settle in to a particular angle under the shoes. Yours looks pretty close to that angle.

I'd suggest using the fin with the float a bunch, in and out of the pool. You will probably discover stuff you didn't expect.

Your floatation is slightly more than mine. It will probably be better for it. Have you tried it to see if that has any effect on performance?

Connor

 

[cdavis]

One other point, the wood looks like it is much larger than my foam. Any effect on performance?

 

[REVAN]

One other point, the wood looks like it is much larger than my foam. Any effect on performance?

I'll need to get back with test results for the real answer, but I don't expect any adverse performance resulting from the floats. I expect they will draft within the wake created by the shoes and be like a ghost with respect to drag.

Also, this design is very preliminary and I have not chosen a method for attaching the floats at this time. So far, I have done a buoyancy test to see that the floats are sized correctly to float the fin. Structural fastening of the floats to the exo-skeletal frame and swim testing will have to wait until next year as I have a lot of business to take care of before the end of the year. I did this on my Christmas day off, but for the rest of the year it is back to other business presently at hand.

 

[mek]

The flotation looks part of the x20 and not an afterthought.....so it looks good as an upgrade option you mentioned on facebook......I hope you will have it out for retail mid 2013...

 

[REVAN]

Today, I did a swim trial of the buoyant X-20 monofin that I posted pictures of above. The float system did not interfere with the swimming qualities of the fin as far as I could tell, and it felt very good. I'm almost inclined to think it swam a little better with the floats installed than without, but it is probably just that I have not been in the water since November. I need to do more testing, but for divers who want a fin that is buoyant, it looks like this will be a good solution.

The floats install with 4 screws, so it is easy to switch the X-20 configuration to get the buoyancy characteristics desired for "this dive". So far, I do not see any show stoppers that would derail this from becoming an option for the X-20, but there is still a lot of work to do. When this option does become available, it could be added to existing X-20 already deployed.

 

[cdavis]

Back to the drawing board. Its amazing how many trys can take to get something right. I had noticed that the fin seemed to have a little less floatation, did not look diverent, but still. . .

Today, I pulled the floats off my fin, intending to do some modifications and found them heavier than they should have been. Cut into the foam and it's wet clear through on one float and partially on the other. So much for closed cell foam.

Looks like some wood floats are in my future.

Ron, will the x20 floats fit mine? What kind of wood did you use?

 

[REVAN]

Ron, will the x20 floats fit mine? What kind of wood did you use?

It would probably need some modification to fit your fin. Yours has a different shaped cross brace that the float would need to work around and the struts are 2 cm shorter than on the X-20.

If you are going to make your own floats, use a soft wood as a hard wood will not add the buoyancy you'll need. I cut my prototypes from a pine 4x4 beam from the lumber yard. You'll need access to a band saw. Good luck!

 

[Kars]

Ok Ron, some considerations for you float design:

1) Wear and tear, think pool training, standing, pushing off walls etc.
2) The wood needs to be dried and well seal coated, or it will absorb water, changing it's properties and rot.
3) Heavy floats add more mass. With every move a diver needs to move that mass around, which cost more energy. Sprinting goes better with lighter fins.
4) the gap between the float and the heal is a place where seaweeds will get stuck, or sand and stones may get in when on a beach.


Otherwise a very good idea to make the fin buoyancy adjustable, it will be better for people with 'heavy legs', fit more dive styles and fit the different disciplines better.
It will also prevent people from loosing their precious to the depths of the ocean.

I hope this is helpful.

Happy new year!

Kars

 

[REVAN]

2) The wood needs to be dried and well seal coated, or it will absorb water, changing it's properties and rot.

Thanks for the feedback Kars. I appreciate it.

My impression is that even if the protective coating is worn off to expose the wood underneath, it is not going to be in the water all the time. So if it absorbs water, it won't be much, and then it will dry out between dives. I figure boats have been built successfully from wood for thousands of years and last for many decades. If this lasts for even just one decade, it will be considered indestructible by monofin standards. Also, floats can be replaced like everything else on this fin if they do wear out.

In general, wood is a pretty amazing building material. I looked hard to find a synthetic material that could do the job and kept finding no viable solution. Wood is one of the few materials that has the right properties of toughness, strength, buoyancy, cost and repair-ability.

 

[baiyoke]

Revan, the space between the shoes (and the floats) do you think it's important to keep it open performancewise (for DYN fx)?

 

[REVAN]

Revan, the space between the shoes (and the floats) do you think it's important to keep it open performance-wise (for DYN fx)?

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.

 

[cdavis]

Sealing the wood grain will be necessary for diving deeper than pool work. On the sections of the wood where the surface is parallel to the grain, should be no problem. However, where the wood is cut across the grain, it exposes old channels(tubes) that were originally used to transport food and water. In the center of a log most of these channels will be sealed, but that is heavy wood. The lighter stuff will be porous. Under pressure, water will be injected into the grain too deep to dry out easily. Should be simple and easy to seal with some thinned epoxy. Might need to be reapplied with heavy wear.