Diving Performance - Beyond Drag (article Series And Discussion)

[ronscuba]

I agree, that is why I made the system shown in Part 3. This is the baby step. Keep everything basically the same, but make it more efficient. Tackling the larger problem of 3 knot cruise is going to require architectural changes to the equipment configurations and will be too large a step for most people to comprehend.

That is one of the benefits of getting the mobility high enough. It can potentially save you a lot of money by eliminating one of the most expensive pieces of diving gear that divers tend to not properly account for, the boat. For those that operate on the cheap and dive from a kayak, or similar, a 3 to 5 knot system could replace it with a far more convenient operating process. Not all, but many dive sites that are presently only accessible with a $100+ boat ride could be reached just by swimming to it.

Yes. I really don't like using BCs. When I do use a BC, I use my DiveRite TransPack, but I tie the edges of the wing to the sides of my harness with bungee cord to keep it from floating free. It makes it like a hybrid BC halfway between a wing and a jacket style setup. It helps.

Eliminating the boat ? That is definitely not a baby step. More like a Godzilla step.

How do you secure the edges of the wing to the harness ? I used to have a Transpac. The softplate had rings on the perimeter, but I don't remember anything on the perimeter of the travel wing ?

 

[REVAN]

@REVAN, ...What is the theoretical improvement of just drag due to the tank using the cone?

The normal front end of a scuba tank would not be bad, except that it has the regulator and hoses clustered in front of it stirring everything up. My setup hides that potential mess from the flow providing a clean transition from the diver's head to the tank. Once that flow is cleaned up and there is high energy flow along the sides of the tank instead of a thick wake, that energy can be recovered with a properly designed tailcone.

This is one of the charts I used in my design process to determine the geometry of the tail cone. This shows incremental drag as a function of aft body contraction ratio. I settled on a contraction ratio of 1.5, and as you can see here, this supports why the tank seems to add little drag contribution to the basic diver.

 

[REVAN]

Eliminating the boat ? That is definitely not a baby step. More like a Godzilla step.

How do you secure the edges of the wing to the harness ? I used to have a Transpac. The softplate had rings on the perimeter, but I don't remember anything on the perimeter of the travel wing ?

I'm not sure how much they have changed over the years. Mine is from 1996. The wing already had a bungee cord laced around the underside of the wing. I used that same cord and laced it through the side D rings on the sides harness to hold it down. It's been so long since I've used the BC, I'm having trouble remembering the details. I don't recall, but I'm thinking I was also using some of the small D rings alongside the tank to help hold it in nice and tight as well. I still use the harness, but I think it's been 10 years since I've actually used the BC.

Yes, eliminating the boat would be huge, not a baby step. The rig in part 3 is not up to that task. It would take something different.

 

[dumpsterDiver]

I always thought a big benefit would be 10,000 psi tanks that were shaped like a turtle shell. Running the hoses a little cleaner would help some I suppose. Another really useful advancement would be much smaller and more powerful scooters and of course electrically heated suits that would not rely upon compressible foam and thus reduce the amount of air in the BC.

Remember the triple 30 tanks that US divers put in a plastic fairing, about 30 years ago? Wish I didn't sell mine now.

 

[fjpatrum]

@REVAN Watching your test videos in part 3 I have some questions.

First, did you do any "baseline speed tests" with the scuba gear and no fairing? A baseline test of freediving versus scuba with the fairing doesn't make much sense if you're trying to convince people you're making a big improvement over existing scuba configurations. It also smacks of the disingenuousness I spoke of before. You're not comparing apples to apples and most people see through those kinds of arguments relatively quickly.

Second, how long is this thing and how tall are you? Being "tail heavy" is just a matter of iteration until you get the right buoyancy balance but you can't just expect a 1.6 meter tall woman (5' 4") to be able to accommodate an extra 10 or 12 inches on tank length.

Third, for those that believe you need to be able to reach your tank valves, what is your solution?

Fourth, how do I (or my buddy) turn off my air if I have a freeflow? Where does the air go? I assume this system isn't sealed but if I have a first stage freeflow/leak inside of it, it's still going to trap air and cause me to have a hell of a time dealing with an ever-growing bubble trying to send me to the surface.

Fifth, what is your expected material? Fiberglass, aluminum, carbonfiber, stainless steel? Marketing it as added ballast to reduce extra weight may be something to consider but you're absolutely going to have to address the durability issue. Any dents or cracks from being manhandled on a boat are going to disrupt your efficiency gains to the point they may be worse than not having it. Can you make it durable enough to prevent real deformation but light enough to be practical?

Sixth, back to the size of it, how do you "conform to the diver's head" in a mass market design. Are you saying there's just a pocket that allows you to "look up" and your head backs up against the fairing? How do you accommodate different headgear? How comfortable is it to turn your head and look at things and how much impact does it have when you "break" the connection between the fairing and the diver's head? How much does it impact looking up (while horizontal) to see the surface at a safety stop?

Finally, you talk about making improvements that will enable a diver to deal with currents. This is, admittedly, stretching the argument a bit but what happens if you get a cross current? This will add to your surface area (and thus drag) in a cross-current. How much extra area does it add and have you considered it? Is there a way to minimize this impact and still get the gains you're trying to achieve?

These are all issues you're going to have to address long before this thing ever gets adopted on any significant scale.

To be honest, I'd try one out for fun but I'd likely never include it as a part of my regular kit. It's hard enough getting diving gear on small planes without adding this much extra bulk. If every dive op had their tanks outfitted, maybe, but otherwise it's all niche. Perhaps for the record chasers but I don't see it going mainstream.

 

[CuzzA]

In my non scientific experience I have found my head to be the most significant source of drag for any type of diving. Move your arms and hands to a point in front of your head and you cut through the water much more efficient. We see it in competitive swimming/diving because it works. You can physically notice the increase in speed. So rather than focus on the challenges of a tank cone, simply adjust your arms and you'll see the same benefits.

As far as the monofin, I see some practical uses for somone who wants to do a far swim from where the entrance point is or wants to cover a lot of ground, but I don't see the practicality in using this for photography or spearfishing. It appears you need forward movement to make any sort of turn. This seems it would be very challenging if you were fighting off sharks while spearfishing. I could see the shark easily getting the upper hand as they try to get behind you. Same goes for photography. I want the ability to hover in place and be able to turn 360 degrees. It doesn't appear you have any ability to make finite adjustments to control your position.

You made the comparison to mammals and fish. The monofin and dolphin kick definitely achieves the forward propulsion, but we still lack pectoral fins to give us the ability to have any sort of agility. That is where the benefit of two traditional fins comes in as I believe they serve as both propulsion and direction, with a trade off of less efficiency.

 

[REVAN]

Part 4 has been published. Unfortunately it's messed up (missing pictures and videos, duplicate videos). I'll have to see if I can get them to make some corrections.

This is the link: Diving Performance, Beyond Drag - Part 4 – DeeperBlue.com

Since that has some problems, I figured I should just put up the original document here and people can have a copy for their own records. The attached pdf contains all four parts.

 

[fjpatrum]

Thanks for sharing the whole thing @REVAN. Interesting white paper.

 

[REVAN]

First, did you do any "baseline speed tests" with the scuba gear and no fairing? A baseline test of freediving versus scuba with the fairing doesn't make much sense if you're trying to convince people you're making a big improvement over existing scuba configurations. It also smacks of the disingenuousness I spoke of before. You're not comparing apples to apples and most people see through those kinds of arguments relatively quickly.

I did, but it was a while ago, back before I started designing Revision 1. Seeing as how my goal was to attempt to make the scuba kit a hydrodynamic ghost (i.e. - get as close to the drag of a freediver as possible), I don't see how comparing against the freediver baseline is being disingenuous.

This is not a marketing video. This video is a record of my testing, and just the very first in-water test at that. I had not worked out any bugs at that point. Not that it was totally bad, but I did need to make modifications to the harness design to get the tank to sit in the proper position on my back. No doubt, the misalignment had a small impact, but probably not anything significant or that is likely to show a difference in kick counts. If you want to know how much drag a scuba kit has, why take my word for it? Strap on your kit and count kicks over a set distance. Then do the same without, and see for yourself. I get the feeling you don't really trust me anyway.


Please, keep in mind this is not a product. I'm not trying to sell you anything here except information and ideas, and the only thing I am charging you is a little of your time to try to get the point across. If a lot of people get really excited about this project, I can come back to it and not leave everyone just hanging. However, now that the article has been published, I'm expecting to be done with this project. I have already moved on to my next project. The article is the terminus (except that I will personally continue to use my new experimental kit when I scuba dive).

I built all of this prototype equipment using moldless construction techniques. I have no production capability unless I go back to the beginning and build molds for production.

 

[REVAN]

Second, how long is this thing and how tall are you? Being "tail heavy" is just a matter of iteration until you get the right buoyancy balance but you can't just expect a 1.6 meter tall woman (5' 4") to be able to accommodate an extra 10 or 12 inches on tank length.

It is 32.5 inches from the base of the tailcone to the back of the head. If I remember correct, this is about 4 inches longer than the tank and valve without the streamlining. So, it is a little longer, but not as bad as you are thinking. Also, the head interface here is designed to rest comfortable against the head. A normal tank setup is going to need an extra inch or two of clearance because the regulator hurts when it hits the back of your head. All things considered, there is not much difference in length.

I stand at 5' 11.5".

Third, for those that believe you need to be able to reach your tank valves, what is your solution?

Fourth, how do I (or my buddy) turn off my air if I have a freeflow? Where does the air go? I assume this system isn't sealed but if I have a first stage freeflow/leak inside of it, it's still going to trap air and cause me to have a hell of a time dealing with an ever-growing bubble trying to send me to the surface.

For production, it would either need an access panel, or extend the valve out through the side of the fairing. The fairing cannot not fill with air and drag you to the surface if that is your concern. A malfunctioning BC can do that, but a malfunction with this cannot.