Diving Performance - Beyond Drag (article Series And Discussion)

[John C. Ratliff]

Reku,

Yes, YMMV (your milage may vary), and "to each their own..."

One of the first things during the Vietnam War that an F-4 would do when either engaging MIGs or being jumped by MIGs was to drop its external fuel tanks, known affectionately as "drop tanks." Why? Because the increased drag of those tanks could prove fatal in a dog fight.

The same holds true with diving (about drag, not dropping tanks), except that we are operating in a much denser environment. Scuba tanks are not streamlined like drop tanks on a jet fighter. Side-mounted scuba tanks also do not present themselves in the water like a drop tank, which only presents it's streamlined diameter to the air.

Today, I was in the pool with a single 72 tank on my back, a Scubapro Mk VII/A.I.R. I regulator without anything else on it, my mask, fins and a BC (my design Para-Sea). It is actually very streamlined, and when I stopped after a stroke, I glided about 15 feet before stopping, using the dolphin kick and my Hammerhead unit for stroking. I'll get into specifics later this week on the theory of this type of swimming, but I mention it because there is a lot to be said concerning streamlining the diver.

If you could, would you post a photo of your kit with all attachments? It would be interesting when comparing our newer concepts with this kit you described above.

SeaRat

 

[Reku]

To be clear, the comment was that the gear that has the tech look can allow someone to attach a lot of equipment to become a "Christmas tree Diver", by virtue of having a lot of D-rings. Not that a Tech diver is a "Christmas tree Diver".

In my view, tech diving involves great thought toward assembling equipment appropriate to doing the dive that is being attempted and training to be able to efficiently use that equipment under the conditions of the dive to mitigate risk to acceptable levels. There is nothing haphazard about it.

However, even without going the "Christmas Tree" rout, Tech has become something of a fashion. There are some divers that are drawn to the cool looking equipment without addressing the issue of using "the right tool for the job". Evidence can be found here on SB with posts like this: Treat every dive like a tech dive

Just because the mountain climbers that go to the top of Everest look cool in their gear, that's no reason to dress like them with crimps, packs, O2, etc... when going for a walk around central park. That's reductio ad absurdum, but I think it helps drive my point that recreational divers would be better served with gear that looks more like my setup than a kit designed for diving the Andrea Doria.

Oh for sure. I see people going into dives way over geared - I assume they are just practicing skills however. Besides caves - the other reason I use SM is because I can't deal with the weight of doubles - and even the rec dives I do require doubles ( one LONG shallow dive as opposed to 2-3 separate dives), so I am using the right tool for me.

 

[Reku]

Reku,

Yes, YMMV (your milage may vary), and "to each their own..."

One of the first things during the Vietnam War that an F-4 would do when either engaging MIGs or being jumped by MIGs was to drop its external fuel tanks, known affectionately as "drop tanks." Why? Because the increased drag of those tanks could prove fatal in a dog fight.

The same holds true with diving (about drag, not dropping tanks), except that we are operating in a much denser environment. Scuba tanks are not streamlined like drop tanks on a jet fighter. Side-mounted scuba tanks also do not present themselves in the water like a drop tank, which only presents it's streamlined diameter to the air.

Today, I was in the pool with a single 72 tank on my back, a Scubapro Mk VII/A.I.R. I regulator without anything else on it, my mask, fins and a BC (my design Para-Sea). It is actually very streamlined, and when I stopped after a stroke, I glided about 15 feet before stopping, using the dolphin kick and my Hammerhead unit for stroking. I'll get into specifics later this week on the theory of this type of swimming, but I mention it because there is a lot to be said concerning streamlining the diver.

If you could, would you post a photo of your kit with all attachments? It would be interesting when comparing our newer concepts with this kit you described above.

SeaRat

Unfortunately my solo tag isn't just for show - I don't have any pictures of me kitted up because I generally don't dive with other people. I'll figure out some way to show you what I am talking about though.

Essentially what I described is the standard way to mount tanks on sidemount when you have stages + deco gas. First you have the sidemounted backgas then you have the deco gas staged under the backgas and finally the stage gas on top of the sidemounted backgas tanks.

IF you have everything the correct lengths and such - your tanks will pull into your sides and assuming you are in correct trim your tanks will be behind your upper arms - there by not effecting drag at all because even if you only had 2 tanks sidemounted your arms would still be in the same position - there isn't that much of a different in drag between 2 tanks - 4 tanks or 4 tanks + 2x AL40.

This is because your tanks are pulled into your body and your arms are basically blocking that part of you. It's like those curved tops on the semi trucks that divert the air over the trailer - same thing - your arms divert the flow around the tanks that are behind them.

That said - I may have lower drag then double BM. but I do have weight from all the tanks - that in itself slows me down quite a bit. I'm not sure I could coast for 15 feet on 1 kick fully kitted out, that's impressive.

crude ascii drawing to try and make sense of this:

This is looking straight at a sidemount diver who is horizontal and in trim.

8O8
.oo

the 8's are the backgas and the stages stacked behind my arms.
the o's are the AL40's - just image they are pushed up under in between the O (my body) and the 8 on each side.


This is a top view from above looking down a horizontal sidemount diver who is in trim.

Line 1: arms and head
Line 2: shoulders
Line 3: top half of tank
Line 4: bottom half of tank
Line 5: legs

..... | O |
..... --| |--
... |--| |--|
... |--| |--|
...... || ||

As you can see from this horrible depiction - the tanks are behind my shoulders reducing the drag.

so like yea less drag!

way too much time on my hands

 

[REVAN]

Revan, your assumption that speed is good is wrong. All wrong.

I'll counterpoint that statement with the overwhelming evidence that nature disagrees with you, not me.

Regarding my proposed 3 knot cruise requirement, this is an important paragraph in my paper that is worth reflecting upon, but I think the point may be easily overlooked.

The entire scuba industry has basically evolved to accommodate this large deviance from these basic system requirements. Personally, I feel that this is one of the reasons that the scuba industry is languishing economically while the sport of freediving is growing rapidly. A freediver in streamlined form with a monofin can cruise at 3 knots and sprint at 5 knots. Freediving technology does a much better job of meeting the speed requirements imposed by the ocean environment. Therefore, it is a more appropriate technology to use in the ocean than is the 70’s era scuba equipment. Can the technology of scuba catch up?​

Evidence that it may be more than just the fishes that live in the ocean who recognize how important the ability to achieve a certain level of speed and efficiency are for operating in the ocean, but humans are more frequently making the choice that mobility is even more important than is having the ability to breath underwater. I think this is a profound revelation buried in the statistics of the diving industry.

As I see it, those who think that hydrodynamics, mobility and speed are unimportant, are members of a contracting group that will ultimately be replaced by a more capable diver that, in one form or another, will better reflect the requirements I have documented here in "Diving Performance - Beyond Drag".

 

[John C. Ratliff]

I put together a presentation for the Northwest Section of the Historical Diving Society, and in it I used this example from the book, The Ocean World of Jacques Cousteau, The Art of Motion, page 21. He was looking at how fish move, and I use it to demonstrate the problems of shape for motion in water. Most divers assume the "C" shape, which is one of the most inefficient forms in the water. What does this mean? Well, it means that there is a lot of turbulent flow around a diver. The simple act of putting your arms out in front of you gives a much more streamlineg effect, and places the diver in the "E" form. Note the lessening of the turbulent flow. My, and Revan's, work is to get a diver to the "D" form, where the diver actually flows pretty easily through the water. That's why I could coast for 15 feet yesterday in the pool.

Concerning the shapes above, by Reku, they are not really too streamlined. They are a compromise to get enough gas to do the types of tech diving that he does. Each tank will have its own effect on the diver's streamlining, taking it down a notch. On top of that, these tanks twist and turn in the water, presenting more of themselves to the water than their cross-sectional area. This provides further turbulence. I'll see whether I can draw what I'm seeing a bit later.

SeaRat

 

[Reku]

I put together a presentation for the Northwest Section of the Historical Diving Society, and in it I used this example from the book, The Ocean World of Jacques Cousteau, The Art of Motion, page 21. He was looking at how fish move, and I use it to demonstrate the problems of shape for motion in water. Most divers assume the "C" shape, which is one of the most inefficient forms in the water. What does this mean? Well, it means that there is a lot of turbulent flow around a diver. The simple act of putting your arms out in front of you gives a much more streamlineg effect, and places the diver in the "E" form. Note the lessening of the turbulent flow. My, and Revan's, work is to get a diver to the "D" form, where the diver actually flows pretty easily through the water. That's why I could coast for 15 feet yesterday in the pool.

Concerning the shapes above, by Reku, they are not really too streamlined. They are a compromise to get enough gas to do the types of tech diving that he does. Each tank will have its own effect on the diver's streamlining, taking it down a notch. On top of that, these tanks twist and turn in the water, presenting more of themselves to the water than their cross-sectional area. This provides further turbulence. I'll see whether I can draw what I'm seeing a bit later.

SeaRat

I don't know if this is any help but - with my body type (slimmer then average) the only tanks I can get to trim out correctly are LP85's (AL80's are just barely out of trim because they float.) - nothing else really trims for me, I've tried everything from LP72's all the way to 130's and quite a few HP tanks. All sorts of brands. Drag and streamlining is really a personal thing. I don't think one answer will work for everyone , but I do think one answer can work for most.

 

[fjpatrum]

We get back to your requirements, @REVAN, that simply don't match what most people do while diving. They're great requirements for you, but they have no bearing on my diving or most people I have dived with so far. Or most people I've talked to about diving. There's a reason people say "slow down" to all of us newbies.

 

[REVAN]

We get back to your requirements, @REVAN, that simply don't match what most people do while diving. They're great requirements for you, but they have no bearing on my diving or most people I have dived with so far. Or most people I've talked to about diving. There's a reason people say "slow down" to all of us newbies.

"most people"? When it comes to scuba diving, the requirements don't match what anybody does! That's because nobody can do it. Nobody has bothered to make it possible. No one has bothered to engineer systems that can do what the environment requires of an independently operating ocean system; to do what even the slowest nektons in the ocean can do. How sad is it to not even be able to keep up with a turtle?

I think you may be having trouble wrapping your head around the concept that a diver who is even remotely close to being efficient in the water would not require large energy expenditures to swim at the modest speeds of a turtle. If you get much slower than a turtle, you are no longer a nekton. You become planktonic, like a jellyfish, and are at the mercy of the ocean rather than your own intentions.

 

[undrwater]

I get the point. Most of my diving activity will be almost motionless....because that's what I like about diving...being planktonic. However, if needed or desired, I'd like to be able to get "over there" quickly if it required little energy. I've been following this thread with interest, and I'm beginning to see a light.

 

[REVAN]

I get the point. Most of my diving activity will be almost motionless....because that's what I like about diving...being planktonic. However, if needed or desired, I'd like to be able to get "over there" quickly if it required little energy. I've been following this thread with interest, and I'm beginning to see a light.

Yea!

Barracuda spend most of their time hovering over the reef not moving much. But they can be fast in an instant when they decide that's what they want. We don't need to be as fast as baracuda to move through the ocean with intent. Cudas are extra fast because it's how they get their food, not because of ocean conditions. But, this shows that you don't spend all of you time moving at you max speed. Go as slow as you want when there's no reason to be fast. Hydrodynamics and swimming performance is about moving with intent and having options instead of leaving it to chance. I totally understand if the "intent" is to just hang motionless most of the time, especially when conditions are nice.