Apparently hovering is physically impossible

[Javik]

I am coming more and more to the conclusion that buoyancy management for new divers like myself is being taught completely wrong, which is probably why it is so difficult for new divers to figure out.

If as a new diver you feel bad because you cannot remain perfectly still above the sea floor, don't worry about it, because it is physically impossible for any diver to do it without breath-holding. Hovering vertically motionless without moving up or down, is basically impossible without dying from it.


Examining the physics of it, hovering at a perfect height/depth is an inherently unstable condition.

Assume you have a weighted and pressurized balloon filled with air that is perfectly balanced at a given depth. (This does not describe a diver because divers must breathe and therefore constantly change their internal air volume.)

Let's move the balloon down slightly in the water. As it descends, water compresses the air, so the balloon shrinks slightly. This causes the balloon to become slightly less buoyant, so it begins to sink of its own accord. As it continues to sink, it is compressed further so its volume decreases further and it further loses buoyancy. So the result is by moving the balloon down slightly from the equilibrium point, it begins to sink and then sinks faster and faster, as its volume continues to decrease as it is compressed.

Okay, let's instead move the balloon from the equilibrium point, up slightly in the water. As it ascends, the compression decreases so the balloon expands. Its buoyancy also increases as it displaces more water, so it begins to rise on its own, and further expands, etc, until it too is rising faster and faster.

The goal of a diver is therefore achieving a balance between rising uncontrollably and sinking uncontrollably.



Perfect buoyancy balance is impossible because of the need to breathe air to survive. Even if you could get your BC's internal volume perfectly balanced, you are constantly screwing this up every time you inhale or exhale.

Therefore because perfect buoyancy equilibrium is impossible, it seems that the real goal is to try to cycle back and forth across that unstable point, to keep the forces balanced:

Assuming all else is in perfect balance and motionless:
- As you breathe in, you will begin to rise
- As you breathe out, you will begin to sink

This drifting up and down with each breath is very small, perhaps at first only a few centimeters of distance around the unstable equilibrium position at the start of each drift cycle.


Therefore:
- As you begin to rise, breathe out. As you begin to sink, breathe in. Try to detect your rising and sinking, and learn to balance your breathing so that it is in opposition to the slight rising and sinking.

- If you begin to rise too much, breathe out more to counteract. If you begin to sink too much, breathe in more to counteract. We have a fairly large lung volume available, so can still breathe in and out slightly with your lungs nearly empty or almost as full as possible, using it as an air bladder rather than your BC.

- If you rise or sink faster than you can control by managing static lung volume alone, now it is time to reach for the BC to adjust it.


Stable buoyancy position management apparently needs to be treated as a game, of constantly adjusting and balancing the breathing cycles, to match the constant unstable drifting up and down.

Can this game be taught, rather than it being left to each new diver to fumble through and figure out for themselves over the course of many dives, and who have to try to do it without an understanding of how to actively achieve it?

 

[divad]

No.

 

[RyanT]

Hovering vertically motionless without moving up or down, is basically impossible without dying from it.

??? Do you mean because you'd have to hold your breath? Not that holding your breath is a good idea, but holding your breath at a stable depth will not inure or kill you because you're not experiencing any pressure changes. Second, it doesn't have be a game or challenge. Breathing shallowly will keep you hovering. In addition, the added or reduced buoyancy that comes from lung volume changes take a few seconds and some simple breathing timing will again keep you hovering. In regards to whether this can be taught, I'll leave it to NetDoc to answer!

 

[Diver0001]

I am coming more and more to the conclusion that buoyancy management for new divers like myself is being taught completely wrong, which is probably why it is so difficult for new divers to figure out.

...snip...

Assuming all else is in perfect balance and motionless:
- As you breathe in, you will begin to rise
- As you breathe out, you will begin to sink

This drifting up and down with each breath is very small, perhaps at first only a few centimeters of distance around the unstable equilibrium position at the start of each drift cycle.


Therefore:
- As you begin to rise, breathe out. As you begin to sink, breathe in. Try to detect your rising and sinking, and learn to balance your breathing so that it is in opposition to the slight rising and sinking.

- If you begin to rise too much, breathe out more to counteract. If you begin to sink too much, breathe in more to counteract. We have a fairly large lung volume available, so can still breathe in and out slightly with your lungs nearly empty or almost as full as possible, using it as an air bladder rather than your BC.

- If you rise or sink faster than you can control by managing static lung volume alone, now it is time to reach for the BC to adjust it.

Oddly, you started out by saying that it is being taught wrong and then explained exactly how it is taught.

You are absolutely correct, of course, that breathing affects your buoyancy and therefore there is no way to remain perfectly motionless. No matter how good you are, you always have to make constant adjustments.

That said, it is possible to get so in tune to the pattern of breathing in and out in such a way that what you see a diver doing is very close to remaining perfectly motionless. The rise and fall that someone with outstanding buoyancy control can get can be limited to maybe 10cm without doing anything particularly special with breathing. The good news is that this is attainable to every diver who works on it because your brain eventually automates the skill in much the same way that you don't think about the gear shifter in your car after a while.

As far as being completely motionless, there is a difference between the perception and the reality. A diver *can* appear to be completely motionless. This is especially true if you think about just the diver's body apart from the slight rising and sinking in the water column. I personally know a number of divers whose buoyancy control is so good that when they stop moving the only way you would know that they are not made of stone is because you can see them breathing. If you asked these divers if they were truly "motionless" they would tell you that they are not. Just as a driver in a car *appears* to be driving in a straight line, the diver who *appears* to be completely motionless is making constant small adjustments. The clue is that the adjustments become smaller and smaller as you dial it in to the point that another diver might not see the adjustments at all.

Stable buoyancy position management apparently needs to be treated as a game

of constantly adjusting and balancing the breathing cycles, to match the constant unstable drifting up and down.

At first, yes. Absolutely. After a while, as I said, most people don't need to think about it anymore.

Can this game be taught, rather than it being left to each new diver to fumble through and figure out for themselves over the course of many dives, and who have to try to do it without an understanding of how to actively achieve it?

Yes. I do it routinely in the pool. There are ways to achieve this knowledge transfer in a very short time. Personally I have a specific way of going about that and in most cases it doesn't even take very long for students to dial it in to the point that they are in control. Naturally it takes experience, more experience than you get in an OW course, in order to fully automate the skill to the point that you don't need to think about it, but achieving full control over your buoyancy can be done fairly quickly.

As you noticed, of course, it's easier to learn it when someone teaches you how then to try figuring it out yourself. A good way to go about this at the point you're at right now would be to take a PPB specialty with an instructor who LIKES teaching PPB and is good at it.

R..

 

[Nirvana]

What you described is correct. However, in practice, it is not so hard as it sounds in your description. First of all, there is considerable drag from the diver, specially if he is in a horizontal trim (and thus maximizing his profile in relation to a horizontal direction of movement). Secondly, considering the mass of the diver and his equipment, both mostly made of incompressible material, the force that results from a small deviance from equilibrium is not enough to impart a significant acceleration. In addition, in all but the most shallow of depths, it is not difficult to arrest an involuntary movement caused by loss of buoyancy control even after a few seconds only by inhaling or exhaling more deeply than usual.

The result is that although there is indeed an unstable equilibrium in terms of buoyancy while diving, the actual forces that are present do not act strongly at small distances from the point of balance. Enough so that, with some practice, it is easy to stay within a few centimetres from a target depth for several minutes, while in a relaxed state.

Finally, all this is indeed taught at scuba classes.

 

[Lorenzoid]

Yes, you have stated the problem and the solution precisely and correctly, and exactly how my instructor explained it to me. If you believe "hovering" is "being taught completely wrong," perhaps it is simply your instructor who did not teach it correctly, not all instructors.

If you are asking whether a student can achieve the goal of hovering essentially motionless within minutes of being taught, I would say no. It is only possible to achieve it with practice. Assuming the instructor explained it as precisely and correctly you did, how much practice will be needed depends on the student's abilities. For me, even with an amazing instructor who explained the issues just as you did, it took me hours of practice in the pool. It's no different than learning any other skill that requires coordination between the brain and body. One can similarly explain something like how to play a musical instrument or how to turn when skiing downhill, but to achieve the goal as described by the instructor still requires practice.

 

[tbone1004]

up or down a few centimeters is hovering but it occurs so slowly you aren't going to really notice it. You're always moving, just most of the time it is too slow to be aware of it. You will get into a rhythm of breathing and set your buoyancy accordingly. I set myself so that when I take a big full breath I will slowly rise, and exhale all the way I will fall, but at a normal breath I won't sink, i.e. slightly negative. My breathing pattern is inhale to a normal breath size, hold it for a few seconds, and slowly exhale for a few seconds, then blow the rest out and repeat. I don't sit with an empty lung because I will start sinking. You're going to move roughly an inch in either direction depending on how big of a breath you took, how deep you are in the water column, and the pattern that you're breathing. The best way to see if you can actually hover is to try to hover in the shallow 3' section of a swimming pool. You are only going to have a few inches above and below you to play with and since you're about as shallow as you can possible get, you will experience an extreme change in water pressure. I.e. it is REALLY hard to hover properly in 3' of water, that's why all of our students and myself when I was a student, had to learn to hover in the shallow section before we were allowed into the diving well. It is REALLY easy to hover in 100ft of water because the pressure change between 105ft and 95ft is basically nothing so when you breathe in, you're going to move much slower in the up or down direction than you would in the shallows because your wing is not expanding or contracting nearly as quickly.

 

[kelemvor]

After some practice it becomes pretty much second nature. I'm sure some of the more experience posters in this thread don't even think much about it. I always focus on buoyancy immediately after descending so I don't contact the bottom. After that I'm pretty much to the point where I don't have to focus much on it. I spent a lot of time in the pool and on easy dives working on buoyancy though.

 

[TMHeimer]

You are correct, as pointed out. Hovering can still be done even if you have more weight than you need (see my "Lotsa Weight" thread in Basic), it just takes more lung work. You can never be perfectly neutral anyway since the air in your tank is constantly becoming less. Those aquarium divers that hover upside down impress me. You can figure out how to hover really well with experience.

 

[cool_hardware52]

Breathing (on open circuit) does impact buoyancy, but we are looking at a total system that includes the mass and resulting inertia of the diver and gear and the drag of the water on the diver and gear.

One of the "dirty little secrets" about diving doubles is the effect of the added mass has on this system.

If the diver times it correctly about the time positive buoyancy due to inhalation over comes inertia and starts to accelerate the diver up, exhaling starts the process in reverse.

Personally I can do ok, but I've dived with folks that look like they are pinned to given depth like a butterfly mounted for display.

Tobin