Maintaining depth in blue water

[The Kraken]

Find the best reference point you can. I dark, open water maintaining a precise depth can be quite problematic without some type of fixed depth reference. Often times just the small floating objects about you can be used. For the most part they are maintaining a constant depth, unless, that is, if one is diving in a down current.

 

[Diving Dubai]

On corrected weighing is sorted, holding a constant depth in mid water really isn't a problem, it just required concentration. By looking at your dive computer you can see the pattern of up and down from your breathing then it's just a case of timing it. You can start practicing gently holding onto the line or DSMB reel. You shouldn't' be holding on tightly, watch your computer and be aware of the depth changes and adjust your breathing rhythm to suit. Once you can maintain a decent depth tolerance +/- 3' then move on to adding some simple tasks. and practice some more.

If I really really concentrate, and go slow I can launch a DSMB while not deviating more than 10cm up or down (4") Generally It will be 12" though.

Being able to maintain a constant depth while concentration on something else , obviously make life easier taking pictures and for more advanced people keeping close to the optimum deco depth

 

[Storker]

By looking at your dive computer you can see the pattern of up and down from your breathing then it's just a case of timing it.

Allow me to disagree on this. The time delay in my computers' (yes, multiple; I always carry a backup) depth numbers is noticeably slower than my depth changes. I find it easier to focus on particles in the water and their movement relative to me than trying to track my depth changes with my computer(s) display. Particularly at safety stop depth, where Boyle quickly takes the wheel after just a small change in depth.

 

[Lorenzoid]

On a related note to what @Storker said about computers not sampling and displaying depth at a fast enough rate to be useful for this, I haven't used a mechanical depth gauge in years, but would one like this react fast enough to be useful as an aid to maintaining a depth? http://www.scubapro.com/en-US/USA/instruments/gauges/products/depth-gauge,-wrist-mount.aspx

If this sort of gauge is not fast enough, sensitive enough, or whatever, is there such a gauge available? Better yet, something with a button to press at one's current depth that subsequently shows on a scale that is large enough to be useful whether the diver has drifted above or below that depth. Yeah, I know: the proverbial "equipment solution to a skills problem."

 

[Diving Dubai]

Allow me to disagree on this. The time delay in my computers' (yes, multiple; I always carry a backup) depth numbers is noticeably slower than my depth changes.

We live in a free world, of course you may disagree. What ever works for you. Except.

Sure a computer (it doesn't matter how many you carry, pick just one) will react with a lag. As will you reactions. Particles etc are also unreliable. You eyes can deceive you, and you can't always guarantee particles are around (what happens on a vacation in nice clear blue water. (some also may find concentrating on particles disorientating) The only thing you can guarantee is the computer on your wrist

All that aside. You know your depth by your computer. You can sense small changes when shallow - not so much when deeper.

When following your computer, you will see how much a breath will affect your change of depth (at any given depth - more so when shallow)

You like me have a metric computer(s) it's easy to see the change of depth reading. If it's changing by multiple 0.1m at once, you're not neutral in the first place. However if you are neutral, each breath won't have a huge impact before you can arrest that impact. You breath in, see yourself moving and breath out.

With practice you can be ahead of these changes. Like today, I was hovering near the anchor line whilst student from another operator were gripped onto it. I could easily keep my SS to within 0.5m (being lazy) whilst keeping in contact with my buddy. No point using the line as a reference as there's a boat attached which is going up and down, likewise the divers on the rope.

The only reference you have is your computer. It doesn't matter it's lag or even if it's inaccurate as you computer is using it's own data. Just follow the changes in depth. Actually it's quite therapeutic and relaxing.

Non of this will work with a mechanical depth gauge.

 

[Diving Dubai]

On a related note to what @Storker
Better yet, something with a button to press at one's current depth that subsequently shows on a scale that is large enough to be useful whether the diver has drifted above or below that depth. Yeah, I know: the proverbial "equipment solution to a skills problem."

I know I can disagree with both You and Storker about not fast enough changes with a computer, Because I had to complete the BSAC buoyancy course for my Accelerated deco course.

To ensure the student maintains the buoyancy within the limits, the task is completed next to a line marked with graduations from which the instructor judges your buoyancy control and within what tolerance. Hence in Blue water (not a pool) I achieved Black qualification (+/- 0.1m or +/-4") using my computer and being attuned to the changes and impacts of my breathing.

To answer you question A decent tech computer will soon let you know if you know if you fall outside the window on a deco stop - specifically if you bust the deco ceiling other than that, trust your computer as your other senses can deceive you

 

[Storker]

A decent tech computer will soon let you know if you know if you fall outside the window on a deco stop - specifically if you bust the deco ceiling other than that, trust your computer as your other senses can deceive you

The depth reading isn't the problem. The response rate is. Apparently, far from all dive computers prove a fast enough response rate to be useful for monitoring depth changes in real time.

This is a general control problem; if your sensor readout is too slow, the system will become unstable. Read up on process control, and you'll see that it's a fundamental problem for any feedback loop, and it generally leads to increasing oscillations. In my case, my computer doesn't respond quickly enough, so by the time it shows that I''m above or below my set depth, Boyle has taken the wheel and I'm yoyo-ing like crazy.

 

[Diving Dubai]

@Storker

Yes, I understand what you are trying to say. The fact remains, the BSAC have a Buoyancy masterclass course, where the student is examined by carrying out a task alongside a reference shot line. The student is graded in accordance with the amount of +/- deviation from a fixed point they attain. In my case (after a lot of practice) I achieved the Black status which is +/- 0.1m while sending up a DSMB. Obviously I' m not the only person who holds a Black status.

The only instrument we have to guide us is a dive computer.

If your yoyo-ing, then I suggest you're not actually neutral or not as neutral as you think you are (the blog post I copied earlier in this thread might help).

I'm not saying it's easy, but anyone with experience should be able to stay within a +/-1.0m window, better a +/- 0.5. It's a skill to be learned, and frankly should be mandatory for Deco diving

 

[Patoux01]

Allow me to disagree on this. The time delay in my computers' (yes, multiple; I always carry a backup) depth numbers is noticeably slower than my depth changes. I find it easier to focus on particles in the water and their movement relative to me than trying to track my depth changes with my computer(s) display. Particularly at safety stop depth, where Boyle quickly takes the wheel after just a small change in depth.

Are you reading the depth or the speed display? It is routinely recommended to only read the depth changes.

(Not gonna explain the whole theory about low pass filters causing lag, right? )

IIRC, most computers have a refresh rate of about 1 Hz.

 

[Basking Ridge Diver]

The fact remains, the BSAC have a Buoyancy masterclass course, where the student is examined by carrying out a task alongside a reference shot line. The student is graded in accordance with the amount of +/- deviation from a fixed point they attain. In my case (after a lot of practice) I achieved the Black status which is +/- 0.1m while sending up a DSMB.

At what depth was this done? Thanks.