Maintaining depth in blue water

[Lorenzoid]

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

Implied, but just want to confirm: The sole source of feedback to you that allowed you to hold a stop within +/-.1m was the computer's display? I mean, you might have used your eyes and ears as other "instruments" to watch particulate in the water and feel pressure changes. Just want to make sure I understand.

I have a Shearwater Petrel, and I suspect it samples depth at a rate of something like once per second. By the time the display shows I am one foot (yeah, Imperial units--feet--are shown to zero decimal places) beyond my target depth, my depth may already be accelerating closer to two feet.

 

[drmwc]

If it's anywhere near the end if the dive, I tend to blob up and use the reel as a visual reference.

 

[Neilwood]

Implied, but just want to confirm: The sole source of feedback to you that allowed you to hold a stop within +/-.1m was the computer's display? I mean, you might have used your eyes and ears as other "instruments" to watch particulate in the water and feel pressure changes. Just want to make sure I understand.

I have a Shearwater Petrel, and I suspect it samples depth at a rate of something like once per second. By the time the display shows I am one foot (yeah, Imperial units--feet--are shown to zero decimal places) beyond my target depth, my depth may already be accelerating closer to two feet.

Not what was stated - the line used would provide feedback as well.

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

 

[Lorenzoid]

Not what was stated - the line used would provide feedback as well.

Yes, IF the student is allowed to watch the line that the instructor is watching--and that isn't clear from what you quoted. IF the student watches the line, then that seems inconsistent with the implication of the statement: "The only instrument we have to guide us is a dive computer." I would think that watching a line would almost obviate the need to watch the computer.

I don't think anyone doubts that having a line as a visual reference helps greatly. But the original question was how to do it without one--perhaps with just a computer and one's eyes and ears. I'm not just making the point to be a pedantic jerk here--I, too, want to master this skill. I have been working on it for years, and while I have improved, I am not yet near the accuracy I would like to reach. I THINK the answer is simply yet more practice. But I am reading all comments here with interest.

 

[charlier]

This is a wonderful and super interesting thread. From my personal experience, keeping still in open water without using fins was challenging. I think that superior trim and a very relaxed breathing style are two critical parts. Quietly reacting to currents and internal waves takes experience. Other than teaming up with better divers, my inspiration comes from watching fish - really. Similarly, on many dives, I would just stop (really stop) and try to stay at the same depth. In time, its worth trying to keep trim at the same depth with a near empty cylinder (say 30 bar) at say 3 or even 2 m. Any thoughts or comments.

 

[KevinNM]

I have a Shearwater Petrel, and I suspect it samples depth at a rate of something like once per second. By the time the display shows I am one foot (yeah, Imperial units--feet--are shown to zero decimal places) beyond my target depth, my depth may already be accelerating closer to two feet.

That's my experience with my perdix. The lag is a bit annoying, makes it hard to hold a 3 ft window when you are off by two feet at that start. So I switched it back to metric. I'll also try to anticipate it better.

 

[KevinNM]

I don't think anyone doubts that having a line as a visual reference helps greatly. But the original question was how to do it without one--perhaps with just a computer and one's eyes and ears. I'm not just making the point to be a pedantic jerk here--I, too, want to master this skill. I have been working on it for years, and while I have improved, I am not yet near the accuracy I would like to reach. I THINK the answer is simply yet more practice. But I am reading all comments here with interest.

There is a dive off of Kona, where you are tethered to a weighted line dropped from the boat in 10,000 feet of water at night, it's pitch black other then your lights. You are looking out into the water for all the crazy stuff that comes up the surface of the open ocean at night. It makes buoyancy control kind of challenging. The DM who was in the water with us, who had done this trip a few hundred times, said that eventually you learn how to do it by your ears.

 

[NAM001]

As far as sample rate of the shearwater's . I don't have mine handy but, is there not a sample rate you can enter into your computer. like 1 second or 10 second rate. Something said the battery life was dependent on sample rate. Of course whether that rate at some point is not reflected on the display I don't know. Either way the computer can only store a limited amount of data x amount of samples and as such perhaps what I read was will store up to say 56 hours of dive info, which would be sample rate driven. AS such at high sample rate it may only hold say 10 hours of dive data samples. Then again I may be thinking about battery life.

 

[Patoux01]

What you mention is most likely the sampling rate for the logbook. Nothing forbids the software to take some data, display it and trash it afterwards.
The data required to display depth does not grow, it is only a few bytes.

Most recent sensors should be able to output at least at 100Hz, so a computer lagging behind baffles me.

 

[Spack9]

Not to beat the horse of weighting, but i was initially way over weighed by my first instructor. Im a 5' 5" male and I weigh 165lbs. I was diving 15lbsin a shorty 3mm in fresh and near 20lbs in salt water. I have just experienced true neutral buoyancy with only one or two quick burst of air in my bc at 8lbs. I feel like many divers are taught to overweight by instructors to be "safe". Also take note of your kick. The flutter can sometimes affect your trim of not careful. Try to slow it down and isolate the issue. The smallest things can throw you off. I find it easy to not focus on my breaths for consistency. If I think about my breaths they will be super deep and throw off my bouancy.