BCD, weights, and buoyancy control questions

[Triad]

Hey, folks! Thanks for the awesome community here. You all played a key role in my decision to start diving. I just did my first OW class yesterday and had a great time, despite some minor equipment issues (my height and weight make it seem like I'm rather larger than I really am!) that will be remedied next week.

What I'm trying to figure out is primarily how buoyant I'm supposed to be with a fully deflated BCD and less than 1000 psi of air. With the BCD fully deflated and 4 pounds of weights, I found that I sank in 5 feet of water when I exhaled and ascended when I inhaled. Every moment I spent underwater, I was trying to control my buoyancy with by breathing, without holding my breath. By the end of the session, I was navigating in that 5 foot pool without breaking the surface or touching the bottom, though it still felt awkward, especially when trying to hover in one spot. But I did well enough that two of the assistant instructors complimented me on my buoyancy control, so I think I'm making progress in the right direction. I have a hunch that it's a good thing that I wouldn't be in a rapid, uncontrolled descent if my BCD were to deflate.

I could certainly ask my instructors these questions, but going in to my first class well-informed helped me immensely, so I'm trying to keep that habit up.

TL;DR: Is it normal/preferable to have a fully deflated BCD near the surface? Should I feel confident being able to control my buoyancy with my breathing with it deflated?

Thanks!

 

[Steve_C]

No matter what it looks like in the videos a diver cannot stay perfectly still in the water. When all is well you will be oscillating about a set depth as you breath in and out. It is the laws of physics at work. When you get it all together the oscillations are smaller but they are there. Essentially you are exhaling as you start up and inhaling as you start down.

In egnineering language you have a stabilizing oscillating feedback controller that has been tuned with a neural net.

 

[RainPilot]

The whole idea is to be neutral as you describe, with an empty wing. This means that if you have a BCD failure you aren’t trying to swim up too much weight.

Also, far more commonly, the greatest pressure changes are shallow. Any gas in your BCD is going to expand and compress quite a lot with even small changes in depth at safety stop depth. The less gas you have in your wing, the less there is to manage and the ascend/expand/ascend faster/oh crap now I’m going up like an elevator cycle doesn’t get a chance to start.

Oh and welcome to the Board and diving, hope you have great fun with both!

 

[Lake Hickory Scuba]

Hey, folks! Thanks for the awesome community here. You all played a key role in my decision to start diving. I just did my first OW class yesterday and had a great time, despite some minor equipment issues (my height and weight make it seem like I'm rather larger than I really am!) that will be remedied next week.

What I'm trying to figure out is primarily how buoyant I'm supposed to be with a fully deflated BCD and less than 1000 psi of air. With the BCD fully deflated and 4 pounds of weights, I found that I sank in 5 feet of water when I exhaled and ascended when I inhaled. Every moment I spent underwater, I was trying to control my buoyancy with by breathing, without holding my breath. By the end of the session, I was navigating in that 5 foot pool without breaking the surface or touching the bottom, though it still felt awkward, especially when trying to hover in one spot. But I did well enough that two of the assistant instructors complimented me on my buoyancy control, so I think I'm making progress in the right direction. I have a hunch that it's a good thing that I wouldn't be in a rapid, uncontrolled descent if my BCD were to deflate.

I could certainly ask my instructors these questions, but going in to my first class well-informed helped me immensely, so I'm trying to keep that habit up.

TL;DR: Is it normal/preferable to have a fully deflated BCD near the surface? Should I feel confident being able to control my buoyancy with my breathing with it deflated?

Thanks!

I recently just made a video about being properly weighted, which in time, you will notice your weighting needs will decrease. This of course is dependent on what exposure suit you wear. Your instructor will be a bigger help than any of us will be,because he will be there with you one on one in the pool, and can help you adjust your buoyancy as needed. In a nutshell, you need to be able to hold neutral buoyancy at any stage of the dive, and preferably horizontal trim (though I would focus more at first on just getting neutral buoyant, then you can shift weight to get the trim), no matter the depth and no matter how much air you have. Here is the video we just uploaded showing you how being properly weighted will allow you to ascend and descend at will. Sometimes you will hear it referred too as having a balanced rig.

 

[Triad]

Thanks for the responses. You all continue to be encouraging and supportive! I just didn't want to feel like I was developing any bad habits just as it seemed I was starting to get a grasp on things.

I recently just made a video about being properly weighted, which in time, you will notice your weighting needs will decrease. This of course is dependent on what exposure suit you wear. Your instructor will be a bigger help than any of us will be,because he will be there with you one on one in the pool, and can help you adjust your buoyancy as needed. In a nutshell, you need to be able to hold neutral buoyancy at any stage of the dive, and preferably horizontal trim (though I would focus more at first on just getting neutral buoyant, then you can shift weight to get the trim), no matter the depth and no matter how much air you have. Here is the video we just uploaded showing you how being properly weighted will allow you to ascend and descend at will. Sometimes you will hear it referred too as having a balanced rig.

Thanks for the video, I'll definitely have a look. I feel like I can never hear too many fresh perspectives or new ideas about buoyancy and weighting since I've made it such a high priority to develop that skill.

The engineering analogy was a good one because it also makes me think of the kind of resonance that develops when you overcompensate for changes! Fine tuning that oscillation is probably what I'll focus on in free moments next week.

 

[KevinNM]

TL;DR: Is it normal/preferable to have a fully deflated BCD near the surface? Should I feel confident being able to control my buoyancy with my breathing with it deflated?

At the end of your dive you should be able to hold a 10ft stop without much if any air in your BCD. So that sounds good to me.

 

[diver0008]

It took me dozens of dives to get my buoyancy dialed in to the point where I was competant making the minor BCD inflation adjustments at any depth to be neutral and let my breathing make the micro-adjustments for navigating tight spaces or getting in and staying close to things I want to look at. I dropped lead weight repeatedly throughout this learning curve. One test that worked well for me in terms of establishing a baseline for weighting was the following:

At the surface with a full tank of air and an empty BCD, lungs full of air should keep your eyes above the water, and a complete exhale should begin a sustained descent.

Currently 10 lbs in salt water with full 3mm wetsuit. 5'10" 155 lbs.

Sounds like you are off to a good start anyway.

 

[Triad]

At the surface with a full tank of air and an empty BCD, lungs full of air should keep your eyes above the water, and a complete exhale should begin a sustained descent.

That sounds like about where I was at! Looking forward to hitting the deep end of the pool next week. I'm kind of grasping the idea that breathing is my means of controlling and maintaining neutral buoyancy, not the BCD or weights. If I'm doing that right, I should be able to simply swim up and down to change depth, adding or removing air from the BCD as necessary to compensate for pressure.

I can't explain it, but I love thinking about this stuff!

 

[diver0008]

I'm kind of grasping the idea that breathing is my means of controlling and maintaining neutral buoyancy, not the BCD or weights

I don't think I'd put it like that. I think that getting the weighting at low as possible, and using air in the bcd (and the tank I suppose vis a vis its weight) to get neutral is the idea, and breathing kind of revolves your buoyancy around that neutrality. But maybe that's what you meant anyway. The deeper you go, the more air you need in your BCD to maintain neutrality. In any event, and in my opinion, it's the most important skill towards relaxing and enjoying the underwater experience, so good for wrapping your head around it. When you get it down, and you are actually using your breathing to move up and down, for me, you actually kind of feel like a fish.

 

[Triad]

I don't think I'd put it like that. I think that getting the weighting at low as possible, and using air in the bcd (and the tank I suppose vis a vis its weight) to get neutral is the idea, and breathing kind of revolves your buoyancy around that neutrality. But maybe that's what you meant anyway. The deeper you go, the more air you need in your BCD to maintain neutrality. In any event, and in my opinion, it's the most important skill towards relaxing and enjoying the underwater experience, so good for wrapping your head around it. When you get it down, and you are actually using your breathing to move up and down, for me, you actually kind of feel like a fish.

Yeah, it's hard to put in to words exactly what I mean, but I think we're on the same page. Sounds like as I go deeper and do more, there are just more variables and more variations on them to adjust to. The problem solver in me likes the sound of that.