Neutral Buoyancy

[nns91]

So I feel comfortable controlling my buoyancy using my lungs now. However, I am not sure how can I identify neutral buoyancy ? (supposing that I have the appropriate amount of weights)

When I descend, I deflate my BCD completely. Once I get to a desired depth, should I inflate my BCD a little bit ?

I feel that it is much easier to exhale and descend than inhale and ascend. Is it normal ?

 

[Superlyte27]

Deflate your BC completely, then inflate to achieve buoyancy?

Seems like a waste of air to me. But... I do it too sometimes. You know why? Because I want to get where I'm going fast. I descend very rapidly, fastest way to do that is with an empty bladder.

But, I'm not sure that's the best way.

Also, remember that neutral at 30' is not neutral at 100'. If you change nothing but depth, you are still going to need more air in your BC as you descend. Seems like a waste to fill what you just completely emptied.

But that's just me.

 

[Mike Boswell]

Assuming you are properly weighted, you will be a bit negative (due to the 5 lbs of air in your tank) on your descent, and wetsuit compression will make you more negative at depth, so yes, typically you have to add air to your BCD at depth. I do this in several tiny squirts until I feel neutral, and then as I use up the air in my tank, I gradually let some of the air in the BCD out. I usually feel the need to start adding air to the BCD at about 40 feet.

On ascent, I gradually deflate my BCD until at 15 feet it is empty, my tank is at 500 psi, and I am neutral at that point.

 

[knowone]

You must be talking about a body of water max depth 10 feet.
Please take the following for the information it contains.
Your concepts and ideas are all wrong.
Study diving literature and speak with your instructor before progressing any further.

 

[Blowin' Bubbles]

If you are trying to descend as quickly as possible--which is not always necessary--the best way to do so is to completely deflate your BCD and slowly fill it when you are at half of your desired depth or whatever works for you. If you're not trying to race to the bottom, it is better to become slightly negative and take your time, especially if you are worried about ear problems. With that said, you should always have reached neutral bouyancy before your reach your desired max depth for every dive. If I'm diving to 90 feet, I make sure to have good bouyancy at 60-70 feet, especially if I'm diving a wall.

If you have neutral bouyancy, when you inhale, you should find that you will rise in the water column and that when you exhale you should fall a little in the water column. If you really want to test whether or not you have achieved good bouyancy, attempt to "hover" at a certain depth for twenty to thirty seconds or so without kicking, just breathing.

 

[Superlyte27]

You must be talking about a body of water max depth 10 feet.
Please take the following for the information it contains.
Your concepts and ideas are all wrong.
Study diving literature and speak with your instructor before progressing any further.

HUH? Care to elaborate so I can make fun of you?

 

[Crush]

Short answer - if exhaling at the surface causes you to sink, and inhaling causes you to float, you are doing very well with your buoyancy.

Adding air to your BC as you descend is a good idea as it will keep you from accelerating downwards as your suit (and BC air) compress.

If exhaling to descend is easier than inhaling to ascend, you might be slightly overweighted. Frankly, it sounds like you are doing well. You can always swim up to ascend.

However, beware:

• Some will tell you that you should be neutral at the surface at the start of your dive, and suit compression at your safety stop will offset the 5# loss of air by the end of your dive. This assumes that you are wearing a suit, and makes no distinction between, say, 3 mil and 7 mil.. Trust me - there is a big difference between diving 3 and 7.
  
• Some will telly you that you should be neutral at the surface at the end of your dive.
  
• Some will tell you that you should be neutral at your safety stop at the end of your dive.
  
• I have not yet heard anyone say that you should be neutral at your safety stop at the start of your dive, but I am sure someone will state this.

Several weeks ago TSandM posted (correct me if I am wrong) that she preferred to err on the side of being slightly overweighted as she once had to swim downwards for the duration of her safety stop in order to not pop to the surface. Her advice seems sound to me.

Finally, some food for thought - in the bad old days divers did not use BCs - they weighted themselves for their operating depth and kicked downwards to get there. Once at the chosen depth, they were neutral (owing to suit compression). At the end of the dive they were even more buoyant that at the beginning (air consumption), and their ascent was straight to the surface (no safety stop).

 

[nns91]

Thank you all for your contribution.

I actually did not want to race down to the bottom. I would pay attention to that next time. So it would be better if I leave some air in my BCD while descending ?

I also can ascend/descend using my breath pretty comfortably now. The thing is when I exhale, I descend almost immediately. However, when I inhale, I do not ascend as quickly. I usually have to hold my breath for a couple seconds to be able to ascend. Is it normal ?

 

[Superlyte27]

if it's not equal, you probably need another squirt in the b/c

I rise and drop pretty equally with inhale/exhale

 

[Stu S.]

in the bad old days divers did not use BCs - they weighted themselves for their operating depth and kicked downwards to get there. Once at the chosen depth, they were neutral (owing to suit compression). At the end of the dive they were even more buoyant that at the beginning (air consumption), and their ascent was straight to the surface (no safety stop).

I was one of them. It depended on the wetsuit you used. A bit of kicking was often required until the suit started compressing around the 25 foot level. Then you went down easier. Pulling yourself down an anchor line was handy. You would start the dive a little over-weighted and end the dive a little light due to air consumption. It was not that hard to do.

Safety stop? Decompression numbers were on the tables and we used them. That was a part of basic training. It was easy with an anchor line for that stop. Without a BC, there was no easy adjustment.

I don't think there is perfect neutral buoyancy. Even subconciously, we are always making adjustments.

Stu.