Question regarding neutral buoyancy

[TMHeimer]

This is a basic scuba page, so I won't express my honest feelings to adding "a couple lbs" other than say don't.

Lots of good advice here, especially this.
Though breathing is used for fine tuning buoyancy-- for things such as swimming up a bit to go over a rock, etc., I recall the most important thing my OW instructor told us: Short bursts adding or subtracting air from the BC. This doesn't take long to figure out, then you won't ascend or descend too fast (unless you want to descend fast....).

 

[Esprise Me]

When I first started diving, I paid a little too much attention to all the "don't hold your breath" and "breathe slowly and deeply" stuff, and it made it hard to control my buoyancy. Learning to just breathe normally helped a lot.

 

[napDiver]

I'll expand on why ppl add 1 or two lbs. Typically new divers arent very good at completely emptying their bcd. They dont know what position to be in and for how long.

The second reason for adding an extra lb or two is because they cant control bouyancy via 20% lung capacity. So when they measure 15 ft @ 500 psi weighting, they are breathing let's say 50%. But if they get excited or start to panick they may breathe at 90%. Well their weight check was performed at 50% and is incorrectly weighted for 90% lung capacity.

As you dive more, ppl will tend to continue to drop weight since their ability to dump most of the air in their bcd, control lung volume level, and lower average peak to trough.

 

[Celt]

I wouldn’t worry about it, because there’s no such thing as neutral buoyancy, not for humans that need to breath at least, but there is ideal buoyancy which is the buoyancy you need for any particular dive, once you understand how to control buoyancy you can suit yourself how you wish to dive.

 

[stepfen]

After establishing neutral buoyancy, your body still ascends or descends as you inhale or exhale.

To help OP with his/her initial concern: what you describe is true BUT the key is hidden in what is called inertia (I think that is the correct term - sorry English is not my first language).
Yes assuming you are perfectly neutral, once you inhale you will start assenting (and descending as you exhale from neutral), BUT there is a lag (i.e. it takes some time) between the two due to inertia. Also, your body with all the equipment etc has a big surface and hence it needs quite a bit of force to move through water. Hence from the moment you inhale (which also is not instantaneous by itself) it takes some time for the upwards momentum to build and then you start moving up noticeably. The art of breathing uw is that with some practice you will learn to "predict" the building of this momentum and counteract it (eg start exhaling at the right moment) before you even move upwards noticeably. Not only this, but you will eventually learn to use this to your favor eg to initiate and maintain slow and controllable ascents or descents with minimal effort.

The problems with new divers (occasionally myself included) is that they get neutral (or think they do) then fill in their lungs with a deep breath, then pause and think to themselves: "what is going on now?" after few moments upwards momentum builds and they think, "oh, I am moving upwards" and then "oh sh*t, maybe I am underweight", after few more moments: "I am now going upwards even faster now, I am definitely underweight" and so it goes. By that time a slow (for the time being) uncontrolled ascent has started - if they realize it on time they can still stop it, but quite often (eg if they are destructed by a nice fish, or while taking a selfie with their go-pro or dealing with an equipment issue) by the time they do it is already too late.

To solve this the diver shouldn't have started with a deep breath to begin with - just a normal breath should do. Then once the inhale is finished and once (or actually even before) you feel the upwards momentum building you should have already initiated your (slow) exhale (to counteract the building up of upwards momentum). With a bit of practice you will see that (normal) breathing won't affect much your buoyancy.

I know that all these are easier said than done, but at least that is what is going on.

I hope it helps.

 

[elmo]

Many divers don’t realise they share your issue, but it is very common. As a former DM, and just watching other divers generally, I’ve seen plenty start an accidental ascent. With practice most learn to stop the ascent soon enough by dumping gas, as you are.
The most common cause of unintentional ascents seems to be diving with your head higher than your feet, coupled with kicking (often unwittingly because holding your legs and body still feels unnatural). The result is you propel yourself forward and up. Once you feel yourself start to ascend you tend to move your legs more and/or move into a more vertical posture because that feels natural. This accelerates the ascent (along with gaining buoyancy as your suit and bcd expand). If you compensate by over-weighting yourself you might get the unintended ascents under control but you’ll need to kick constantly to hold your position in the water. This means you can’t stay in one position and will waste energy and gas. The solution takes practice but it is worth it. Learn to control your posture (trim) in the water so that you remain horizontal. If uou do that, then even if you do kick unintentionally you’ll move forward but not up. Next practice keeping your legs still. It is much harder than it sounds.

 

[Norwegian Cave Diver]

Buoyancy is part of the trinity of diving - Buoyancy - Trim - Propulsion. Each one affects the other. Most or perhaps all new divers swim in what think is a horizontal position in the water but in reality they are in a heads up position. So they are swimming along - adjust their BCD to be neutrally buoyant - and then they slow down or stop - now they find they are sinking - the (1) natural reaction is to become more vertical in the water and start to kick to remain at the same depth. This solves the problem temporarily but now instead of resting they are working to stay at that depth. (2) the second choice is to add air/gas to the BCD to become neutrally buoyant and now it is time to swim again but with more air/gas in the BCD they find themselves rising in the water. Why? Because their buoyancy is based upon swimming in a heads up position instead of a horizontal position. Think about what happens when you are in your vehicle driving down the road and you roll the window down and you put your arm out. If your arm is horizontal then it is streamlined and there is no resistance - but it you raise your arm so it is in a slightly hand up position then you feel that air wanting to push your arm up. You're doing the same thing when you're diving in a heads up position. The water is flowing across the front of your body and this is affecting your buoyancy as you swim. So TRIM affects your BUOYANCY. You should be able to stop swimming - be horizontal - take normal breaths - and stay in position - and stay at that depth.

 

[boulderjohn]

If I were to work with you based on what you wrote, my first step would be to evaluate your weighting. My long range diagnosis is that you are overweighted, probably by a lot.

In order achieve neutral buoyancy, you must balance the amount of extra weight (lead) you are carrying with the appropriate volume of air in the BCD and the amount in your lungs. Every pound of lead you don't need requires about 15 fluid ounces of air to compensate. If you are carrying only 4 more pounds than you need, then you must have the equivalent of 2 quart bottles of air in your BCD.

That air expands and contracts with changes in depth. The shallower you are, the more that happens, and that is by a significant amount.

If you only have a little air in the BCD, then you can overcome minor changes in depth through your breathing. If you have lots of air in the BCD, then your lungs will be overpowered by that changing volume in only a few feet of depth.

 

[Coztick]

My approach is to adjust to neutral buoyancy when my lungs are half full.
My breathe cycle pauses at this point.
That way, I can still breathe slowly and deeply without affecting buoyancy.
Starting at neutral, both an inhale and an exhale is less than full breathe but both satisfy the need to breath. Together, they are a full breathe.
Normally I breath in, then exhale to neutral followed by a short pause. Then breathe out, then inhale back to neutral, short pause. The pauses are only 2 or 3 seconds.
Remember, throughout your dive, you will need to vent your BC to remain neutral as you consume your breathing gas.
Buoyancy swings are greatest in shallow water so that's the best place to practice...

Cheers!

 

[wetb4igetinthewater]

I'll expand on why ppl add 1 or two lbs. Typically new divers arent very good at completely emptying their bcd. They dont know what position to be in and for how long.

The second reason for adding an extra lb or two is because they cant control bouyancy via 20% lung capacity. So when they measure 15 ft @ 500 psi weighting, they are breathing let's say 50%. But if they get excited or start to panick they may breathe at 90%. Well their weight check was performed at 50% and is incorrectly weighted for 90% lung capacity.

As you dive more, ppl will tend to continue to drop weight since their ability to dump most of the air in their bcd, control lung volume level, and lower average peak to trough.

This is a joke, right? Or just an indication of really poor open water training?

New divers have to develop situational awareness from scratch. When you overweight them, they have to add gas to their BCD to compensate. As they are not aware of ascending slightly, that extra gas also expands, exacerbating the increase in buoyancy force pushing them towards the surface.

Most people don't drop weight as time goes on as they don't do continued weight checks. They don't know what a proper weight check is.