Ascending from shallow dives

[TMHeimer]

We all know the way to safely ascend. Lately I have been noticing that I can often ascend from 20' without releasing air from my BC and don't have to add air to keep my head above the surface to check location with just minimum finning. From 30' I do have to release a little air when very close to the surface. I am ascending according to PADI's "safe" rate of a foot a second. Am I now doing something wrong? What are the physics to explain my not needing to add air on the way up?
I obviously know there is a difference when ascending from deeper dives.
When I am diving I am maybe 2 feet off the bottom and swimming horizontally neutral with ease.

 

[BoltSnap]

What are the physics to explain my not needing to add air on the way up?

Are you really asking this question the way you have it written the way it is now?? "Add air on the way up"???? I never have to add air to go up, I let air out as appropriate/needed NOT add air.

 

[herman]

First off you should never be adding air on the way up, letting some out maybe but never adding, remember, any air in your BC or wetsuit will expand going up. If you are properly weighted and not wearing much of a wet suit, you should not need any air in your BC at your safety stop and with little air in the BC and minimal wetsuit expansion, slight changes in breathing should be all that's needed to control your final accent... I dive with little to no wetsuit often and almost never use the BC at all because I am properly weighted.

 

[Diver-Drex]

As you ascend the air already in your BCD expands making you more buoyant. The air within your wetsuit is doing the same thing. So there is no need to add air. In fact it is normal to have to vent air during ascent to prevent a runaway. This is taught in OW. I suspect (hope) you already know this.
At 20ft near the end of your dive you are neutral with no air in your BC. That’s great. Any decrease in depth will allow the air in your wetsuit to expand and this makes you positive. As you continue to ascend you get more and more buoyant. At the surface at the end of your dive you are positive with no air in your BC. Again, that’s great.

 

[boulderjohn]

I think the OP made an unfortunate wording error that is confusing people. He did mention adding air while ascending, but in the full context, I believe he meant something else. He is saying that he does not need to release air while ascending in order to maintain a safe rate, and he does not need to add air after reaching the surface in order to keep his head above water with only moderate finning. He wants to know how this can be true.

The answer, I believe, is pretty simple: that is the way it works when you are properly weighted and ascending from shallow depths.

1. When you are properly weighted, there is very little need for air in the BCD. It will not expand enough during ascent from a depth like that to make a major impact on buoyancy.
2. In a proper weight check, the diver floats at eye level with no air in the BCD. If such a diver has a little air in the BCD, then he or she should easily be able to keep the head above water with light finning.

 

[TMHeimer]

Are you really asking this question the way you have it written the way it is now?? "Add air on the way up"???? I never have to add air to go up, I let air out as appropriate/needed NOT add air.

SORRY ALL--Obvious typo, I meant release air!!!!

 

[TMHeimer]

I think the OP made an unfortunate wording error that is confusing people. He did mention adding air while ascending, but in the full context, I believe he meant something else. He is saying that he does not need to release air while ascending in order to maintain a safe rate, and he does not need to add air after reaching the surface in order to keep his head above water with only moderate finning. He wants to know how this can be true.

The answer, I believe, is pretty simple: that is the way it works when you are properly weighted and ascending from shallow depths.

1. When you are properly weighted, there is very little need for air in the BCD. It will not expand enough during ascent from a depth like that to make a major impact on buoyancy.
2. In a proper weight check, the diver floats at eye level with no air in the BCD. If such a diver has a little air in the BCD, then he or she should easily be able to keep the head above water with light finning.

Thanks. That explains it. I guess that 43 pounds I need for my farmer john wetsuit is not too much weight, as some have suggested many times.
I should've thought it through in that if you are diving deep you obviously have added more air to offset suit compression thus have to release more as you ascend. Explaining why I do have to release a little from 30' as opposed to 20'.
Perhaps in my very early dives I was releasing air (too much?) as that was the routine explained in OW.

 

[bladder]

Sounds like you wrote it correctly- add air to keep your head above the surface to "check location" as you put it - AT the surface.

I don't know about anyone else but I typically need to add air to my BCD when I surface at the end of a dive otherwise I'm treading water to stay afloat.

 

[TMHeimer]

Sounds like you wrote it correctly- add air to keep your head above the surface to "check location" as you put it - AT the surface.

I don't know about anyone else but I typically need to add air to my BCD when I surface at the end of a dive otherwise I'm treading water to stay afloat.

Yeah, well I'm just talking about a little peak to see my location. For a surface swim or resting on the surface of course you inflate some.

 

[Imla]

3 feet pr second??