Bouyancy issue - what happened to me?

[Spencermm]

I was on my 10th dive- 1st dive away from checkout platform, which is at 20 ffw.
I had, earlier that day(dive#8), started to learn a slight degree of control of my bouyancy at that depth. I was wearing 20 lbs. of weight, which seemed to be good for me.
At dive #10 DM said we could swim around the lake in groups of 4 w/ a DM. So I am swimming around just thrilled beyond words at how it felt to do so(max dept was 26' and we were swimming with the terrain which had us yo-yo-ing about 5 ft either way). I had no air in BC. After about 5 minutes I started to float up a bit. I tried to let air out of bc- didn't help. I thought well maybe, since I am nose down trying not to ascend, the air is stuck in the bottom of the bladder- so I tried letting it out of the bottom valve. Nothing. I even reached back to try and feel any air in the bladder- felt no air.
Any way, I swam my a$$ off to get back down. After a few minutes the problem, whatever it was, ceased to exist.
WHat was causing this? Was it the yo yo thing? Was my rapid breathing due to being excited a factor? It didn't feel like I had too little weight.
Any help,
Spencer

 

[Jimmer]

How much pressure was in the tank? If your tank pressure was lower on that dive than when you set your weigthing, you would be more buoyant. Also were you using an identical tank? Ie. standard 80's all the time, or did you switch from a neutral 80 to a standard 80? or steel to aluminum?

 

[spectrum]

It could be a number of things.

As mentioned, how much air was in your cylinder when you decided 20 pounds was good? Had you taken the pressure lover than on prior dives?

The question I have is at the end of the dive... Were you able to make a controlled ascent then or were you overly buoyant? If you were OK at the end then it speaks a transient matter like pumped up lungs or trapped BC air.

Being excited or swimming hard playing follow the leader could pump up your lung displacement.

Of course once you took charge and swam it back down your neoprene compressed and let you resume being neutral.

If you were at 26 feet and were wearing any significant neoprene and had no air in your BC and were neutral then you were under weighted. At that depth you should be experiencing significant neoprene buoyancy loss that needs to be counteracted with BC air volume. That sort of diving can be done but it requires considerable lung volume and the control of same.

Pete

 

[Spencermm]

How much pressure was in the tank? If your tank pressure was lower on that dive than when you set your weigthing, you would be more buoyant. Also were you using an identical tank? Ie. standard 80's all the time, or did you switch from a neutral 80 to a standard 80? or steel to aluminum?

Was using identical tanks. I didn't think about tank pressure. I went down with 3000 psi(guessing) and probably had 1000-1500 at the point I started poping, as it was near the end of the dive. If it in fact was the tank pressure, how would this same scenario be effected by greater depths- say at 100'?

 

[Jimmer]

The buoyancy change of the tanks will be the same no matter of the depth. Of course the change will happen faster when you're deeper. My bet would be the lower pressure in the tank is what caused you to start to be too light. Recheck your weighting with 500 PSI in a tank and use that amount.

 

[spectrum]

If it in fact was the tank pressure, how would this same scenario be effected by greater depths- say at 100'?

While down deep the excess positive buoyancy of the cylinder would be offset in total or part by the loss of neoprene buoyancy due to compression. As you returned to a lesser depth with perhaps even less air in the cylinder you may have found yourself alarmingly buoyant.

Pete

 

[Spencermm]

It could be a number of things.

As mentioned, how much air was in your cylinder when you decided 20 pounds was good? Had you taken the pressure lover than on prior dives?

The question I have is at the end of the dive... Were you able to make a controlled ascent then or were you overly buoyant? If you were OK at the end then it speaks a transient matter like pumped up lungs or trapped BC air.

Being excited or swimming hard playing follow the leader could pump up your lung displacement.

Of course once you took charge and swam it back down your neoprene compressed and let you resume being neutral.

If you were at 26 feet and were wearing any significant neoprene and had no air in your BC and were neutral then you were under weighted. At that depth you should be experiencing significant neoprene buoyancy loss that needs to be counteracted with BC air volume. That sort of diving can be done but it requires considerable lung volume and the control of same.

Pete

Zero problems on ascent. We ended the dive by swimming with the slow sloping bottom right up to 4' then I stood up. After reading your notions I bet it was the lung displacement(I was puffing like a train) and the neoprine thing. I remember being very surprised at how the problem just faded away after I finally got back down.
Thanks!

 

[El Cid]

Being a rookie myself, I would think it could be lung displacement. You might have spent your entire $10 (motorcycle concept) on swimming down and don't think sometimes that there is another way to solve the problem by just exhaling. I'm trying to fine tune bouyancy and breathing now and from what I hear will probably will still be working on it at dive 1,000.

Keep in mind that its way tougher to master your bouyancy at 20 ft than 60+ft. The change in bouyancy vs. volume at those greater depths is much less on a percentage basis. Keep working on it, and enjoy the sights down there!

 

[Charlie99]

Zero problems on ascent. We ended the dive by swimming with the slow sloping bottom right up to 4' then I stood up.

That you can finish the dive being under control all the way up to 4' depth definitely shows that you were not underweighted.

Possibilities ----

1. You were sucking in big breaths and keeping your lungs full. This can add 5+ pounds of buoyancy. After a while, controlling your buoyancy by changing lung volume may become automatic. Your first action if you are getting too buoyant is to exhale.

2. You had air trapped in the BCD bladder. Reaching back and feeling to see if there is air in the bladder is not a very sensitive or reliable test. Sometimes air can be trapped on one side or the other the bladder and you not only have to open a valve, but also roll from side to side or do a little underwater hula dance to get the air bubble to move over to the same side as the dump valve.

3. Air trapped other than inside the BCD. It is possible to get air inside the wetsuit, trapped between the BCD and wetsuit, etc. This is a likely scenario if the problem just mysteriously went away without any further dumping of air from the BCD.

4. Initially, wetsuits will have more buoyancy until they get fully saturated (that's why a wet wetsuit is heavier than a dry wetsuit). This is not likely to be your problem since this is usually only an issue for the first few minutes of the first dive of the day.

Charlie Allen

 

[spectrum]

Zero problems on ascent. We ended the dive by swimming with the slow sloping bottom right up to 4' then I stood up. After reading your notions I bet it was the lung displacement(I was puffing like a train) and the neoprine thing. I remember being very surprised at how the problem just faded away after I finally got back down.
Thanks!

Then you had adequate weight but found some excess buoyancy for a while. That gets it to the pumped up lungs or a bubble trapped in the BC.

Diving at a more relaxing pace is preferable. If you find yourself needing to work hard then don't be afraid to make the breaths deep at both ends. You may be sucking in huge lung fulls of air but be just as aggressive on the exhale. That will keep your average buoyancy closer to normal and be a healthier respiration pattern.

This stuff is pretty simple once you understand it, like most things there are logical explanations.

Pete