buoyancy issue

[arabianply]

It seems like a foolish question after my thirty dives but, during a recent dive I encountered a buoyancy problem towards the middle and end of my shallow dives (between 10 and 15 metres) whereby I had to keep deflating my BCD in order to keep from floating to the top.

I distinctly remembered to always deflate my BCD on the way down till hovering but someways toward the middle and end of my dives, i kept floating away and when I deflated I was surprised to find that there was so much air inside.

I know that I didnt accidently keep inflating anytime. Nor was my BCD hose valve leaking inside, so where did this exta air come from ?

 

[Marek K]

OK, I think we need some more information:

Is this the first time you noticed this happening?

If so, was this after you changed anything in your equipment configuration? Different type of tank? Different suit? Different amount of weight?

You said this was toward the end of your dive. Did it happen while you were surfacing, or while you were at your dive depth?

--Marek

 

[m3830431]

Is you inflater leaking into you BCD?

 

[espenskogen]

It seems like a foolish question after my thirty dives but, during a recent dive I encountered a buoyancy problem towards the middle and end of my shallow dives (between 10 and 15 metres) whereby I had to keep deflating my BCD in order to keep from floating to the top.

I distinctly remembered to always deflate my BCD on the way down till hovering but someways toward the middle and end of my dives, i kept floating away and when I deflated I was surprised to find that there was so much air inside.

I know that I didnt accidently keep inflating anytime. Nor was my BCD hose valve leaking inside, so where did this exta air come from ?

If you have air - any air - in the bc during the deep section of the dive, then that air will expand and become a lot more air on the ascent. Which is why we control our ascent/keeping neutral by letting air out of the bc on the ascent.

E

 

[dkunstman]

Another thing to consider is that an aluminum tank becomes bouyant as it is depleted. If your air was getting down to 800 or less this was most likely a factor for you if you dive aluminum tanks.

Dennis

 

[Marek K]

Is you inflater leaking into you BCD?

He didn't think so.

If you have air - any air - in the bc during the deep section of the dive, then that air will expand and become a lot more air on the ascent. Which is why we control our ascent/keeping neutral by letting air out of the bc on the ascent.

Another thing to consider is that an aluminum tank becomes bouyant as it is depleted. If your air was getting down to 800 or less this was most likely a factor for you if you dive aluminum tanks.

Maybe, and maybe. First two things I thought of too. Which is why I thought we needed more info --any equipment changes (i.e., from steel to alu tank)? When during the dive (if while surfacing, then probably expanding air)?

It sounded like it all of a sudden happened... or that at least he hadn't noticed it on previous dives...

--Marek

 

[ScubaMike14]

Another thing to consider is that an aluminum tank becomes bouyant as it is depleted. If your air was getting down to 800 or less this was most likely a factor for you if you dive aluminum tanks.

Dennis

EXACTLY what I was thinking. As you burn your tank up it becomes much lighter than when you first jumped in the water. This is most notable with an Aluminum 80. See if your local LDS has a steel tank like an LP 85 or 95 you can rent. Try diving with this and see if there is any difference.

Mike Rushton

 

[BIGSAGE136]

You are losing the weight of the gas.

 

[Walter]

It's normal. Deflate the BC.

 

[Timotheus]

EXACTLY what I was thinking. As you burn your tank up it becomes much lighter than when you first jumped in the water. This is most notable with an Aluminum 80. See if your local LDS has a steel tank like an LP 85 or 95 you can rent. Try diving with this and see if there is any difference.

Mike Rushton

Careful here - all tanks change buoyancy as you deplete your air supply. I have an aluminum 80 tank which starts at -2 lbs and ends at +4 pounds. I also have a Pressed Steel E7-100 which starts at -8.5 pounds and ends at -1.0 pounds. The difference with steel tanks is that their ending buoyancy is still on the negative side at the end of the dive, while aluminum tanks cross over to the plus side. Either way, you have to carry enough weight to keep yourself neutral at the end of the dive.