Floated Up and Couldn't Get Down

[herman]

Don't stress. Are you really really sure your BCD was empty? Also, if you are diving with a Jacket style BCD, you may actually need that much weight or more. They tend to make you more buoyant based on the way they change your shape (and thus the buoyant force acting on you). AL80 tanks tend to get more buoyant as you use the gas in them, so there's also that. Consider asking the DM to do a weight check with you on your next dive.

This is a misleading statement that never seems to go away. The tank material has absolutely no bearing on the CHANGE in buoyancy during a dive, which is what we use a BC for. All tanks get more buoyant as gas is used from them. 80 cf of gas used will cause the exact same change in buoyancy whether it comes from an aluminum tank, a steel tank or one made from any other material. How much weight needed to compensate for the tank material does vary depending on the tank material but once that is determined, it remains a constant throughout the dive.

 

[kelemvor]

This is a misleading statement that never seems to go away. The tank material has absolutely no bearing on the CHANGE in buoyancy during a dive, which is what we use a BC for. All tanks get more buoyant as gas is used from them. 80 cf of gas used will cause the exact same change in buoyancy whether it comes from an aluminum tank, a steel tank or one made from any other material. How much weight needed to compensate for the tank material does vary depending on the tank material but once that is determined, it remains a constant throughout the dive.

True, but an empty aluminum tank is positively buoyant where steels (or at least the models I own) are negative even when empty. The penalty for failing to account for tank buoyancy with a steel is a slight over-weighting. The penalty for failing to account for tank buoyancy with an aluminum could be uncontrolled ascent. Unless you're right at the edge of your BCD's limits, the latter situation is more serious in my opinion.

 

[nolatom]

Just a practical tip, you've gotten good advice already.
If you're unsure of proper weight, or trying to shave off a pound or two of weight and think you can but not sure you won't end up too buoyant at the safety stop and on those last 15 feet surfacing, *don't* do that experiment on a dive where it's a free ascent (drift dive, shore dive, "live boat" dive).

Do it on a boat dive with a nice big anchor line or tie-in line for descent and ascent. Much easier to cope with positive-buoancy at the end with that big ole rope to hang onto.

 

[herman]

True, but an empty aluminum tank is positively buoyant where steels (or at least the models I own) are negative even when empty. The penalty for failing to account for tank buoyancy with a steel is a slight over-weighting. The penalty for failing to account for tank buoyancy with an aluminum could be uncontrolled ascent. Unless you're right at the edge of your BCD's limits, the latter situation is more serious in my opinion.

I acknowledged that in my last line, proper weighting Is necessary regardless of tank material. Swapping between tank materials almost always requires a change in weighting, just as changing tank size does. To be completely accurate, not all AL tanks end up positive and some steels go positive so even saying steel always remains negative and alum always becomes positive is not a true statement. But even if that were true, the fact remains that the swing in buoyancy is the what we use a BC to compensate for (among other things) and that never changes for a given volume of gas no matter what the tank material is.

 

[seaseadee]

This is a misleading statement that never seems to go away. The tank material has absolutely no bearing on the CHANGE in buoyancy during a dive, which is what we use a BC for. All tanks get more buoyant as gas is used from them. 80 cf of gas used will cause the exact same change in buoyancy whether it comes from an aluminum tank, a steel tank or one made from any other material. How much weight needed to compensate for the tank material does vary depending on the tank material but once that is determined, it remains a constant throughout the dive.

Oi Vey. Ok Yes, the change is the same irrespective of tank material. HOWEVER, Aluminum tanks start out negative and end up positive as opposed to steel tanks which usually stay negative. Happy now?

 

[rongoodman]

Oi Vey. Ok Yes, the change is the same irrespective of tank material. HOWEVER, Aluminum tanks start out negative and end up positive as opposed to steel tanks which usually stay negative. Happy now?

Yes, except that you will have added extra weight to start with to compensate for the Al tank ending up positive, so once the gas is gone, you're in the same place whichever tank you've chosen.

 

[JimJam2]

Same happened to me on a multi-level dive. Used to descending then ascending upright. Slow ascent, not in upright position and air from BCD would not escape. Now I know better - use the rear dump valve when trying to get back down

 

[KristenK]

Thank you everyone. Had 2 more dives and then went very well!!! (Saw a huge turtle with 3 shark suckers on his back....plus so many other amazing things.)

I definitely had an air bubble in my vest. I practiced releasing it in different ways....all successful. It was a good learning experience.

Now...off to plan our next trip!

 

[GreggS]

Glad you got it worked out. And you may want to see if you can get by with less weight than you are now carrying. The less weight you carry, the less air you need in your BC, the better you can control your buoyancy, the better your trim, and the less air you'll consume. Good luck with your diving, and have fun wherever you may be underwater.

 

[Neilwood]

Thank you everyone. Had 2 more dives and then went very well!!! (Saw a huge turtle with 3 shark suckers on his back....plus so many other amazing things.)

I definitely had an air bubble in my vest. I practiced releasing it in different ways....all successful. It was a good learning experience.

Now...off to plan our next trip!

What I found worked best for me (I have a wing with a butt dump) is when finning along is to lift my hips slightly (effectively the start of a stomach crunch) which allows the air to migrate to the dump which allows me to vent it (be careful as it can vent more quickly IMHO than the inflator). Apart from ascent/descent, I never use the inflator buttons for venting - I just use the butt dump with small short pulls (you will develop a feel for how much you move the cord before it vents and how quickly it works). I aim for the point at which it just cracks the valve and no more.

When ascending, remember that any air in the BCD will expand so if you have added any to start your ascent you might need to vent it bit by bit as you move up. If you are at 10m and put in even a small amount of air, it will double in volume and buoyancy by the time you are at the surface.