Ascending without BC's deflation / inflation

[Den7]

I was just wondering if are there any instances when at a certain point in time during an ascent a diver ends up with a completely deflated BC and simply has to swim up? In fact, does anybody happen to know if it would be easier or harder to control your buoyancy by trying to swim up (thrust) your ascent having your BC totally deflated?

 

[tkdgodess]

My BC is never empty on a line or free ascent. I can stop my ascent at any time by releasing a bit more and say do a safety stop in midwater. Not a good explaination, but it's gently floating to the surface by managing the air in the gear... If I am following bottom contours back to the beach, and my tanks are on the emptier side, a completely empty bc and drysuit makes it so I can swim back to knee deep water and remain submerged, and hopefully scare any dogs playing on the beach. Swimming up with an empty bcd means if you stop kicking for whatever reason you are going back down, and you'll have to add air to complete any stops.

 

[kanonfodr]

Most of the time I weight myself to require no gas in my BC with about 1000 PSI in my tanks, so I am doing my ascent completely on lungs. It's pretty easy once you get used to it, and you learn lots about how your exposure suit compresses and expands with depth change, and how that in turn affects your bouyancy needs.

Peace,
Greg

 

[merxlin]

Ideally, you should be able to "swim up" your rig with no air in your BCD/wing from any depth. This would be necessary should there be a catastrophic failure and the bladder not be able to hold any air. At your safety stop with a nearly empty tank and if properly weighted you should need very little air to hold your stop.

 

[herman]

Properly weighted (assuming little wetsuit and single tanks of 100cf or less) you should never need to adjust your BC or swim up. Using your lungs you can control your bouyancy with no need of a BC or swimming. Huge tanks, doubles or thick wetsuits are a differnet matter. I dive mostly warm water with a 3mm shortie or less, my BC is never used and frankly the only reason it is even there is to keep the dive ops happy. If you are constantly having to adjust the air in your BC as you change depth and are not wearing a thick wetsuit, you are overweighted. Proper weighting and breath control are the keys to buoyancy control, not constantly adjusting your BC.

 

[Bubbletrubble]

I was just wondering if are there any instances when at a certain point in time during an ascent a diver ends up with a completely deflated BC and simply has to swim up?

This could definitely happen in a catastrophic BCD failure. Being properly weighted would make it easier to recover from such a situation.

In fact, does anybody happen to know if it would be easier or harder to control your buoyancy by trying to swim up (thrust) your ascent having your BC totally deflated?

It all depends on how one is weighted, from what depth the diver is ascending, and how much positive buoyancy the exposure protection will regain during the ascent.

Every now and then, I see a novice diver (here in SoCal where 7mm wetsuits are commonly worn) do something like what you described. When the diver is ready to ascend, he will exhaust all of the gas inside the BCD, making himself negatively buoyant (sometimes crashing into the sand below), and then swim up from depth against that negatively buoyant force. The thinking here is that the diver will minimize the chance of an uncontrolled ascent, in the event that gas isn't released in a timely manner. Ascending in this way is a lot more work than it needs to be. In fact, it can increase the risk of DCI if the diver inadvertently holds his breath while exerting himself during the ascent. A diver should initiate an ascent while being neutrally buoyant (by inhaling deeply or kicking up a little) and then exhaust gas from the BCD in very small, short bursts as needed. Ascending in this way is nearly effortless and yet maintains proper buoyancy control (being able to arrest the ascent, i.e., get neutral, at any point in the water column).

 

[Den7]

Ideally, you should be able to "swim up" your rig with no air in your BCD/wing from any depth. This would be necessary should there be a catastrophic failure and the bladder not be able to hold any air. At your safety stop with a nearly empty tank and if properly weighted you should need very little air to hold your stop.

Thanks for sharing! This is exactly what I was thinking about! Did you read my mind? I will try this during my next dive.

 

[markmantei]

While not fully empty, I usually will be slightly negatively buoyant and kick to ascend, while venting the bc as necessary to maintain the slight negative buoyancy. I thought this was preferable in order to more finely control ascent rate, and to be able to easily descend should a boat surprise you. Can the experienced divers chime in to confirm or deny that this is preferable?

Now that I think of this, that means I need to kick slightly to maintain depth during safety stop, which makes no sense, I should re-establish neutral buoyancy for the safety stop.

To the posters advocating ascending on the lungs, does this not place you in danger of a lung over-expansion injury? I certainly use lungs to control buoyancy at depth and for "micro" ascents and descents, particularly with photography, but would not dream of it during an ascent to the safety stop or surface.

 

[Den7]

This could definitely happen in a catastrophic BCD failure. Being properly weighted would make it easier to recover from such a situation.

It all depends on how one is weighted, from what depth the diver is ascending, and how much positive buoyancy the exposure protection will regain during the ascent.

Every now and then, I see a novice diver (here in SoCal where 7mm wetsuits are commonly worn) do something like what you described. When the diver is ready to ascend, he will exhaust all of the gas inside the BCD, making himself negatively buoyant (sometimes crashing into the sand below), and then swim up from depth against that negatively buoyant force. The thinking here is that the diver will minimize the chance of an uncontrolled ascent, in the event that gas isn't released in a timely manner. Ascending in this way is a lot more work than it needs to be. In fact, it can increase the risk of DCI if the diver inadvertently holds his breath while exerting himself during the ascent. A diver should initiate an ascent while being neutrally buoyant (by inhaling deeply or kicking up a little) and then exhaust gas from the BCD in very small, short bursts as needed. Ascending in this way is nearly effortless and yet maintains proper buoyancy control (being able to arrest the ascent, i.e., get neutral, at any point in the water column).

Hmmm... interesting. I've never thought of that. But the idea to minimize the chance of uncontrolled ascent like that is quite unusual but worth attention. Most probably I was more on the weight side and exposure protection buoyancy I guess... You made a good point here though. Let alone it is much more work

 

[Bubbletrubble]

While not fully empty, I usually will be slightly negatively buoyant and kick to ascend, while venting the bc as necessary to maintain the slight negative buoyancy. I thought this was preferable in order to more finely control ascent rate, and to be able to easily descend should a boat surprise you. Can the experienced divers chime in to confirm or deny that this is preferable?

Well, if you are diving in an area with boat traffic, then it would make sense to be slightly negatively buoyant as you near the surface, just in case you need to duck down to avoid a careless boater. At deeper depths, feel free to manage your ascent how you see fit. I try to kick as little as possible on most of my dives, so it's not surprising that I prefer to stay neutrally buoyant most of the time. On most dives, I'm super-relaxed and not exerting myself at all. If you're diving to get a good work-out, then I suppose you could kick all the time if you wanted to. One disadvantage of doing this is that you'll run through your gas supply faster.

Now that I think of this, that means I need to kick slightly to maintain depth during safety stop, which makes no sense, I should re-establish neutral buoyancy for the safety stop.

Theoretically, it's beneficial to maintain a low level of activity during a safety stop. It's probably easier to do this while being neutrally buoyant, though.

To the posters advocating ascending on the lungs, does this not place you in danger of a lung over-expansion injury? I certainly use lungs to control buoyancy at depth and for "micro" ascents and descents, particularly with photography, but would not dream of it during an ascent to the safety stop or surface.

Ascending on the lungs does not necessarily imply that the diver is ascending with a closed airway. Keep in mind that any residual gas inside your lungs (after exhalation) contributes to buoyancy. "Ascending on the lungs" means that the divers are simply varying the depth of their breathing. FYI, people with bigger lungs can compensate for a buoyancy swing as large as 10 lbs. of lift. For a recreational diver, that's almost certainly less than the buoyancy swing of a single tank (full vs. empty).