Ascending/Decending/Buoyancy

[Eric Sedletzky]

When diving with heavy steel tanks, I have to dump a lot of air to break contact with the surface. Then, immediately start adding back to control the descent. Once those heavy tanks start down, they accelerate faster than AL tanks.

With AL tanks, I can just go head down. That’s harder to do with steel doubles because the mass of the tanks wants to fight big changes in direction. It also can create a big weight shift, especially with deco bottles.

I have to add air to both the dry suit and wing. Suit to fight off the squeeze, and wing to control the descent.

I stay horizontal and close to neutral all the way to the surface. It’s better to control the ascent and easier to level off for any potential deco stops.

This is a question in basic scuba about buoyancy in a recreational single tank configuration and you’re talking about big heavy steel doubles and stage bottles?

 

[KenE]

As a basic rule I find these steps help control descent:
1. let enough gas out to get head underwater and then stop letting air out
2. if I stop descending I exhale until I start moving again
3. then, as mentioned above, use the inflator as a brake to slow descent
4. before reaching desired depth, not bottom, I hit the brakes again
5. all other depth changes occur with lung volume, not bcd
On ascent:
1. I use lung volume to start ascent and use dump valve as brake to slow ascent to safety stop.
2. same process to surface

Weight check is best done at 15-18 feet with a bottom at 16-19 ft., dump all air from bcd (you will sink to bottom, use one hand to stay off bottom), start dropping lead until you start to come off bottom then take one back. This is optimal weight if you tank is around 500psi, if not than add one more pound back and do it again when tank is emptier (next dive, etc).

 

[DeepSeaExplorer]

There are divers that learn to dive in steel tanks and dry suits.

 

[tursiops]

There are divers that learn to dive in steel tanks and dry suits.

With cloubles and deco bottles? Nah.

 

[DeepSeaExplorer]

Well, I’m on my phone in a car and didn’t notice the forum. But, it’s nice to know the scuba police are real.

 

[tursiops]

Well, I’m on my phone in a car and didn’t notice the forum. But, it’s nice to know the scuba police are real.

LOL! You are on your phone in a car and you are worried about the Scuba police?

 

[steinbil]

With cloubles and deco bottles? Nah.

To be fair, the 3 words about deco bottles were not central to the post, and it was relevant to the discussion. I took my OW in steel doubles and a drysuit, so it's not unthinkable that others might do the same, especially in cold water. In any case it's not harmful to learn about what is done in slightly different/more advanced scenarios, especially when it doesn't confuse or conflict with any other advice given. Begin with the end in mind, and all that...

 

[BlueTrin]

Well, I’m on my phone in a car and didn’t notice the forum. But, it’s nice to know the scuba police are real.

 

[John C. Ratliff]

When diving with heavy steel tanks, I have to dump a lot of air to break contact with the surface. Then, immediately start adding back to control the descent. Once those heavy tanks start down, they accelerate faster than AL tanks.

With AL tanks, I can just go head down. That’s harder to do with steel doubles because the mass of the tanks wants to fight big changes in direction. It also can create a big weight shift, especially with deco bottles.

I have to add air to both the dry suit and wing. Suit to fight off the squeeze, and wing to control the descent.

I stay horizontal and close to neutral all the way to the surface. It’s better to control the ascent and easier to level off for any potential deco stops.

No one really replied to this, so I thought it appropriate to say something. If you have to dump a lot of air to break surface, you are overweighted. Those steel tanks count as part of the weight you carry. If you are diving a dry suit, you should not have to use a BCD (Buoyancy Control Device), as you don’t have wet suit compression to deal with. Yes, add air to the dry suit to prevent squeeze, but all that means is that you are already compensating for the suit. The BCD is not necessaary for this compensation, as you are already doing it by adding air to the dry suit. We used to dive dry suits without a BCD, and we were neutral in the water too. The photo below is of me in an Aquala dry suit, sans BCD, as the BCDs had not yet been invented in 1974. (Photo by Bruce Higgins.)

SeaRat

PS, this has nothing to do with the "scuba police." It has to do with good, basic technique.

 

[steinbil]

If you have to dump a lot of air to break surface, you are overweighted.

Not necessarily. The wing might also hold more air than you need, maybe to float a heavy rig. The amount of air you need to dump to descend is irrelevant – imagine having a giant balloon attached to you on the surface, you might still be balanced without it. The amount of air you need to float, however, is relevant.

If you are diving a dry suit, you should not have to use a BCD (Buoyancy Control Device), as you don’t have wet suit compression to deal with. Yes, add air to the dry suit to prevent squeeze, but all that means is that you are already compensating for the suit. The BCD is not necessaary for this compensation, as you are already doing it by adding air to the dry suit. We used to dive dry suits without a BCD, and we were neutral in the water too. The photo below is of me in an Aquala dry suit, sans BCD, as the BCDs had not yet been invented in 1974.

The reason you "need" the wing is to offset the weight of the gas, not the tanks. So bigger volume of gas (big doubles) = you must be overweighted at the beginning of the dive, otherwise you would be severely underweighted when you're low on gas. Yes, the drysuit can also compensate for that. But a BCD/wing is easier to control and you have redundancy in the drysuit. I assume that diving with doubles before the time of BCDs meant one less layer of protection against possible issues - you would need to use/inflate the drysuit or breathe down the tanks or dump gas from the tanks to be able to comfortably ascend.