Ascending/Decending/Buoyancy

[aquaticj10]

Hi,

In my pool sessions I have almost exclusively been using my LPI hose to adjust my buoyancy in the pool (i think im slightly overweighted too). Is this typical or is descending/ascending meant to be based on breath control?

My typical situation is to dump all air in BCD til i hit the pool bottom, then do 5-7 ish presses on my inflator hose to bring me to neutral buoyancy. I've been doing some research the past few days and this seems to be entirely incorrect. Any input is greatly appreciated!

 

[tursiops]

It is a best practice to learn to dump just enough air that you settle out at the depth you want. This is hard in a pool, but excellent practice. Most do this by letting out enough gas to sink, then adding a bit more in while descending to stop sinking.

 

[rongoodman]

Well, when you're on an actual dive you don't want to touch the bottom at all, both to avoid disturbing the things living there and also to avoid stirring up silt and sand which can mess up the visibility. I usually dump most of the air in my wing on the surface and start off head down, going flat in the water as I approach the bottom. A few taps on the inflator will slow and stop me when I got to where I want to be. Just being flat in the water slows things down. The BC only needs to have enough in it air to balance the weight of the gas you're carrying and make up for the compression of your wet suit with increasing depth. Any more would imply that you're carrying too much weight. I usually initiate ascents by going a little head down and doing a back kick or two, although a deep breath would probably work. Ascending in that position puts the expanding gas in the wing right under the rear dump and also has me in position to fin back down if things start moving too quickly.

 

[Scuba_Jenny]

With my gear, on a beach dive when I descend, I let the air out of my BP/W till my head is under water. Seems to be just about the right amount. I've done this off boats in deeper water and it works well also. Though sometimes I need to pump a little back in on some of the deeper sites.

 

[scrane]

Hi,

In my pool sessions I have almost exclusively been using my LPI hose to adjust my buoyancy in the pool (i think im slightly overweighted too). Is this typical or is descending/ascending meant to be based on breath control?

My typical situation is to dump all air in BCD til i hit the pool bottom, then do 5-7 ish presses on my inflator hose to bring me to neutral buoyancy. I've been doing some research the past few days and this seems to be entirely incorrect. Any input is greatly appreciated!

Depending on how much air is left in your tank, 5-7 spurts to get neutral sounds like you are overweighted. The only way you can determine proper weighting is if you are neutral at your safety stop with 500 psi in your tank and little or no air in your BC.

 

[Outbound]

Depending on how much air is left in your tank, 5-7 spurts to get neutral sounds like you are overweighted. The only way you can determine proper weighting is if you are neutral at your safety stop with 500 psi in your tank and little or no air in your BC.

I was about to type the same thing when I read your response. Five to seven presses of the inflator in a pool means overweighted for sure.

 

[Kendall Raine]

Dumping and crashing (into the bottom) is something you'll quit doing after a few open water dives. Dumping and then adding a little air at a time on the way down (offsetting the descent acceleration as your wetsuit compresses) will help you control the descent so you never touch the bottom and avoid the overfill/underfill yoyo.

With practice you'll learn to fine tune your buoyancy with your lungs. That is, you will rise or descend slowly in the water based on whether your lungs are full or empty without messing with your BC. Think trim tabs on airplanes. Getting your BC and lungs "in synch" takes practice. Obviously, this does not suggest holding your breath on scuba. Not at all. Instead, it means the act of breathing will become part of maintaining neutral buoyancy.

Also, you'll likely find that with experience you can reduce the amount of weight you're using. As others have said, it sounds like (based on the amount of air you're adding to your BC in a swimming pool) you're currently currently substantially over weighted. Not being over weighted means you'll need less air in your BC, be in better trim and better able to use your lungs to fine tune buoyancy. This in turn will mean you'll breathe less and spend more time in the middle of the water column instead on either end of it. The end goal with weighting is to be able to hold your safety stop at the end of the dive with a near empty tank and almost nothing in your BC. Again, this will take practice, but if you focus on this every dive you'll pick it up fast.

 

[John C. Ratliff]

Okay, I’m an old-time diver, vintage diver, who worked on buoyancy compensation in the 1970s and 1980s for the profession. We used to teach to do a buoyancy check on the surface as the dive started. Here’s how:

—Get into the water with all your gear on, and a full tank or tanks (doubles).
—Empty your BCD; no air in the BCD.
—Take a full breath, and stay vertical in the water.
—Note whether you are floating or not. If not, you need to remove some weight from your weights. If you are floating, you should be floating with you eyes at the water line. If you exhale, you should sink.

This way, as your tank empties you will gain a little buoyancy, at the end of the dive, and remain neutral on a normal breath at the end of the dive at about 10 feet depth.

Now, this may need to be modified if you are using a high pressure steel tank (which are very heavy in the water and have a larger buoyancy change than a steel 72 cubic foot tank (2150 psi steel tank).

For descending, we used to swim down, and just before the bottom use a power inflator to add some air to compensate for buoyancy loss of the wetsuit. For dry suit divers, this is probably not necessary, as they don’t loose buoyancy and air is added to the suit to reduce/eliminate the potential for suit squeeze.

The divers who descend by decreasing buoyancy while overweighted (according to the procedure above) and then adding air are what in the 1970s we called “push-button divers.” This is now how descents are taught my many agencies, but is not as efficient as swimming down (although it may save some exertion).

Ascending, we used to swim up, but now that is also now done with the BCD by many divers, who add air to the BCD to ascend, and again ascend in a horizontal position (which is not an efficient way up concerning streamlining).

There are definite advantages to this style of descending and ascending, but there is also the potential for being completely dependent upon the BCD for ascending and descending. One disadvantage is diving in a river in current, where the current can carry the diver to places (s)he doesn’t want to go if swimming down is not in the skill set.

Just some historical information on how we used to descend and ascend.

SeaRat

 

[kaylee_ann]

What I did was empty my BC and exhale, descended, then put a little more air in to slow it down when I was deeper and descending a bit faster.
When reaching my desired depth, I either added a puff or two of air to obtain neutrality, or did nothing. The rest- maintaining neutral buoyancy and small/medium depth changes- are, or should be, through breath control. That’s my way of doing it anyhow.

 

[L13]

The divers who descend by decreasing buoyancy while overweighted (according to the procedure above) and then adding air are what in the 1970s we called “push-button divers.” This is now how descents are taught my many agencies, but is not as efficient as swimming down (although it may save some exertion).

Ascending, we used to swim up, but now that is also now done with the BCD by many divers, who add air to the BCD to ascend, and again ascend in a horizontal position (which is not an efficient way up concerning streamlining).

Most (if not all) agencies modern direction is to NOT use the BC to initiate depth changes (except initially leaving the surface).

Instead think of the buttons as brakes:

• The add button is the down brake (or fine tune if drifting down)
• The dump button is the up brake (or fine tune if drifting up)