More buoyancy questions

[demonic_death]

Hi guys!

I took my open water(also my first time at salt water) this weekend and I had some problems with my buoyancy. I know how to do the fin pivot and I am pretty much neutral at the bottom. The thing is, the sea I am diving at has uneven terrain. Some pretty corals/wildlife were sitting on this huge rock above the ocean floor, and I wanted to get a closer look. Upon kicking up, I just ascended very quickly and I tried to vent all the air from my BCD ( due to panic ), and yet I couldn't sink. Luckily my buddy (the assistant instructor) was able to pull me down. Upon reaching the rock mentioned, I had to quickly re-inflate my BCD just to keep from hitting the corals. I want to avoid this from happening again(lest I get DCS from rising all the way up), what should I do next time?

Should I vent air out of my BCD first before I go on higher ground? And how come I wasn't able to sink even when I vented all the air (at least I thought I did) from my BCD? I am just using a rental BCD, so I don't know the brand. Thank you in advance for any help that you can give. Thanks to the other divers who have been helping me out in the past, you guys rock!

 

[Avic7]

I have the same problem, YOU are letting air in and out to quickly depending on if your ascending or decending. You should let air in or out in short bursts. It has to do wtih momentum. Cuz your in water, you don't immediately ascend or descend, it takes a few minutes to adjust. So if you let air in or out slowly you can adjust more efficiently. What I try to do when I descend for example, is let my air out of my bcd in short bursts giving myself time to adjust inbetween bursts and exhaling at the same time. Once I reach the bottom, I fill my bcd with enough air so that I have neutral buoyancy and control the rest of the dive with the air I breathe into my lungs.

 

[PaulChristenson]

Hi guys!

I took my open water(also my first time at salt water) this weekend and I had some problems with my buoyancy. I know how to do the fin pivot and I am pretty much neutral at the bottom. The thing is, the sea I am diving at has uneven terrain. Some pretty corals/wildlife were sitting on this huge rock above the ocean floor, and I wanted to get a closer look. Upon kicking up, I just ascended very quickly and I tried to vent all the air from my BCD ( due to panic ), and yet I couldn't sink. Luckily my buddy (the assistant instructor) was able to pull me down. Upon reaching the rock mentioned, I had to quickly re-inflate my BCD just to keep from hitting the corals. I want to avoid this from happening again(lest I get DCS from rising all the way up), what should I do next time?

Should I vent air out of my BCD first before I go on higher ground? And how come I wasn't able to sink even when I vented all the air (at least I thought I did) from my BCD? I am just using a rental BCD, so I don't know the brand. Thank you in advance for any help that you can give. Thanks to the other divers who have been helping me out in the past, you guys rock!

It sounds like you would really benefit from taking the PADI Peak Performance Buoyancy course...

Paul in VT
just back from Belize

 

[ScubaFreak]

The PADI peak performance buoyancy course is good, but only if you already have some understanding of the principle of buoyancy.
I believe that students need some open water experience before really getting to grips with what buoyancy is all about, then, by all means take the PPB course.
I think it's a great course and I often see how much it helps students with buoyancy problems.

Do a search on buoyancy control, and you should get a wealth of information back on techniques to help with your control.

Scubafreak

 

[diversteve]

Some good tips here:

http://www.scubaboard.com/showthread.php?t=98091

 

[markfm]

If you're fairly shallow, you get maximum pressure changes with small depth changes, so even a little air left in the BCD expands quickly. Your attitude in the water can affect how well a given dump method works, too. If you're slightly head down or twisted, the dump point might not be where the air is; you might need to use a rear dump in that case.

 

[RICHinNC]

Bouyancy is like practicing a musical instrument. Gotta spend some time on the scales to play the riffs.

Dont think going to a pool and practicing is dumb and a waste of time. If you can do it in 12...and especially 4 ft....you can do it at depth.....practice practice practice

 

[herman]

Welcome to the board.

Do go read the link posted above, lots of good advise there.
If I had to guess, 3 problems come to mind. You are most likely overweighted, you make adjustments that are too large and don't wait long enough for the changes you have made to take effect. These are very common mistakes made by new divers. Too much weight requires you to have lots of air in your BC to compensate for it. The problem is when you make fairly small depth changes, esp in shallow water, the expansion and contraction of the air in your BC makes staying neutral very difficult. If you have lots of air in the BC, you get lots of change in buoyancy for a little change in depth. In the example you give, I would not have to change the air in my BC at all. I would have used breath control to change depth and never touched my BC ( I am assuming a warm water dive with little or no wetsuit and no more than a 10 ft depth change). Another possible contributing factor is the way you deflate your BC. Your left shoulder must be at the highest point to effectively deflate the BC completely otherwise you trap air in the BC. Slow down, relax and do a good weight check, that and a little practice will make a big improvement.

 

[boulderjohn]

Herman makes a good point about breath control--you should be able to handle these depth changes without messing with your inflator hose at all. Your lungs should be your primary buoyancy control mechanism.

Let's say you are drifting in a current and approaching a coral head. You will need to go over it, level off, and possibly go back down the other side. As you start to rise, you should immediately anticipate that you will become more bouyant as you rise and begin to compensate with a long, slow exhalation. If you do it at the right rate, you will level off instead of continuing an uncontrolled ascent. As you continue at that depth, breathing normally, you will probably be OK with the same amount of air in your BCD. As you reach the other side, another long exhalation will start your descent. Again, anticipate, and start a long, slow inhalation before you reach the bottom.

This all assumes that you are not significantly overweighted. If you are, then you will need to have a lot of air in your BCD to compensate. That will magnify the effect of the air in your BCD as your depth changes. If you are properly weighted, you will not have a lot of air in your BCD while you are diving, and your lungs are more important to you.

 

[MikeFerrara]

You'd think they'd spend a little more time on this before certifying folks wouldn't you?


you need to make fine adjustements with lung volume and anticipate the changes that will be needed in the bc. If you wait till an adjustment is needed before starting to make it it's almost too late and you've been caught behind.

get in some shallow water and practice slow controled horizontal ascents and descents. Don't do too much other diving until you get a better handle on it because uncontroled ascents can be dangerous not to mention the buddy seperations and everything else that they can lead to. Also it can be really hard to manage any kind of other problem if you can't control your position in the water column.

This stuff about getting a handle on the very most basic aspects of diving AFTER being turned lose with a card is absolute and utter nonsense and dangerous to boot!