jd950:
Well, maybe it was a dumb question. I do have trouble remaining horizonal when not swimming, as my legs start sinking unless I arch my back quite a bit. The problem was less remaining at a certain depth than the problem of ascending a bit while swimming and trying to slow or stop my ascent before I overshoot. I have to deflate the BC to do so. I realize proper breathing and weighting are a part of this, perhaps the biggest part, but I find it frustrating to first try lifting the deflater hose up to let air out and then roll to one side to try and use the dump valve to get air out.
Hi JD950,
If you are over weighted then you are carrying a bigger bubble in your BC. This greater air volume will make for a more volatile buoyancy situation as you move up and down in the water column. A big bubble will force you to ride your BC valves and won't be much fun. Remember to set your weight so that you bob at eye level at the end of your dive with an empty BC, an average breath, your feet still (crossed) and about 500 PSI in your cylinder. A deep breath should get your mask out of the water and a deep exhale should sink your mask. Do all of this while breathing from your regulator. The end of the dive is the defining moment for your weight requirement and you want just enough to let you stay down in the shallows with a light cylinder.
Remaining horizontal as you swim is usually addressed by where you place your weights and this includes how high you wear your cylinder on your back. You say that your legs sink. I'm going to ask you to think instead that your chest is floating, Picture yourself as a see saw. If your BC has trim pockets move 4-6 pounds from your waist to your back, You can also wear the cylinder higher if that works. Another option is to get an extra cam band and strap some weight to the cylinder towards the top but down near your back so you don't become tippy.
It sounds like you need to work on weight and trim first. With that under control you will begin to be at ease. You will be able to relax your breathing and even begin to modify it a bit to help manage buoyancy but you need to clear up these issues in order.
As for venting the BC I think that will all fall into place as you turn down the noise. Some BCs do have a trick where you need to position your self just right to empty them 100% Again with weight and trim in order you will start to have true 3 dimensional freedom and positional control will be trivial.
jd950:
I guess a lot of you simply use the BC as a surface flotation device and a holder for weights, and do not inflate or deflate as a means of adjusting buoyancy. I'm just not there yet and may never be. I thought if some particular BC would make this process easier it would be nice to know when I go to buy one.
Most divers especially with a significant wetsuit must use their BC during the dive. This is the biggest reason for the Buoyancy Compensator. As the name implies it lets us compensate for changes in buoyancy. With a significant wetsuit the divers becomes much more negative as he or she dives deeper and the BC allows the diver to establish neutral buoyancy.
The other variable is the buoyancy of your cylinder. Every breath you take makes the cylinder lighter. Typically this amounts to about 5 pounds over a dive. This is 5 pounds of extra weight that you need to carry so that you will not be too light at the end of the dive.
It may help to visualize that a pound is negated by about a 1 pint volume of air. Remember that the volume (buoyancy) of that air will double or halve every 33 feet as you go up and down. If you are wearing 5 pounds of extra weight (don't confuse this with the 5 that offsets air use) and are at 33 feet and rise 16 feet (1/2 ATM) that air will expand by 50% and you will be 2.5 pounds lighter. At the same time your wetsuit is expanding at a fast rate and adding to your positive condition. My point is that there is a real relationship between the amount of air in your BC, the depth you are at and how much your buoyancy will fluctuate with depth changes.
With practice and correct weighting you will be much less reliant on the BC and depending on your exposure protection will be able to wander up and down in the water column to some extent with little more than modified lung volume.
In all likelihood you just need practice. The first step is recognizing the need. If you dive with a spirit of continuous improvement you will get there. Someone here on the board said that you need to think "in trim". Especially initially you need to look at yourself critically and slowly make adjustments.
jd950:
Apparently the problem is my skill and technique, and not an equipment issue, although I have to say that holding hoses over your head and rolling to put dump valves in the right spot to release air does not seem very sophisticated for devices that are otherwise basically inflatable bags costing several hundred dollars.
That lack of sophistication equates to simple reliability in my book. There are some much more gadget oriented BCs emerging but I don't see the point.
In your other post you mention having lots of water in your BC. That is not uncommon especially if you are riding the valves. As you evolve you will use them less and not keep them open needlessly. You will see that water volume drop with experience. I have observed some definite plateaus where my water volume dropped noticeably and continues at a reduced level.
BC Valves can be a bit like playing then piano. There is a feel to them. For certain critical moments they are made to vent a lot of air. For subtle control try feathering them quickly to release just a burp. Remember that a change in buoyancy will take several seconds to be reflected in your vertical motion.
Take your time and work through the details. It will be worthwhile.
Pete
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