perpet1:I assure you I am not wrong although with my extremly limited experience and brain power it may seem that way or it just may be my improper dive technique.
Now you yourself state that this is a skill that takes practice. The practice you speak so hightly of, is it limited to finding that perfect trim or are there techniques you must use? This is because it does not just happen once you have properly adjusted your trim. This is a skill that requires overt action on the part of the diver. I stated that yes, if you employ the proper technique then you can overcome the shift in your CB but with no action what you are saying is impossible.
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Your correct there's more to it than just balance (where the weight is placed and some of us have explained this about 1000 times. However with the right weight placement the shift in CG will be small and and barely noticable.
Your description is very true whan a diver has a thick wet suit, AL tank, traditional bc and all their weight on the waist. As this diver descend the suit will compress and lose buoyancy. Air will be added to the bc. The buoyancy is then shifted from all over to the upper body which is above the weights and the diver goes vertical.
We're trying to sugest that you shouldn't go diving dressed like this because it's a pain. Put some weight up by the bc. That weight might be a plate or a steel tank or trim weights or whatever. When you're done you'll have little weight on your hips. It also really halps to get rid of the thick wet suit and use a dry suit beause of the constant volume (buoyancy) of the suit. Using the dry suit greatly reduces or eliminates CG changes with depth.
Now the CG changes during the dive are small and only exist because we just can't get things perfect.
Now learn how to use your boddy position and you're set. You can hover horizontal inches off the bottom and ascend or descend in that position at will