I've only dived with a BC so I find this topic pretty curious. How do you achieve neutral buoyancy without a BC especially the deeper you go? Can you hover without a BC?
First off, remember BC stands for Buoyancy COMPENSATOR, not for "I am carrying way too much weight and I have no idea what proper weighting is compensator", so exactly what are you compensating for?? There are only 2 things, exposure suit compression and the gas used from your tank. Both of these are known values and totally predictable. You also have to understand that a normal male has around 10 lbs (5ish kg) of total swing in their body buoyancy from empty to full lungs. If you PROPERLY weight so that you are neutral with 1/2 a breath that gives you a buoyancy swing of +/- 5 lbs around the neutral point. With this in mind, you just have to do the math. Assume for a minute that you dive with no wetsuit (or something like polartech that has no shift in buoyancy- which is what I use a lot). That removes one varibles, leaving only gas use. An 80 cf tank swings about 4 lbs (2kg) from full to a reasonable end pressure, an amount that is within the realm of lung volume but an amount that is a little difficult to deal with (I can do it but it's not fun). However if you weight for a half tank (1500 psi) instead of a full or empty one the total math changes some. You now have only 2 lbs of swing above and below the neutral point of your gear, a fairly easy amount to deal with using lung volume alone. But there is more to the story. If you have spent any time diving you have no doubt noticed that nothing happens fast when buoyancy is concerned and small buoyancy changes are additive, several deep inhales will cause you to rise even though you have not actually changed from being neutral with half a breath. In no BC diving you take advantage of these things. An occasional deep breath followed by several normal ones is plenty to deal with a couple of pounds off neutral- like when I have a full tank (the extra 2 lbs above neutral I weight for), same for an empty tank, a deep exhale or 2 followed by normal breathing handles an extra few pounds of positive buoyany. Once you get the hang of it, this becomes natural and you don't really think about it, much the same way you do minor steering corrections in a car while you drive- you do them but don't really think about them once you have spent some time on the road.
Wetsuit adds in a bit more but within reason, they can be delt with as well and you have to understand there are differences in wet suit material, some is not suited for no BC diving due to it's large buoyancy swing. With a wetsuit of reasonable thickness and material, the swing is in the 5 lb range, more than is easily to handled by lung volume alone but with proper weigthing and with a few more simple diving techniques it is still fairly easy to do.
I will add this is for reasonable tank sizes and wetsuits. Diving double steel 120s and a 7mm wetsuit is just not practical but for warm water, single tank diving, it is my prefered way to dive.
