It can be done but how elegant you are depends on staying within the bounds of physics.
Start with the reason for a BC, it's to compensate for changes in buoyancy... clever name, huh? And what are those changes? First you will deplete your 80 CF air cylinder's weight by about 5 pounds on a dive. Then any neoprene will be subject to compression and buoyancy loss. Lastly any other junk that can trap air will become heavier during the dive as air escapes. These are the drivers behind a BC.
Now consider that most divers can vary their lung volume by breathing shallow or deep enough to effect a 5-6 pound buoyancy change. That number is pretty close to the change in cylinder weight over the dive. This means that neoprene needs to be minimal and stuff like BC padding and fuzzy dice want to stay on the beach.
With correct weighting and that other stuff limited you can begin your dive keeping your lungs a little full on average. This just means messing with your breathing patterns so you breathe deep and full then refill right away after exhaling. Your lungs must expand and contract but you want to have the AVERAGE volume be bigger. As you approach the middle of the dive you will be truly neutral and with a little propulsion or volume change your depth will drift wherever you want. it's an amazingly liberating feeling. Later in the dive as your cylinder gets light you will breath lightly for a lower AVERAGE lung volume and remain neutral this way.
The more neoprene you add the less elegant This becomes. First you need to start to "swim the dive". You will sometimes see in movies that divers would swim at a good clip to get some "lift" to stay off the bottom. If you stop you may be touching off with a fingertip.
In any case you need to weight your self for that perfect middle of the dive effect. As neoprene and depth increases this gets more complex. Finally you need to make sure you can make a safe ascent with a near empty cylinder. Sometimes an anchor line or stone enter into the equation. This is not the same diving we espouse to where you can hang in a prone position anywhere anytime but in that limited bandwidth you can come darned close..
Most steel cylinders are too negative for this to work. When I did it with an HP 80 I needed a buoyancy belt made with foam blocks in a pocketed soft weight belt. With an AL80 it's easier to just Add a few pounds to find that tipping point. The venerable LP72 is usually a very good choice.
This is not the sort of dive that will be appropriate often for most diver's needs but it is a fantastic way to experience buoyancy control in it's purest form. Keep in mind that unless you add some sort of vintage horse collar you will be without surface flotation so acess your skills and support system accordingly.
Here is an old thread where I asked the same sort of question years ago.
Pete
