could you be more specific? Some bc come weight-integrated so you wouldn't necessarily see the weights. But unless you're diving a hookah system (where there is a pump at the surface pumping the air to you) it's highly unlikely they're diving without any form of bc on.
posting the pictures or links to them might help people understand exactly what you're asking about.
In the early days of diving there was no such thing as a BC and today there are a lot of us who still do not wear one unless required to do so by a dive op. IF you are diving properly weighted, you are in effect diving with no BC even though you dont realize it, more on that later. It does require proper weighting, something that has sadly been forgotten with the invent of the BC. Remember, BC stands for buoyancy compensator and is supposed to compensate for shifts in buoyancy during a dive, it is not intended to hold up a bunch of excess weight....although many (most?) divers today use it that way. The buoyancy shift comes from 2 things, wetsuit compression and reduced negative buoyancy due to air being used from the tank. In warm water I rarely wear a compressible wetsuit and the shift in an 80 cf tank is only 4 lbs. Now consider that an average male has about 10 to 12 lbs of total buoyancy control with their lungs, a 4 lb shift easy to deal with. Plus, properly weighted that shift is reduced to 2 lbs, -2 at the beginning of the dive and +2 at the end and dead on neutral at mid pressure. Heavy wetsuits do make it more difficult, requiring a little more technique and there are times, like tech diving, where lots of equipment are necessary that make a BC necessary but at that point it really stops being a BC and becomes a lift bag for equipment that has a secondary use as a BC.
Back to why you should be in effect be diving without a BC even though you are wearing one. If you
properly weighted, which IMO is dead on neutral at ½ tank pressure, at the beginning of the dive you should have NO air in your BC, if you do, you are overweighed. No air means the BC is not adding any positive buoyancy. At this point you will be about 2 lbs negative, assuming an 80 cf tank, but this actually helps to you submerge and get some of that trapped air out of your gear. Even though you are slightly overweighed by 2 lbs, it is very easy do deal with using breath control alone. As you dive, you get closer to dead on neutral so there is no need to add air to the BC and finally at the end of the dive you are 2 lbs light, no need add air for that and again a very easy value to deal with using proper breath control. Plus it makes you slightly positive at the surface. Notice no where in that dive did you add air to the BC, so while you are wearing one, since you neither added or removed air in effect you did not have it on. Once you learn proper weighting and breath control you can shed the BC altogether. I do suggest you spend some time getting use to not using it before moving on, just for safetys sake. This is the technique I suggest to anyone wanting to learn to dive the way Jacque and Mike Nelson did. Try it and you will likely shed the BC whenever possible, the feeling of freedom is hard to describe.
