I really don't mean to be an ass, but I think there's quite a bit more dives done per year nowadays than in 1970. Even then, you can see that the average value on the first 15 years or so is higher than on the last 15 years, which is also much flatter (for some reason).
However, didn't the first BCD pop up in 1970? Can't tell when they became mainstream though...
Not saying it's linked to BCDs, as I believe it has more to do with the training and reliability of gear.
As for reversing your Hammerhead, I'm not sure how well that'd work, I think your fins/body will be working against it and you might end up not moving at all.
Controlling buoyancy has always been an issue ever since even the first wetsuits came out. Wetsuits crush down at depth and get heavy at depth, always have and always will no matter how trick the material was or is. Even Rubatex crushes down, maybe not as bad but it does, I know I have several of them.
Before some sort of marketable BC came along divers were always trying to figure out how to fix the heaviness problem. There were some pretty ingenious devices invented back then that never made it out of the garage like ballast tanks like a submarine would have. Then horse collars were modified and later made to use at depth to offset heaviness.
Most divers just compromised and would weight themselves light enough that they would start to get really light at a out 20' at the end of the dive. Safety stops weren't really considered for no deco profiles and divers would just float up as slow as the expansion of the suit would let them. Depths were limited to avoid crawling around on the bottom, even though there was a lot of that. Diving was hard you had to keep moving and streamlining was actually a consideration in that regard. Just look at all the covers and shells invented during that time that Cousteau used.
At some point the soft bladder dominated as the go to design for ballast and from there the first recognized poodle jacket came on the market. Some say it was the SP Stab jacket, that orange thing that was a sewn up vest with an air cell and it had a plastic pack sewn into the back of it which held the tank but the strap slots in the pack portion were not used. Instead the vest fabric was supposed to support the tank but it worked pretty poorly. For some reason this was overlooked and that style of product took off. They all copied each other and went to the wide panels of fabric to hold the tank to the diver but it never was very stable. At the same time as all this was going on scuba was being marketed to a whole new group of people, families and just regular people. It was no longer just for alpha type young males and a few women that could keep up. So this new style of gear was perfect for marketing and also relieved a lot of the "hard work" that was associated with scuba just a few years back. And it made it easier for instructors to teach since with push button ballast if a diver was a tad too heavy all they had to do was hit the elevator button and they were all set. Unfortunately this new device also IMO got badly abused throughout the years to what we have today, and yes, it bas been documented that people have indeed died because of abusing the BC in the form of gross overweighting. Not only have these new BC's gotten so complicated and over designed, they are also really expensive and they are very cumbersome. I think they are way too bulky, I think integrated weights are a horrible idea, and I think they are very counter productive to efficient scuba diving. Streamlining and all considerations for a smooth slipstream went out the window many years ago. All the obsessions with efficiency died out with the old crew many years ago. The newer divers who stepped in to the sport recently have no idea what scuba configurations used to be.
At least the BP/W is a step in the right direction, but I also think the flat or slightly bent doubles style plate is not completely optimal for single tank diving. IMO the tank needs to be dropped down into the grove in between the shoulder blades and the tank set a little lower. The modern doubles plates are too square and wide on top and don't allow the tank to snuggle in close enough, the plate rests across the high points of the shoulder blades. Those older plastic packs that narrowed down were actually a perfect design but unfortunately they went out in the garage sale along with all the rest of the old knowledge. If only someone invented a simple wing back then to go into one of those packs or a metal version I don't think we would be dealing with the abortion known as the modern poodle jacket today.
What would be really cool would be a ballast system that was hidden or somehow integrated into the torso area of wetsuit. I think for optimal drag resistance even a small wing produces some drag. I found that the channel in between the tank and the bare back of the no BC diver is an important area for water to channel through. This would be the area that the wing would normally occupy.
I know for most divers this is really splitting hairs, but for drag obsessed divers this is a problem.
Maybe at some point in the future hydrodynamics and efficiency will make a comeback, who knows?
