tridacna:
No no. No as stupid as you think. I'm afraid that your solution regarding the BC is the "inelegant" solution.
In theory, his thoughts are actually quite clever. Simple physics.
Remember that there is a difference in weight between starting and ending your dive. Specifically, the weight of the air consumed in your cylinder. For the sake of this argument, assume that you begin your dive neutrally bouyant. If you wish to remain so throughout the dive, you have to gain the exact amount of weight that your tank is losing. Otherwise, you get lighter reflected by most beginners who struggle to make their 20ft safety stop.
Now if you take a solid walled semi-sealed cylinder with you that is 5lbs bouyant. Add 5lbs of lead inside. Neutrally bouyant right? As you dive, you leak enough water into the cylinder to match the air being lost by the cylinder - you will remain neutrally bouyant. No question. If you could build a device that somehow matched gain to loss, it would be a neat device to have. Your overall bouyancy would only change based on the compressibility of your wetsuit.
His experiment was exactly that. It sorta worked. Difficult to match exact gains vs losses. Remember that only a crazy PhD inventor (he is exactly that) would even try this! My argument was that he should have done this in a pool. Not leaping from a boat into the ocean wth a jug of 5lb weights dangling from his waist!
Let's talk about some simple physics, shall we?
Water in water is neutrally buoyant, right? So in actuality he’s adjusting his buoyancy by venting a little air, not by adding water.
So what, right? Letting water in is the same as letting air out.
The difference is that all he’s really doing is venting air from the bottle instead of his BC.
My first though was that the only advantage to his bottle is that he’s bringing a small amount of non-breathing air to vent, instead of venting a small amount of his breathing air. But the amount of air being vented is really too small to worry with.
And, if he didn't take 5# off of his weight belt when he brought the container, he's carrying 5# extra, which means he added extra breathing air to his BC to get neutral at the beginning of the dive, which negates the small advantage I mentioned.
Or am I missing something?
Of course, this was just a test set-up, with the goal of an automatic BC. I remember hearing of an auto-adjusting BC that someone tried to bring to market, but it was unreliable and complicated. Sorry, I don't remember the details, but I'll bet the idea is already patented.
I'll stick with venting air from my BC.
Added later: The BC I was thinking of might have been made by Watergill. I know that they made a regulator that had a unique 'safety' device. It 'sensed' the divers breathing, and if it thought the diver wasn't breathing, it slowly added air to the BC to bring the corpse to the surface.
