What are your thoughts about our constant buoyancy BCD ?

[NAM001]

I dont believe that is what is being said at all.

So my understanding of this thing is that it makes the bc, including the static buoyancy parts of a dive kit like regs, tank (but not the gas inside the tank), valves, etc neutrally buoyant at all times once it is set. It does nothing for the buoyancy shift of the tanks as air is used, nor does it do anything to compensate for buoyancy shifts due to wetsuit compression, that all still has to be done by the diver manually. Is that correct?

So it would be functional in the situation described above about swimming over a wreck (ie going from 60' to 30' then back down to 60'), but is otherwise a bc that maintains it's own buoyancy. And by "functional" I mean it would save the diver from 2-4 button pushes in the given example.

 

[Dr. Lecter]

I dont believe that is what is being said at all.

No, he's more or less correct. The system boils down to a non-rigid "rigid tube" - using an extremely stiff "bladder" inflated by gas of sufficient pressure that it will matter little whether it's at 30' or 300' as to how compressed or expanded the bladder is. Based on how much high pressure gas you add into the rigid bladder, you can set it to provide approximately X lbs of lift throughout a wide array of depths.

The reason it's being sold as a 'set it and forget it' is that (1) it's supposed to be activated after the initial decent, when most of the buoyancy swing in neoprene should have already occurred, and (2) the designers aren't really thinking about the fact that some divers burn through an enormous amount of gas over a dive, such that weight swings of as much as 15+lbs per tank/30+lbs per set of doubles can occur.

But for someone on a normal single tank dive with minimal neoprene, they should be able to drop to 30' or so and then dial in whatever positive buoyancy they need to achieve neutral and then do the rest with breath control; even if they drop another 100', the positive buoyancy from this device will remain more or less constant, so the only swing will be neoprene compression making them negative and gas usage making them positive.

This is probably way too much complexity and failure modes for the only divers it would suit, however - single tank tropical divers, maybe single tank dry suit…definitely not someone in 7mm neoprene - and would not work as well for tech because of the extra large gas volume swings (among other issues). Putting it on a mini-sub, though…great idea.

 

[NAM001]

Sorry Dr , After rereading the comment you are correct and I am in error. I got too hung up on those that think it was dynamically comping through the dive.

No, he's more or less correct. The system boils down to a non-rigid "rigid tube" - using an extremely stiff "bladder" inflated by gas of sufficient pressure that it will matter little whether it's at 30' or 300' as to how compressed or expanded the bladder is. Based on how much high pressure gas you add into the rigid bladder, you can set it to provide approximately X lbs of lift throughout a wide array of depths.

The reason it's being sold as a 'set it and forget it' is that (1) it's supposed to be activated after the initial decent, when most of the buoyancy swing in neoprene should have already occurred, and (2) the designers aren't really thinking about the fact that some divers burn through an enormous amount of gas over a dive, such that weight swings of as much as 15+lbs per tank/30+lbs per set of doubles can occur.

But for someone on a normal single tank dive with minimal neoprene, they should be able to drop to 30' or so and then dial in whatever positive buoyancy they need to achieve neutral and then do the rest with breath control; even if they drop another 100', the positive buoyancy from this device will remain more or less constant, so the only swing will be neoprene compression making them negative and gas usage making them positive.

This is probably way too much complexity and failure modes for the only divers it would suit, however - single tank tropical divers, maybe single tank dry suit…definitely not someone in 7mm neoprene - and would not work as well for tech because of the extra large gas volume swings (among other issues). Putting it on a mini-sub, though…great idea.

 

[DaleC]

I just tried out a constant buoyancy rig this weekend. I may be changing my mind because it worked great!

(2:08) shows the technical details

[video=youtube;N4EraGi8pqs]https://www.youtube.com/watch?v=N4EraGi8pqs[/video]

 

[Couv]

While I applaud the ingenuity, I think you've forgotten that a buoyancy control device is meant to compensate for suit compression and loss of ballast as gas is used. As this device compensates for neither, it is of little use.

Equipment that is very negative can be made more buoyant by adding a rigid container such as a capped off piece of ABS or PVC pipe which would provide constant buoyancy.