What are your thoughts about our constant buoyancy BCD ?

[sunnyboy]

From what I can understand of the operation it is essentially a fixed volume container that air is added to. Adding air to a fixed volume container will not change buoyancy.
You can do the same by by using a fixed volume container of a specific volume. If I am 10 pounds overweighted then a fixed volume container with 10 pounds of buoyancy with get me neutral. However it won't compensate for wet suit compression at any depth. Hope you didn't spend much money on this.

Yes it will. A scuba tank (say an AL80) with 3000 psi is heaver than the same tank with 500 psi. Basic science. Air has weight. More air into a fixed volume increases the pressure, but it's still more air in the vessel ,and so weighs more.

 

[eelnoraa]

The device uses a bladder that does not inflate at all until about 3 atm pressure. It's pressure volume characteristic is such that it changes only about 3 lb in buoyancy from 96 feet to the surface. Thus, it is essentially rigid with constant volume. In answer to your other question, the device will not compensate for changes in buoyancy due to wet suit compression. In actual diving with a 3 mm full suit we found that you can go from 40' to the surface without having to let out air.

So you are saying that the bladder will remain in constant volumn from surface to 96ft without need to inflate air? This bladder better be very rigid. As pressure increase from 1ATM to 4ATM from surface to 96ft. If the bladder is so rigid, how do you plan to change it volumn by injecting air into it? Since a 3 ATM change in pressure can't changes it volumn.

Also, keep in mind, buoyancy for the diver means a lot more than buoyancy for the BC. Everything together needs to neutral, not just the BC. If this BC can't compensate for wetsuit buoyance change, what is the use? Only for people tropical divers?

---------- Post added August 15th, 2014 at 12:44 PM ----------

.... The buoyancy change with this device during a recreational dive is small enough that the diver can control buoyancy by shifting the tidal volume. Air does not have to be put into the bladder or expelled from the bladder after an initial adjustment.

This is not accurate. Assuming no exposure suit related buoyancy change, the amount of total buoyancy change is at least the gas in a tank. HP100 is 8lb. Why I think tidal volumn can compensate this (for a short time), it sure can't be comfortably at all. Now put on a 7mm wetsuit. You can easily have 20lb shift between surface and 100ft. How can I maintain neutral with your ABCD?

 

[boulderjohn]

I would like to address the issues described on the safety portion of the web site:

Problems with buoyancy during a dive are a common cause of dive injury and death. In 2008, DAN reported that 1.2% of all dives were complicated by problems with buoyancy and/or rapid ascent. These problems were of sufficient magnitude to justify an incident report to DAN. In 2006, there were 32 reported fatalities from breath holding during a rapid ascent.

These problems are caused by a fundamental property of standard BCD's, that is that they expand in volume when they rise in the water column, which makes them more buoyant, thus resulting in a faster rise and so on and so on, leading to what is called a "runaway ascent."

Embolisms occurring because of breath holding during runaway ascents is indeed a major safety problem, and a joint DAN and PADI study identified it is by far the leading cause of non-medical scuba fatalities. The problems were not, however, caused by the change in buoyancy associated with the expanding volume leading to an unplanned runaway ascent. These divers were intentionally trying to get to the surface as fast as they possibly could because they were out of air. They were holding their breath because they either forgot their CESA training or thought they could not exhale all the way to the surface. If their BCD were not expanding and pulling them to the surface, that would make the problem even worse.

Consider, too, the buoyant emergency ascent, when the diver drops weights and counts on expanding air to get him to the surface quickly in that emergency.

I have studied all of the DAN fatality reports ever written in the past. I even studied (and have a copy of) the studies that preceded the DAN studies, going back to 1970. I don't believe there have been many dive fatalities in which a diver lost control of their BCD and went shooting to the surface, so I don't see that there is a big safety advantage to the BCD. In fact, since it makes it harder to perform the emergency ascents in the cases that really do happen and really are problematic, it could be argued that it is a safety liability.

 

[eelnoraa]

Yes it will. A scuba tank (say an AL80) with 3000 psi is heaver than the same tank with 500 psi. Basic science. Air has weight. More air into a fixed volume increases the pressure, but it's still more air in the vessel ,and so weighs more.

Oh, now I see the point. So basically a constant volumn rigid container. Buoyancy is changed by changing weight by adding or release air inside. My next question is at 3ATM (45psi), what is the swing of the weight? Sure it will depends on the volumn of the container. Take an example of diver diving a AL80, 6lb swing from 3000psi to empty. The container will needs to be 60 times the size of AL80 to swing the same weight at 45psi ????

 

[g1138]

delete

 

[KeithG]

how much cheaper will this be than a normal BCD?

 

[Doppler]

We have developed a BCD that does not change buoyancy with depth. This prevents runaway ascents and descents. With it you do not have to inflate and deflate the BCD during a dive. It allows the diver to precisely compensate for overweighting and the compensation is fixed regardless of depth. Details are at Home. We have not yet commercialized this technology and would like to get feedback from divers before doing so. Do you think this would be a useful feature ? Are there disadvantages we may not have thought of ?

Like the vast majority of divers who have responded to your question: What are your thoughts about our constant buoyancy BCD? I have to tell you they are not positive... in fact my thoughts are extremely negative especially if you intend to market this to sport divers.

I can see a very limited application window in the milpro market, but not attached to a diver.

Anyhow, good luck (based on the consumer survey you've taken here, you will need it).

If you are attending DEMA or any milpro shows, please PM me.

 

[Dr. Lecter]

Yeah, this idea might be awesome for something like a SDV. Little to no gas venting necessary, stable bouyancy, etc. Just lousy for divers themselves.

 

[captain]

Yes it will. A scuba tank (say an AL80) with 3000 psi is heaver than the same tank with 500 psi. Basic science. Air has weight. More air into a fixed volume increases the pressure, but it's still more air in the vessel ,and so weighs more.

But all you are doing is transferring air from one tank to the other, you are not gaining or losing weight.

---------- Post added August 15th, 2014 at 08:40 PM ----------

The only way to make an adjustable volume ridge buoyancy device is a movable piston in a cylinder sealed at one end and open at the other end. A mechanically or hydraulically driven piston that can move back and forth the length of the cylinder varies the volume of the cylinder. In order to increase buoyancy the piston is driven away from the sealed end of the cylinder thereby increasing volume in the cylinder, to decrease volume the piston is driven into the cylinder towards the closed end decreasing volume.

 

[boulderjohn]

I wanted to address also the statement some have made about it being an equipment solution to a skill problem. I hate that phrase in general, because it is too often a glib dismissal of what can be a good idea. If you think about it, the existence of a BCD at all is an equipment solution to a skill problem, since we could do a dive with the tank under our arms. I wish that phrase would go away so that we can look at each innovation to see if the benefits it brings to a dive outweigh its negative characteristics.

Let's assume that your system does precisely what it says it does--maintains constant buoyancy during a dive. How much benefit does that provide? As some have pointed out, you don't have to have too many dives under your belt before you can handle the buoyancy changes in a BCD without a whole lot of effort. It isn't all that hard, frankly. So the benefit over existing systems is not that great. As I pointed out in a previous post, the benefit you list for safety is not really there, and it is actually a drawback.

So what are the other drawbacks? For one thing, I have to figure this will cost more than a conventional system. You also have the problem that sometimes you want the buoyancy to change, so you will need to add a way for the diver to make the changes when they are desired. You have the concern about failure. In the current simple system, any failure can usually be easily solved. Will failures be easily solvable in this system? Could a simple failure cause the runaway ascent it is supposed to prevent?

So, if you ask me if I want to pay extra money for a system that does for me what I can easily do myself, adds some other skills I don't need to worry about now, interferes with my ability to perform certain functions, interferes with my ability to do an emergency ascent, and adds unnecessary failure points that I don't really need, then I would say that right now the answer is no.