Self-ditchable weights

[alewar]

In the book "Caverns Measureless to Man", Sheck Exley mentions that when they were trying to break the deep diving record on air, they used some sort of weights that released themselves as soon as the diver looses consciousness. The strategy was to descend more or less until going unconscious, then automatically ascend thanks to this system and be caught by safety divers above you, gaining consciousness again at a shallower depth. Unfortunately he never elaborates on this weight system. Does someone know more about that?

 

[nimoh]

In the book "Caverns Measureless to Man", Sheck Exley mentions that when they were trying to break the deep diving record on air, they used some sort of weights that released themselves as soon as the diver looses consciousness. The strategy was to descend more or less until going unconscious, then automatically ascend thanks to this system and be caught by safety divers above you, gaining consciousness again at a shallower depth. Unfortunately he never elaborates on this weight system. Does someone know more about that?

holding a weight in your hand will release automatically when you go unconscious

 

[alewar]

That was my first thought too, but then why just don't write "they were holding the weights in their hands" instead of "special weight system..."? Besides, at some point he tells that a couple of his friends died after disabling the system for some reason.

 

[Akimbo]

holding a weight in your hand will release automatically when you go unconscious

I guess it depends on how you define unconscious. The instructors in a Performance Freediving course I took told us that releasing and holding your weightbelt wasn’t all that effective. Apparently there is some sort of reflex that maintains a diver’s grip for a significant period of time after they become unconscious, but before hypoxia becomes severe enough of make extremities go limp. I can only guess the same phenomenon could occur to Scuba divers who lose consciousness for other reasons.

It gets really complicated because Scuba and surface-supplied divers don’t necessarily stop breathing when they lose consciousness. As a result, monitoring breathing is not a reliable indicator. It is hard to imagine a reliable method that doesn’t require a lot of delicate electronic sensors and a computer. I can see how a failure of a drop-weight or auto-inflation system would be as or more dangerous than the problem it is intended to solve.

 

[Rich Keller]

If they did this like free dive record attempts the weights are attached to a cable from the surface to the bottom in such a way as they will be able to free fall along the cable without getting hung up. The diver may also be tethered to the cable so that he does not drift too far from the cable and the coroners people waiting to recover the body when it comes up.

 

[John C. Ratliff]

The only thing I can think of is that the system would be attitude-dependent. In other words, if the person was weighted balanced so that he/she would go upright (head up) when relaxed, and would require energy to remain head-down, then if the diver went unconscious, that diver's body would rotate head-up, and the weights would be dumped. I have a backpack that has cylinder weights which would slip out in a vertical position except for a key that is in the weight column. I did the same thing with a set of double tanks on the original "floater" USD AL 2475 cylinders, which were 6 pounds buoyant when empty in fresh water (12 pounds for the doubles). I put a PVC tube between the cylinders, and inserted 6 two-pound weights into the tube, held in by a heavy-duty wire key. Without that key, the weights would fall free in a vertical position. The Dacor CVS (Constant Volume System) works in a similar manner. I have no idea whether this type of system is what Sheck was talking about, only that it exists and could work in this manner.

SeaRat

 

[Akimbo]

The only thing I can think of is that the system would be attitude-dependent…

Do you think that is really practical? If I understand correctly, you propose a weight tube that requires removing a key/pin/lock shortly after beginning your descent and re-pinned just before beginning your ascent? Sounds like a bigger hazard than the base problem. I don't think I could be that disciplined.

 

[Sitkadiver]

This looks like what Exley may have been using. There's a similar setup, where the release is attached to a swim float that the dive holds between the thighs until they're ready to ascend, but I haven't seen one in many years. Essentially the kidney bean shaped float also allows the diver to get into a head down position very quickly.

[video=youtube;ZgPalnCyhbo]http://www.youtube.com/watch?v=ZgPalnCyhbo[/video]

 

[John C. Ratliff]

Do you think that is really practical? If I understand correctly, you propose a weight tube that requires removing a key/pin/lock shortly after beginning your descent and re-pinned just before beginning your ascent? Sounds like a bigger hazard than the base problem. I don't think I could be that disciplined.

Nope, I was simply stating that something like that was possible, as opposed to holding a weight belt in one's hand. I had thought that at the end of the dive, the diver would simply go vertical and dump the weights, rather than re-pin.

SeaRat