Thoughts on Bounce Dives

[Rhone Man]

The most famous ScubaBoard example of a deep bounce dive on air took place several years ago in Cozumel. An experienced dive shop owner, one of her divemasters, and a good friend planned a bounce dive to 300 feet on air.

This is a not entirely uncommon story in Cayman. Every few years it seems some young and dumb instructor will go to the wall and try to bounce to 300 feet. Some come back, and some don't.

I'll tell a story not because it reflects well on anyone, but at least it has a happy ending.

I started diving at aged 9 (with my Dad) and got certified at 12. Living in the Caribbean I dived frequently, and by the time I was 15 I was by most measures a fairly experienced diver. Although like most 15 year olds, I was dumb as a bag of hammers in the ways of the world. Anyhow, when I did my AOW (which you could only do once you were 15 in those days) my instructor decides that I am going to experience narcosis I am going to experience it *properly*, and so we go to 180 feet (on single tanks, obviously). Being 15 of course I thought this was the greatest thing ever, and I was puffed up like a peacock. My recollections of that dive are still pretty vivid. First thing I noticed was that trying to breathe through my Sherwood Brut was like sucking glue from about 150 feet. When we got to 180 feet I discovered that bizarrely someone had written Egyptian hieroglyphs all over the sea floor. Well naturally I stopped to try read them. Then, with a bit of bad luck, my inflator got stuck to open when I was adjusting my bouyancy. I say bad luck, but that kind of panicked me, and snapped me into a bit more sense. I disconnected my inflator, swam to my instructor and kept about eight feet above him (where the narc was noticeably less, although still chronic tunnel vision). After 5 minutes we ascended as planned. We did a 5 minute deco stop as per the US Navy tables and then got out of the water. On the boat it occurred to me that I didn't check my pressure gauge once during the dive.

As an adult I have been back to 180 feet a few times on air, but now I do it with a twinset and deco gas. As an adult (and as a result of many drunken years in college) I am much better equipped to deal with narcosis, but I know enough to know that I still am pretty shaky below about 165 feet.

 

[RJP]

A fast descent to about 200 on air with controlled ascent using recreational limits is totally dooable on a normal size tank as a first dive.

This is what's known in logic as a faulty premise.

A dive to 200ft is, by definition, outside recreational limits.

Accordingly... it is not "totally dooable" at all.

 

[boulderjohn]

This is a not entirely uncommon story in Cayman. Every few years it seems some young and dumb instructor will go to the wall and try to bounce to 300 feet. Some come back, and some don't.

I'm working on a name for the psychological factor I think is in play here. Perhaps it already exists and someone can provide it. For now I will call it "Best I've Seen" Syndrome.

It happens when people with limited experience determine, possibly accurately, that either they or someone they know is the best they have ever seen at some activity. They then conclude that the person in question must therefore be among the best there is. I saw that when I sponsored a high school chess club, and a new player joined, complete with his entourage declaring him to be one of the chess world's greatest players. He was actually a rank beginner who could be destroyed by the weakest player in the club. A recent scuba example is Dr. Guy Garman, who perished after an attempt at a record deep dive, after which the web site of the local divers promoting the attempt said that "he knew more about technical diving than anyone on the planet." That statement was patently absurd--he was a relative beginner. He probably did, however, know more about technical diving than any of his friends on that Caribbean Island, which led both him and those friends to assume he had to know more than the rest of the world as well.

Scuba DMs and instructors who do all their diving on tropical resorts may accurately determine they are among the best divers in those waters, and they then go on to assume that they are also among the best in the world. They know that other divers, divers who must be at about their skill level, go to 200-300 feet with some frequency. Since they have never been anywhere close to the training those divers endure before being certified to do that, they cannot even imagine it. They consequently completely underestimate the dangers and overestimate their ability to deal with them.

 

[Akimbo]

It's generally accepted that at about 217 feet air becomes toxic...

Generally accepted by who and where did 217' come from?

 

[dumpsterDiver]

218 is 1.6 ATM on air

 

[RJP]

218 is 1.6 ATM on air

So at 1.599... 217' is totally dooable!

 

[Akimbo]

218 is 1.6 ATM on air

Duh, I'm still using 2.0 since it has worked without an OxTox incident since I started diving. That's why the Navy limit on air was 285' when I was in school.

 

[Colo Hippie]

I can only think of one instance that I would CONSIDER a bounce to 200ft on one tank of air. That would be to attempt to rescue my buddy and that would have to be quickly assessed based on multiple things. It would not do anyone any good to be recovering 2 body's instead of one.

 

[Akimbo]

... It would not do anyone any good to be recovering 2 body's instead of one.

Or lose two bodies instead of one.

 

[Patoux01]

Generally accepted by who and where did 217' come from?

pO2 of 1.6, I guess, if my silly-to-decent units conversion is correct. edit: oops. Someone forgot to refresh the page on opening the browser.

I've personally done 55m without any issue, got out with 130b per tank (2 s80), the guide did it on a single tank with a slung s40 that he didn't use. We spent about 4 minutes below 50m, so I'd consider it a bounce dive, although you could make them much more bouncy than that.

As long as there's some sort of redundancy, that kind of diving is doable, but honestly, I don't think it's a very useful dive if there's nothing to see down there.