What are the risks of many bounces between the surface and 15-20' / 5-7m of water?

[@dam]

A few years ago I was on a Scuba Pro boat on the great barrier reef. To extend our pre-lunch and pre-dinner dives, I'd snorkel around until I found something interesting in 10-20'/3-7m of water, go check it out for a while, gradually work my way to the surface (sometimes unintentionally as the direction I'd be going would be getting shallower), snorkel some more, check it out, etc. One of the Dive Masters said this kind of "bounce diving" is dangerous.

I'm going to Cozumel next month, and the hotel offers shore diving. I hear there's not much to see, so I was interested in a similar strategy; snorkel until I find something interesting, check it out breathing out of the tank, snorkel some more, etc.

So, is this dangerous at all? It doesn't seem like it should be since you're only absorbing nitrogen for a short time and then you're breathing unpressurized air for a while, quickly reducing your nitrogen saturation.

 

[lowviz]

...//.....Scuba Pro ....//.......bounce diving....//.....

-subscribed...

 

[FuzzyNutz]

The stretch of coast at least around Hotel Cozumel is pretty shallow, about 15-20' max. I'd say kit-up and go for it! Your whole dive will be at or above safety stop depth. And while the shore diving isn't amazing, I always found something cool on every dive. And besides, I'm underwater blowing bubbles for an hour or more, so I'm happy .

I've only shore dived around that one area, so I can't comment on what it's like elsewhere on the island - but I'm sure others will chime in.

 

[DivemasterDennis]

Also, fairly shallow free diving is not the same as diving on scuba, where even at shallow depths you must pay attention to ascent rate and, over time, nitrogen absorption. Any instructor who has had a class of five or more students doing controlled emergency ascents one after another will tell you that the risk is minimal, but present. For that reason, in large classes we distribute ascent skills among different dives. If you have scuba gear on, the better practice is to stay at depth until you are done with dive, rather than bounce up and down. However, if you are snorkeling and frees diving, I would think nothing of it and enjoy you plan!
DivemasterDennis

 

[@dam]

I'm not going to emergency-ascend every time I come up...just gradually float up. If I don't see anything else nearby on the way up, I'll snorkel around for a while until I find another interesting area.

 

[Dirty-Dog]

I don't think you're going to find many people who will claim this is particularly dangerous. You're diving at safety stop depth. While there are some slow tissues that might be taking on nitrogen at this level, it's not much.

According to Suunto Dive Manager (and I think we all know how conservative Suunto is...) after spending 500 minutes (which is the longest dive SDM allows) at 20 feet, you will have managed to get one slow tissue compartment to 88%. The other slow tissues are 75% or less, and the fast ones have no significant nitrogen. Yes, your snorkel/dive habit will result in starting your next dive with a tiny bit more nitrogen. If you're diving a computer, it will compensate accordingly, but I really doubt you'd see a significant difference in NDL on your next dive.

Given the conservatism built in to even the most liberal model, I do not think there's any major cause for worry here.

Of course, as always, the only way to be SURE you don't get bent is to not dive.

 

[GrumpyOldGuy]

I would think the only real danger is forgetting when you are on scuba vs.. snorkel and holding your breath on ascent.
While it might technically be described as bounce diving, its really stretching the description past the limits of reason.

 

[j yaeger]

just call it "power snorkeling"!
i'm in for the no worries!-no holding breath on ascents is a problem,however
have fun
yaeg

 

[Diversauras]

I think one of the hyperbaric doctors needs to be asked, the way I see it once you have been on scuba and have gas in your tissues you risk being bent because of how rapidly you move vertically in the water column.

 

[TSandM]

You're not going to get symptomatic DCS from diving to 20 feet, at least not according to any tables or computers. I will tell you a personal experience story, though. I did a night training dive with my buddy when we were working on bag shoots and ascents. Our max depth for the night was about 25 feet, but we did 7 or 8 ascents, not all of which were well-controlled. On the way home from that dive, I felt HORRIBLE. I was so tired, I could barely keep my eyes open to drive. I felt like I did during residency, when I'd do 48 hours or more without any sleep. Talking to my buddy the following day, it turned out he wasn't as bad as I was, but he felt crummy that night, too.

Now, we had some rapid ascents involved, but it has still made me VERY careful about multiple ascent days. (My husband, who is a PADI instructor, says he feels awful the day the OW divers do their CESAs, too, where he has to do anywhere from 2 to 8 or 10 of them, depending on how many students there are and whether they get it right the first time.)