Thoughts on Bounce Dives

[boulderjohn]

I don't think it's a very useful dive if there's nothing to see down there.

If there is something to see down there, then you should have what it takes to stick around and see it, not bounce right back up to the surface. If you are doing a bounce dive, that pretty much means you are doing it for the same of doing it, not for sight seeing.

 

[Patoux01]

If there is something to see down there, then you should have what it takes to stick around and see it, not bounce right back up to the surface. If you are doing a bounce dive, that pretty much means you are doing it for the same of doing it, not for sight seeing.

I guess it depends what you want to see.
On the Coolidge (Vanuatu), the swimming pool lies at 55m. You can drop down there, have fun for a few minutes swimming in an underwater pool, and then you end your dive. Sure it's not the dive of your life, but it's fun, so why not?

 

[Kevrumbo]

It's generally accepted that at about 217 feet air becomes toxic. Go deeper on air and do so at your terminal peril. 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 (i.e. no residual Nitrogen). The risk in this dive is the narcosis that you WILL experience. Tunnel vision. Potentially magical thinking. Lack of focus. Now, on their own these things aren't that big of a deal and can be fun, but when you are dropping like a rock and supposed to be paying ABSOLUTE STRICK UNWAVERING attention to your depth gauge, narcosis can be deadly. In sum, don't bounce unless you go with an experienced diver who understands the physiology and has some emergency diving experience.

Without reference to personal beliefs vis a vis whether bounces are dumb... Thoughts or concerns of a technical nature would be great.

A 60m/200' bounce dive on a single AL80/11litre per bar cylinder, you will need well over half a tank (130bar out of a full tank of 200bar) just to get both you & a buddy to the surface in an emergency air sharing contingency --and that's assuming an "under control" max recommended ascent rate of 18m/min, a "non-stressed & nominal" breathing rate of 2 bar/min per ATA for both divers, and also most likely performing a deco/"safety" stop of several minutes with whatever air remains.

So after reserving 130bar for the contingency above, that leaves you 70bar of gas usable for the dive. Assume you use 20bar of this usable gas on the fast descent to level off at 60m (initial exertion entering the water, inflating the BCD for neutral buoyancy at depth etc) --so you actually have 50bar usable at 60m.

At 60m (7ATA), your gas consumption rate will increase sevenfold from 2bar/min to 14bar/minute, so with only 50bar usable from above, you've got a maximum of three minutes at this depth. In short conclusion, this bounce dive is "doable" on a single AL80. . .

BUT YOU ABSOLUTELY HAVE NO ERROR MARGIN WITHIN THE ABOVE NARROW PARAMETERS, FOR EITHER YOURSELF OR YOUR DIVE BUDDY.

 

[dumpsterDiver]

If there is something to see down there, then you should have what it takes to stick around and see it, not bounce right back up to the surface. If you are doing a bounce dive, that pretty much means you are doing it for the same of doing it, not for sight seeing.

I don't agree with this. Our diving is supposed to be fun. Your definition of fun maybe hanging in the water column looking into the snot filled mask of your buddy for an hour. If someone has fun bouncing down and back and avoids 50 minutes of hang time,- who am I to judge... Same crap we read here almost daily. It is fine to plan to dive a deep wreck, but by definition ition. Setting a personal depth record is irresponsible. I,m not buying anyone else's definition of what constitutes my fun.

 

[bryanmc57]

I know two people, one deceased and one in a wheelchair for life who might disagree with you.

 

[Rhone Man]

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

I know that most people on this thread already know this, but just for the record, this is not actually true. At 217 feet you are breathing oxygen at a partial pressure of greater than 1.6 ATA which is the rate at which oxygen toxicity sets on in an accelerated timeframe and so is the recommended maximum safe partial pressure, but (a) even at that ppO2 you will never get oxygen toxicity onset fast enough to affect a bounce dive, (b) 1.6 ATA is still relatively safe for shorter exposures - if you want to black out instantly you need a lot richer mix than that, and (c) there is a lot of anecdotal evidence that the higher ppN2 of air means that you can tolerate higher partial pressures of oxygen without toxing (don't want to turn this into a deep air thread, but just sayin').

Just putting it out there for the record.


---------- Post added October 9th, 2015 at 07:19 PM ----------

I don't agree with this. Our diving is supposed to be fun. Your definition of fun maybe hanging in the water column looking into the snot filled mask of your buddy for an hour. If someone has fun bouncing down and back and avoids 50 minutes of hang time,- who am I to judge... Same crap we read here almost daily. It is fine to plan to dive a deep wreck, but by definition ition. Setting a personal depth record is irresponsible. I,m not buying anyone else's definition of what constitutes my fun.

I kind of agree. People climb mountains in bad weather and don't see a thing, but do it for the satisfaction of having done it. If people want to do it just to do it, go ahead. But do it safely. Or at least don't ask others to recover your body if you don't.

 

[AfterDark]

I've never heard a body asking to be recovered. The families often ask for recovery of a body in the name of closure. Aren't bounce dives considered to be < 5 min?

 

[Superlyte27]

At 217 feet you are breathing oxygen at a partial pressure of greater than 1.6 ATA which is the rate at which oxygen toxicity sets on in an accelerated timeframe and so is the recommended maximum safe partial pressure,

Are you using Common Core Math? Because I've counted it on my fingers and toes twice now, and it don't line up.
217 / 33 +1 = 7.5757575758 x .21(air) = 1.590909

 

[Akimbo]

I concur that the word "greater" makes it incorrect.

... 217 / 33 +1 = 7.5757575758 x .21(air) = 1.590909

Which is 1.6 ATA when rounded. Sure you can get crazy and use less rounding, like 33.0142999 FSW/ATM and 20.9460% Oxygen in air (both average and rounded) where you come up with 1.586221589 ATA, but it is still 1.6 ATA rounded.

 

[dumpsterDiver]

LOL.... ain't air 0.208 anyway... like I said in my original post, PP O2 is not really the issue here.

In two days SB has one guy saying that anyone can freedive to 130 with a couple lessons and this guy gives out some very bad advice about how best to do a bounce dive.