Negative Entries - A Bad Idea???

[tursiops]

According to that CMAS definition above.... a dive to 40 meters on 40% meets the definition of a "Sport Dive".

That is not what it says. You missed the comma...

 

[stuartv]

Look......You posted the above and then I simply stated that diving to 40 meters on 40% is a bad idea. According to that CMAS definition above.... a dive to 40 meters on 40% meets the definition of a "Sport Dive".

Yes, it does. So?

Nobody in their right mind would actually DO that, no matter how you label it. But, yet, it does meet the definition of a Sport dive. And again, so what? That doesn't make the definition wrong.

The definition tells us that any dive to 41m (or more) - on ANY gas - is no longer a Sport dive.

It also tells us that any dive - to any depth - using gas with more than 40% O2 is also no longer a Sport dive.

What is the problem you have with this?

 

[tursiops]

What is the problem you have with this?

He is confused by the syntax. He is reading

"diving to a depth no greater than 40 meters, using only compressed air or Nitrox (with no more than 40% oxygen) as a breathing gas,"​

but missed the comma after 40 meters.

 

[inquis]

Generally, commas can be replaced with "and", so I can see the confusion. Arguably, a clearer statement would be to define what is NOT rec diving as exceeding 40m or 40%. Hopefully everyone can agree to that. (Substitute your agency's max depth as appropriate.)

From there, the logical operations are clear:

not rec = >40m or >40%​

rec = not(not rec)​

rec = not(>40m or >40%)​

rec = (not >40m) AND (not > 40%)​

Yes, the swap from OR to AND is correct. Boolean logic 101. That leaves:

rec = ≤40m and ≤40%​

which is exactly what was (verbosely) stated.

The problem is that such logic rules are not intuitive for many, so again, defining "not recreational diving" would have been better understood by all.

 

[scubadada]

And I feel
Like I've been here before
And you know it makes me wonder...

What Defines a "Tech" Diver

So just curious as to what folks think either defines or qualifies someone as a "Tech" diver. Is it planned Decompression? Planned penetration? Overhead environment? Use of any gear beyond what is typically considered needed for "recreational" diving? Salvage diving with use of...

scubaboard.com

 

[Divin'Papaw]

You’re over-thinking this.

Negative entries are appropriate and necessary for navigation purposes on a hot drop over a specific objective.

Most of our boat dives in Palm Beach County, which are just about 100% drift dives over a bottom of known depth, are negative entry. In Southeast FL you want to be on the surface as little as possible. The top currents are almost always different than the currents on the reef/wreck. If you spend much time at all on the surface you will miss your target.

 

[Eric802]

To sum up:
- Negative entries are not necessarily bad and sometimes required due to conditions;
- Get your weighting right, regardless of how you're entering the water; and
- Bad sentence structure can lead to confusion.

 

[Divin'Papaw]

To sum up:
- Negative entries are not necessarily bad and sometimes required due to conditions;
- Get your weighting right, regardless of how you're entering the water; and
- Bad sentence structure can lead to confusion.

One or two more items ... be sure to have a rigorous personal pre-dive checklist. This is a good idea before every dive, but can be life-critical on a negative entry. Make absolutely certain your inflator is connected and functioning and prebreath both 2nd stages to ensure your gas is on. It also helps to be able to reach your value. I typically test this once during each day of diving. It helps me to lock in that muscle memory on where that valve is located and exactly where I can find it. Each time I do it I typically say to myself, "wow, it feels like it's further back there than I remembered!" I then close it a few turns and then open it fully. I like to do that at least during my first dive of a dive trip or weekend. Muscle memory is critical in an emergency. No thinking involved.

 

[Midlomac]

Reading this old threard. Good discussion. 40% O2 at 40 meters is PPo2 of 2. No, that's not sport or recreational diving, and no certifying agency would say it is. We can't take one of two lines of the training manual and ignore the context of the rest of the guidance. Hopefully we all agree on that.

Divin'Papaw makes great points above about negative entries. There are times when negative entries are helpful. I've been on boat dives where due to rough seas and strong surface currents the captain has instructed us to enter negatiely so we can catch the down line quickly, but it does add risk. Even with the above mentioned checks, there's still potential for thing to go wrong; e.g., boat bounces when you step off and your yoke reg connection gets smacked and loses solid connection to the tank, mask pops off and you're disoriented,...

A few years back I read a report in the back of the DAN magazine about a guy on a boat dive with new gear who stepped off and went straight down. He wasn't trying to do a negative entry, but he did, and was found at the bottom (about 80 feet, I think) unresponsive. His air was off. You can imagine him finding it out as he's going down, exhales, and then nothing when he tries to inhale. Yes, it was a fatality. We all hope we'd handle a situation like that calmly and rationally; evalute our options, pick what's needed and do it (reach back and turn on air, ditch,...). But when a true life or death situation is occuring, so can an amygdala hyjack where rational thought goes away and you're just reacting in a very primative way to try and stay alive. That's why we think through scenarios and practice things like reaching our air valve, ditch and don, ... knowing what to do to stay alive and stay in control. But many police officers who train regulary with their firearms have it happen when a true lfe or death situation happens. So, it can happen even if you think you can handle it/ have prepared. So if I don't have to do a negative entry, I don't. If I decide I want to practice it, I tell my buddy, have them go in first and watch as I come in.

Just got back from a week of easy diving in Roatan. Four boat dives a day. Captain and DM didn't require you to signal all good before descending, so almost everyone was entering negatively. It was just easier than having some air in your vest/ wing, dumping, and then swimming down. I love this sport, but I know I can't breathe water. I think about that guy (and his family) every time I'm doing my BWRAF gear check when we get to the dive site, and as I pump some air into my wing as I stand up to get ready to step off.

 

[MB NZ]

I do like a rapid entry, negative descent fast drift dive, or at least I used to. It was the only way to get on to some sites I have dived in the past. Not for the fainthearted and turns SCUBA in to an adrenaline sport! Empty BCD/wing, and SWIM down hard. No need to be overweighted. If something wasn't right with kit, or ears, abort the dive ASAP. Divers and boat handlers need to be competent and work as a team.