Quiz - Recreational Dive Planner™ - Max Time

[Steve_C]

Misc comments. Off NC be it ledges or wrecks, out of the port I use, the standard is a 1 hour SI. (These are typically 80 to 105 ft). The depth variation of structure is usually 20-30 ft. So multilevel plus some times you go above the wreck and just watch things. On a couple shallower sites, 60 ft, it is 1 hour if you are on air and 30 min on Nitrox. Most divers use NItrox. Even once above the wreck there may be something interesting and you spend some time at 20ft or 30 ft.

The only time I have seen a longer than one hour SI is when diving in a quarry.

 

[boulderjohn]

With the BSAC definition it doesn’t matter if I ascend at 3 or 15m (BSAC’s maximum) a minute, I would still reach 6m at the planned bottom time target.
Using a slower ascent rate than PADI use in their calculations could compromise their validity.

For example, for someone riding the deco line, there would be a 3 minute variation:
* 5 minutes at 3m/min.
* 2 minutes at 9m/min.

When the research was done on the PADI RDP, they used the 60 FPM ascent rate, which was then standard. Yes, the numbers are based on that research, so they can't really change that. If you read what they say, though, you will see that them say repeatedly that you should "ascend no faster than 60 FPM." There is no mention of a rate that is too slow. If you read all the DAN articles on ascent rates, you will see pretty much the same thing--no mention of a rate that is too slow. That bothered me for a long time.

Last year I got a lot of help from Simon Mitchell in writing an article on current thinking on ascents on decompression dives, and I wanted to follow that up with an article on current thinking on ascents on NDL dives. The current research on decompression dives shows that ascending too slowly (deep stops) really is an issue, and I assumed I would find similar issues with NDL dives. If you look at my last posts from about a year ago, you will see that I announced that I was beginning to research the topic. Simon Mitchell declined to participate, telling me there was not enough research done, and he did not have a firm opinion. I have completed my research and decided he was right. That is why I have not tried to publish what I learned.

As a part of that research, I got information from someone at PADI who was intimately familiar with the PADI RDP research. He told me that although they used the 60 FPM ascent rate as a maximum rate, they found that going slower did not seem to matter. They were also researching multi-level dives in that project, so they had a lot of experience with slower ascents. So as far as PADI is concerned, then, there is no problem ascending slower than the maximum rate, and that is why they do not put out a "too slow" warning. That is the reason DAN does not have a "too slow" warning, either.

At some point, obviously, you can ascend so slowly that you go into deco, but that is pretty slow. (A computer will tell you that, but a dive table won't.) As long as you are not ascending too fast, your ascent rate on an NDL dive does not make enough difference to impact the tables.

 

[EFX]

The problem is that very few people use tables for their diving, and those table computations in your log book are no longer necessary.

For a year after I got recertified with PADI I used the RDP before I got my first computer. I routinely used the RDP for multilevel dives where there were two well defined levels and a few times for a three level dive. I used a wind-up dive watch that had a bezel for tracking elapsed time so I knew how long I spent at each level. Once I got the computer, a Mares Puck, it was like taking a breath of fresh air.

 

[boulderjohn]

As long as you are not ascending too fast, your ascent rate on an NDL dive does not make enough difference to impact the tables.

If you were bored enough to go back to some of my posts on this topic years ago, you will see that I said just the opposite, that divers using the tables and ascending much slower would need to adjust for the increased time of ascent. I was wrong.

 

[scubadada]

When I first dived, 1970-80, using USN tables, we ascended at 60 ft/min and there was no such thing as a safety stop. When I was recertified in 1997, we used PADI tables, the ascent rate was 60 ft/min, and we always did a 3 min safety stop. I've been diving a computer since 2002. For a while I ascended at 60 ft/min to 60 ft and then at 30 ft/min, with a 3 min SS. Later, I started ascending entirely at 30 ft/min, and did a safety stop of 3 or 5 min, the latter when I had come to within a few minutes of NDL. At some point I changed the ascent from the SS to 15 ft/min. Now, I ascend at 30 ft/min, adjust my SS, of at least 3 min, to give me a SurfGF of not higher than mid to high 80s, and make the final ascent at 15 ft/min.

So, for about 2,100 dives, 2,000 no stop, I've done just fine, no inkling of DCS. Of course, I'm much older now and I see my ascent strategy as considerably more conservative than it once was

 

[Storker]

When the research was done on the PADI RDP, they used the 60 FPM ascent rate, which was then standard.

IME, even 10 m/min (33 fpm) is pretty fast. I've done exercises trying to ascend at 10 m/min, and it wasn't easy. It was a lot faster than my usual ascent rate.

I'd have serious issues trying to ascend at 18 m/min. Particularly if I were to stop at 5-ish meters for the SS instead of emulating a Polaris missile.

 

[scubadada]

When the rate was 60 ft/min, I ascended slower than that. Now, I ascend a bit slower than 30 ft/min also. It's not hard ascending from my SS at 15 ft/min.

 

[TMHeimer]

I took PADI OW in 2002. It was all tables. After a long break from diving, I took NAUI OW in 2017. It was all tables, too.

When I took the PADI divemaster exam four months ago, there were table questions and eRDP questions, but no computer questions.

The information posted by Tursiops about instructors having a choice is news to me—very encouraging news.

Has anyone here reviewed PADI’s new latest-and-greatest e-learning system to see how it handles it?

Interesting. I think I recall some eRDPml questions on the "old" PADI DM exam in 2009, but not any regular RDP questions. Could be wrong, it was a long time ago. It would be surprising to find RDP questions on a DM exam, being that this is (was....) OW course stuff. When I took Nitrox in '06 someone in the class needed review of the RDP before we could start on the nitrox tables. Frustrating at the time.

 

[Storker]

When the rate was 60 ft/min, I ascended slower than that. Now, I ascend a bit slower than 30 ft/min also. It's not hard ascending from my SS at 15 ft/min.

Well, IME ascending slowly from the SS isn't as hard as being able to stop at SS depth when you've been ascending from the bottom to the SS at 10-18 m/min (33-60 fpm).

When I did those exercises, we were allowed to stop at ~9m and ascend slowly from that depth to the SS/shallow deco stop. It gave us a bit of a margin. I'm not certain I'd be able to ascend at 18 m/min from, say 30m/100' to 3-5m/10-15' and then make the stop.

 

[boulderjohn]

Now, I ascend at 30 ft/min, adjust my SS, of at least 3 min, to give me a SurfGF of not higher than mid to high 80s, and make the final ascent at 15 ft/min.

SurfGF on a computer is a game changer for me. I keep my computers in tech mode, so I don't get any sort of safety stop countdown the way most divers do. When I am doing NDL dives with friends using recreational computers, I watch them counting down the safety stop to the precise second they are allowed to ascend. Meanwhile, I have looked at my SurfGF, and if I like what I see there, I am good to go up whenever they are. I did a number of dives in the 50-60 foot range for an hour each on EANx 36 this winter, and when I reached the SS level with my buddies, my SurfGF was usually between 43-50, well below what I would have been happy surfacing with after deeper dives. My buddies were doing the same dives with the same mix, so I assume their would have been the same if they had had a computer to show that, but we all waited until their computers counted down that magic 3 minutes.

So, for about 2,100 dives, 2,000 no stop, I've done just fine, no inkling of DCS. Of course, I'm much older now and I see my ascent strategy as considerably more conservative than it once was

Here's the problem--what makes your ascent more conservative? There is no question that the lower the SurfGF the better, but what is more conservative BEFORE you reach that stop? My question is genuine. After researching it, I don't know. As some of you know, I got bent last year after a two tank recreational dive that should have been ultra safe. That was before I did my research. Now that I have completed my research, I do everything the way I did before, because I have no idea what to do to make it safer, other than wait out the SurfGF to something ridiculous.