Place of dive tables in modern diving (Split from the basic thread)

[CAPTAIN SINBAD]

I think th concern is that if I were to do 10 dives using RD I would get bent and then be told “Of course you got bent, you only did ten dives with it. If you coul show with other models that you won’t get bent using RD, you might have something, but I am yet to hear anything that definitively validates this type of diving. Properly used PDCs and tables get people to the surface safely. While I have not read up extensively on RD, I am yet to hear anything that woul show by a previously accepted method that it is better or safer than other methods.

Well the critics of ratio deco fall in two categories. The first is those who believe that there is task loading involved and the "mental mathematics" will cause you to miscalculate actual decompression limits and stop times.Thus you will get bent, not because the RD profile is intrinsically risky but more because you will make a calculation error since there is no computer there. The second category of critics is those that believes that even when you get your averages and limits right, this correct calculation of RD could cause you to surface outside the limits set by any established algorithm on some dives.

In my own skepticism of RD I have been in the second category. I have tried the "mental mathematics" underwater and it is really not as hard as it may sound. In fact it gives you some very solid numbers within which you can plan your dive and it is very hard to mess up. Now the skepticism (at least on my end) is whether this simplified block math with rounded numbers will get you out within established algorithms or would you be exceeding GF 100/100.

In order to do a risk evaluation of that aspect, you may not even need to jump in and do the ten dives. You will just have to run a few profiles on Multi-deco to see how they add up under your preferred algorithm. Give it a shot. Do a few test profiles and see how much risk you are taking under different algorithms.

The few Min-Deco test profiles that I ran on Multi-deco (with 60 mins intervals) did not exceed Buhlmann 100/100 on up to 4 repetitive dives. After that you may have to double your safety stops but UTD recommends repeat profiles for up to 3. This is only for min-deco limits that I listed in my earlier post. In other words, you are not taking any significant risk on these dives if you choose to dive that way for any reason.

Now I have not run their Tech 1 dives but I am sure they are not as "suicidal" as internet forums would make you believe. The fact that they are not suicidal does not mean that they are the optimum way of decompressing.

 

[Kevrumbo]

IMO, problem is if you did the typical liveaboard week-long itinerary of 3 to 5 repetitive dives per day on Air or Nitrox right up to NDL, you will have a significant slow tissue inert load by day 5 on any particular model PDC or Table algorithm, and therefore subject to the same increased risk of DCI

Why would you do this? That's just abusing your body and the algorithms. I've done many a liveaboard and have yet to be bent. That's no accident.

Because Pete, that's the typical "unexpected/unexplained" DCS casualty lament of the recreational vacation single tank diver -worst case with an undiscovered PFO:

"But my dive computer said it was OK. . ."

 

[The Chairman]

Because Pete, that's the typical "unexpected/unexplained" DCS casualty lament of the recreational vacation single tank diver -worst case with an undiscovered PFO:

It's still just "noise".

However, stupid is as stupid does. When a diver exceeds the limits of NDLs they are heading down that slippery slope. A PDC can't think for you. It can't adjust your mindset. It can't make decisions based on your health, your fatigue or anything else. If you blindly follow any protocol, you're asking for trouble. But you know that.

 

[oldschoolto]

But, MOST DIVERS DON'T... That's the whole point of understanding the NDL and gas/time/depth....

Jim...

 

[TMHeimer]

But, MOST DIVERS DON'T... That's the whole point of understanding the NDL and gas/time/depth....

Jim...

Could be. Would be interesting to know what % of divers do and don't. Impossible to know.

 

[The Chairman]

MOST DIVERS DON'T

Citation needed.

 

[Eric Sedletzky]

A table question for the experts:

This is for the first dive of the day, using the PADI RDP dive table.

You start your dive and it takes you 5 minutes to descend to 100 fsw. You stay at 100’ for 10 minutes, then you decide to go up to 70’. It takes you two minutes to go from 100’ up to 70’. How long can you stay at 70’ before you hit your NDL and have to go up?

 

[stuartv]

A table question for the experts:

This is for the first dive of the day, using the PADI RDP dive table.

You start your dive and it takes you 5 minutes to descend to 100 fsw. You stay at 100’ for 10 minutes, then you decide to go up to 70’. It takes you two minutes to go from 100’ up to 70’. How long can you stay at 70’ before you hit your NDL and have to go up?

The PADI RDP I just found online says the NDL for 100fsw is 20 minutes.

In which case, you arrive at 70' after 17 minutes total dive time and can stay for 3 minutes before you must begin your ascent at 30fpm to your safety stop.

Disclaimer: I've never taken a PADI class, but I believe for NDL diving, PADI, SDI, NOAA, etc. tables all work the same way. Max depth determines NDL and all your dive time counts towards when you have to start your ascent, including the time you spent on initial descent.

 

[boulderjohn]

A table question for the experts:

This is for the first dive of the day, using the PADI RDP dive table.

You start your dive and it takes you 5 minutes to descend to 100 fsw. You stay at 100’ for 10 minutes, then you decide to go up to 70’. It takes you two minutes to go from 100’ up to 70’. How long can you stay at 70’ before you hit your NDL and have to go up?

If you are going with the PADI RDP exclusively, it's simple. Your maximum depth is 100 feet. The maximum time for that is 20 minutes. That time includes the descent, and it ends when you begin your direct ascent to the surface with a safety stop). If you are hanging at 70 feet, it is part of your dive to 100 feet. When you left 100 feet, you were at 15 minutes, so you have 5 minutes from the time you left 100 feet until you begin your ascent to your safety stop. If it took 2 minutes to get to 70 feet, you have 3 minutes left.

 

[lowviz]

I get two whole more minutes of downtime.

222222/(100^2) = 222222/10000 (I did that in my head.) If my PDC died at 70' I'd already be so far off 'conservative' that I'd just come up.