understanding dive tables better

[KenGordon]

And the NDL you're given is based on your residual nitrogen load from your previous multi-level dive. Everyone should be taught the concept of nitrogen loading and residual nitrogen load. It's not rocket science and what the computer tells you isn't magic either.

This will not let you plan the second dive until just before you get in the water, especially with a short surface interval. Using tables, or these days planning software, allows the planning to happen long enough ahead to have a hope of changing the plan to give better diving.

The OP is doing the right thing. He is seeing what will happen ahead of time. This gives him options he will no longer have once the first dive is done. If the short second dive is unsatisfactory he could choose different site and so depths, he might be able to stay shallower on the first one, he could extend the surface interval, he could dive Nitrox, he could decide to do the stops on the second dive.

Playing 'what if' with a dive plan is quite valuable.

Once he gets in the water he might find that he gets more time or less time, that will depend on the tables, the computer and how square his profile is. Having planned the dive he can start to see how that pans out over a number of dives and so factor that in to similar dives in future.

Planning is not a hard skill, it can be learned while in a warm, dry place. It gives peace of mind on the dive and an opportunity to improve your enjoyment on the diving by making informed choices.

 

[Storker]

I use a dive computer, and I still keep Air, EAN32 & EAN 36 tables around so I can get a quick look if I wish (seldom do, granted).

Chalk me up in that camp.

I don't like planning dives on my DC. I think it's awkward and darned slow. So I've been using my tables for a quick and dirty plan ever since I certified OWD. And you can even plan a multilevel dive on the PADI RDP (at your own responsibility, mind you). These days, I've dived quite a few of my "standard" profiles so many times that I often don't need to check the table. But I still keep my air, EAN32 & EAN36 tables with my dive log, and I still check them sometimes. Unless I choose to use the DivePlanner app - which basically is an electronic version of the RDP - on my smartphone, that is.

 

[NAM001]

Hi, so ive been diving for a little over a year and have quite a few dives under my belt now. however I am starting to do some deeper dives (apx. 100ft) and I would like to have a better understanding of the dive tables. when looking at the SSI tables and just for an example if I dive to 100ft for 20 minutes I would be f group designation. so being an f group with apx. 1 hour surface interval should mean I do my next dive as an e group. now this is where I get a little confused. so for my second dive being an e group if I was to dive to 80 ft does this mean I am limited to a 7 minute dive? any clarification on this matter would be greatly appreciated. I ask this because I am doing 2 wreck dives tomorrow and I want to make sure I'm doing this right.

I used table SSI Dive Table . you are correct in your answer of 7 minutes available for the next group E dive at your PLANNED DEPTH. a couple of things to look at.... look at the residual nitrogen table. you have 2 numbers top and bottom add them and each column adds to the same number. that number is the max time at the selected depth. what the numbers are saying is that you are suffering a say 60% time penalty and you have a remaining 40% to use. for your example 100 ft 20 min group F.. you do 1 hour SI and that puts you in group D not E. group D being 46 min to 1:29. drop down to residual gas and you get 80 ft 18 over 12. you have still 18 min penalty and 12 minutes you can use at 80 ft. Again 18+12 equals 30 . Look at the top table at the max time at 80 ft..... It is 30 min. You can take a shortcut but less accurate method. sometimes. 100 ft 30 min group f down to SI 1 hour to group d and then GO UP to your new depth and it will be close. If you did that you would go up from group d to 80 ft and land on 15 leaving you with 15 more minutes till you hit 30 min ndl. always cut those remaining times down so the 15 remaining would be perhaps 2-5 less as a safety margin for table misuse error.

 

[_Ralph]

There is a YouTube video (2 or 3) by a shop in Tennessee that goes over the above posts method of using tables.

While it's based on the PADI table, sounds like the SSI is set up very similar.

The video is called How To Use the PADI RDP or something like that.

Edit: ScubaNashville is the shop (and YouTube Chanel) PADI Dive Tables Introduction 101 is the first video.

_R