RDP Tables - Surface Interval Questions

[namerg]

Hello there,

I have been reading about RDP but got lost in calculating surface interval.

Question: you dive at 70' for 30min and then make a second dive to 50' for 4min. What would be the minimal surface interval to perform these two dives safely?

So, Why the answer is is 24min

I know that 70' 30min is Group O then I got lost. Can some one explain me like if I was 5 years old? Thanks for your help.

 

[Roatan Joe]

No surface interval would be required for a second dive to 50 ft. for 4 minutes.. Where do you get 24 mins?

You could be a diver in pressure group as high as W and still go down for 5 minutes to 50 ft.

As you said, you end the first dive as an O diver, so if you wanted to go down immediately without a surface interval to 50 ft. you would need to add 47 minutes of residual nitrogen time (RNT) to your planned dive. The no deco limit is 80 mins, so you have 33 mins. available at 50 ft. 80 mins - 47 mins RNT = 33 mins of bottom time available.

Of course you wouldn't want to dive like this to the absolute no deco limits, but that's the info I believe you wanted from the RDP..

Pages 24-27 of the PADI RDP Instructions shows how to figure minimum surface intervals.

This is a good website to practice tables: http://www.aquaholic.com/divetables/

EDIT: Did you by chance mean to ask why as an O diver why a 24 minute minimum surface interval would be required to dive to 50 ft. for 47 minutes?

If that's the question, then here's the answer.

Go to Table 3 and follow the 50' row over to 47 minutes (blue shading). Notice that is in Pressure Group J. Now flip the table over and look at Table 2. Follow the row for pressure group O over to where it intersects with pressure group J. Minimum Surface Interval is 24-28 minutes..

 

[Diver0001]

Hello there,

I have been reading about RDP but got lost in calculating surface interval.

Question: you dive at 70' for 30min and then make a second dive to 50' for 4min. What would be the minimal surface interval to perform these two dives safely?

So, Why the answer is is 24min

I know that 70' 30min is Group O then I got lost. Can some one explain me like if I was 5 years old? Thanks for your help.

The missing surface interval exercise breaks down into three questions:

1) what group am I when I finished my first dive?

and

2) what group do I need to be at the START of the second dive in order to not exceed the NDL?

and

3) how long do I need to wait between dives to go from the group I had after dive #1 and the starting group I needed to do dive #2?

What you have discovered already is that you can answer the first question.

So let me lead you through this case so you can see how to answer questions #2 and 3.

// full solution.

Question #1 is what my group is after the first dive? You already worked it out to "O". that is correct.

Question #2; what do I need to be in order to make the 2nd dive without exceeding the NDL? For this you need to flip the table over and use the back side. The dive is to 50ft so you need to find 50ft on the table (see image). 50ft is the black circle on the image. The next thing you need to do is to find the NDL. Your dive needs to fit in an NDL of 4 min. So read to the right until you find 4 min (or more) on the blue line... the adjusted NDL. I circled this in blue; read up to see what group this is

Question #3; how long to you need to wait to go from group "O" to group "W".

In this case, from O to W means you don't need a surface interval at all. You can make these dives back to back.

If the second dive had a bottom time of 47 or 48 minutes instead of 4 minutes then you would have needed to be a group J (see if you find this). In that case your surface interval from group O to group J would have been a minimum of 24 minutes.

R..

 

[namerg]

Ohh ok, as soon as I switch to the computer I will check it ou. Thank you guys.

---------- Post added November 21st, 2014 at 06:54 AM ----------

Go to Table 3 and follow the 50' row over to 47 minutes (blue shading). Notice that is in Pressure Group J. Now flip the table over and look at Table 2. Follow the row for pressure group O over to where it intersects with pressure group J. Minimum Surface Interval is 24-28 minutes..

Got it. Sweet

 

[DiveNav]

....... as soon as I switch to the computer I will check it ou. ......

Once you switch to dive computers there is no coming back (to the tables)

 

[namerg]

I heard that. Can you really trust the dive computer 100% ?
Not sure if I am being extra cautious. But will do the calculation through the RDP tables, note them down. Then I can use the eRDP device or the dive computer. Makes sense? Maybe or not at all

 

[diver 85]

Do they still teach 'the tables'???........I figured they'd skip that part of diving now.....AND-----I can't wait till you take your classes-----& PASS................(j/k'ing of course)......

 

[Roatan Joe]

You can trust the computer 100% as long as it doesn't fail. If you are worried about the computer failing at some point, dive with a back up computer.

Of course, if you're at 80 feet and the computer says your NDL is 4 hours, your better common sense judgement should tell you that something is wrong with your computer. If you want to use tables, then by all means use tables, however you may decide to quickly change your mind after you do a dive to 100 ft. and realize the tables will only let you do a 20 minute square profile dive and everyone else using computers will normally be down for 50+ minutes doing a multi-level dive..

 

[namerg]

Hmm, so you are saying no one uses nowadays the RDP tables ? If so, let's bring the dive computers then. This weekend I have the confined classes.

---------- Post added November 21st, 2014 at 10:14 AM ----------

Thank you Roatan Joe.

 

[decompression]

Sadly, most OW students don't have common sense if all they've learned is follow your computer.


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