Padi RDP Question

[jrv331]

Im studying for my upcoming owd exam and have a question on an RDP example. I found som examples on a web site and thought I was doing pretty good until this question:
4) You are doing 3 dives today. They are to 39 feet for 30 minutes, 55 feet for 30 minutes and 91 feet for 10 minutes. Order your dives in the recommended order (deepest first), then compute your ending letter designation AND the minimum surface intervals between each dive.

I got the order right but was way off on groups and times, I cant even figure out how they came up with the correct answers. Could one of you walk me throught this, I know it appears to be above the "starter" level but Im curious now. If it matters I got it from here :
Dayo Scuba -  PADI RDP , its problem 4 at the very bottom.
Thanks
John

 

[jseteroff]

There should have been a booklet labeled instructions for use that came with you RDP. Read through it again and see if you can figure it out that way. Find your depth/time on table one, then follow the row across until you find your appropiate surface interval. Then go down and that will be your pressure group after the interval. When you flip the table over, the after surface interval pressure groups are along the top, follow it down to your planned depth, the white half of the box is your residual nitrogen time. the Blue box is your max bottom time. When you surface add the white box to your actual bottom time. this is the time you use on the front table to find your pressure group again. ex if your RNT is 30 min and you dive to 20m for 10 min then you look up 20m for 40min to find your pressure group at the end of the second dive. If you still can't figure it out, send me a PM with your phone number and I will call and walk you through it.

 

[jseteroff]

removed for double post

 

[jrv331]

OK, this is the best I can come up with - hope its not to confusing. 91 ft for 10 min puts me in group E. For the second dive of 55ft at 30 min I need to be in group V, which requires no SI. Since theres no SI im still in group E, which means my RAT is 30min for the dive and 17 residual. So 50ft at 47 min puts me in group S at the end of the second dive. For the thrid dive 39ft for 30 minutes I need to be in group V, again requiring no SI so Im still in group S. Using the RAT of 85 and 30 means my bottom time is 115, @40 feet ends me in group X. IM assuming the example had the correct answers: E/0/E S/0/S X

No where in any manual or on line example does it say that if your SI is zero, your still in the same group. If this is the case then I understand completely.

 

[knotical]

You're not wrong. You need to be no more nitrogen-loaded than a group I diver. E is less saturated than I. It's just a weird problem.

 

[jseteroff]

you are correct in your problem. Regarding the manual, it may not say that if you don't have a surface interval then your group is the same, but when your read the table, the intervals start at 0:00. if you follow the column down, you will see that it is the same pressure group you started at.

 

[fisheater]

There are two "tricks" to the problem.

One. Because your minimum required pressure group in both cases is MORE than your current pressure group, you don't need any surface interval.

Two. You need to use your current pressure group to compute your repetive dive, not your "minimum" pressure group (which turns out to be much greater).

 

[jrv331]

Thanks for all the help, I can only pray this type of question will not be on the exam.

 

[CamG]

Greetings jrv221 and this type of question will be on the exam and a few more like it.

PADI wants to make sure you know the material inside and out, forwards and backwards.
Seems a little difficult but it is really not that bad once you get into the water all the hassel of exams and confined water start to fade.
The key to the exam is to not get to anxious and read all questions through entirely and use a clean sheet of paper to make notes on.
You will be allowed to use the RDP be sure to read the information on the slate as it will help you answer several questions as well.

I hope that you find this helpful PM me if you have any more questions it has been a while since I have taken or assisted in giving the exam but I will try to help anyway I can.

CamG Keep Diving....Keep Training....Keep Learning!