Help! I'm RDP brain dead!

[susan6868]

Okay, in preparation for my next level of training, I hid my computer, as well as the new spiffy PADI calculator, and went back to basics. I dug out my old plastic RDP tables and set to work, on my own refresher course.I want to be able to plan dives manually, with ease. Yes, we learned this in the Open Water course, but it's been a while, and with a computer, I honestly haven"t done it manually since my first 10 dives!
Found a website from Dayo Scuba in Florida and went through the practice questions until I hit a roadblock. Unfortunately, there is no solution to this one problem on their site, so I have no way of checking it. Here's the question:


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.

As I mentioned, the "ANSWER" button for this particular quiz question on their site is not operating and I'm stuck. When I line up my dives, deepest to shallowest, I run into a problem finding the first SIT.
After diving 10 min at 91ft, I think my pressure group would be "E".
However, when I go to the back of the RDP (table 3) and look at the next dive, 55 ft for 30 min, it tells me I need to be in pressure group "I".
So, when you go back to the front of the RDP and try to find the minimum SIT to do get from group E to group I, you find you're really going backwards for lack of a better term.

I'm stowing both my pride and embarassment in hopes that someone out there can
explain how to work this problem and what the correct answer is.
Please, no hazing, I'm mortified as it is.................
Thanks
Susan

 

[3-Ring Octopus]

Oooo..math problem...woohoo!!

End of 91' dive you're an E...with 17 minutes RNT for your second dive...
which is TBT of :47 at 60' which makes you an S upon exiting...with 85 minutes of RNT...
which leads to a TBT of 115 minutes at 40' which makes you and X upon exiting...

Which means that you have a minimum 1 hour SI after the last dive...but it would appear that all three dives COULD be made with NO/NEGLIGIBLE SI between them and still fall within the RDP.

Cheers,
Austin

We didn't on this set of dives...but if we DID encounter a problem where we exceeded a NDL with figuring on no SI's, you can calculate the minimum by going to Table 3 and using the blue number in each pressure group. i.e....if the second dive (the 55' dive) was planned for say :45 instead of 30...you find the pressure group you'd have to be in to make it by finding the highest pressure group which has :45 in the blue numbers on Table 3 for your given depth of 60'...which would mean you'd have to be an A to make that dive...which would mean a minimum SI of 1:28.

 

[NadMat]

susan, You have to be an I or better to stay in ndl, but since you are an e you work it using that column on table 3. hope that helps

 

[susan6868]

Oooo..math problem...woohoo!!

End of 91' dive you're an E...with 17 minutes RNT for your second dive...
which is TBT of :47 at 60' which makes you an S upon exiting...with 85 minutes of RNT...
which leads to a TBT of 115 minutes at 40' which makes you and X upon exiting...

Which means that you have a minimum 1 hour SI after the last dive...but it would appear that all three dives COULD be made with NO/NEGLIGIBLE SI between them and still fall within the RDP.

Cheers,
Austin

We didn't on this set of dives...but if we DID encounter a problem where we exceeded a NDL with figuring on no SI's, you can calculate the minimum by going to Table 3 and using the blue number in each pressure group. i.e....if the second dive (the 55' dive) was planned for say :45 instead of 30...you find the pressure group you'd have to be in to make it by finding the highest pressure group which has :45 in the blue numbers on Table 3 for your given depth of 60'...which would mean you'd have to be an A to make that dive...which would mean a minimum SI of 1:28.

Thanks Austin, but where are you getting the 17 RNT number from? Because I'm an E after the first dive, am I correct in assuming I can do the second dive without a surface interval to 60 feet as long as 38 minutes with a 17 RNT?

 

[NadMat]

since austin is offline, I'll take a stab.

17 RNT is the number in white at intersection of E group and 60', just above the blue 38 ABT max figure. In order to figure TBT for next dive group you must add this to ABT for dive to find designation to start last dive with.

and yes you are correct in your assumption, if you mean can you make the second dive starting with 17 RNT, the 38 is max ABT to stay NDL .

 

[Doc Intrepid]

"Okay, in preparation for my next level of training, I hid my computer, as well as the new spiffy PADI calculator, and went back to basics. I dug out my old plastic RDP tables and set to work, on my own refresher course.I want to be able to plan dives manually, with ease..."

May I interrupt your thread just long enough, Susan, to congratulate you for taking the initiative to make this effort? I think its a laudible effort, and I suspect that you will be real glad that you've taken the time to review dive planning like this one day. Well done...

Doc

[/HIJACK]

 

[crpntr133]

If you want more practice go to Scubatoys web site and download their table tutor.

It may be posted on here what the code is so you can use it endlessly. If not PM Larry and he will give it to you.

 

[Toolbox-13]

If you want more practice go to Scubatoys web site and download their table tutor.

It may be posted on here what the code is so you can use it endlessly. If not PM Larry and he will give it to you.

I second the Table Tudor it is a great download and you can choose the table you use. PADI, NAUI, SSI, US NAVY etc...
if you mention you are a SB member Larry will give you the Table Tudor for free. I also applaud your efforts, maybe I'm a old school diver but batteries go dead...lol...I use my Navy tables

 

[Dive1Dennis]

Oooo..math problem...woohoo!!

End of 91' dive you're an E...with 17 minutes RNT for your second dive...
which is TBT of :47 at 60' which makes you an S upon exiting...with 85 minutes of RNT...
which leads to a TBT of 115 minutes at 40' which makes you and X upon exiting...

I like to review the tables from time to time. I ran this one through before reading Austin's answer and got the same pressure groups and came to the same conclusion that you can do the dives without surface intervals. :14:
Must be right, right?

 

[3-Ring Octopus]

I keep in practice by running all of my dives on the tables (even though I dive with a computer handy...) when I log them. I have yet to really "push the limits" (diving in coldwater with awful air consumption helps that..lol), so I have never ended a day of diving outside of the tables, although with a computer that's entirely possible.

And to concur with everyone else...yes..the batteries on your tables never die....

Cheers,
Austin