Dive Problem: Dive Shallow then deep

[faze]

I am still amazed at the number of divers, from novice right through to the highest echelons who are not aware that the reverse profile "rule" was a myth. Many still adhere to "deepest dive first" and many schools still send out the deep boats in the morning and the shallower ones in the afternoon.

Not enough has been done by the certification agencies to educate and inform - and lets face it - it has been 13 years!

 

[jpbutler]

I am still amazed at the number of divers, from novice right through to the highest echelons who are not aware that the reverse profile "rule" was a myth. Many still adhere to "deepest dive first" and many schools still send out the deep boats in the morning and the shallower ones in the afternoon.

Not enough has been done by the certification agencies to educate and inform - and lets face it - it has been 13 years!

it still makes tremendous sense in terms of nitrogen loading on repetitive dives and subsequently extending ndl and minimizing deco obligation to do the deeper and/or longer dives first.

jpb

Sent from my GT-P7510 using Tapatalk 2

 

[Bob DBF]

I noticed you were using computers. Had you said you were using the RDP, caution would probably be advisable as the RDP calculations for multiple dives assume that you are doing your deepest dives first.

Are you implying that planning reverse profiles will put you in deco when the RDP shows you in NDL?



After looking through PADI OW manual from the early '80"s I didn't find a suggestion against reverse profiles, even in the "General Rules" listed for using the dive tables. Having been a diver well before my card training, I had noticed the advantage of doing the deeper dive first but, most of my effort was on calculating the SI for max bottomtime at the same depth.

Bottom line is to stay within NDL unless you are planning a Deco dive.




Bob
-----------------------------------
I may be old, but I’m not dead yet.

 

[fire_diver]

Are you implying that planning reverse profiles will put you in deco when the RDP shows you in NDL?

I read it as just the opposite. The RDP may be giving you less bottom time (or putting you in deco) when a dive computer may give you more time.

 

[Bob DBF]

I read it as just the opposite. The RDP may be giving you less bottom time (or putting you in deco) when a dive computer may give you more time.

Since a computer can calculate a multilevel dive on the fly, I understand that there will be a difference beween the computer and the RDP, as would be a difference if you used the "Wheel".

My point is that the RDP is designed to calculate NDL regardless of how you select your depth for each dive. If, indeed, "the RDP calculations for multiple dives assume that you are doing your deepest dives first", it seems to me that using the RDP for reverse profile dives would be inaccurate and therefore dangerous.

It is this type of misinformation that made the OP ask the question that started this thread. Dive tables, including the RDP, are designed to keep the diver within NDL when used properiy.



Bob
----------------------------------------------
I may be old, but I’m not dead yet.

 

[Diver0001]

That year is interesting in regard to reverse profiles. The major reverse profile workshop a decade ago included an investigation into the history of the prohibition of reverse profiles. It turns out the first example that could be found was in a 1972 PADI OW manual. That manual suggested that divers do the deepest dive first. PADI participated in the conference, and they had no record of who wrote that suggestion or why. I believe the "why" is answered in the posts above--shorter surface intervals by the tables. (This was before the invention of the PADI RDP, so they were going off Navy tables.) In each succeeding edition of that manual, the language got stronger until it became a strict prohibition--again with no explanation of why.

You'd have to check with Dr. Powell about this but I seem to recall reading somewhere that reverse profiles were not included in the test protocol for the RDP..... and since it wasn't tested it may have been promoted to a "rule" on the thinking "better safe than sorry". It could explain the "why".

R..

 

[windapp]

Are you implying that planning reverse profiles will put you in deco when the RDP shows you in NDL?.

According to the General Rules section of the RDP, "Plan repetitive dives so each successive dive is to a shallower in depth"

The RDP tracks two tissue compartments when you do deep dives, and follow them with repetitive dives. The first is the controlling compartment for the first dive. The second is the 1 hour compartment. The compartments in between is not accounted for, and neither are the slower compartments. The rules in the RDP are there to ensure that none of the other compartments become controlling compartments when you are using the tables, and if they do, they will be accounted for by the times for the particular depth in the table. So, yes, it is possible by not following all of the RDP rules to end up in Deco even though the table says you are not.

---------- Post Merged at 10:20 PM ---------- Previous Post was at 10:12 PM ----------

It is this type of misinformation that made the OP ask the question that started this thread. Dive tables, including the RDP, are designed to keep the diver within NDL when used properly.

Exactly, and if the table rules do not allow a particular dive profile, other methods must be used to calculate the profile in order to assure it is safe.

 

[Diver0001]

According to the General Rules section of the RDP, "Plan repetitive dives so each successive dive is to a shallower in depth"

The RDP tracks two tissue compartments when you do deep dives, and follow them with repetitive dives. The first is the controlling compartment for the first dive. The second is the 1 hour compartment. The compartments in between is not accounted for, and neither are the slower compartments. The rules in the RDP are there to ensure that none of the other compartments become controlling compartments when you are using the tables, and if they do, they will be accounted for by the times for the particular depth in the table. So, yes, it is possible by not following all of the RDP rules to end up in Deco even though the table says you are not.

Seems to me that the RDP is based on a 12 compartment model. The 1 hour compartment is used for the surface interval, not the dive.

R..

 

[windapp]

Seems to me that the RDP is based on a 12 compartment model. The 1 hour compartment is used for the surface interval, not the dive.

R..

I believe you are correct about the 12 compartments, although the 1 hour compartment is also used for the shallowest dives. However, the RDP can only track one compartment at a time, so it is important to follow all of the table rules as these rules ensure that the RDP is tracking the controlling compartment.

 

[Kharon]

What you are describing are reverse profile dives. A condition SDI (Deep Rec course) makes on this type of dive is that the deep part of the profile be no more than 40 FSW greater than the shallow part of the profile. That is for both a single dive and consecutive dives. What you are describing exceeds that requirement by 55 FSW - more than twice the requirement. Might be safe. I wouldn't do it. I'd probably snorkle at Sombrero and save the diving for the Thunderbolt.