Quiz - Recreational Dive Planner™ - Max Time

[HKGuns]

Good question. These help with my effective use of the tables.

 

[hammet]

Any one ever notice that the part Table 3 is completely pointless? You can use the first table to find your bottom time just by starting at the pressure group you are in after your surface interval and subtracting that starting value from the maximum allowed time (the number at the bottom of the column in black highlight). This is not the case with US Navy dive tables apparently where the repetitive dive time times do not match up with the the first table through subtraction of residual nitrogen time.

(note: this holds true for every repetitive bottom time on Table 3 EXCEPT for the second pressure group for the depth rows of 80, 90, 100, and 110 feet and the third pressure group in the 120 foot row and fourth pressure group 130 foot row where the Actual Bottom Time squares are blank)

 

[Storker]

Be wary of using BSAC 88 Tables against others. The definition of bottom time is fundamentally different; PADI’s is dependent on whether a safety stop is required or not.

The fundamental difference between the PADI RDP and quite a few of the others, like USN, BSAC-88 or our national table, is the slowest compartment. The PADI RDP clears you a lot faster than the others I've mentioned. I've read somewhere that dropping the slowest compartment in the PADI RDP algorithm was specifically due to PADI catering for resort divers who wanted to do 3-4-5 dives in one day, and the risk was considered acceptable. What's interesting is that my Suunto clears me about as quickly as the PADI RDP does. The allowed BT for the 2nd dive varies by plusminus a couple minutes between those.

Me, I prefer at least a two-hour SI. The main reason being that I usually don't have a peon available to switch my tank without me even having to doff the gear. Getting out, kitting down, taking a leak, drinking some water and perhaps having a bite to eat, swapping tanks and kitting up again in less than two hours is just too hectic. Slowest tissue notwithstanding. As a bonus, I don't have to worry as much about building up N2 in my slowest tissues and getting an "undeserved" hit on day 3 or 4.

 

[scubadada]

The fundamental difference between the PADI RDP and quite a few of the others, like USN, BSAC-88 or our national table, is the slowest compartment. The PADI RDP clears you a lot faster than the others I've mentioned. I've read somewhere that dropping the slowest compartment in the PADI RDP algorithm was specifically due to PADI catering for resort divers who wanted to do 3-4-5 dives in one day, and the risk was considered acceptable. What's interesting is that my Suunto clears me about as quickly as the PADI RDP does. The allowed BT for the 2nd dive varies by plusminus a couple minutes between those.

Me, I prefer at least a two-hour SI. The main reason being that I usually don't have a peon available to switch my tank without me even having to doff the gear. Getting out, kitting down, taking a leak, drinking some water and perhaps having a bite to eat, swapping tanks and kitting up again in less than two hours is just too hectic. Slowest tissue notwithstanding. As a bonus, I don't have to worry as much about building up N2 in my slowest tissues and getting an "undeserved" hit on day 3 or 4.

The PADI RDP SI credit is based on the 60 min compartment, whereas the USN SI credit is based on the 120 min compartment. This accounts for the greater SI credit for the RDP vs. USN tables. I don't know about other tables.

See @Pedro Burrito quiz from April 6 Quiz - Recreational Dive Planner - Tissue Compartment and Half-time

 

[Storker]

The PADI RDP SI credit is based on the 60 min compartment, whereas the USN SI credit is based on the 120 min compartment.

Are you agreeing with me, or are you arguing with me? I really cant tell, but it appears to me as if you're agreeing with me. Hypothesis #3: you're adding information to a point not worth arguing

 

[tursiops]

I've read somewhere that dropping the slowest compartment in the PADI RDP algorithm was specifically due to PADI catering for resort divers who wanted to do 3-4-5 dives in one day, and the risk was considered acceptable.

I think more accurately it was deemed to be no additional risk...mainly because the BTs were also dropped a bit.

 

[boulderjohn]

The rationale for the PADI RDP has been explained many times. The impetus was created by a scientist (Richard Rogers) frustrated by what he considered to the ridiculous limitations imposed by the use of the US Navy tables on shallow recreational dives. The US Navy had created the 120 minute compartment and made it the basis of surface intervals without a whole lot of research as to whether that was appropriate for any dives, let alone shallow recreational dives. It really didn't matter to them--their divers usually did one dive a day. Rogers suggested a study to see what was appropriate for the diving done by recreational divers, and he wanted that research to look at multi-level options as well. (The wheel used for multilevel diving was actually the primary intent of the research, not a later addition as many would think.) PADI agreed to back the research. The research was extensive.

The research indicated that for most recreational dives, the 40 minute compartment would do just fine, but for some dives the 60 minute compartment would be safer, so that is what was adopted. In order to make it more conservative, they decreased the bottom times for first dives. In order to make it more accurate, they nearly doubled the pressure groups to decrease rounding. They created the wheel to make multi-level dives to 3 levels possible. The PADI RDP is thus very different from the US Navy tables and all the other tables that are actually derived from them.

The resulting RDP has a range of safety, as is true of all tables. Short, shallow dives are completely safe, but as dives increase in depth and time, they get gradually riskier, and as you get close to required decompression, it becomes prudent to be a little safer. That is why the WX and YZ rules were added for multiple long, shallow dives. Safety stops were a problem, not so much because of what to do as what to call them. How do you say something that is optional is required on some dives? They ended up saying that they were recommended for most dives but required for dives specifically close to the NDLs. (They probably regretted that terminology shortly thereafter.)

Modern computer algorithms are all pretty close to the PADI tables. They are not at all close to the US Navy, NAUI, SSI (etc.) tables. I have read posts by people who say they follow the Navy, SSI, or NAUI tables by memorizing a short cut to the first dive limits and then using that short cut for subsequent dives; however, a diver following those tables to the first dive limits would be required by those limits to have nearly twice the surface interval provided by resorts today if they were truly following those tables. Divers who actually do that practice just described are really just winging it for subsequent dives.

 

[tursiops]

Any one ever notice that the part Table 3 is completely pointless?

It's for those who find subtraction challenging.

 

[Storker]

I think more accurately it was deemed to be no additional risk...

Po-tay-to, po-tah-to

 

[tursiops]

Po-tay-to, po-tah-to

Really?
"acceptable risk" could also mean greater risk.
"no additional risk" definitely does not mean greater risk.
Po-tah-to, To-mah-to