padi table vs. SSI table

[mgri]

I've started through OW again after a 7 year hiatus. I was PADI and know I'm doing it through SSI.

I was comparing my dive charts side by side and I noticed how conservative the SSI table is to the PADI.

What really struck me as odd is how the RT times on the SSI table 3 do not match its corresponding groups dive time on table 1. Like the PADI table does.

For instance 50 feet for 50 mins on a PADI table puts you in group I. If I look at table 3, group I for 50 ft I see an RT of 50. This makes sense.

On the SSI table a 50 ft for 50 mins puts you in G. Table 3 shows RT for G at 50 ft to be 56 RT

Does this make sense to anyone? Is my PADI table out dated or is SSI super conservative?

 

[navy85]

Although it looks like you might have an older PADI table, the concept you describe still works the same on the newer table. I took my OW a little over 2 years ago - my RDP version is 1.0 010 PDK9. On it, 50 min at 50 ft puts you in Pressure Group P in Table 1...In Table 3, PG P at 50 ft gives you a Residual Nitrogen Time of 50 min. Haven't done anything with SSI, so I can't help you there.

 

[Walter]

The PADI tables (RDP) is very liberal. For initial NDL's it is somewhat more conservative than the US Navy Tables and more liberal than most other agencies' tables. For repetitive diving, the RDP is much more liberal than the US Navy tables and other agencies' tables.

While I don't have a copy of the SSI tables, I do have copies of the RDP (I can't check my RDP right now, PADI is making a copy of it, I hope to have it back early in the week) and several other tables. An RNT of 56 minutes at 50 feet in letter group G is correct for US Navy, PDIC, MDEA, NAUI & YMCA tables. I wouldn't say the difference is SSI is super conservative. The RDP is very liberal.

 

[mgri]

Thanks, Guess I'll stick with the SSI table and play it safe. Of course those longer bottom times at depth sure look nice on the PADI table

 

[Walter]

Take a nitrox class.

 

[mgri]

I'm doing nitrox with my OW class and I plan on diving nitrox when I can. Inevitable, I'll be in a situation where nitrox isn't available and I'll have to go back to air tables. I just wanted to get a feel of which table to use.

Mark

 

[Al Mialkovsky]

computers are nice, but like Padi vs SSI there are conservative computers and some not so conservative.

 

[Snowbear]

Al Mialkovsky once bubbled...
computers are nice, but like Padi vs SSI there are conservative computers and some not so conservative.

My conservative Suunto gives me way more bottom time than any table - and lucky for me it gives credit for deep stops (Yay RGBM!)
p.s. I couldn't do many of the recreational dives I do using the PADI table, expecially if I were to follow the rules about adding 10' for cold water!:wacko:

 

[mgri]

I am planning on getting a computer but I've worked with computers long enough to know how flaky they can be.

bad programming, software bugs, erratic hardware failures... I figure the safe thing to do is to know the tables inside out, plan dives on software, cross reference to tables to make sure they don't totally disagree and then "dive the plan". The main thing about computers I like is their ability to log your dive for you, calculate SAC rates, show ascent speed, etc. I don't think I would feel comfortable about riding a computers no-deco calculations on the fly.

Mark

 

[DA Aquamaster]

The old PADI tables were pretty much straight US Navy tables. The "new" PADI Recreational Dive Planner is based on doppler limits like the SSI tables but also incorporated other major changes from the standard US Navy format and reflected an entirely different decompression model:

1) The PADI RDP uses a 6 hour out, or the assumption that all nitrogen is off gassed in 6 hours. The US Navy tables and the SSI tables both use a 12 hour out and factor in residual nitrogen for 12 hours after the last dive. (This probably means very little for one or two dives fairly close together in the day but made me nervous when doing multiple dives per day and/or diving over multiple days.)

2) Consequently the RDP uses more repetitive groups (A to Z) and the time required to pass from one group to another is much shorter. The SSI tables uses the standard US Navy groups (although only A to K are used or shown) and times and the only significant change is in the lower doppler limits.

3) The PADI RDP also uses many more possible bottom times than the US Navy or SSI tables which for the most part had times 5 minutes apart. The RDP uses more times with the result that at 130 feet you can use 1 to 10 minutes in virtually 1 minute intervals as opposed to the US Navy or SSI table's sole option of 5 min at 130'. So the RDP not only offers more bottom time but also removes one of the fudge factors traditionally used in dive tables to increase the saftey margin, ie. forcing you to use a next greater time in 5 min intervals.

4) The PADI RDP also REQUIRES a 3 min "saftey" stop for all dives over 100 ft and for the longest 4 time intervals at all shallower depths. This in my opinion raises the question of whether the required saftey stops are really just deco stops by another name. If it's required, you can't skip it, you had better have a sufficient independent air source to ensure you can make the stop if you lose your primary air supply, and are essentially engaging in overhead diving. So the bottom times are much more permissive, but there is a catch.

The RNT question:

The PADI RDP allows 80 minutes at 50' and with a 50 min dive to ft you end up as a Group P diver with an RNT of 50 min. and an allowable bottom time of 30 min.

With the SSI table you are allowed 70 min at 50' and a 50 min dive to 50' results in a Group G diver with an RNT of 56 min. and a correspondingly shorter allowable bottom time of 14 min.

For comparison the old Navy based PADI tables allowed 100 min at 50' (and 140 min with a 10 min deco stop at 10 ft., or 160 min with a 21 min stop at 10'.) Of course 100 minutes at 50' would leave you as a Group L diver with a long surface interval required to have any useful bottom time.