PADI tables for shallower than than 35'

[Bob3inFL]

I got certified last weekend and want to use the skills. This weekend looks beautiful for a Lauderdale by the Sea Beach Dive (sunny, west breeze <8 knots). The areas I'll dive are all 30' or shallower. When I apply my lessons learned with PADI dive tables I see I can stay down for 3 hours -- not likely on one 80 tank. I'm trying to figure out how strictly the "rules" apply. Specifically:

1) One section of the dive is 30', the rest is 20'. Is it important for me to do the deeper 30' one first, then the 20'?

2) If we surface to chat in the middle of the dive, do these depths require repetitive dive calculations and surface times?

I know the rules and want to follow them, especially for my first "unsupervised" dive, but don't know how relevant they are to these depths. If the answer is "always follow the rules strictly" I'm fine with that, I'm just looking for wisdom to plan properly. Thanks.

 

[JohnnyC]

What does PADI say regarding table use when your actual depth or time isn't listed, go to the next deepest depth, or longer dive time. In this case you'd do exactly that, even if it's the shallowest depth on the table.

 

[divad]

Are you talking about the ledge past the end of the pier @ the mooring balls?

 

[Bob3inFL]

What does PADI say regarding table use when your actual depth or time isn't listed, go to the next deepest depth, or longer dive time. In this case you'd do exactly that, even if it's the shallowest depth on the table.

Yes, I've done that. At 35 feet I have a theoretical 205 minutes... but one tank of course. If I spend 40 minutes at a time with a 5 minute surface interval I can go down and up three times for 120 minutes -- also longer than I have air. The PADI tables seem to give me more time than I have air at a depth like this. So I'm wondiering of the deeper-then-shallower rule applies, too since I'm in the same depth category.

 

[Bob3inFL]

Are you talking about the ledge past the end of the pier @ the mooring balls?

Yes, but close to the end of the pier, not further out toward the wrecks.

 

[boulderjohn]

Unfortunately, the tables still include the deeper dive first rule, which really went out of existence years ago. There is no reason to worry about it.

The "rule" had its beginning as a suggestion in a 1972 PADI OW manual. No reason was stated. The suggestion eventually became a rule over the succeeding manuals. In a 2001 workshop about that rule, PADI said it did not know who made the original suggestion, or why. The workshop concluded that there was no safety reason for the rule, and it could be ignored. If you have enough surface interval to do the second dive at whatever depth you want, go ahead and do it.

If you plan two dives on the tables and then reverse the order, you will see with almost dead certainty why the original suggestion was made. If you do the deeper dive first, you have a much shorter surface interval between the dives. This was especially important in 1972, because they were then using the US Navy tables, which had seriously long surface intervals already.

If you do go to the surface and chat during a dive, you should usually treat it as a second dive when you go back down again. In such shallow water, though, you can use your judgment. It really isn't going to matter.

 

[divad]

Just make sure you have enough gas to get back to near shore without surfacing. Drunken boaters and ski-poohers are way more dangerous than NDLs.

 

[KevinNM]

Yes, I've done that. At 35 feet I have a theoretical 205 minutes... but one tank of course. If I spend 40 minutes at a time with a 5 minute surface interval I can go down and up three times for 120 minutes -- also longer than I have air. The PADI tables seem to give me more time than I have air at a depth like this. So I'm wondiering of the deeper-then-shallower rule applies, too since I'm in the same depth category.

You pretty much don't have to worry about DCS when you stick to the shallows, at least as a new diver on a single al80. Your air will run out long before you hit the NDL. But get a computer. Even a cheap zoop will be great as a tool for a new diver, as it's easy to not dive the profile you think you are diving, and the NDL drops steeply if you go deeper than you planned.

 

[gassed]

Agreed with Kevin.
Short of diving to, say 40 ft., staying at 40 for 20 minutes and then coming straight to the surface there is no way to use a table to accurately relay relevant data. You are getting absolute limits based on very conservative approximations using a table.
A computer will take into account actual stats and puts those numbers to use in real time. It also gives you one place to see depth, dive time and NDL in one quick glance,
As noted, at the depths you mention, you will run out of air before NDL.
Its great to be cautious. As a new diver I remember 100 things running through my head at once. Watch your air, watch your depth, but take a look around and enjoy things once in a while.

Enjoy!

 

[Colliam7]

First, good for you for thinking about these questions, and asking them! That suggests you are on your way to becoming a thinking diver!

My answers to your questions:

1) One section of the dive is 30', the rest is 20'. Is it important for me to do the deeper 30' one first, then the 20'?

No. Boulderjohn has provided a good response. In addition, all of the dive will be shallower than 35 feet, so you are within the boundaries of that group at either / both depths.

2) If we surface to chat in the middle of the dive, do these depths require repetitive dive calculations and surface times?

No. You have already noted that you are very unlikely to exceed the NDLs for a dive to 35 feet (or shallower) simply on the basis of air consumption. Many divers surface at some point during a shallower dive, and then re-descend, and treat to total time (including the surface chat) as part of their dive time.