Multi-level repetitive dives

[Web Monkey]

My dive group is going to Bonaire in 2 weeks. We're planning on diving as much as possible while there but also want to make sure that we remain safe.

We all have computers but I'd like to use this opportunity to double check my comp against the tables, and because I'm a total geek. I only went through the 'whiz bang' 5 minutes of PADI table instruction when I took the class but I do remember the basics. My question is; how do I work the tables for 4 or more dives per day? We're thinking about early morning, midday and night diving while there.

You really can't use tables to "double check" your computer, since your computer and the tables use different algorithms and different input data. Tthe computer knows your actual depth and time at every moment, while you can only estimate it for the tables.

If you're looking to safely do many repetitive dives, I'd recommend nice slow ascents, stay very well hydrated, well away from the edges of your table or your computer's "deco" alert, and according to our very own Dr. Deco, avoid physical exertion right after diving.

Terry

 

[Brett1971]

???This is an advanced scuba discussion??? Sorry, but this is somewhat frightening. Compared to the computer calculations, the table calculations will be very inaccurate for the multilevel profiles but wiil be a very conservative estimate of NDL. Isn't this something that should be reasonably clear following OWD certification?

Good diving, Craig

Yes Craig, it is 'reasonably clear' but that's exactly why I asked the question; I want to learn and increase the knowledge that I already have. I figured the best way to do that would be to ask people who are more knowledgeable on the subject than me; that way I can make sure that my understanding is accurate and maybe learn something in the process. I'm sorry my question isn't as advanced as you'd like.

Brett

 

[Brett1971]

You really can't use tables to "double check" your computer, since your computer and the tables use different algorithms and different input data. Tthe computer knows your actual depth and time at every moment, while you can only estimate it for the tables.

If you're looking to safely do many repetitive dives, I'd recommend nice slow ascents, stay very well hydrated, well away from the edges of your table or your computer's "deco" alert, and according to our very own Dr. Deco, avoid physical exertion right after diving.

Terry

Thanks Terry! I guess double check was the wrong wording...I really just want to compare what the table says as to what my comp says. I see heated discussions on here advocating one over the other; I've never really given it any thought but figured a whole week of diving would allow me to experiment a bit.

I appreciate the advice though!

Brett

 

[Brett1971]

Brett1971 if you are using you computer dive most likely you will be at the limits or over the limits for the table. Let say you start you dive at 80 ft and you are their for 15min then you go to 40ft for 30 mins what letter are you? Tables are meant for a square profile not multilevel diving. PS I hate the Padi wheel to do they still have a warehouse full of those things.

You're right, I hadn't really thought about it like that. I guess we really are going to be doing square profiles anyway...enter the water, go to our deepest point and work our way back to the shore. I guess what kinda threw me off is that this is going to be the first time any of us have dove from shore. I've always been on a boat when I dive.

Thanks!

Brett

 

[Jim Lapenta]

You can use the rdp for multilevel planning but it does require you to keep accurate account of your depths and bottom times when you change those depths. If you are doing reef dives in Bonaire on the reefs from shore and diving like you said I'd advise, just for practice, planning an actual mutilevel. Say heading out from the shore to say 70 feet for 20 minutes. Go along the reef for 18 minutes then ascend to 50 and come back in the opposite direction for the same time. Stay as close to planned depth as possible. Then when you get to your entry point ascend to say 20 and swim around for another 20 minutes, air permitting, then do your final ascent. See how close you come to your projected planned pressure group in actual times as it may be a bit off due to current, hitting the exact entry, etc., and compare it with your comp reading. You may be surprised at the outcome depending on your computer's algorithm. I did a few of these types of dives when I was there from the house reef a Divi Flamingo. Helps keep things fresh and reinforces the value of tables should your comp crap itself.

 

[rstofer]

What you propose, shore diving out to some depth and then cruising back to the beach, underwater, is NOT a square profile. Unless you want to consider every moment under water as time at the maximum depth, the tables won't help you.

Suppose it took you 10 minutes to swim out and down to 80 feet, following the bottom contour. Then you swim around for 10 minutes and take another ten minutes to get back to shore, again following the contour. To use the tables properly, you would need to treat this as a 30 minute 80 foot dive. Clearly, it isn't.

The way to use the tables for this kind of dive is to swim out and back on the surface and truly dive a square profile. Swim out on the surface, drop down to 80 feet, swim around and ascend. See your dive tables for the 80 foot NDL and don't forget your safety stop.

You just can't use tables 'half way'. It's an all or nothing kind of deal. The tables are for square profiles and that's all they can be used for. Or, you need to consider every bit of time underwater as though it were at the maximum depth.

Dive your computers and call it a day. Buy a spare computer if you think it's necessary.

Richard

 

[Jim Lapenta]

If he plans a multilevel then they can be used for that. The rdp can be used for multilevels if accurate data is kept. Just plug in a 0 surface interval between levels. This works on the erdp as well. And a straight out descent to 80 feet on Bonaire depending on the reef itself should take no more than 5 minutes. At Divi if you head straight out at steady pace I hit 75 ft 4 minutes into the dive and then did the dive as previously noted. The final ascent from the top of the reef at 25 feet or so is no different than the straight slow ascent I teach my OW students. I have no problem if they take 10 minutes to come up that final 15-20 feet.

 

[DA Aquamaster]

Padi now makes a multi level electronic dive planner eRDPml. Electronic version of the wheel.

I have been bothered by the eRDP for awhile but have not been able to put my finger on it.

I think my major issue is that if I work something on an RDp or the Wheel, I get a very visual indication of exaclty how close I am to the endge of a pressure group, square profile, etc, so I am able to identify when I may want to add soem conservatism. With an eRDp, a diver puts some numbers in and gets some numbers out and it is literaly a "trust me" situation.

I am not sure that is a step in the right direction - and the batteries never die on a Wheel or an RDP.

 

[Doc Harry]

Padi now makes a multi level electronic dive planner eRDPml. Electronic version of the wheel.

To err is human, but to really screw-up takes a computer.

I'll take my wheel and tables, danke.

 

[rstofer]

But the Wheel and eRDP-ML are only useful AFTER the dive. It is very unlikely you will have an exact profile before the dive. I suppose you could use the Wheel under water but it's out of the question for me unless I can bring my reading glasses.

I liked the square profile approach of writing ANDLs on a slate. It was simple and I understood it. None of the other schemes seem to do much before the dive and after the dive they can only tell you whether you need to head for a chamber.

I'm a strong supporter of tables and square profiles. For boat dives it works pretty well. But for multi-level diving and the increased down time it delivers, I don't see a way around using a computer.

Richard