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Edward Wang writes: > [ cut profile diagram ] > > This was in Pacific ocean, water-temp:52F, surface: calm. vis: 50ft. surge ~2ft. > Total dive time: 55minutes. Very relaxed dive, (in such a good contions). > Lots of H2O drinks before and after. > > If I go by PADI I'm 5 minutes over the limit. If I go by PADI "correct to every > depth and time" I came out as in "Q" presure group, no-deco needed. > > The real question is how do you guys use your table to caculate this multi-level > dive? (Besides using a computer) It should go without saying that if you don't dive with a computer you should dive according to the tables. The dive plan should have included plans for various times and depths. So, for example, for a table only dive to 20m (65ft) I would take down the times for 24m (80ft) and 28m (90) as well, just in case the plan changed underwater. I assume from your description that you are using the PADI RDP. This assumes a square profile - this dive is 'V' profile. What about the PADI Wheel? It should have no problem with this profile. I don't own one so maybe someone else can do the calculation. The Suunto solution should also be able to reconstruct this dive. On the RNPL tables a dive like this takes bottom time as being the time "from leaving the surface until you have reascended to shallower than 9m" (30ft) for the final time before surfacing. IMO if you are considering this dive retrospectively on RNPL, it may not worth considering the 4mins spent at 35ft to be part of your bottom time - I take it that you did not simply spend 4 mins at 35ft, but that 35ft was the deepest you were during those 4 mins. So assuming 51 mins at 70ft, on RNPL you were still well beyond the NDL of 38 mins and should have made a 5 min stop at 10m (33ft) and a 15 min stop at 5m (17ft). However, of the 55 mins you spent only 5 mins at maximum depth and 45mins at 50ft or shallower. This dive almost qualifies as a square profile at 50ft with a short checkout below this in the middle. A square profile to 50ft on most tables will give an NDL BT of over 70 mins. NOTE: I am not suggesting anyone should ever plan a dive this way, nor that anyone should extrapolate from the tables. Just that I would regard the given profile as extremely unlikely to result in a DCS incident. > Furthermore, how to caculate multi- > descend/ascend dives. (Isn't this the case of cave diving?) Before computers, cave divers simply had longer decos. They also used (and still do use) custom tables and special gas mixes to reduce the time. The penetration distance was limited by the amount of gas which could be ported in - mostly a financial restriction. This is why rebreathers are seen as so cheap and cost-effective by cave divers. I have pictures of cave divers porting in sleds with 30-40 cylinders on them. In most wholly submerged caves the deco is carried out at the entrance which simply means a boring wait for the divers, gas supply is no problem. Sump divers often set up camps between sumps to allow large surface intervals between dives. Teams can camp inside the caves for days with porter divers bringing in food, tanks, etc. Alan.
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