Just started my certification course and am wondering about the following:
1. Using Naui dive tables, what happens if you stay longer than the maximum dive time you are supposed to stay without a deco stop? As an example, what if you go down 60-ft and go beyond the maximum dive time of 55 minutes to, say 65 minutes? Is this dangerous or does it mean you just need a longer deco stop?
Since you are using NAUI tables, a certain amount of deco information is provided. The MDT (NDL to PADI divers) is 55 minutes for 60' However, if you overstay to 80 minutes you MUST make a 7 minute stop at 15'. This stop is MANDATORY.
Recreational diving is based on the concept of a direct ascent to the surface at any time. A mandatory deco stop moves the dive outside recreational concepts.
Is it dangerous to use the NAUI tables exactly as given? I doubt it! If it was significantly more dangerous, the tables would have been revised years ago. As far as I know, the 1989 edition is the most current version and it requires an ascent rate of 30 fpm while PADI still allows 60 fpm.
Every agency is recommending a 3 minute
safety stop at 15 feet. But the safety stop is not mandatory. Those deco entries on the NAUI table ARE mandatory. Skip them and you will very likely wind up in a chamber.
There is also a significant difference in how bottom time is measured. For NAUI, it is the time between descending from the surface and ascending back to and reaching the surface. The entire round trip. Obviously, it doesn't include the mandatory deco time (although the tables don't say that). Since you can only ascend at 30 fpm, you need to cut 2 minutes off the MDT of a 60' dive so you are back to the surface on time. You really have just 53 minutes from the time you leave the surface until you must begin your ascent for the first (non-repetitive) dive.
2. What about on your second dive if you go beyond the adjusted maximum dive time (AMDT)?
Even with the extended bottom times and mandatory deco, you still wind up with a letter group. There is no change in the procedure, you just do the surface interval and plan the next dive.
You should be discussing this with your instructor. Most of the folks around here are working with the PADI tables and NAUI concepts are different.
Ask your instructor. Don't rely on a single word I have typed. If you mess this up,
you will wind up in a chamber or paralyzed or dead.
Personally, I never went beyond the MDT. I never wanted to test the deco entries.
Richard