Sirto:
Here's a senario I'd like some info on.
If I were on a multi-day, multi dive/day trip and my computer battery died what do I need to do (yes, I know, change the battery).
I think I have seen people indicate that you'd need to take a full 24 hours off to degass before starting to dive again with the computer. I can understand skipping any more dives that you would have done that day, however, let's assume it died after the last dive of the day (say 3 pm). By looking at the dive tables for surface interval I see that a 9+ hr SI will get you down to letter group A regardless of where you were at the start of the SI.
Looking at the dive table for repetitive dives you find that the residual nitrogen time for group A ranges from 3 minutes to 7 minutes. So, couldn't you dive on the following day using your computer and just adjust for this RNT?
I'm just trying to understand the logic for skipping the next day.
Hi,
It depends on the specific computer you are using.
I do not know about other computers but the Cochran Commander and the Gemini both allow you to replace the batteries without loosing residual nitrogen information. It assumes that you have fresh batteries on hand and replace the batteries before the batteries in the computer go completely dead. When you replace the batteries you need to be fairly quick about it, I seem to recall that when I asked Cochran the representative indicated that you would be fine if the Computer only had
all of the batteries removed for about 2 or 3 minutes or less. He indicated that the computers
may even retain the nitrogen information for as much as 10 to 15 minutes if you are lucky, he did however warn me that this was really stretching it and he was comfortable with the 2 to 3 minute reccomendation.
The Gemini has dual battery compartments on the tank unit and you can take as much time replacing the batteries on the tank unit so long as one set of good batteries remains in while you replace the other, as the dual battery compartments are configured in a redundant backup type arrangement, not concurrent usage arrangement. The wrist units are configured with only one battery compartment and this is where the 2 or 3 minute time frame is involved.
As I indicated I am not intimately familiar with the battery changing procedures on other computers, there may be others that allow you to replace low but still servicable batteries in the middle of an extended string of dives without loosing residual nitrogen information.
Frankly, if you are taking an extended dive trip it would be a good idea to replace the batteries BEFORE you even depart for the resort, while you are still at home. Batteries are relatively inexpensive, just buy two sets, one goes in the computer and the other set goes in the save a dive kit just in case. By the way, remember to put some silicone grease on the "O" ring when you replace those batteries so the battery compartment does not flood. I replace the batteries in my computer every year and a half or so, more often if I am planning either an extended trip or extremely cold dives. Cold water will degrade the performance of batteries so even relatevely fresh batteries will not perform like new.
The reason you would want to allow 24 hours before starting with a "fresh" computer is because the computer will assume that you have NO residual nitrogen in your body tissues. It will use the assumption that you have no residual nitrogen as the starting point for all of its calculations for any and all dives you make until you completely off gas to the baseline again. Remember, a computer will take you through a long string of dives tracking your residual nitrogen. If you give it a false starting point ALL of the calculations it will make will be incorrect relative to what is happening in your body. Is this really a game you want to play?
Best of luck,
Mark Vlahos
