EFX
Contributor
I have no idea how to tell my Shearwater computers that I am breathing O2 at the surface. Please tell me how to do that.
You can't select O2 for the surface. I have a Perdix also.
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
I have no idea how to tell my Shearwater computers that I am breathing O2 at the surface. Please tell me how to do that.
Yes. This is correct. Keep in mind that for a relatively mild EAN mix, the difference in residual N2 off-gassed during ascent is pretty small. However, during a surface interval, the difference is more significant.Okay, I assumed all deco schedules reduced a critical amount of nitrogen, but you’re say because the gas is enriched it leaves less residual nitrogen and so lessens the surface interval, if that’s true would breathing 100% O2 on the surface also reduces the surface interval?
Ok, "millions" is of course just a rhetoric figure.
But CMAS or BSAC affiliated clubs make diving courses in almost every european city, all the year around, at prices which are roughy half of PADI, and borrowing you the equipment for free for the course. People interested into diving usually choose the cheapest option.
PADI is strong only in diving resorts, when people are on holidays and find that in their hotel or resort there is a diving center, and they want to try it. When back at home, usually people understand how poor was the training, and if they did like the experience, they continue with a longer, serious course in the local diving club. So yes, PADI makes a good business on holidays location, not in European towns.
I have no figures comparing the number of OW certifications released every year in Europe, but I suppose that the two numbers are not very different.
In UK I am told that BSAC is well ahead of PADI in the number of divers trained each year...
You responded that being on the surface does not matter--you are "'still diving' but on the surface."When I reach the surface, my Shearwater computer assumes I am breathing air, and it gives me no other option. It would be a piece of cake for them to add code that allows me to identify a different breathing mix and track my tissue off-gassing accordingly, just as it does under water, but they will not do that, I assume because it has not been studied.
The computer doesn't care you are on the surface. (The Shearwater Perdix stores the pre-dive surface pressure). For all practical purposes when you are back on the surface the computer continues to calculate tissue loading. You are essentially "still diving" but on the surface. T
You can't select O2 for the surface. I have a Perdix also.
The computer does not calculate NDL using any assumed amount of offgassing on ascent. How could it? What value of ascent do we use? 20 fpm? 30 fpm? 60 fpm? You are correct in that two divers, one using air and one using EAN36, if dove to the same NDL would have an equal N2 loading. On ascent to the surface the nitrox diver would have less residual N2 in their tissues because of "wash out" due to the higher O2. So, these are two different issues. NDL is defined as the time remaining at the current depth before mandatory deco stops are needed. Or, to put it another way it is the time remaining where a diver may ascend directly to the surface. There is no ascent implied in the definition. In my spreadsheet the algorithm I use does not use ascents. I posted the algorithm in another thread.
OK, so if the computer doesn't care I am on the surface, how is it possible that it assumes I am breathing air and will not let me tell it anything different? You said it was still diving--I can change gases while I am diving.
I don't think anyone here has claimed that. PADI OW is roughly the same as CMAS 1* or BSAC OD. AFAIK neither of those classes teach staged deco. But unlike PADI, as you climb the ladder, you get to learn deco theory and practice and are certified for simple backgas deco without "going tech" with all those bells, whistles and woo. Both CMAS' and BSAC's equivalent to PADI DM (3* or DL, respectively) qualify you for simple deco dives.None of the WRSTC members teach decompression as a part of OW training.
One way to add a surface O2 feature would be with a time out. You could designate O2 for say 15 minutes but would have to reaffirm O2 use every 15 minutes when a timer went off. Avoids the left on O2 overnight issue without being too difficult for intentional surface O2 off-gassing. Available in some tech mode only.It assumes you are breathing air because that is what most if not all divers do when they reach the surface; they take their regulators out and breath air. From the standpoint of the calculations the computer doesn't care that you are underwater, on the surface, or 10,000 ft above sea level. But, it does "know" that the in-water dive has ended and you are on the surface, and it restricts your gas to air. (The Shearwater Perdix manual has some information on this.) I posted my guess why Shearwater doesn't allow another gas on the surface. You should ask them why?