Can anyone suggest a computer for returning to altitude after a dive

[inquis]

Deleted... Necro thread.

 

[SKS22]

Nah, the manual (as are most Garmin manuals) is lacking detail.
Descent Mk1 - Viewing the Surface Interval Widget


I have reached out to a contact I have within Garmin for a more detailed explanation of what the percentage means.

I need to do a dive where I get close to NDL (or even a bit of deco) and see what the percentage is immediately after surfacing. That would at least show me what percentage is considered "safe".

I think the percentage correlates roughly with the post dive letter one would get using dive tables.

I know this is old but I'm replying to ATJ cause he's basically the Garmin guy. He comments on Garmin stuff and keeps up with the board. I only show up occasionally which is why I'm years late on this thing. I very much appreciate his various comments re the descents. Helped me (and probably a lot of other folks). I figure ATJ is the best dude on the board to check my theory and if it makes sense, to pass it along.

So I've used PADI RDP and Navy tables for years for reasons I won't waste time on. When I finally got a modern fancy computer, the Garmin Descent MK2i, I was also confused by the surface interval widget and what the percentage meant, so I tracked some dives with my trusty Padi RDP AND the new Garmin and found that the percentage displayed in the surface interval widget was pretty close to the letter I would get from the RDP. Not a perfect match, but pretty close. To compare them I basically used 26 as a denominator since there are 26 letters in the alphabet and the number of the letter as a numerator then converted to a percentage. To get around the fact that dive tables assume square profiles I used the computer's average depth when using the tables rather than the maximum depth. Using that procedure, I found the computer's percentage be close to that of the RDP. So in conclusion I think the surface interval widget is giving users a real time pressure group letter that updates with the passage of time and changes in altitude. Based on that I would not allow the percentage to reach 100 because that would correspond with a Z on the recreational dive planner, which means an unacceptable risk of getting bent to those who can't make a decompression stop or enter a chamber.

Regarding the original question, in case somebody stumbles back on this topic later, I don't think less than 1000 ft matters much for regular recreational diving because the PADI Advanced Open Water manual does not bother providing theoretical depth at altitude until 1,000 ft, and even at 1,000 ft the difference between theoretical depths and actuall depth is minor -- between 1 and 5 ft. Put another way, if Op was diving at the home's altitude adding 125 feet to actual bottom depth and observing the resulting no decompression limit would be safe. So I would say that Op is almost certainly fine heading home right away.

 

[Tim R Alcoser JR]

Great info! This is of importance to me as I recently moved to the mountains. My home is at 6,400 feet. The type of diving I do rarely exceeds 60 feet off the beach, but I typically do at least 2 dives.

The drive home typically averages about 1 1/2 to 2 hours.

Based on everything I'm gathering here, I'm assuming it's better to play it safe and just get a hotel for the night on monthly dives?

Anyone else live up at altitude?

 

[inquis]

@Tim R Alcoser JR - much depends on the dive times, surface interval, and packup times. Also is all of the dive around 60 ft or do you gradually ascend? Nitrox is an easy way to improve your situation if gas is the limiting factor of your dive time.

Bottom line: I think it would be quite feasible to drive home the same day under many conditions. Others, perhaps not.

 

[Blackcrusader]

Great info! This is of importance to me as I recently moved to the mountains. My home is at 6,400 feet. The type of diving I do rarely exceeds 60 feet off the beach, but I typically do at least 2 dives.
The drive home typically averages about 1 1/2 to 2 hours.
Based on everything I'm gathering here, I'm assuming it's better to play it safe and just get a hotel for the night on monthly dives?
Anyone else live up at altitude?

I do but I never drive back up the mountains right away even in Taiwan I normally overnight at sea level after a days diving. A lot of the dive sites are several hours drive away.

 

[Tim R Alcoser JR]

On my first dive back in the ocean at the Dr. Bill Bushing Dive Park, I played it safe and got a hotel for the night on the mainland as my Garmin Descent G1 said I technically needed to wait until 6:23 AM the next day before "flying".

My next step is to get Nitrox cert for sure and that should be enough time with the boat crossing, dinner and a slow drive home.

 

[Angelo Farina]

My next step is to get Nitrox cert for sure and that should be enough time with the boat crossing, dinner and a slow drive home.

I am not sure that diving with Nitrox will shorten the time before flying: if you still "ride the NDL" you will end up staying more time on the bottom, at a smaller equivalent depth (thanks to reduced pp of Nitrogen).
A longer, shallower dive will load more your slow tissues, which of course will take more time to offgas after emerging.
If you want to offgas more quickly, you should dive deeper and shorter.
Of course I assume that in either case you dive to the edge of NDL, as it appears to be the norm nowadays for recreational diving.

 

[boulderjohn]

I am not sure that diving with Nitrox will shorten the time before flying: if you still "ride the NDL" you will end up staying more time on the bottom, at a smaller equivalent depth (thanks to reduced pp of Nitrogen).

Contrary to what many people seem to believe, if you use nitrox, you are not required to stay down all the way to the NDL. People are allowed to surface earlier than that, and many people do.

For example, if you are doing a dive to, say, 80 feet on EANx 36, according to the PADI tables your NDL is 55 minutes. You don't have to spend 55 minutes at 80 feet--which most people could not do anyway without a really big tank. You can ascend after, say, 40 minutes, which would be a very reasonable dive time if it was spent entirely at 80 feet. If you are instead doing a multi-level dive using a computer, you can have an even much loonger dive without going anywhere close to the NDL.

So, yes, if you use nitrox, you should be able to ascend to altitude sooner than if using air. Your problem is that unless you use the US Navy or NOAA ascent to altitude tables and make the necessary conversion, you will be just guessing about it.