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

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kirstyjay

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Location
Tenerife, Spain
# of dives
0 - 24
I live 600-700m above sea level and I am trying to research possible dive computers that would let me know when it's safe to return home after a dive.

The variety of computers available is simply mind-boggling, so if anyone has any suggestions, I'd appreciate it.

I'm a newly qualified PADI OWD, but I live in the Canary Islands with ample opportunities to dive, so I would think that I'll be going at least once a month and would like to invest in some kit that would reflect this frequency of diving, regardless of price. I'd rather save up and buy something I'll use for years than have to spend more replacing stuff later.

Many thanks!

Kirsty
 
I am not aware of any dive computers that will do what you want. Most dive computers only have a 24 hour count down timer that tells you when it is safe to fly after your last dive.

There is a way to manually calculate the time required to wait before ascending to altitude using the NOAA or US Navy Dive Tables. The bad news is that you also have to figure your last repetitive dive group by using the NOAA or US Navy tables for all of your dives for that day. There are no dive computers that will tell you what your repetitive dive group is at the end of a dive.

Attached is a copy of the US Navy Air Dive Tables (you need a different table if you are using Nitrox) and the US Navy Ascent to Altitude Table.

CAUTION -Do not use any other tables (NAUI, PADI, SSI) and the Ascent to Altitude table. The repetitive dive group letters from other agencies may be different than the US Navy Dive Tables.
 

Attachments

  • US Navy Dive Tables 2007.pdf
    274.9 KB · Views: 127
  • US Navy Dive Tables Ascent to Altitude post dive.pdf
    213.8 KB · Views: 148
Hilariously when in a pub/bar/old people’s home in Tenerife at 11pm I got a phone call from a paranoid member of our party whose hotel was at 600m. She was lucky as due some mathematically challenged claims by the odd person earlier in the day I had checked the tables.

Decompression Tables 88 Level 1-4 (with slate)

By the time you have got back to shore, sorted you kit out etc you are likely to be ok. Maybe have lunch or dinner first.

These tables have a ‘transfer table’ which says ‘given a tissue code at one level (eg sea level) if you move to another level this is your new tissue code OR it is not allowed. To make it simple always assume you start from G (is you had stops) and find whatever SI gets you to a tissue code that allows you up to level 2. Don’t completely ignore the weather.

Ps there is enough info at the front of the tables to figure out how to use them, or find a BSAC diver locally, there is the odd BSAC centre there.
 
The Luna by Uwatec has a symbolic representation of safe altitudes that lights up after a dive that changes based upon offgassing.
Screenshot_20200119-152334_Dropbox.jpg
However, the first prohibited altitude starts at 1000m, so your destination at 600m would not even register.
Personally, the comment above about using a surface interval sufficient to get your kit put away would be all the delay I would consider, barring three dives in a day to near-NDL.
 

Attachments

  • galileo_luna_eng.pdf
    3.2 MB · Views: 143
If you are buying for the future, the Shearwater Perdix or Teric will show your GF as you drive up the mountain. This will enable you to pull over and wait at any point where it became worrisome after any number of dives.
Take a look at the Shearwater website and look at the video that portrays the tissue compartments bar graph.
See how the graph blooms on final ascent. It will then retract toward normal during the surface interval, but would begin to rise again upon ascent. All you need to decide upon is an acceptable maximum.
For most technical divers, having a "GF99" of 70 would be just fine during the drive home.
Talk to a tec diver about what all that means. I wish there were an easier way to explain it, but for the altitude you have described, I don't think there's much of an issue.

EDIT: See comments later in this thread. Shearwater has a technique to tell the device that you've switched altitudes. It's not continuous (although the box monitors changes).
 
As some tables (e.g. DECO2000) cover the range of 0-700m, and the fact that diving in Saba has you diving at sea level but staying at altitude with no reported major DCS increase I would not worry to much. Practice a slow accent from 6m upwards, take your time packing up and you should be fine. Also, try to speak to other local divers how they cope with that situation.
 
Thanks for all the replies. The only reason I asked is that I met a diver that had a computer that did this and he also lives at altitude but I can't remember the name of the computer he had now. I'll have a look at all the links!
 
The Scubapro G2 has this built in. From the manual:

"
upload_2020-1-19_19-20-37.png

The prohibited altitude classes are displayed
by yellow (factory initial setting color)
segments inside the stylized mountain icon.
These can be combined with gray (initial
factory setting color) segments indicating
the current altitude. In the example above,
the diver is presently at altitude class 1
and should not reach altitudes of class 4
or higher.
upload_2020-1-19_19-22-4.png

The G2 has an altitude warning. If you
reach an altitude that the G2 considers
incompatible with your current residual
nitrogen levels, it will warn you with an
altitude warning."
 
I live 600-700m above sea level and I am trying to research possible dive computers that would let me know when it's safe to return home after a dive.

The variety of computers available is simply mind-boggling, so if anyone has any suggestions, I'd appreciate it.

I'm a newly qualified PADI OWD, but I live in the Canary Islands with ample opportunities to dive, so I would think that I'll be going at least once a month and would like to invest in some kit that would reflect this frequency of diving, regardless of price. I'd rather save up and buy something I'll use for years than have to spend more replacing stuff later.

Many thanks!

Kirsty
As I understand the basic factors involved, I cant see a need for it. what you are saying is you live 2k above sea level. if you can dive and do a surface at that altitude ,,, then the dive at sea level would be like doing a SS at 2 ft. Since you should probably be driving to that altitude over an hour or more period it would be the same as going at sea level form say 2 ft to the surface in that same hour or so.
 
I go with take your time and not worry about it. I've done the Shearwater observation just to check. My typical drive home after a weekend of diving involves crossing 4000'+ mountain range (I think that is about 1300 meter). And it is pretty much leave the ocean and drive up a mountain. I off gas faster than the ascent being a factor plays in. It is a fairly slow ascent, even though the mountain is fairly steep it takes half an hour to get up there. If you were diving that would be half an hour to ascend 4 feet of water. You are looking at half that. The mountain just can't be driven up fast enough to be an issue (unlike an aircraft that can climb rapidly).

So I go with by the time you get out of your gear, get everything packed up and ready to go you are really safe. I add in having a sit down dinner to add a little buffer time, not be in a rush to leave the beach. I am sure your PADI OWD won't put you anywhere near the gas loading I do on 150'+ planned deco dives. The 'guidelines' that have been taught forever are based on a huge safety buffer on top of the absolute worst case situation. Add in every step along the way wants to play it safe and add even more buffer. I've watched places pad so much safety buffer it's nuts (24 hours before you can leave, take a horrible traffic route because it is only over a 2000' pass instead of 4000' and doubles the drive time).

This is Scubaboard, so there will be the Shearwater recommendation. Which is a good one as it is a great basic computer and will work through the most advanced diving you will ever get to. But as pointed out above it tells you what is going on and not trying to give you an interpretation of the data. Here is what it is, this is what it means, This is good, this is bad.
 
https://www.shearwater.com/products/perdix-ai/

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