Considering a new dive computer..

[dmaziuk]

It would really be a good idea if one of our more experienced members would do a thread explaining the Bühlmann algo / GF as it pertains to Rec divers and with only the info Rec divers really need.
For instance, when I was doing my research, all the information I came across was geared to the tech divers, so it was really difficult to grasp it. As an example, it wasn't until the SurfGF thread that I really got that GF low is not relevant to NDL dives. Before it was confusing to me when I saw Mares have their default Rec GF at 85/85, but the came across Shearwater having different GF low settings for each of the Rec GF (40/85 for instance).

This would be good for those like me who do not have any plans on going tech.

The only people who did any serious work on no-stop diving are DSAT. The 1994 DSAT Report is available from Rubicon Foundation (PDF) for free.

Dr. Wienke did some largely theoretical musings on repetitive diving past the 6 days that DSAT people stopped at. The evidence accumulated since appears to be at odds with many of his theories.

ZH-L model does not pertain to Rec divers at all, in the sense that it pays no special attention to either no-stop, or repetitive dives. Like the others it has tissue compartments and M-values, but it has no special "gradient reduction factors" for repetitive diving, nor DSAT's "sit every sixth day out" written recommendation. It's just a straight exponential model generalized to altitude and helium diving.

Do not confuse Eric Baker's Gradient Factors, as in e.g. 85/85, to "GF surf" or "99" or whatever they call it this week. The former was designed as a way to add extra conservatism to your mandatory decompression schedule and was never intended for no-stop diving. The latter is a way to visualize the theoretical gas loading in one of your hypothetical tissue compartments relative to some theoretically-derived and statistically-adjusted M-value.

 

[JamesBon92007]

I installed bi-focal lenses in my mask so I could read my i300. Lately I've been using an Aladin Pro from about 1991--it's very easy to read it just doesn't do Nitrox, have a thermometer, or the date. But that's OK--it tells me my No Deco time and when I can fly.

 

[halocline]

Hi, I am considering upgrading my dive computer. I have the i300c and it works fine. I have dived with buddys who have the shearwater perdrix ai and i770. The display, ease of reading in low viz and at night, the extra options all seem pretty sweet to me. I do like better the shearwater of the two. I am wondering if it’s really worth the money to upgrade to this level of dive computer for a recreationnal diver? I’m hesitant to buy anything right now thinking that maybe something new will come out with 2020 .. any advice would be great!

I personally think it's a waste of money to spend $800+ on a dive computer for single tank, recreational diving, but it's your money to waste. If you have a dive computer that you can see and use easily and provides time/depth/N2 loading info, that's all you need. The air integration feature is completely unnecessary, but again, it's your money and you should freely spend it on what you want. I used an aeris atmos for more than 10 years for all my diving and eventually bought a used petrel when I needed a technical computer for cave diving. I do like it quite a bit for cave diving but I still use my old atmos on the occasional sunny reef dives I enjoy.

In terms of safety, you are far better off just learning some basic things about decompression theory, just the basics of compartment models, and about factors that are associated with DCS incidence. There is some good, easy to read information in the PADI encyclopedia of recreational diving, of all places. Once you get a sense of how dive behavior (and out-of-water behavior too) affects N2 loading and off-gassing, you will likely dive in a more conservative manner, which is how you lower your risk of DCS. For example, long stops at 10ft in NDL diving are VERY effective at clearing those faster tissue compartments that frequently control recreational dives.

 

[happy-diver]

THE FIVE WAYPOINTS AND SIMPLE ASCENT BEHAVIOR

 

[Ben_3]

I personally think it's a waste of money to spend $800+ on a dive computer for single tank, recreational diving, but it's your money to waste. If you have a dive computer that you can see and use easily and provides time/depth/N2 loading info, that's all you need. The air integration feature is completely unnecessary, but again, it's your money and you should freely spend it on what you want. I used an aeris atmos for more than 10 years for all my diving and eventually bought a used petrel when I needed a technical computer for cave diving. I do like it quite a bit for cave diving but I still use my old atmos on the occasional sunny reef dives I enjoy.

In terms of safety, you are far better off just learning some basic things about decompression theory, just the basics of compartment models, and about factors that are associated with DCS incidence. There is some good, easy to read information in the PADI encyclopedia of recreational diving, of all places. Once you get a sense of how dive behavior (and out-of-water behavior too) affects N2 loading and off-gassing, you will likely dive in a more conservative manner, which is how you lower your risk of DCS. For example, long stops at 10ft in NDL diving are VERY effective at clearing those faster tissue compartments that frequently control recreational dives.

I am curious to why a good / expensive computer would be a waste on single tank dives other than the unnecessary tech options..?

On the other hand I do dive multiple tanks just not tech yet. Maybe one day.

 

[dmaziuk]

I am curious to why a good / expensive computer would be a waste on single tank dives other than the unnecessary tech options..?

If you can see and use it easily.

I can see my <$200 one easily in the sunny Caribbean water and it does not get any easier than checking the battery before a trip and maybe changing the timezone on arrival. As far as not getting bent, since I don't do planned decompression dives, I don't need my computer to match any planning software... If I overstay my no-stop limit to the extent that the ceiling's not clear by the end of the safety stop, it may compute me a sub-optimal deco schedule, but since I don't do that in the first place, I'm OK with that.

 

[Kyle0692]

I have both the Perdix AI and the Aqualung i750 (previous gen of the i770). Originally I started with the i750. My dive shop was converting to Scuba Pro G2 wrists and this was their last one - they cut me a deal on the 750 with a transmitter for $750 new. I have a little over 100 dives with the 750 now and I would say overall it is a good computer. I wanted a computer with AI as I am not a big fan of having an extra hose and also having my tank pressure on my wrist helped me to keep a better track of where I was at on any given dive. Now that I have a bit more experience, I check my pressure less often as I have a better feel of my gas consumption.

The biggest two issues with the 750 in my opinion, the issues are big, is the poor visibility of the computer’s display in bright sunlight even at 100% brightness and poor battery life. To see the display I have to cup my other hand over the computer at times to see my stats which can be annoying. Second, battery life is not good. Even at 50% brightness, I may get 15 HRs before having to change batteries. At 100%, I am usually getting 10. The batteries are CR2’s vs the Perdix which as others have mentioned use AA’s. With all that being said unless the i770 has greatly improved upon those two items, I wouldn’t consider it unless you found a very good deal. Other than these items, the computer is easy to use and you can download all of your dive profiles to keep an electronic log which I really enjoy. If someone here has experience with both the 750 and 770, feel free to chime in on these two items.

Now for the Perdix. I bought a Perdix AI when I started my technical dive training. Compared to the i750, this computer is the end all do all from shallow rec dives to deep technical. The menus and screens are extremely intuitive, the screen is highly visible in all conditions, and battery life is much improved. I am on my 1st battery still with 20HRS and a little under half of it has been used up.

If you are considering tech diving in the future and have the money, I would highly recommend the Perdix to you so you invest once and can grow in to the computer later down the road.

Hope this helps some,

Kyle

 

[outofofficebrb]

I personally think it's a waste of money to spend $800+ on a dive computer for single tank, recreational diving, but it's your money to waste. If you have a dive computer that you can see and use easily and provides time/depth/N2 loading info, that's all you need. The air integration feature is completely unnecessary, but again, it's your money and you should freely spend it on what you want.

I am curious to why a good / expensive computer would be a waste on single tank dives other than the unnecessary tech options..?

On the other hand I do dive multiple tanks just not tech yet. Maybe one day.

None of us need to own a car; we can rent or borrow, or even take public transit. For those that can afford to and choose to buy a car, some buy something simple that can get them from point A to point B. Others get a luxury European export. Both get the job done because you get to where you need to go but with a different experience. This purchase is largely driven by what budget and possibly expendable income the buyer/owner places on it and it is going to be different for everyone else. This is similar to a dive computer, in a sense. "Waste" and "worth" is highly subjective and that's okay so long as everyone is respectful (which everyone here has been) and dives safely.

 

[Ben_3]

I have both the Perdix AI and the Aqualung i750 (previous gen of the i770). Originally I started with the i750. My dive shop was converting to Scuba Pro G2 wrists and this was their last one - they cut me a deal on the 750 with a transmitter for $750 new. I have a little over 100 dives with the 750 now and I would say overall it is a good computer. I wanted a computer with AI as I am not a big fan of having an extra hose and also having my tank pressure on my wrist helped me to keep a better track of where I was at on any given dive. Now that I have a bit more experience, I check my pressure less often as I have a better feel of my gas consumption.

The biggest two issues with the 750 in my opinion, the issues are big, is the poor visibility of the computer’s display in bright sunlight even at 100% brightness and poor battery life. To see the display I have to cup my other hand over the computer at times to see my stats which can be annoying. Second, battery life is not good. Even at 50% brightness, I may get 15 HRs before having to change batteries. At 100%, I am usually getting 10. The batteries are CR2’s vs the Perdix which as others have mentioned use AA’s. With all that being said unless the i770 has greatly improved upon those two items, I wouldn’t consider it unless you found a very good deal. Other than these items, the computer is easy to use and you can download all of your dive profiles to keep an electronic log which I really enjoy. If someone here has experience with both the 750 and 770, feel free to chime in on these two items.

Now for the Perdix. I bought a Perdix AI when I started my technical dive training. Compared to the i750, this computer is the end all do all from shallow rec dives to deep technical. The menus and screens are extremely intuitive, the screen is highly visible in all conditions, and battery life is much improved. I am on my 1st battery still with 20HRS and a little under half of it has been used up.

If you are considering tech diving in the future and have the money, I would highly recommend the Perdix to you so you invest once and can grow in to the computer later down the road.

Hope this helps some,

Kyle

Thanks for the info on the aqualung I have only seen 1-2 from à distance. With the info I have I'm going shearwater they seem to have a better rep.

 

[tursiops]

Thanks for the info on the aqualung I have only seen 1-2 from à distance. With the info I have I'm going shearwater they seem to have a better rep.

Good call.