oceanic dual algorithm

[HeatCker]

my question has to do with oceanic's dual algorithms, dsat vs pelagic z+
i'm just wondering what algo do you choose when doing square profile wreck dives
say one single day, 2 or 3 dives, with a 1 hr surface interval in between
water temp in the 45 F range
follow rope down to wreck, follow rope up to buoy marker
recreational wreck dives, no deco, in the 90' - 110' range
thanks

 

[Marie13]

I always used the more liberal one. And I only wreck dive unless I’m at a quarry.

I have a Oceanic Geo 2.0 for sale in the classified section if you’re looking for one.

 

[HeatCker]

thanks for the offer marie, but i already own an oceanic.
yours is listed at a good price, if i needed one i'd snap it up quick.
for local diving, one tank dives, i use my suunto vyper, it gives me all the time i need on single tank dives.
for multi day and/or multi dives i use the oceanic and dive it in the dsat setting, and i usually do typical rec profiles, deep slowly angling up to the surface.
as you well know, great lakes wreck diving is different, its a square profile.
if i'm reading the manual correctly, pelagic z+, is more suited for this type of diving.
i'm just wondering if anyone familiar with the dual algorithms could tell me if i would get more bottom time with z+ on single day multiple wreck dives.
this might be a hard question to answer as everyone is diving shearwater these days.
thanks for you answer.

 

[runsongas]

for a single dive day, it makes sense. dsat is better when multiple dive days are involved. on a single day though, the difference between the suunto and z+ are small unless if you do something the suunto hates on the first dive, which generally doesn't happen on a square profile.

 

[scubadada]

Hi @HeatCker

Actually, I would advise you to dive the decompression algorithm you are comfortable with. You are doing repetitive, no stops dives, either algorithm is appropriate. DSAT is a relatively liberal algorithm on 1st dive and repetitive dives. PZ+ is middle of the road for 1st and repetitive dives. DSAT will give you longer NDL times for both first and repetitive dives. A comparison of 1st, clean dive NDLs will give you an idea of the difference, here they are shown for 32% nitrox

Though the algorithms behave differently, DSAT approximately maps to a Buhlmann GF high of around 95 and PZ+ maps to around 85. Suunto RGBM gives a pretty liberal 1st dive NDL and then behaves more like PZ+, unless you are penalized for short SI, fast ascent, or some other algorithm infraction.

I have about 1900 dives with DSAT on my primary computer. I have dived a number of backups including Cochran, Oceanic DSAT, Dive Rite Buhlmann, and now, Shearwater.

 

[HeatCker]

thanks all, for your answers and explanations

 

[Belzelbub]

For rec dives, it probably doesn’t matter too much. I dove for years with Oceanic computers on DSAT. I now use a Shearwater, and my daughters both have Oceanics with dual algorithm. I started looking into the differences and comparisons with how I have my Shearwater set, and switched theirs to PZ+.

Prior to getting my Shearwater, I was researching algorithms, and came across this comparison. Now these were deco dives, but it shows how the DSAT computer reacted very differently. On the same two dives, almost all the other algorithms finished the dives with a required deco stop of 0-5 minutes, the DSAT computer required more than 20 minutes of deco.

A sense of algorithm

If you stay well under NDLs, then I don’t think you’ll have a problem with either. If you tend to push it, DSAT will punish excursions quite severely compared to the others.

 

[scubadada]

For rec dives, it probably doesn’t matter too much. I dove for years with Oceanic computers on DSAT. I now use a Shearwater, and my daughters both have Oceanics with dual algorithm. I started looking into the differences and comparisons with how I have my Shearwater set, and switched theirs to PZ+.

Prior to getting my Shearwater, I was researching algorithms, and came across this comparison. Now these were deco dives, but it shows how the DSAT computer reacted very differently. On the same two dives, almost all the other algorithms finished the dives with a required deco stop of 0-5 minutes, the DSAT computer required more than 20 minutes of deco.

A sense of algorithm

If you stay well under NDLs, then I don’t think you’ll have a problem with either. If you tend to push it, DSAT will punish excursions quite severely compared to the others.

Hi Brian,

Do you have experience diving DSAT into deco or are you relying entirely on the article? I have been diving DSAT on my primary computer since 2002, about 1900 dives. I have been aware of the article you cite since it was published in 2009. It is entirely inconsistent with my experience with DSAT. I have always wondered if they dived it on the conservative setting, which would be more conservative than diving PZ+.

I have 82 light deco dives on DSAT, average 5 minutes, range 2-14 minutes. My computer has never behaved as illustrated in the article. My last 25 light deco dives have been with a backup computer running Buhlmann, first a Dive Rite Nitek Q and now a Shearwater Teric. Both of these computers have been running GF 75-80/95. The deco obligations of the computer running DSAT, an Oceanic VT3, have matched the computer running Buhlmann, very closely.

This article has been cited several times on SB, my own experience is at odds with the results. Perhaps others with experience similar to mine will speak up on the topic.

 

[Belzelbub]

Hi Brian,

Do you have experience diving DSAT into deco or are you relying entirely on the article? I have been diving DSAT on my primary computer since 2002, about 1900 dives. I have been aware of the article you cite since it was published in 2009. It is entirely inconsistent with my experience with DSAT. I have always wondered if they dived it on the conservative setting, which would be more conservative than diving PZ+.

No, I never took the DSAT Oceanic into deco. It’s entirely possible that it was in conservative mode. That also seems consistent that the only other computer to rack up close to that amount of deco was also in a conservative setting.

Now that I think about it, you are probably right. I did a deep dive with the Oceanic last year for a Deep certification. During the dive, one of the students came up with a medical issue. This student had pretty much the same profile as me. When I checked my log on Diverlog, it showed around 16 minutes of NDL time remaining at the deepest point. When I checked in Subsurface, it showed 3 minutes. Both were pulled from the same computer. Subsurface, calculated the NDL using Buhlmann on a fairly consevative GF. When I set it to a less conservative GF, it got closer to the DSAT NDL, but didn’t show more.

 

[dmaziuk]

as you well know, great lakes wreck diving is different, its a square profile.
if i'm reading the manual correctly, pelagic z+, is more suited for this type of diving.

Not necessarily. DSAT was primarily tested for multi-level profiles because those were bits "specific to DSAT algorithm". Square profiles were already well tested by USN by then and DSAT "building on" USN tables. It doesn't follow that Buhlmann's general model (not specifically tuned to no-stop diving) with Pelagic's "Z+" tweaks, whatever they are, is "better suited for that type of diving" -- DSAT had at least one square profile a day in their test schedule.