Question Do we have viable alternatives to Shearwater?

[Wibble]

Set the Suunto Eon to the Buhlman algorithm and it will not lock out. This feature is over 4 years old.

And do you really plan to miss over 4 minutes of Deco and then go on another dive?

The issue with Suunto is the CYA (cover their arse) by turning a $$$$ computer into a brick for two days at the drop of a hat. Changing modes for example.

Deco isn’t a fixed “law”, it’s merely an algorithm with lots of conservatism added. There are many reasons to cut short one’s deco without this being dangerous. For example you’ve set your conservatism lower — which adds more deco time — but you need to get out due to conditions or other circumstances: you’ve set your gradient factors to 50:75 and you’re at SurfGF of 80** and need to get out; that’s not a problem and you shouldn’t have any surface time penalty.

With Shearwater, no issues.

With Suunto, the computer’s now bricked for two days.

4 mins of deco isn’t a large amount. From my experience, it’s about 7 “GF highs” which will be well under the 100% value.


** SurfGF: Surface gradient factor: this is your tissue loading at any point in the dive should you be instantly transported to the surface. On NDL dives this will always be less than 90. On deeper decompression dives this can be 400 or higher, i.e. instant death should you be on the surface with that tissue loading. This drops quite quickly during your hours of deco, eventually reducing down to the GF high setting when you can ascend slowly to the surface.

I don't believe that Suunto will have a SurfGF data box as they're still wedded to their proprietary RGBM deco model (or whatever extended TLA they use). Shearwater does have SurfGF as they use the defacto standard Buhlmann deco algorithm and you can have this on the middle or lower rows of data in technical mode.

 

[ofg-1]

Hey all,
What is a decent alternative to Shearwater computers for OC Trimix?
CCR capable would be nice, but not a must have.
150 meters capable

Gotta ask, do you see yourself doing open circuit trimix dives to 150 meters?

 

[SelfDiver]

Gotta ask, do you see yourself doing open circuit trimix dives to 150 meters?

100-120m about 10 times a year with 150 twice a year

 

[rongoodman]

I'm always curious about this. What would be the correct behaviour for a computer when the parameters of the model have been exceeded and it knows full well its calculated ascent profile is no longer even an approximation of a "good" one?

What do you mean by "the parameters of the model have been exceeded"? Off-gassing will still continue at a predictable rate even if you've violated a deco ceiling.

 

[David Carron]

What do you mean by "the parameters of the model have been exceeded"? Off-gassing will still continue at a predictable rate even if you've violated a deco ceiling.

A model like ZHL16 can predict a safe ceiling, but ascents which violate that ceiling are outside of its domain.

A related example might be a 25m dive with GFhi around 75. At the 15th minute the diver does a rapid, uncontrolled ascent to the surface where he remains for two minutes before redescending to 25m. Just before the uncontrolled ascent he was probably very close to his NDL, but ZHL16 is now predicting a further 5 minutes of problem-free NDL bottom time at 25m. Note that this example hasn't even violated ZHL16's ceiling but there's no real doubt that its calculated ascent profile is - at best - sketchy.

You could also consider a dive with 45 minutes of deco starting at 21m, where the diver ascends directly to the surface for a few minutes before starting the stops. Those stops will be significantly reduced, although again there's no real doubt that executing this calculated ascent profile is - at best - sketchy.

 

[kensuf]

Divesoft Freedom, Ratio something or other, and Garmin will all do the job. I know a number of people sporting Garmins these days.

 

[rongoodman]

A model like ZHL16 can predict a safe ceiling, but ascents which violate that ceiling are outside of its domain.

Based on what? Are you saying that off-gassing works differently following a deco violation. (We had a poster here a few months ago making that very claim in support of RGBM but was never able to point to any research backing it up.)

 

[David Carron]

Based on what? Are you saying that off-gassing works differently following a deco violation. (We had a poster here a few months ago making that very claim in support of RGBM but was never able to point to any research backing it up.)

I don't think that there's significant doubt either that ZHL16 is a purely dissolved gas model or that the constraints of physical decompression are not purely those of dissolved gas transfer (otherwise at the very least there would be no limit on ascent speed).

 

[NothingClever]

What would be the correct behaviour for a computer when the parameters of the model have been exceeded and it knows full well its calculated ascent profile is no longer even an approximation of a "good" one?

Not intending to be inflammatory or contentious (I’m a hugger not a hater) but that’s a strange question that seems to shift responsibility for prudent judgment and control from the diver to the DC.

 

[pdwh]

apeks DSX?

Had one and sent it back. It bricked (red screen, no recovery) in the middle of a dive. They authorized a replacement unit but after two months of waiting (backorder), I returned it and bought a Shearwater Peregrine TX (which works with the two Apeks transmitters I bought). Haven't had a single issue with the Shearwater and the screens easier to see.