Galileo Luna and Mixing Algorithms

[JBreezy]

Hello!

So I was looking for a fairly inexpensive backup computer to get before an upcoming trip to Bonaire. I am currently using a Sherwood Sage (DSAT - modified, I believe). Anyhow, I stumbled upon (what seems to me) a pretty good deal for a used Galileo Luna + transmitter. I've heard really good things about this computer (with the exception of the IR transfer), so it piqued my interest.

My question is how the ZHL-8 ADT MB algorithm would compare to what I'm currently using. If anyone has compared the two side by side, I would love to hear your experience. My understanding is with the MB and other extra stop turned off (L0), ZHL-8 is pretty middle of the road as far as conservatism where DSAT is more liberal. I was wondering how close these to algorithms could be expected to be in terms of NDL and if I were to make sure to watch whichever computer gave me lesser NDL, does anyone foresee any issues with running two computers with different algorithms?

Sorry if this has been done before, most of the comparisons I saw involved ZHL-16, which brings me to another question - it seems no one uses ZHL-8 anymore. Is this an indicator I should avoid it altogether? I've read some people actually prefer it to ZHL-16. Just curious for some current opinions.

Thanks in advance!

 

[CandiveOz]

As a general rule, when it come to a backup computer I would recommend a computer with the same algorithm or one that is more liberal. In your case, a used Sherwood or Oceanic would be the appropriate choice. This issue was addressed in the following post and may help you with your decision.
Matching Dive Computer Algorithms

In saying that I do own a Galileo Sol which is the big brother to the Luna. In fact one can upgrade the Luna to the Sol specs so essentially it’s the same computer. I really like my Sol and haven’t had any issues with the computer or air integrated transmitter. Both the Sol and Luna can be upgraded to ZHL-16 ADT MB with the Trimix upgrade. With the Luna, you first need to purchase the PMG (Predictive Multigas Gas) upgrade before installing Trimix. The Sol already has PMG. I haven’t upgraded to Trimix since I don’t dive it and apparently ZHL-16 ADT is a little more conservative than ZHL-8 ADT MB.

As for ZHL-8 ADT MB, it has been out there for decades and is a reliable algorithm. Yes, it is more conservative than DSAT but this is not necessarily a bad thing and depending on the type of diving you do, may not be an issue.

You mentioned that the Luna you are considering is used, so if you buy it and decide it’s not appropriate, you can always sell it. The price differential wouldn’t be that different as compared to buying a brand new computer then selling it in the secondary market.

As I have said I really enjoy diving with my Galileo and if you have any other questions regarding the Luna, just ask.

 

[JBreezy]

Thanks for the input. I've been through that thread, and several of the ones linked in there (at least most of the way through). It was hard to find any info on ZHL-8 in relation to DSAT via searching.

I did finally come across the chart below, which made me a bit hesitant, as unless I am reading it wrong, shows quite drastically lower NDLs with ZHL-8 compared to DSAT. I'm okay with being a bit more conservative than DSAT, especially since that is one of, if not the most liberal algorithm excepting those in which you can modify GF values, but this seems a bit extreme the other direction, if the chart is accurate.

I was also hoping someone who has used both together might be able to chip on on how these perform over multiple dives/day for multiple days. Can I assume that ZHL-8 will behave similarly to ZHL-16 in that respect, but a bit more conservative? Also, am I correct that with Scubapro computers, if I turn the MBL to L0 and turn off the other additional stop they throw in that it would behave like most other computers without the additional stops?

Thanks for your input!

 

[CandiveOz]

Hi @JBreezy
Like I said, if you are interested in just a backup then just choose a Sherwood or Oceanic and you won’t have to worry about all this stuff. But if you are interested in trying different algorithms then his may be a unique opportunity. Just to clarify; my understanding is that Scubapro's implementation of ZHL-16 is a little bit more conservative than ZHL-8; not the other way around.

In terms of comparative analysis, Scubalab conducts tests every year on the current models which is discussed in these forums. The tests are based on four multilevel dives all within NDL limits. The tests give you a side by side comparison so you may find that useful if no one chimes in with the experience of actually diving with DSAT and ZHL-8/16. In fact, if you get the Galileo, you may become the Scubaboard’s subject matter expert regarding these two algorithms – the actual diver you are looking for.
How to properly assess the relative conservatism of various algos/computers for Rec divers?

Below are the NDLs of both computers. As you can see the Sage is more liberal than the Galileo.

DSAT was specifically developed and tested as an NDL multilevel multiday dive algorithm. While it allows decompression it does not recommend it. The Sage manual states;

“It should not be utilized for any competitive, or repetitive square wave or decompression diving, as it is intended solely for recreational use.”

On the other hand the Galileo is a decompression dive computer and allows you to plan decompression dives.

This may or may not be important to you. Again, based on your diving, the difference between the two computers may not be material because the conservative computers tend to “catch up” in terms of NDL as you get shallower during your dive. The worst case scenario is that the Galileo may recommend a short deco while the Sage may indicate you are clear to surface. This is not necessarily a bad thing. Remember, “Liberal” doesn’t mean “Better”; coming from a diver who has been treated for the bends.

To specifically answer your question, if you set the Galileo to L0 and turn off PDIS and turn off Workload, the computer will follow the NDL limits stated above. But even if you set the microbubble to higher level (L1-L5) these are soft limits; meaning the computer will not lock you out if you ignore them. Only L0 is a hard limit. If you set the Sage to a more conservative level, it will lock you out if you do not follow the deco profile even though you are actually diving within the NDL of the standard default setting.

Even though the Galileo has been around for over a decade, the computer is actually more sophisticated than many new dive computers offered today including the Sage.

 

[scubadada]

Hi @JBreezy

Your Sherwood Sage was manufactured by Pelagic Pressure Systems (now owned by Aqua Lung) and runs DSAT, exactly the same DSAT run by other computers manufactured by PPS, Oceanic and Genesis. Your Sage will always be more liberal than a Scubapro (Uwatec) Galileo Luna running Buhlmann ZH-L8 ADT MB. The Luna would always control your dives and you would have to ascend on its NDL, or be willing to clear a decompression obligation to avoid being locked out of its use as a computer. If this is acceptable, the Luna would serve you well, actually, as your primary computer under this description.

I am with @CandiveOz, I would probably just buy a 2nd computer running DSAT and have the two match very closely. You can always not dive them to the NDL limit to increase your level of conservatism. The Oceanic Geo 2.0 is currently available for $270, as it will be replaced by a Bluetooth version, the Geo 4.0

Best of luck in your computer purchase