What's the point of these 3 gas computers?

[Puffer Fish]

A quick look at Suunto.com gives this:

"Decompression calculations are based on the Suunto Deep Stop RGBM model, which provides iterative deep stops as an alternative to traditional safety stops."

Where can I take a look at the "Suunto Deep Stop RGBM model" and use it to plan a dive to 300 feet? I assume this is readily available so I check what stops the computer will require on a particular dive?

I cannot speak to the Suunto, but the Galileo allows dive planning with up to three gasses, and allows you to adjust how conservative the calculation is. To your point, it allows you to see the calculations in the dive planner, including gas switching points to compare to another program.

It will also show you what the profile would be, if you stay on the gas you are on.. and don't change.. just in case.

However, it only does this to a depth of 189 ft, and does not allow the use of O2 below 21%, so it is clearly not a trimix computer.

You can do this with or without the wireless transmitters. Doing a quick check against the Decochek program, they appear to be very similar (did not check a lot of different profiles)

As you can use the change gas alerts (I have done a night dive, with my light out and used the safety stop alert to tell me when I was at 15 ft, it is a fairly nice system) as a safety reminder... and any mistake you might make is auto corrected, not sure that this might be a better way to go. It would still involve a dive plan... but as a backup, it is far more capable of doing any changes that a person would be.

 

[FishOutUvH2O]

I cannot speak to the Suunto, but the Galileo allows dive planning with up to three gasses, and allows you to adjust how conservative the calculation is. To your point, it allows you to see the calculations in the dive planner, including gas switching points to compare to another program.

It will also show you what the profile would be, if you stay on the gas you are on.. and don't change.. just in case.

However, it only does this to a depth of 189 ft, and does not allow the use of O2 below 21%, so it is clearly not a trimix computer.

You can do this with or without the wireless transmitters. Doing a quick check against the Decochek program, they appear to be very similar (did not check a lot of different profiles)

As you can use the change gas alerts (I have done a night dive, with my light out and used the safety stop alert to tell me when I was at 15 ft, it is a fairly nice system) as a safety reminder... and any mistake you might make is auto corrected, not sure that this might be a better way to go. It would still involve a dive plan... but as a backup, it is far more capable of doing any changes that a person would be.

Since you brought up the Galileo, maybe you can explain how the Profile Dependent Intermediate Stops (PDIS) function (standard with Sol, optional with the Luna) works and how it factors into a dive profile. Some of the functions on my wife's Sol are a mystery to me.

To the Op-Sorry about the slight hijack.

 

[Puffer Fish]

Since you brought up the Galileo, maybe you can explain how the Profile Dependent Intermediate Stops (PDIS) function (standard with Sol, optional with the Luna) works and how it factors into a dive profile. Some of the functions on my wife's Sol are a mystery to me.

To the Op-Sorry about the slight hijack.

I just love the use of acronyms..what you don't get with the luna appears to be the multi gas calculation capability... you do get the deep stops.

There is a huge amount of calculations needed to do all the multigas calculation on the fly...that program is not included with the Luna.

You do get the adaptive bottom time... based work load calculated off of SAC rate.. while the Sol can use either or both SAC and heart rate.

Keep in mind that the computer, when using multi gas, will calculate where to use each gas, and indicate it to you, but if you change anything, it will continuously adjust to the next best profile..don't use your 2nd gas at the first 50 ft stop, and it will put the gas in for the next stop...while showing what your timing would be if you don't change at all.

If you are using the tranmitters, it also adds the calculation for each gas as you are using it, against the planned needs...so you can see if you are headed for a gas issue.

With everything turned on, it is adjusting for water temps, work load and gas mixture...would be hard to do manually, but also really ugly if it broke in the middle of the dive.

 

[RJP]

Awesome suggestion to push your CNS clock above 100%.

Any other great suggestions?

Here's a great suggestion for you...take a look at what V-Planner spits out for that dive and you'll see that it's barely 50% of CNS clock:


Dec to 130ft (2) Nitrox 28 50ft/min descent.
Level 130ft 17:24 (20) Nitrox 28 1.35 ppO2, 115ft ead
Asc to 70ft (22) Nitrox 28 -30ft/min ascent.
Level 70ft 40:00 (62) Nitrox 50 1.53 ppO2, 32ft ead
Asc to 20ft (63) Nitrox 50 -30ft/min ascent.
Asc to 15ft (63) Nitrox 50 -30ft/min ascent.
Surface (64) Nitrox 50 -30ft/min ascent.

OTU's this dive: 107
CNS Total: 52.4%

 

[RJP]

Apart from the O2 issue that Rainer pointed out,anyone using 50% is presumably advanced nitrox/deco certified (regular nitrox maxes out at 40%)
If deco certified why not just do it as a deco dive and stop messing about trying to do an extended NDL dive?

Sounds like a great idea for a cyber-dive, however in the real world given the choice of doing the exact same dive as a deco dive or a no-stop dive, I'd opt for a no-stop dive from a pure safety/conservative standpoint. Beyond that however, if you wanna spend an extra 10-20 minutes hanging in 48deg water on a line that's hopping up and down in 4' seas...you go right ahead. I'll be on the boat!



Additionally, available gas quantity and mixes come in to play (that pesky "real world" thing again) as well as lost gas contingencies, etc. At a .7 SAC rate and with 1/3rds contingency planning, the above dive requires 240cf of back gas if you did it as a deco dive with 28% and O₂. Unless you're diving double 120's or larger and plan on running them bone-dry you're not gonna have enough back gas. Further, with a "lost gas" plan for the O₂ you're now looking at needing 270cf of gas, and 25min of deco. Beyond losing the O₂, what if you simply don't have 100% O₂ available to you logistically or economically?

Lastly, there are advanced nitrox certs that limit a diver to non-deco dives (eg TDI Advanced Nitrox, DSAT Tech 1) but with mixes greater than 40%. Sure, these courses are often taken along with deco procedures, but not always. Or perhaps the diver hasn't completed the deco portion of their training.

Again, not saying that it's the perfect example but there are quite valid reasons to do a dive as a no-stop dive, that actually require less "messing around" than if you were going to do it as a deco dive.

 

[gumbo717]

Thank you all for the useful info!

I have been on the Algol a couple of times and one of my goals is to be able to do this dive as a deco dive not a dive where I am trying to extend my NDL. It would seem much easier to do this as a deco dive with two gases (back gas and deco mix) and off gas at your required stops than to carry three different mixes to extend a NDL.

Understanding the concept that my VT3 should be able to do the three gas extend the NDL type dive, I have not heard strong arguments or opinions about which computers would be better or more capable for planned deco diving. Any suggestions or does anyone think these marketed three gas computer are suitable for deco diving (like the VT3, T3). I am not fishing for a way around cutting tables but I also know that divers ride their computers and carry tables and bottom timers for if and when the computer fails.

 

[DA Aquamaster]

So if I did a 90min deco dive to max depth of 150', in an overhead environment, but did it all on back gas, it wouldn't be a "tech" dive?

Right - that's the problem with the gas switch definition. At the time however I think it served the purpose of separating divers using accellerated deco from "normal" divers just doing decompression.

That is not so much the case now. maybe more importantly, by that definition if a rec diver goes OOA and switches to his pony, it is a tech dive? Probably even more so if he plans to do it. We'd all agree that is pretty stupid.

Part of the issue in technical diving is the use of accellerated deco/deco gasses (requiring a gas switch), but the presence of a soft or hard overhead and the consequent inability to directly access the surface is an equally large issue that will be present on all "technical" dives.

 

[DA Aquamaster]

Apart from the O2 issue that Rainer pointed out,anyone using 50% is presumably advanced nitrox/deco certified (regular nitrox maxes out at 40%)
If deco certified why not just do it as a deco dive and stop messing about trying to do an extended NDL dive?

In the 1990's I commonly did just that and after doing it 4-6 dives over a 2-3 day weekend, I generally felt like crap on Monday morning. I started using accellerated deco with 50 to 100% O2 in part because it reduced the required deco, but also in part becasue I felt better after the dives, and in particular after repetetive deco dives.

 

[RJP]

Thank you all for the useful info!

I have been on the Algol a couple of times and one of my goals is to be able to do this dive as a deco dive not a dive where I am trying to extend my NDL. It would seem much easier to do this as a deco dive with two gases (back gas and deco mix) and off gas at your required stops than to carry three different mixes to extend a NDL.

Point is you would only need TWO gasses to do it as an extended NDL dive. And you'd be off-gassing on the wreck at 70' on 50% instead of hanging deco on a line with nothing to do but count down.

 

[Puffer Fish]

Sounds like a great idea for a cyber-dive, however in the real world given the choice of doing the exact same dive as a deco dive or a no-stop dive, I'd opt for a no-stop dive from a pure safety/conservative standpoint. Beyond that however, if you wanna spend an extra 10-20 minutes hanging in 48deg water on a line that's hopping up and down in 4' seas...you go right ahead. I'll be on the boat!



Additionally, available gas quantity and mixes come in to play (that pesky "real world" thing again) as well as lost gas contingencies, etc. At a .7 SAC rate and with 1/3rds contingency planning, the above dive requires 240cf of back gas if you did it as a deco dive with 28% and O₂. Unless you're diving double 120's or larger and plan on running them bone-dry you're not gonna have enough back gas. Further, with a "lost gas" plan for the O₂ you're now looking at needing 270cf of gas, and 25min of deco. Beyond losing the O₂, what if you simply don't have 100% O₂ available to you logistically or economically?

Lastly, there are advanced nitrox certs that limit a diver to non-deco dives (eg TDI Advanced Nitrox, DSAT Tech 1) but with mixes greater than 40%. Sure, these courses are often taken along with deco procedures, but not always. Or perhaps the diver hasn't completed the deco portion of their training.

Again, not saying that it's the perfect example but there are quite valid reasons to do a dive as a no-stop dive, that actually require less "messing around" than if you were going to do it as a deco dive.

It is an interesting issue.. with my SAC rate, assuming my worst case, I could easily do that dive with a 133 cf tank and two 40 cf pony's (213 cubic ft of gas) and use the three gas profile (which is shorter)...I suppose I would also need a 4th tank ...would make an interesting rig...the main tank with 3 pony's attached.

The galileo has 5 additional levels of Conservative adjustments (L1 thru L5) and it runs the standard (L0) at the same time... one could do a no deco dive in L0, while the computer is running L5.. and see how easy that is to do... may try that one of these weekends... would be worth the laugh.