Trimix dive computers and planning

[Peter Guy]

OP -- the simple answer to your question of why there are different algorithims is that there are different theories on how the body responds to Nitrogen loading. Outside of gross violations of protocol, the reality is that NO BODY knows exactly why someone gets bent (or doesn't get bent) on any one particular dive. Until, and unless, science comes up with some "unified theory" of decompression, there will be differences.

My advice is -- Follow Boulder John's advice (and buy, read and study Deco for Divers).

 

[Bombay High]

Hi.
I have recently started tech diving and when i am 18 i will continue to the TDI avanced trimix level. (not all in 1 go, i will gain more expirience between each course). i have started to save up for a dive computer for tech as i have a suunto gekko now and am thinking of upgrading so i might aswell get a trimix capable computer. i understand that a lot of tech divers use a bottom timer and depth gauge and write their plan on a slate, but what if you have to change your plan during your dive? Anyway i think that i would probably do that and still have a trimix computer just to be on the safe side. I have looked at a few trimix computers like the liquidvision and the suunto hel03 and the NHeO3 and the shearwater predator and so far i think that the HNe03 would be the best option for me considering the price. If anyone has any suggestions then that would be great.

i would be looking for a computer that is trimix cabable with any ratio of each gas e.g from 8 - 100 and including 100% O2, and any amount of helium and nitrogen.
also i would want to be able to use it for recreational diving with just 1 tank of air or nitrox.


Also i was wondering why some computers and not "compatable" with some deco planning software aprt from the reson that they use different algorithms. surely if your compuetre says your deco is over then it is over?

Thanks very much everyone##!!!!!!!!!!!

really appreciaite it

Any trimix computer should fulfill your criteria. I think you should do your training before buying.
Your computer makes calculations based on a mathematical model - the "Algorithm". It knows nothing about you.
You can choose any algorithm and follow it, it does not mean it will work for you and that you will not get bent.
You need to understand that deco theory is just theory, and those computers are just devices that make calculations.
If it says your deco is over, it may or may not be the case.
As you dive more and more, you will understand how your body responds to deco profiles, and you will come to your own conclusions about what works for you.
Do not blindly follow a computer.

 

[orange_diver]

Lynne, how closely does the VPM on your X1 match up with RD? I'm especially interested in the deep stops portion and is VPM penalizing you as they don't believe in doing them to the same extent as RD. also are you running +2? thanks.

 

[TSandM]

I'm running +3. I don't do the deep stops the way RD teaches them (note that I'm only diving in the 150 foot range). I do 30 fpm to 2 ATA above max depth (or average, depending on how the profile looked) or to 70, depending on the dive.

So far, VPM has cleared every dive by the time I've finished my planned deco.

I don't know what would happen with deeper dives, especially if you started the stops as deep as recommended.

 

[boulderjohn]

Another difference between RD and VPM is in mid range of deco if you are using the RD S-curve approach. VPM does not do that.

 

[orange_diver]

Thanks. Seems to be just what Ross advocates which makes sense. Rounding up that would put you at 80 if you stuck to the 150 avg for instance.

I'm running +3. I don't do the deep stops the way RD teaches them (note that I'm only diving in the 150 foot range). I do 30 fpm to 2 ATA above max depth (or average, depending on how the profile looked) or to 70, depending on the dive.

So far, VPM has cleared every dive by the time I've finished my planned deco.

I don't know what would happen with deeper dives, especially if you started the stops as deep as recommended.

 

[orange_diver]

Good point. GUE AFAIK also no longer (for awhile now) uses an S-Curve. Those stops are all equally distributed whereas VPM seems to be more exponential.

Another difference between RD and VPM is in mid range of deco if you are using the RD S-curve approach. VPM does not do that.

 

[boulderjohn]

Good point. GUE AFAIK also no longer (for awhile now) uses an S-Curve. Those stops are all equally distributed whereas VPM seems to be more exponential.

Really? I am not GUE, but I did have a talk with JJ last year about this. He said that they no longer accepted the oxygen window theory on which it was based, but they were still using it on the basis that it had been working. I would be very interested if they have stopped teaching it now.

When I took my RD class, it was from UTD and Andrew Georgitsis. He, too, said that they no longer saw the old oxygen window theory as compelling, but he came up with two other reasons to still do the S-curve, neither of which I recall at the moment.

I am not personally a fan of the S-curve myself.

 

[orange_diver]

I'm not GUE either but that was word on the street at least a year ago. I took RD from AG also probably before you bc he was still touting the O2 window pretty strongly -- and still does in his current RD online materials i believe. I've been out of tech diving for many months due to some medical issues but if i returned i wouldn't use it either. Seems to not be proven beneficial and leaves you with less gas in that 40 if you have to spend 5 mins at 70' sucking on it.

Really? I am not GUE, but I did have a talk with JJ last year about this. He said that they no longer accepted the oxygen window theory on which it was based, but they were still using it on the basis that it had been working. I would be very interested if they have stopped teaching it now.

When I took my RD class, it was from UTD and Andrew Georgitsis. He, too, said that they no longer saw the old oxygen window theory as compelling, but he came up with two other reasons to still do the S-curve, neither of which I recall at the moment.

I am not personally a fan of the S-curve myself.

 

[TSandM]

I think, from having listened to the T1 classes in Egypt, that GUE teaches both the S-shape and the linear pragmatic, and recommends the linear pragmatic as being far simpler for the diver to remember underwater.