Computer + Plan or 2 Computers for Deco Diving

[doctormike]

I agree with you that a BT and depth gauge are technology but they, to me, seem a lot less susceptible to failure than a DC.

Link?

I agree with you. I’ve never said a table + BT is optimal, just that it’s an acceptable back up. I’m responding to Johnny’s passionate reaction that started after I agreed with your first post in this thread about running the dive off a computer with slate + BT as backup.

OK, I'm confused. We have plan A and plan B. People said that they liked plan A better because of reasons. You seemed to be pushing back against that, saying that we shouldn't make that case here but rather lobby training agencies to outlaw B if we really thought that A was better.

I think that @JohnnyC said it best: "There's literally no good reason in this modern age to CHOOSE a bt/slate IN LIEU OF a second computer. You can certainly choose to do so, but there's no valid argument other than, 'I choose to do it this way.' "

I’m clearly confused....where did I said that it was an optimal solution? I’m arguing that it’s an acceptable solution and that it’s not mandatory to have two computers.

Correct. No one said it was mandatory to have two computers. Who are you arguing with about that?

 

[CAPTAIN SINBAD]

It depends. If on standard gases, Computer and Ratio Deco (bottom timer). If best mix, then Computer with bottom timer (slates).

 

[rjack321]

When you start out doing piddly short 20min "tech 1" dives in the 140-160ft range I think there's quite a bit of merit in going through the exercise of writing out a backup plan on a slate. Perhaps thinking about your contingency gas volumes a bit more than you otherwise would. Ditto talking about what the backup and contingencies are with your buddy including stuff like over/under 5 mins, deeper/shallower 10ft, first stops, backgas to get to your first stop (min gas) extended first stops, last stop at 20ft or 10ft, gas volume, shared deco gas ascent plan, etc.

Slate is a vastly better planning trigger for all of that. Especially at the entry tech level you need to be forcing/conditioning your brain through repetition of the (depth/time/gas/deco) boundaries and plans. The reality is that we can all get a bit lazy and slates are a good tool that encourage good pre-dive habits. If nothing else, running the numbers in (e.g.) multideco shows you the gas volumes you need - something a second DC wont necessarily do.

Second DC is better in the water for sure but deco dives need to start before you get wet.

Entry level tech dives are "cut with an axe" deco anyway so if your backup schedule isn't optimal its nothing 5 extra mins shallow wont fix. Once you graduate beyond 1 deco gas, max 30mins deco kinds of dives to longer/deeper multigas plans a second DC is more and more relevant. Hopefully by then the principles of tables and contingencies have been drilled into you through repetition of the slate plans that you can type your 215ft plan into multideco and pretty much know all of the times/stops/volumes already so actually writing them down is less and less necessary.

 

[rabe]

2 computers, plus a deco plan written (kept in my pocket)

 

[wetb4igetinthewater]

Remember, PADI still allows teaching on ones knees and promotion of secondary donate as the best method of air sharing. The IANTD cave diver manual has an entire section on chakras. Let's not pretend that the certifying agencies are on the cutting edge of scuba diving instruction. PSAI still has a "narcosis management" course despite the overwhelming evidence that you can't actually condition away narcosis. They're corporations firmly entrenched in the status quo

Somewhat OT: Yeah, I wish all agencies would go with online/digital only materials (some have) and keep up with science/update those online/digital materials (I don't think anyone does really). Example: deep diving courses. Alert Diver | Performance Under Pressure recommends "an ideal gas density of 5.2 g/L, with an absolute maximum of 6.2 g/L. " For the ideal, that's about 100 feet/30 meters. I will admit I was critical of GUE for switching to trimix at 100 feet, I do understand that they were right. Of course naysayers will say "I've had 1000s of dives at X depth and nothing happened." How nice for you. You didn't have an incident. But if you did, it may not have turned out quite so nice. It all comes down to risk management. All agencies should refactor their deep diver courses with this info. My opinion.

Less OT: I wish agencies would advise for technical diving to use the same algorithm when using two computers just as gasses should be the same.

Not OT: dive computers in gauge mode are more reliable due to the number of components (code) being less. However, do we care that a dive computer in gauge mode is 0.000000000000000001% more reliable? I don't.

Two dive computers, dive plan on slate.

 

[ChuckP]

When you start out doing piddly short 20min "tech 1" dives in the 140-160ft range I think there's quite a bit of merit in going through the exercise of writing out a backup plan on a slate. Perhaps thinking about your contingency gas volumes a bit more than you otherwise would. Ditto talking about what the backup and contingencies are with your buddy including stuff like over/under 5 mins, deeper/shallower 10ft, first stops, backgas to get to your first stop (min gas) extended first stops, last stop at 20ft or 10ft, gas volume, shared deco gas ascent plan, etc.

Slate is a vastly better planning trigger for all of that. Especially at the entry tech level you need to be forcing/conditioning your brain through repetition of the (depth/time/gas/deco) boundaries and plans. The reality is that we can all get a bit lazy and slates are a good tool that encourage good pre-dive habits. If nothing else, running the numbers in (e.g.) multideco shows you the gas volumes you need - something a second DC wont necessarily do.

Second DC is better in the water for sure but deco dives need to start before you get wet.

Entry level tech dives are "cut with an axe" deco anyway so if your backup schedule isn't optimal its nothing 5 extra mins shallow wont fix. Once you graduate beyond 1 deco gas, max 30mins deco kinds of dives to longer/deeper multigas plans a second DC is more and more relevant. Hopefully by then the principles of tables and contingencies have been drilled into you through repetition of the slate plans that you can type your 215ft plan into multideco and pretty much know all of the times/stops/volumes already so actually writing them down is less and less necessary.

OMG - I do piddly short tech 1 dives no offense taken at all!

I think Johnny’s point was that the cost involved - BT verses used 2nd computer makes it pointless to go the bottom timer route - few bucks more and you have a cleaner path to the surface

I use two identical computers showing different info so I don’t have to flip thru screens. Wrist slates with written plans and at plus 5, 10, expected backgas amounts at certain times during the run. I do the same thing for big boy dives too - I just don’t have the experience not too.

I looked at the idea of BT and slates but it really was a foolish way of doing things considering costs and the inaccuracies of square profiles verses what I really dive - it just didn’t make sense.

 

[ls23]

It might make sense if you are doing deep hypoxic dives or are on a rebreather, but I'm a long way off to that.

In this modern age there also isn't a good reason not to run two Garmin GPS on your 20 minute drive to work, I'd just find it a little bit ridiculous.

 

[kensuf]

While many would say that if you have two computers, you probably don't really need to write out a set of tables, no matter what, you still have to plan the dive and have an idea of what you're looking at before you splash. Only a fool does a deco dive without knowing what his run-time will be before he gets in the water.

 

[doctormike]

While many would say that if you have two computers, you probably don't really need to write out a set of tables, no matter what, you still have to plan the dive and have an idea of what you're looking at before you splash. Only a fool does a deco dive without knowing what his run-time will be before he gets in the water.

Absolutely. This^

 

[loosenit2]

if you can't afford $400 for a used Shearwater

where are the commonly available $400 Shearwaters at? I routinely see used Perdix in the 700 range but not 400.