Computer + Plan or 2 Computers for Deco Diving

[runsongas]

two shearwaters and a written deco plan on the slate with contingencies.

ride the shearwaters as possible. maximum depth and run time already pre-determined even while riding the shearwaters for deco.

 

[JMBL]

My experience while diving trimix (normoxic) :

For a long while : RT + electronic timer & depth gauge, 2 of them (in fact one was my NiTek Trio in depth gauge mode)

Then : Petrel + RT + 1 electronic timer & depth gauge

Since I got my Nitek Q : 2 computers + RT

Diving with 2 computers is the most convenient, but it DOES cost money, and it's a part of the equation that can be modified easily.

 

[NothingClever]

Gentlemen, perhaps a more fruitful investment of your energies would be the academic and training development chairs of the various certifying bodies that still teach the use of deco slate + BT as an acceptable method (in conjunction with another method to track depth and time). Wouldn’t it be a nobler endeavor to convince them to update their curriculum to the standard you’re espousing rather than chipping away at stray individuals on the internet?

For TDI, those people are Sean.Harrison@tdisdi.com and Dennis.Pulley@tdisdi.com .

I concur a second deco computer is useful and ideal but the absence of one and the use of a deco slate + BT in its stead doesn’t make the dive inherently unsafe. If that were the case, then I think DAN and certifying bodies would have already campaigned conclusively to eliminate the inclusion of tables + BTs from their courses. Consistently, I think they would have decisively established a policy that diving with two computers is a mandatory certification requirement rather than a good option (current state).

From page 4 of the Shearwater Perdix owner’s manual, the use of tables is contemplated with the self-evident implication that it is an acceptable backup...

“Never risk your life on only one source of information. Use a second computer or tables.

This computer will fail. It is not whether it will fail but when it will fail. Do not depend on it. Always have a plan on how to handle failures. Automatic systems are no substitute for knowledge and training.

No technology will keep you alive. Knowledge, skill, and practiced procedures are your best defense (Except for not doing the dive, of course).”

While you may zero in on “Use a second computer...”, the way I read Sherwater’s warning is to not become over-reliant on technology. My method of accomplishing that is by continuing to use a deco slate + BT.

Also, I think there are three important considerations at play that warrant attention but are getting conflated.

- Safety
- Affordability
- Facility in planning

Safety - already addressed above.

Affordability - At the beginning of the thread (and still), I approached things from a perspective of “Where do I want to spend my money?” I am blessed with the abundance and will be for the rest of my life to easily afford things like a second Shearwater and not have to look for used ones. I probably should have not used the word “need” when I wrote, “When I need to make a decision between....”. Regardless, I was trained that one deco computer and a deco slate + BT is a safe practice so I’m simply choosing to spend my money elsewhere. I have a raft of observations of fellow professionals who could easily afford upgrades in life but didn’t because what they had was acceptable and safe and they chose to spend money elsewhere. For me, it’s a matter of priorities and focus rather than a shortage of money.

Facility in planning - Shearwater wins but it’s not really drastically slower to run through V-Planner and then transcribe the main dive plan and contingency plans to my slate. The planning speed advantage of a deco computer isn’t significant enough to compel a purchase. I like spending the moment to absorb the data, too.

I’m willing to listen to good arguments and I like evolving my position on matters when it’s warranted but thus far the arguments aren’t outweighing vetted course materials that explicitly state a deco slate + BT is an acceptable method to track a deco dive.

 

[JohnnyC]

Nobody is arguing that it's not an acceptable method (in terms of being usable), simply that it is far less optimal than a second computer. The relative cost of which is so minor as to be moot.

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." Any other argument against is specious at best.

As a counter example, on several occasions you've mentioned using V-Planner. This is entirely contradictory to your entire argument as you're actually paying money, both to Ross as well as Shearwater, to utilize a less optimal solution to the issue of decompression planning. Barring any semantics or pedantry, you're paying extra for regular unleaded when race gas is half the price.

 

[NothingClever]

"I can't afford a redundant piece of life support equipment because $200 will keep me from buying $8000 worth of new wheels" is an interesting argument. Stuff like that is why the Rouse's decided to dive air instead of trimix, and we all know where that got them.

Made up quotes and immediately throwing the Rouse grenade make you sound desperate. I think you have a lot to give but that probably wasn’t your best shot. You’re a DM.....I think you got better in you.

I dunno man, you gotta pay to play safely. When safety takes a backseat for insignificant reasons, bad things tend to happen. It's not that you can't do those dives with a bottom timer and tables as backup, there's just no good reason to.

This paragraph seems conflicted. At the end of the day, I think your position is that you’d like to see the use of a deco slate + BT as a back up essentially “outlawed”. I refer you back to my recommendation. Perhaps you should invest your passion in a campaign to inform the leaders of certifying agencies that diving with a deco slate + BT is unsafe rather than trying to chip away at matters with individuals on the internet.

 

[NothingClever]

The dilemma of near simultaneous postings....my last might suck entirely after I get done absorbing yours which appeared while I was writing.

 

[doctormike]

While you may zero in on “Use a second computer...”, the way I read Sherwater’s warning is to not become over-reliant on technology. My method of accomplishing that is by continuing to use a deco slate + BT.

OK, your BT and depth gauge aren't technology?

While I always appreciate a good straw man argument, this one is pretty silly.

If you are doing a deco dive and your computer dies, you are better off having another dive computer rather than trying to put the ascent plan together with your BT, depth gauge and tables. The chance of both DCs failing is probably about the same as the chance of one DC and one BT failing. The computers know what you actually did, so you also get a more accurate ascent plan.

The fact that training agencies haven't outlawed BT/Depth Gauge/table as a backup to a DC doesn't mean that it's an optimal solution in 2019. As has been explained upthread, just because they consider something acceptable doesn't mean that it's the best choice. Would you think that air is the best gas for a dive to 180 feet just because of this class?

The OP asked people here what we do and why. So that's the question that we are answering. Do you think that we shouldn't be doing that?

 

[JohnnyC]

Made up quotes and immediately throwing the Rouse grenade make you sound desperate. I think you have a lot to give but that probably wasn’t your best shot. You’re a DM.....I think you got better in you.



This paragraph seems conflicted. At the end of the day, I think your position is that you’d like to see the use of a deco slate + BT as a back up essentially “outlawed”. I refer you back to my recommendation. Perhaps you should invest your passion in a campaign to inform the leaders of certifying agencies that diving with a deco slate + BT is unsafe rather than trying to chip away at matters with individuals on the internet.

Desperate? Nah dog, I've just got a hell of a lot of experience. Been there, done that, have enough crappy free scuba t-shirts.

Btw it says divemaster because I can't actually change it, believe me, I've asked. It's a function of how the forum software works. But, if you'd like to bring up experience and certification levels as a method of espousing validity, I'm a CCR diver, a cave diver, deep trimix diver, and I need to update my dive count, because it's significantly greater than the 2500 dive maximum in the profile. Suffice it to say, my level of experience tends to validate my opinions. Your relative lack of experience (I have to assume based on available data, your profile isn't actually visible), and promotion of certifying agencies simply allowing bt/slate use as a positive argument for why your opinion is superior, is elementary at best. I think you've got better than hiding your profile and running to a course manual. Hey, I can take cheap, snarky, irrelevant shots too.

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, and are trying to broadly appeal as best they can. That means they still allow certain things despite being less optimal. The use and promotion of VPM for example. With the wide margin of acceptance within the TDI standards for student and instructor performance, it's hardly something I would use to try and validate an argument. I say this having taken and observed several TDI courses, of which there were wildly different levels of acceptable performance required of both the student and instructor, even on the same course.

Outlawed? Not sure how you got that. That's a significantly different opinion than, "there's no reason not to use 2 computers." Feel free to keep reaching though, I'm excited to see when you start breaking out the ad hominem stuff for realsies.

 

[NothingClever]

Nobody is arguing that it's not an acceptable method (in terms of being usable)

I definitely misunderstood yours and the points of others then.

You can certainly choose to do so, but there's no valid argument other than, "I choose to do it this way."

I choose to do it this way.

Well, shoot....that was easy.

Any other argument against is specious at best.

I don’t think I ever argued against a second computer. It would be difficult because I know I’ll cave at some point and buy another Perdix. I’ve only intended to argue that a deco slate + BT is an acceptable back up.

As a counter example, on several occasions you've mentioned using V-Planner. This is entirely contradictory to your entire argument as you're actually paying money, both to Ross as well as Shearwater, to utilize a less optimal solution to the issue of decompression planning.

I bought V-Planner before I purchased my Perdix. I couldn’t have predicted every expense to arrive at a perfect cost sheet. But, I may be misunderstanding you again....Are you saying In the sentences above that Shearwater’s deco planning feature is also sub-optimal?

 

[NothingClever]

OK, your BT and depth gauge aren't technology?

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.

If you are doing a deco dive and your computer dies, you are better off having another dive computer rather than trying to put the ascent plan together with your BT, depth gauge and tables. The chance of both DCs failing is probably about the same as the chance of one DC and one BT failing. The computers know what you actually did, so you also get a more accurate ascent plan.

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.

The fact that training agencies haven't outlawed BT/Depth Gauge/table as a backup to a DC doesn't mean that it's an optimal solution in 2019. As has been explained upthread, just because they consider something acceptable doesn't mean that it's the best choice.

I’m clearly confused....where did I say 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.

The OP asked people here what we do and why. So that's the question that we are answering. Do you think that we shouldn't be doing that?

I think we’re doing that but I also think it’s migrating into arguing rather than informative discussion.