Ambitious newb: Researching PDCs and relevant background info

[Lorenzoid]

Thanks, Imla. This statement kind of highlights part of the problem I was having.

As a neophyte, I started with "I want to go SCUBA diving." Which immediately became "I want to get OW certified." That turned into "what agency should I get certified by?" I chose SDI and, along the way, learned that SDI teaches diving using a PDC. So, then my attention turned to "what PDC should I get?" And so I started shopping online (looking at what's available, reading manuals, reading reference material sites to understand PDC features that I didn't understand at first, etc.).

And there is where your statement starts to highlight an issue that resulted in this thread posting from me: How am I supposed to know what questions are "faaar away" for me?

The online course descriptions for PADI and SDI do NOT, anywhere that I saw, make it clear that ALL Rec diving is based on diving to NDL. I still haven't actually found a definitive statement to that effect from either of those agencies. So, from boning up on PDCs and reading about what the next steps are in training, after OW, I got the impression that Deco stops and gas switching might actually be part of more advanced Rec diving. That I might actually learn about those things in an Advanced or Deep certification course. Thus, some of the questions in my OP.

In the meantime, I have done my own independent studying and have learned how to read the USN dive tables (and NOAA and PADI) and understand how to develop a dive plan that includes deco stops (based on the USN tables for that) - including for repetitive dives. I understand about the different decompression algorithms. I know what Gradient Factors are, what the "standard" values used are, and how they are used. I understand about CNS Oxygen Toxicity and O2 tissue loading and how to use the charts for that to calculate O2 tissue loading (and find it surprising that there are not Residual O2 Tables, like there are RNT, for help in calculating repetitive dives - and that some people believe a 90 minute O2 half-life is appropriate for those calculations, but nobody is stepping up and making that "official"). I took high school and college Chemistry and Physics, so the actual chemistry and physics behind these things is somewhat second nature to me. I have known Boyle's Law (PV=nRT) by heart (and understood what it means and how to apply it) since high school.

I haven't taken any actual certification courses on any of this and there is no WAY I would presume to know everything I need to know about it all to actually go and do those kind of dives. But, I would bet a dollar that I could take a written test on those subjects and score at least in the middle of the pack compared to a group of people who have taken those courses. But I digress....

So, while it may be a while before I have any need for a more advanced computer, I like to understand ALL my options before buying anything expensive. I do not like to buy things on the basis that someone on the Internet told me "that xyz is more advanced than you'll need any time soon, so don't worry your pretty little head about it." I like to KNOW why it's more expensive - what the extra money would be getting me - so the decision to buy something cheaper is based on my own knowledge. That way, if I end up wanting to replace whatever I buy with something else, I don't have anyone to blame but myself.

And isn't that the real message behind all of diving? Don't take anyone else's word for anything. Take responsibility for yourself and make your own decisions. Don't do a dive on the basis that someone else says so, and don't buy a PDC on the basis that someone else says "that's all you need." Learn the factors that are relevant to making a dive and then decide for yourself whether to do the dive. Learn the factors that are relevant to buying any piece of equipment and then decide for yourself what to buy.

On that basis, I want to say thank you to all of you that have stopped in to answer my questions and the many of you who post here on SB with a lot of good info that I have already read. Thank you for helping educate me so that I am able to make better decisions for myself - whether we're talking about actual dive decisions, or just equipment purchases.

Assuming you actually absorbed the material you list above, you are going to be very very bored in OW class. You're talking things that are way beyond OW level. In class, try to let others who have not studied such advanced topics get a word in, and not be the teacher's pet (or worse, the teacher's PITA).

 

[stuartv]

Assuming you actually absorbed the material you list above, you are going to be very very bored in OW class. You're talking things that are way beyond OW level. In class, try to let others who have not studied such advanced topics get a word in, and not be the teacher's pet (or worse, the teacher's PITA).

No worries there, my friend. I am 47 years old. I have no interest in showing off or being the teacher's pet. And my class is a group of 9 people, which I organized. So, it's my g/f and a couple of friends and their families - including 3 teenagers. I will definitely be looking out to ensure that THEY all get plenty of instruction (from the instructor, not me!).

My only personal goal in OW class is to make sure I don't let overconfidence lull me into missing something the instructor says that I don't already know. I know that I've learned a lot, but I have no illusions about thinking I know everything.

 

[scubadada]

Howdy! This is my first post here, but I have been doing a lot of reading here and elsewhere on the intertubes.

I am signed up for an SDI OW class at the end of the month. I have no certification at all yet. But, I have been around diving my whole life (Dad, brother, and cousins have all been certified forever), done a lot of snorkeling, and did a discovery dive in Maui last year, which felt completely at home to me.

So, I'm anticipating getting my SDI Computer Nitrox cert either at the same time as OW or immediately after. All in prep for some Caribbean diving in December. I've read up on lots of dive sites I hope to visit someday and many of those are deeper than 20m. So, I'm expecting that I will go on to get Advanced and Deep certs.

I currently have snorkeling gear but no SCUBA gear. I'm trying to decide now what I want to buy before going to Mexico in December. If money were no object I would go ahead and get everything except tanks, but that's not in the financial cards right now. So, I'm debating just getting my own computer, for now - ideally, to have it before my OW class, so I can get used to using it then. Additionally, I am very much a "buy once, cry once" (as I read someone say on here) type of person.

After reading up on everything I can find, what I THINK I want is a wristwatch computer with AI and Nitrox support.

And after reading another thread here with similar questions, I already know that there are a number of very experienced tech divers on here who think AI is useless or worse. And I do understand the reasons for those people feeling that way. But, I also understand the reasons some of the AI proponents like them. For me, just doing warm water Rec diving in the near- to mid-term, it seems like a nice convenience. All my info is in one place. Less hoses to fudge with (if it's wireless AI). More detailed info to help me learn about my own SAC. An alarm to alert me if I'm paying too much attention to the pretty fishes and don't notice that my air has gotten too low.

I understand the more experienced divers don't need that. And, on Tech dives, many want to not have it. But, from my one discovery dive, I know I'll be looking at my SPG a lot, for a while. And, at the same time, I don't yet have the habits that come from experience such that I will always remember to check it often enough. So, for my current needs, it seems like AI is a good idea.

---------- Post added September 3rd, 2014 at 03:44 PM ----------

Also, from what I've read and what I believe I will want to do, it seems like having a computer that supports multiple gases is something I will want. But, I have unanswered questions relating to that subject. They include:

- People use hypoxic mixes for more BT on deep dives. But what does "deep dive" mean in this context? Is a hypoxic mix something that one might use in dives to 40m? Or does that only make sense for Tech dives that go beyond Rec limits?

- For dives to 40m or less, it still might make sense to use Nitrox and pure O2 as a deco gas, right? Or does Rec diving simply never involve switching gases during a dive? (and how said is it that I can read as much as I have on SDI and PADI sites and not already know the answer to that?)

- For dives where a gas switch is done, how is that physically accomplished (in a Rec dive scenario if that is applicable)? Do you dive with a 2-tank harness and a manifold connecting the tanks, and have the Nitrox turned on and the O2 turned off, then turn one off and the other on at the first deco stop? Do you have a completely different reg setup on the O2 tank from the Nitrox tank? Do you just use a side mounted pony bottle for the O2, with its own regulator?

- A bunch of the more expensive Rec diving computers say they support multiple gases. But, it looks like you don't enter a dive plan into the computer to tell it when you plan to switch gases. So, if you're relying on the DC to tell you when your NDL time is up, how can it know to allow you extra time because you're going to switch gases? When you program in all your different gases, does it make assumptions about what you're going to use and the order you're going to use them, so that it will reflect your extended BT capability based on all the gases you're carrying?

- And if you have AI, with transmitters for all your gases, does the DC calculate ATR based on all the gases being available? Or just based on the you're currently using?

- If the DC "knows" that you're going to, say, use Air for the first, deepest, part of the dive, then ascend and use Nitrox for a while, then stop and use O2 for deco, does it prompt you to switch gases at the right times? I guess it can't without AI.

From what I've been reading, I just have the feeling that the idea of using a DC to tell you when to head for the surface, on any dive involving more than one gas, is probably just not going to survive meeting the real world.

OTOH, if you assume that dives will always be NDL dives, to a max of 40m, with only one gas, then a PDC with air integration just seems like almost a no-brainer. Especially if you are going to use a DC anyway, and especially if the AI is via hose. I mean, how much would I pay for the cheapest PDC ($200), plus a console with a SPG ($45)? Versus, say, the Oceanic Pro Plus 2.1, which is hose AI (with a compass) and which is $400.

---------- Post added September 3rd, 2014 at 03:45 PM ----------

Okay, so those previous questions were really just for me to get info to understand how I would (or might) use a computer in the future. Now on to the real questions, which are finally getting around to being relevant to this subforum. :-D

- Several people in the other long thread I read suggested to the OP (who was asking about a PDC for Rec use now and Tech use later) advised him to get a Nitrox-capable PDC and use it in Gauge mode. If you're just going to use it in Gauge mode, why does it matter if it's Nitrox-capable?

I expect many of my dives to be after flying somewhere. And I don't have the budget right now to buy a PDC and a full reg set. So, if I am going to fly and rent a regulator (and BCD), then it seems to make sense that I would buy a wrist-mounted PDC. And one with wireless AI means I probably wouldn't use the AI at first (since I don't see installing my transmitter onto a rental 1st stage. But, after I eventually get my own reg set, then I could use the AI, too.

So, I've been boning up on wrist computers that are AI-capable. The least expensive I've found is the Sherwood Amphos Air, which is on sale for $680, with transmitter. And the next most is the Hollis TX-1, for $750, with transmitter. Or $500, without the transmitter.

The TX-1 looks like it has everything I would ever possibly use. It looks like it would be great for Rec diving and using the wireless AI. And, later, if I wanted to use it without the AI, on Tech dives (if I ever go that far), it supports numerous gases, Trimix, hypoxic mixes, Gradient Factors, etc.. Probably way more than I'll ever use. But, the display alone looks like it's worth the extra $70 over the Sherwood Amphos.

I saw many recommendations on here for the SW Petrel. $850 plus shipping means probably $130 more than the TX-1 (which offers free shipping from LP). I like the Petrel display. But, I think I would actually enjoy the wireless AI and the smaller size and wristwatch styling of the TX-1 more. The TX-1 even supports Buhlmann with Gradient Factors, so I think it would actually support any activity that the Petrel would, which means the Petrel offers no real advantage other than the bigger screen - for me, who has no intention of ever diving professionally, though I may eventually pursue some technical certifications just to allow me to do additional fun diving (e.g. deeper, longer, or caves). I do realize you can pay an extra $70 for VPM-B on the Petrel, which I guess the TX-1 doesn't support, nor have a way to upgrade to. But, as I said, I don't expect to dive professionally, so I'm skeptical on ever feeling like I need that. If I get to that point, I can use V-planner and do my own plan and then use any of these just as gauges, right?

I realize all that sounded like I'm just seeking some kind of validation for a decision that I already made, but I'm not. I'm really on the fence about whether to go "whole hog" with something like the TX-1, or just go inexpensive and have an analog console for pressure (and maybe depth and maybe compass). I just HATE the idea of spending even $200 on a PDC, doing OW certfication and one week of diving in Mexico and coming back wishing I had just spent the $750 in the first place.

Further, if I go the inexpensive route, I'm not sure I could really get away with $200 for the PDC. I have compared dive tables (USN, NOAA, PADI, and some others) and done other reading and have concluded that it seems like the PADI RDP is more conservative than the USN tables (I know it's a generalization, just based on a single dive - but I have also compared repetitive dive scenarios). And it seems like all the different PDCs are at least as conservative as the PADI RDP. Some (like Oceanic and Sherwood) being close to the RDP and others, like Suunto, being signifcantly more conservative than the RDP. Plus, reading on here it seems that Suunto is not well-regarded for reliability. Given all that, I think I want a PDC that is the most liberal - since it will still not be any more liberal than the RDP. Which means it uses the DSAT model. Which means, from what I can tell, Oceanic, Sherwood, and Aeris. And I think I want one that shows O2 saturation level, too, not just N2 (since I intend to use Nitrox). So, it looks like I'd have to spend at least $250. Plus, buy a console with a SPG.

I guess what it comes down to is, should I spend $300 for a PDC and a SPG. Or should I go ahead and ante up to $750 for a TX-1 (with a AI transmitter)? Or $500 for the TX-1 w/o TMT? Or should I do something else? Buy a used computer and a $45 SPG? Like I said before, my most pressing goal is to have my own PDC to use during my OW cert and then diving in MX using rental gear. Secondary is not spending money on something I'll want to replace in the next 6 months or 1 year.

And if you actually read all that.... Thank you!!

Ambitious newb or perhaps a touch of OCD. Take it easy, slow down. I'm certainly in favor of diving with a computer. You might start with a non AI computer such as the Oceanic Veo2 or Geo2, I dive the Geo2 as a backup. Both are fine computers for around $400. If you must have AI, the Oceanic VT4.1 is on sale until the end of the month for $800, with transmitter and download cable. I dive the VT3 as my primary and like it very much.

Best of luck, good diving, Craig

 

[TSandM]

I think buying a computer as your first purchase is a reasonable decision. Knowing the computer and understanding the screens it shows you is important, and many computers nowadays will also allow you to download information for a dive log, which is nice.

Wireless AI, which my husband uses, is finicky. The computer and transmitter don't always sync, and the transmitter is hard on batteries and doesn't have a battery readout, so sometimes you're surprised that it doesn't work. In order to avoid losing a dive, we feel it's necessary to have an SPG, which gives you back the hose you're trying to avoid, so the only real reason to buy AI is to have the information on your wrist. With the money an AI transmitter will cost you, you could buy a nice wetsuit.

As far as worrying about multiple gases . . . Most computers nowadays, and certainly any wrist computer with AI capability, will do air and Nitrox. The essence of recreational diving is having the surface as an option, so it does not include running up significant deco obligations, and certainly not enough to require accelerated decompression and a deco gas. I would be willing to bet that well over 90% of the people who learn to dive NEVER go on to do any diving that involves staged decompression, and I would not plan my first computer purchase based on the idea that you will. As is said over and over again, by the time you get to tech or cave diving, you will have sunk so much money on gear and training that a bottom timer won't loom large in the equation

You read a lot about a lot of things on SB that represent a VERY small proportion of the diving being done out there. I am a very big proponent of buying gear that can carry you into the future, if that gear is a) perfectly functional for normal recreational diving, and b) not significantly more expensive than other options for recreational diving. A multi-gas, decompression-capable computer fails the second test, and the people who write the algorithms for them will tell you they are not designed for shallow repetitive diving.

 

[stuartv]

Ambitious newb or perhaps a touch of OCD. Take it easy, slow down. I'm certainly in favor of diving with a computer. You might start with a non AI computer such as the Oceanic Veo2 or Geo2, I dive the Geo2 as a backup. Both are fine computers for around $400. If you must have AI, the Oceanic VT4.1 is on sale until the end of the month for $800, with transmitter and download cable. I dive the VT3 as my primary and like it very much.

Best of luck, good diving, Craig

You read a lot about a lot of things on SB that represent a VERY small proportion of the diving being done out there. I am a very big proponent of buying gear that can carry you into the future, if that gear is a) perfectly functional for normal recreational diving, and b) not significantly more expensive than other options for recreational diving. A multi-gas, decompression-capable computer fails the second test, and the people who write the algorithms for them will tell you they are not designed for shallow repetitive diving.

Thank you to both of you for taking the time to share your thoughts with me. As it turns out both of these comments leave me with the same thought:

If you think $400 is a reasonable amount to spend on a good Rec PDC, then why not spend $500 for the Hollis TX-1 and thereby at least have the ability to add AI in the future if I want it? With the additional bonus of having a very capable Tech PDC that may very well still be perfectly serviceable on the day that I do pursue some Tech certs? People who tout the SW Petrel certainly seem to feel like buying one now and using it as a Tech PDC 3 years from now is perfectly reasonable.

For $500, the TX-1 seems almost like a no-brainer for anyone who is considering Rec PDC beyond a $200 Aeris Manta. From what I can tell, it is absolutely just as good a Rec PDC as its somewhat less-capable Oceanic equivalents. If I'm recalling correctly, it looks like it may be pretty much just the same as the Atom 3.1, but with more Tech capabilities. And it can be had for $500! Why even consider a VT4.1 for $800 when the TX-1 with transmitter is only $750?!

---------- Post added September 4th, 2014 at 11:15 PM ----------

perhaps a touch of OCD.

Best of luck, good diving, Craig

Oh, and Craig, what gave me away? LMAO!!

This is the problem with me getting signed up for this and then having to wait over a month before the classroom part even happens. My g/f told me she would give me SCUBA lessons for Christmas - in 2012! We've never been able to make it actually happen - until now. I bought all new snorkeling gear and paid for the class last weekend. I read through the entire SDI OW "textbook" Monday morning and did all the "exams". Took about 2 hours because it was really all old news to me.

So, yes, I am OCD'ing out just a wee bit at the moment...

 

[DiveNav]

Whatever dive computer brand / model you end up purchasing, make sure you learn how to properly use it.

Alberto (aka eDiver)

 

[Imla]

Actually... What you can do for that month, is go to the gym, or the pool... Swim laps, run, train weights...

 

[lv2dive]

Frankly I would get a wrist mounted veo for around 200$ and be done with it. You can run it in nitrox mode for recreational diving and gauge mode if you move past recreational.

I do not believe one person has recommended you go with something that has AI or spend extra to have ability to add AI... The reason is that there truly is little value. There is truly little value, especially for someone as detail-oriented as yourself (you can easily figure out your gas consumption (sac/rmv) etc after the dive on your own). The primary drawback for the wireless AI is that it is known to be failure-prone so everyone backs it up with a hosed SPG.

You are not going to get justification for an AI computer from the majority of people on this board - there is just not enough benefit to warrant it. Sure it's shiny and *seems* like a good idea but at the end of the day, YOU should be tracking everything that computer is going to do for you. And btw... Just from reading your posts in this thread.... I have a feeling you would ;-). Save your $$$ for for future equipment needs, I would be willing to bet you don't stop at aow! <g>

Thank you to both of you for taking the time to share your thoughts with me. As it turns out both of these comments leave me with the same thought:

If you think $400 is a reasonable amount to spend on a good Rec PDC, then why not spend $500 for the Hollis TX-1 and thereby at least have the ability to add AI in the future if I want it? With the additional bonus of having a very capable Tech PDC that may very well still be perfectly serviceable on the day that I do pursue some Tech certs? People who tout the SW Petrel certainly seem to feel like buying one now and using it as a Tech PDC 3 years from now is perfectly reasonable.

For $500, the TX-1 seems almost like a no-brainer for anyone who is considering Rec PDC beyond a $200 Aeris Manta. From what I can tell, it is absolutely just as good a Rec PDC as its somewhat less-capable Oceanic equivalents. If I'm recalling correctly, it looks like it may be pretty much just the same as the Atom 3.1, but with more Tech capabilities. And it can be had for $500! Why even consider a VT4.1 for $800 when the TX-1 with transmitter is only $750?!

---------- Post added September 4th, 2014 at 11:15 PM ----------



Oh, and Craig, what gave me away? LMAO!!

This is the problem with me getting signed up for this and then having to wait over a month before the classroom part even happens. My g/f told me she would give me SCUBA lessons for Christmas - in 2012! We've never been able to make it actually happen - until now. I bought all new snorkeling gear and paid for the class last weekend. I read through the entire SDI OW "textbook" Monday morning and did all the "exams". Took about 2 hours because it was really all old news to me.

So, yes, I am OCD'ing out just a wee bit at the moment...

 

[TSandM]

I don't know anything about the Hollis computer.

If I were going to advise a new diver on buying a computer, I'd tell them to buy a wrist unit, that is Nitrox capable and downloadable. I'd also warn them to make sure they can read the display EASILY in low light.

If I were going to spend money to upgrade from the basic gauge, I'd spend it on an OLED display rather than AI capability.

 

[lv2dive]

+1

Ease of reading SO MUCH more important than gadgetry!!!!

...

If I were going to advise a new diver on buying a computer, I'd tell them to buy a wrist unit, that is Nitrox capable and downloadable. I'd also warn them to make sure they can read the display EASILY in low light.

If I were going to spend money to upgrade from the basic gauge, I'd spend it on an OLED display rather than AI capability.