Dive Comp for OW+AOW

[spectrum]

Why run the other way? Instructors should know about different computers and can be a valuable source of information. If the OP is planning on buying a computer, why not get advice on different models?

I should certainly hope instructors know about computers and are perfectly capable of guiding a student. The fact of the matter is that a huge number of divers never stay with the sport long enough to derive any benefit from the computer. Having a computer will not make them any better as divers. In fact it will short circuit all of the basic theory they were (hopefully) taught. The OP asked if it's advisable to buy a computer to go along with his OW & AOW classes. I say wait to see if you like diving before you move to the next echelon of investment.

The debate of when to buy gear will always be there. Common wisdom is to try a few things, perhaps borrow or rent enough to identify likes and dislikes. Lacking local gear that I cared to rent I did a lot of advanced study and pool testing and my wife and I both certified in out one gear. There was no need for a computer for the type of diving we were doing locally. In preparation for a dive trip we made the move.

Ebay and bankruptcy courts are littered with the shattered dreams of divers that over invested or prove to be under inspired.

A diver can make the investment when his or her diving and abilities dictate, not just because they are doing OW or fast tracking into AOW (another debate). It's not like insurance enrollment where you have to sign up now or wait.

I just had some OW students buy gear while they were taking their class. They got to use their own gear from the get-go and while I was there to help them with it. We spent plenty of time on decompression theory and tables but spent just as much time working through all the functions of their computer. Really, how many recreational divers do you see using tables only to dive with?

As I said we certified in our own gear, it was a calculated risk and for us it payed off. Many divers are very susceptible to being manipulated and spending for the sake of spending. I am not saying this is the case with you or your affiliates.

I see many divers who dive sans a computer and by the same token many computers that go on dives where they are of no real value except to maintain statistics. Not every diver's dives or diver's locales are the same. Not every diver does exclusively boat diving and goes to 100 feet with lots of air and a great SAC.

It's scenario dependent and should be based on need unless someone is a gear junkie with disposable cash. In general I would rather a diver spring for a pair of nice steel tanks to have at the ready than to own a computer but miss dive opportunities for want of an air cylinder. At least around here the cylinders have much better resale value.

If the OP isn't sure if diving is for him, then wait to buy the computer until you know for sure.

I think that was my point. Having not been diving that needs to be the default advice position.

I recently taught a EAN class, I had the students bring in their computers so we could go over setting them to EAN Mode. One of the students found out THAT night that his computer wasn't EAN compatable. If I had been there helping him to pick one out, he would have known it was or wasn't compatable.

That's really good but not every new diver has a guardian angle like you. Many run out ill advised and buy according to the wrong criteria. Please take this as a compliment wen I say that the situation you present is above average in the industry as I have experienced it.

Pete

 

[Colliam7]

Hopefully, you'll be learning to dive using the tables, not a dive computer.

I would agree, that having a computer for OW and AOW is not necessary. You'll be working on developing aptitude, if not proficiency, with the tables. Even if you are in a OW or AOW class where all other divers have a computer, do not be daunted by that. The focus should be on the skills of the course, and computer skills, while great to have, are not part of the requirements.

Having a cheap water-resistant watch as a timer is appropriate for AOW. While I appreciate the basis for the advice to consider buying a used air-only computer on eBay, you would still be buying something that you will probably ultimately want to sell. You might wish to wait for a computer purchase until you have better characterized the kind of diving you might be doing as a certified diver.

From a financial perspective, I would encourage you to consider spending money on a good reg before a computer.

 

[The_DivePirate]

I have a question for Ann Marie since she is an instructor. Please forgive my ignorance as I have not taken AOW.

Scenario:

You and I agree to go on a dive. The dive is on a wreck with the bottom at 80ft. There is moderate current necessitating us using the line to descend and ascend. We are both using AL80s. Assume the wreck has 20ft of profile so we will be between 80 and 60ft during the dive.

During our pre-dive briefing, what would you suggest we use as a turn pressure for the dive? Please bear in mind, that even if something goes wrong, I am not interested in trying a CESA from 80ft, and I would set a requirement of being able to have both of us complete our three minute safety stop.

So again, at what pressure would you suggest we end the dive and begin our ascent?

Thank you.

Well, not being a pro diver as of yet, but, as a dive pro I would think her answer would be, your'e not certified to 80' as an OW diver.(PADI anyways) Just a thought.
As far as the computer goes. A computer is like a calculator, you shouldn't use one, until you know how too use the tables first. also, unless you have an abundance of cash the standard SPG will work fine for cheap. Save your money and wait until you know which way you are headed in SCUBA.(air only,NITROX, or TRIMIX) Three computers could get spendy!!!! But, if you are seriously in the market for a computer, the SUUNTO Cobra with the pro pak/disconnect is an AWESOME computer. It has software that allows you to download it to your PC and is air intergrated. Also, it is
NITROX compatable to 40% EANx. There are others cheaper, but I've always found YOU GET WHAT YOU PAY FOR.
Also, if your instructor is at all affiliated with the shops profits, I'd be worried the place is in it for the money, not the new diver!! You'll have plenty of time to dump a WAD of cash!!! Another thing, you'll here it over and over again, don't by gear your first year!!! I know from first hand experience, DON'T DO IT!!! :no :no Rent or try to borrow from other divers, most divers that have been diving for at least a couple years, have the gear they bought their first year they were diving Heck, my gear has evolved many times in the not quite 2 years I've been certified. I know it's hard, but give it a try. Maybe you have a local club that could help in the purchase of used quality gear that you can dive until you find the right equipment.
Have a GREAT diving and be safe.

Divesafe/Train hard
Joe

 

[UKdivemaster]

Hi,
i'ts not really an official rule but in the UK we tend to turn the dive around (i.e. start heading back home) at a half tank = 100bar (1500psi) and look to get back on the boat at 50bar (700psi) - or before you get into the red section of your pressure gauge.

With regard to endinf your dive profile - if you a learner i would start looking to ascend at 70 bar (1000psi) this gives you enough air to ascend, do a safety stop and get back in the boat without any worry.

As a general rule if you are doing a very deep dive give yourself a bit more time/air to ascend - but if you are in shallow water you can wait a bit longer.

Also worth a mention is you should (if possible) try and do the deepest part of your dive first and then gradually ascend towards the end of you dive. So in your example above - start at 80ft and aim to be finishing the dive at 60ft.

With regard to a computer a couple of pointers:
a) if you can afford one then get one - they are a huge help for depth and making sure you don't ascend too quickly
b) if you can't afford a computer then look at buying the Wheel -as this lets you plan multi-level dives and gives you more bottom time
c) I would suggest that either buy cheap with a view to changing it or buy expensive
d) if you planning on doing lots of diving - get a computer that is nitrox compatible
e) air integrated computers are nice - but expensive and not really necessary unless you have cash to spare... the transmitter tends to break :-(

 

[UKdivemaster]

oops - just a second thought

in the PADI system a computer is a not a replacement for the table or the wheel. If you are learning to dive you need to be completely comfortable with the tables.

With regard to Colliams comment about regs vs.computer - this depends on your diving location and the rental gear available. If you in the UK and diving with a good school we wouldn't take you deep until you were confident - so i would look at computer - out in the US i think colliam7 may be right; although it depends on where you are training

 

[The_DivePirate]

e) air integrated computers are nice - but expensive and not really necessary unless you have cash to spare... the transmitter tends to break :-(

Only remote air integrated have transmitters to break. My Cobra is air integrated and runs off a hose, and has never had an issue. Maybe in the UK you only have remote units, but in the states we have both, and it's nitrox capable to 40% EANx.

 

[Steve_Dives]

Not required. If deep is part of the AOW, you might need to rent a computer if you do not buy one.

If you are not constrained by a budget, it might make sense. You will have to do everything from tables for the class, but you can learn to use the computer in a supervised environment. Seeing how it works relative to the tables could also be beneficial.

If you are deciding between regs, a BC, or a computer, the computer would be the last thing I would purchase.

 

[PerroneFord]

Well, not being a pro diver as of yet, but, as a dive pro I would think her answer would be, your'e not certified to 80' as an OW diver.(PADI anyways) Just a thought.

The question was in regard to AOW. So I assume we are diving below OW depths, and I believe that AOW, even in PADI, would allow a dive to beyond 80ft.

But the point being, no matter HOW you run the math, you'll run short of gas LONG before you reach NDL if you are properly turning the dive and safeguarding air supply for yourself as well as your buddy. A computer makes it VERY easy to violate what would be needed to make a safe ascent together if you wish to do it at 30fpm, and do a 3 minute safety stop. NDL (on the PADI table) for 60ft is 55 minutes. I know VERY few divers who could push near an hour at 60ft on an AL80, deal with a gas failure at depth, make a normal ascent sharing with their buddy, including safety stop, and get back aboard the boat.

UKdivemaster's suggestion of turning the dive at 1500psi or 100bar is just about where you'd have to do it to make this work, assuming everything goes perfectly. How many recreational divers turn a dive at 1500 psi? Add the computer in the mix which lets you push that NDL further, and we eat into air reserves even more.

 

[mjatkins]

But the point being, no matter HOW you run the math, you'll run short of gas LONG before you reach NDL if you are properly turning the dive and safeguarding air supply for yourself as well as your buddy. A computer makes it VERY easy to violate what would be needed to make a safe ascent together if you wish to do it at 30fpm, and do a 3 minute safety stop. NDL (on the PADI table) for 60ft is 55 minutes. I know VERY few divers who could push near an hour at 60ft on an AL80, deal with a gas failure at depth, make a normal ascent sharing with their buddy, including safety stop, and get back aboard the boat.

In fairness, your original post described the dive as being between 80 and 60 ft. As I'm sure you know, the RDP has an NDL of 30 minutes for a dive to 80 ft. Since you mentioned "the PADI table", I assume you would use it as apposed to a computer or other method. Since the RDP offers no credit for multi-level profiles we would have to base your whole dive on that 80ft depth. We also teach that to be prudent we should dive "well within our limits" which will pull our NDL back a few minutes more. To stay outside of the grey area on the RDP would call for a bottom time of no more than 25 minutes, which I believe is within the breathing range of most recreational divers; even fairly new ones. For many of us, we could have enough air to accomplish all that you mentioned and still go over that 25 minute mark if we weren't careful.

Thanks for the debate.

Matthew

 

[PerroneFord]

Matthew, please don't see this as a debate. I don't view it that way.

I backed off the 80ft profile to the 60ft profile as in a dive, VERY few people spend a lot of time swimming around on the sand looking at the hull of a boat. So lets look at it from the perspective of an 80ft dive for 25 minutes. I am a fairly heavy breather, as I am a very large guy. My dive planner shows the following for a 25 minute dive to 80ft.

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 2

Dec to 80ft (1)
Level 80ft 23:24 (25)
Asc to 20ft (27)
Stop at 20ft 2:00 (29)
Surface (29)

68.2 cu ft TOTAL

Basically, it says that I would need 68 cuft of air to complete this dive with my safety stop. At minute 25, if my low pressure hose ruptured, and I had to shut off my tank, I would have burned about 60 cuft of air or roughly 3/4 of my tank. Converted to PSI, that would be 2250 gone and 750 left. If we assume my buddy breathes similarly, we now must share 750 psi to get to the surface. That gives us 375psi to find the line (while sharing an octopus), get to 20ft (or 15ft), finish a safety stop, and get to the boat.

How many of your AOW students could make this ascent? If you have the opportunity, I suggest you try it. Have one signal at 1000psi, and have his buddy cut off his tank, go on the octopus, make their way to the ascent line, then do the 30fpm ascent from 80ft. See how much air they hit the surface with. And remember, we are talking about a dive where we are backing OFF the NDLs. Not diving a computer which is routinely sold to EXTEND the NDL beyond the tables.

When I started to run the numbers, it was sobering. It didin't take me long to realize that the ONLY way to hit the surface given what is routinely taught in OW or AOW, was a CESA. There simply wasn't enough left for two divers, under stress, to ascend normally if there was a failure late in the dive.