How Much Reliance on Dive Shop Planning?

[AdivingBel]

I replace my (and my wife's) DG03 battery every couple of years (approx. 100 to 150 dives). $2 battery (cr2450) and I don't replace the o-ring. I just check it for nicks and use a very small amount of silicon lube and button it back up. Good to go. No problems and have over 400 dives (each) on it. Easy peasy...

 

[ToyZuki9615]

Another point which I did not see mentioned is the NEED for a computer if you plan to dive a LOT.

Tables may work fine for 2-3 dives in a day, but if you want to log some serious bottom time on a trip, a computer is the only way to go. Yes, you can try to manually map your actual dive profile on a slate and at the end of every dive calculate your true NDL, but I would imagine after 3-4 dives with only 1 hour surface intervals between you will be stuck starting in a pretty high Pressure Group. Plus, I don't really care to be spending that much time topside calculating my true NDL, and you're adding some serious probability of human error causing you to take a nitrogen hit.

My dive vacations are planned dive vacations where I log 5-8 dives a day. I do not see tables or an eRDPML planner as a reasonable option.

 

[CT-Rich]

I remember getting physics lessons in my SCUBA certification classes (1980). Gas laws, how to calculate multi-level dives, the repetitive dive groups. What a pain in the a**. If you never go deep and limit yourself two dives, the tables would be fine, but considering how much all the gear costs so you can enjoy diving, a basic single button puck for less than a couple of hundred bucks seems like almost nothing.

 

[dmaziuk]

I remember getting physics lessons in my SCUBA certification classes (1980). Gas laws, how to calculate multi-level dives, the repetitive dive groups. What a pain in the a**. If you never go deep and limit yourself two dives, the tables would be fine, but considering how much all the gear costs so you can enjoy diving, a basic single button puck for less than a couple of hundred bucks seems like almost nothing.

Yes but on the flip side if they're going to dive The Deep and then not dive until next year, they might as well wait for next DEMA, Xmas sales, or deep 6.

 

[FinnMom]

I would add a couple of points:

The cost of a computer is not the cost of the computer. You will need to replace the battery every second year, and that means a battery AND o-ring. For some folks this is trivial, for others it will be a $50 shop bill to have someone else do it. And in theory, someone needs to pressure test that computer after the new o-ring has been put in, to see if it was done properly. If not, the computer will flood and be ruined. (That's the difference between having the guy at the flea market change your watch battery, and having an authorized shop do it.) Would I trust a dive shop to have the right equipment or do the pressure test correctly? No, based on how I've seen shops do repairs.

Second, I've heard DAN speakers and read publications, and maybe I've missed it. The use of dive computers does not seem to have lowered the incidence of decompression sickness. The tables (any of them, because there are different sets now) still seem to work just as well. With no moving parts to break. And no repeated maintenance costs.

Probably the only "irreplaceable" benefit of the computers, is that they all have some type of (often crude) ascent speed indicator in them. And a slower ascent is a safety factor. There used to be some dive watches that had that, but the computers are actually cheaper. They don't generally seem to make the ascent rate a very prominent feature though, just some bars on the side and then a warning. Given the total cost of a computer?

If you're only diving infrequently, it might be more effective to rent one. Or at least, start that way, to get an idea how you like different computers.

And meanwhile listen to every shop saying "Oh, that brand is crap, don't buy it" while the anonymous online reviews all talk about how many fail, right after the warranty expires. (sigh)

My Suunto Gekko lasted for 6 yrs on its original battery. The nice thing about user-replaceable batteries is that you carry a battery kit (includes o-ring etc.) and use it when it is needed. There is no need to pre-emptively change the battery. It really is easy to do by yourself, and nowadays plenty of free videos show you how.

 

[CT-Rich]

I am yet to flood the battery compartment on any computer. I bought a replacements online for less than a weekend of air (4 fills) if you think a possible 20-30 bucks every other year is too much money, you are in the wrong sport. What does it cost to replace floats and lines, hydro testing and visuals on tanks. Regulator servicing, not to mention that wetsuit don't last forever, every dropped knife that needs to be replaced or the tank of gas that was wasted , just find out that weather is a blowout...

Diving doesn't have to be expensive, but cheap computer will replace three different pieces of gear (watch, depth gauge, and plastic card with tiny numbers plus a thermometer) for about the same/ slightly more money and will automatically record all of it for future reference...

When my computer died over a dive weekend, I still dove. Not knowing the depth, was a bit annoying, time and airpresssure was problematic (my buddy Was going to run down her tank first). It was very old school, but you know what the first thing I did Monday morning was? Bought a new battery.... Why? Because knowing all that stuff makes the dive that much more relaxed.

And I am a cheap skate bastard when it comes dive gear....

 

[halocline]

We are both newly certified with 8 logged dives apiece. We are both very comfortable in the water.

My specific question is whether I should invest in a dive computer. What I have now is a PADI eRDP. When I plug in the planned dive times, depths, and surface intervals, I come perilously close to the limits of a no decompression dive.

There is an alternative to a dive computer, but I don't think it will be much less expensive and it will certainly be less convenient. You could buy a dive planner app for your smartphone, use it to plan a multi level dive (assuming the DM can provide you with a reasonable approximation of the the time/depth plan) and then dive the plan using a timing device and a depth gauge. But the dive computer is much easier.

I'm not sure this is really a safety issue as much as it is an enjoyment issue. If you are diving a multi level dive to 75 ft, using a single AL80, and you watch your ascent rate and do a nice long safety stop, it's pretty unlikely that you will be in trouble regarding N2 load at the end of the dive, at least on a single dive. But, you're definitely going to be less confident and comfortable without the computer reassuring you that you're not in trouble with NDL.

A nice thing about new divers using computers is that they all come with ascent rate alarms. (Well, it's nice for the new diver that needs training in controlling ascents, not so nice for those around listening the beeps) This is a legitimate reason to use one IMO.

You might have a look at the chapter on decompression theory in the PADI encyclopedia of recreational diving. It's not that complicated an explanation and there's good information in there. One thing that's useful is that studies have shown extended shallow stops to be very effective in reducing N2 load in recreational diving. So if you're ever feeling like you might have pushed your NDL, spend 10 minutes at 15 ft instead of 3. There's really no downside to this practice and it will make a difference in how you feel post-dive.

 

[Rred]

"One thing that's useful is that studies have shown extended shallow stops to be very effective in reducing N2 load in recreational diving. "
Can you share some URLs?

 

[boulderjohn]

"One thing that's useful is that studies have shown extended shallow stops to be very effective in reducing N2 load in recreational diving. "
Can you share some URLs?

I don't know of these studies, either.

I do know that in the raging debates about deep stops in technical diving, it appears that people who use deep stops are best advised to lengthen their shallow stops, but that is with people breathing pure oxygen on those stops and working to overcome exceptional tissue loading from a dive. That is not what is happening in recreational diving.

The best way to reduce the N2 load is to get the highest possible gradient between the N2 levels in the body and the N2 levels in the air, provided that enough N2 has already left the body to make that pressure safe. A safety stop is designed to make sure enough N2 has left the body to make it safe enough to ascend to the surface, and extending that safety stop a bit can ensure that it is safe for you to go to the surface. Once it is indeed safe to surface, though, going to the surface is the most effective way to reduce the N2 load.

 

[kelemvor]

I think the primary reason for computers is from the shops and boat operators who say "DIVE COMPUTER REQUIRED" when they are booking classes or dives. Honest, there's no other reason than making profitable repeat sales and service. Safety is NOT their prime consideration.

You think wrong, in my experience. The only operators I've dove with that required a computer also provided one at no extra cost. Florida Keys Dive Center and some other op on the east coast that I can't remember. The DM had a bucket of spare computers you could borrow if you didn't have one. Looked like mares pucks or similar.

In addition to the safety provided by using tables vs a dive computer, you might want to also consider adding a hard time limit beyond that set in the tables for all your diving. If you added say an overall dive time limit of 5 minutes on every dive it would greatly improve your safety.