How Much Reliance on Dive Shop Planning?

[Neilwood]

Just adding my tu'pence worth - buy the computers (one each) or rent them from the shop.

Tables are great for a simple square profile dive or even multi level (where you start at one depth and then ascend to another fixed depth). If you can guarantee that your dives are such a profile then go with them but they are giving you a heck of a lot of needless work. If you stay deep a short time longer, hang at a different depth or ascend at a different rate, you can effectively throw your dive plan out the window. If you hang a few feet higher at depth, the table can't give you credit for it.

Computers are better IMHO as they calculate your actual dive in real time. Spending a couple of minutes deeper becomes no big deal as you can see how that affects your NDL and adjust accordingly (spend a bit shorter at a higher level or simply move yourselves up a few metres). Just moving up a few feet can shift your NDL considerably

Most computers will also monitor things like your ascent rate and stop times as well as letting you download all the information such as the profile which you can look at at a later date.

 

[Rred]

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)

 

[RandomGuy1]

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.

Not necessarily true. Some computers have rechargeable batteries and you can just plug up and recharge. Some also take just a quarter and a AA battery. That is a good point as for something to look at when purchasing a computer.

 

[Doby45]

Mares Pucks are $150 New instead of a used Zoop.
Mares Puck Wrist Computer

Puck Pro's are $195 new.
Mares Puck Pro Wrist Computer

I've dove the Rhone with DiveBVI. You can't get much deeper than 75' since the bow is in the sand at that depth.

The entrance in the bow is the same place they filmed the famous scene in "The Deep" where Jackie Bisset exits quickly. It's an easy dive and the sides of the ship are open in places so there's "outs" if you're not comfortable with the overhead obstruction.

Also do both halves (2 dives) - I found the back more interesting - there's a big driveshaft, a lot of mechanical stuff - even a small silver spoon welded to the deck by electrolysis. In one area a few feet of marble floor survived. IIRC the back is a bit shallower and runs uphill.

At the very back is a huge prop - you don't even realize what it is at first until you swim between it and the rudder. The back is collapsed so you mostly swim over it - or along one side you can get under the deck but it's all blown out on that side so there's no penetration possible.Lots of stuff lives there since it's been down so long.

Our "newbie" diver did it as dive #12. without issue. If you go with DiveBVI there will be at least one DM in the water - possibly 2 - one leading and one trailing the group. Actually they're all instructors afaik.

I was not meaning to push a specific agenda/computer. I just know that I have personally used the ZOOP as my first computer and know that the computer is easy to use and setup. I was not aware of the price of the Puck but I can say that the single button is a pain in the ass. I have an instructor friend that was teaching a class and the shop supplied pucks to all the students for the class and I used one as well, needless to say it is not very intuitive. Just my experience, spend your money how you choose and I will dive with you all the same.

 

[doctormike]

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.

Yeah, that's a design flaw. Better to get a rechargeable computer or one that lets you replace the AA battery any where in the world with a quarter in about two minutes. Although those computers are probably more expensive, so you probably don't save much by doing that.

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.

I don't mean to be snarky, but I don't think that you appreciate the reason why so many people dive computers these days. They are not designed to decrease the risk of DCS when compared to tables. If anything, they would increase the risk of DCS, since the average table diver is actually doing a profile that has less nitrogen loading than was in the dive plan. A dive computer gives you "credit" in terms of calculated NDL for time above the bottom, which translates to longer dives which might theoretically put one at increased risk for DCS. The fact that the incidence of DCS in recreational computer divers is extremely low is reassuring.

Yes, you can put together a watch and a depth gague for slightly less money than a cheap dive computer, use tables, and accept the shorter NDLs. Or you can do what most people do, which is to spend a small percentage of your year's diving expenses on a device that will take care of that for you, and if it happens to fail one day, then the only downside risk is that that particular dive will be shorter.

 

[ronscuba]

Go ahead and be snarky Mike. We are New Yorker's !

 

[archer1960]

That is exactly why I made the original post. The first dive is 75' for 30 min. The eRDP shows the max no decompression time at 75' is 35 min. IF the dive goes a little deeper, say 80', and IF it goes for 31 or 32 min, that puts it over the no decompression time according to the eRDP.

Now I know the entire dive won't be at 75', or 80', but I don't know what the max no decompression time is for the particular dive profile the operation uses. My question was whether to trust the people that have been doing it several times weekly for decades, or to carry my own dive computer. I've been convinced, and will carry my own computer.

The use of the term "perilously" is because of my own self imposed conservatism here, particularly because we are really just starting out, with only 8 dives so far. It's really the wrong word to use here. My understanding is that the time the eRDP is giving me is conservative, meaning going to 75' at 35 min is a safe dive. My concern is that the dive may go a few feet deeper, and may go for a few minutes more - I don't know that, but I want to prepare for that. It is clear to me now that the only way that I will be comfortable if that happens is with my own computer.

Given that you have only 8 dives, there's a very good chance that your limiting factor will be air, rather than NDL, unless you're renting big tanks.

 

[Rred]

Gee, Mike, let me say first that I appreciate your clarifying up front that you don't want to be snarky, and that I didn't read your message as snarky at all. See, if I wanted to be snarky (and I don't!) I'd point out that you need only have said "I do not think" and let it at that.(VBG)

Yes, I'm aware that computers can do many things and have many benefits. But aside from extending your bottom time, which can also be read as "reducing your safety factors", 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.

Yes, a computer is a nice way to figure out saturation and safety for a "Gee, I was at fifty feet for...and then seventy feet for...and hey, how'd I get to 90 feet? How long have I been here?" but the tables still *suffice* for a safe dive, even if it isn't a "maximum" profile. I don't want maximum profiles, I'll accept a little less dive time and err on the side of safety.

And in exchange for that, I save the money up front. The annual o-ring changes. And have no worry about mixing electronics and seawater and aw shucks, I'd have to abort the dive if the damn thing flooded?

The computer can help coach my ascent rate. That's got real value to me. But all this fuss with numbers and what George Carlin (RIP) called "MORE STUFF" ? Nah. I go diving to get away from all that.

 

[doctormike]

But all this fuss with numbers and what George Carlin (RIP) called "MORE STUFF" ? Nah. I go diving to get away from all that.

Yup! Sounds like dive computers are not for you..!

 

[Rred]

Richie-
Good point but aren't the rechargeable ones limited to the more expensive computers, designed for heavier use? And don't they still recommend changing seals (for those that have them) on a regular basis, to maintain water resistance?