Article: Dive Computers and the Magic Bracelet Syndrome

[AFdivedoc]

You can view the page at http://www.scubaboard.com/forums/content.php?r=722-Dive-Computers-and-the-Magic-Bracelet-Syndrome

 

[Donnah]

This should be required reading for all divers!

It also helps to look at the computer occasionally. Years ago we were diving Truk. A very experienced diver, solo, borrowed a camera for the first time. My husband and I could see the flash below us on the deck as we ascended. Boat manager asked where the fellow was and said "Well, he'll come up when he runs out of film." He ran out of film, then looked at his computer. Big Oops! He drained the hang tank and most of a second tank doing in-water deco. Every once in a while someone would put on a mask and wave at him. All turned out well, but he lost the next day of diving. It could have been a very bad situation -- I think the nearest chamber was in Guam.

 

[Jim Lapenta]

Great article and says what I have been telling new and not so new divers for years! Thanks Gary!

---------- Post added January 1st, 2014 at 10:47 AM ----------

This article should be a sticky in the new divers forum and/or the computer forum in the classifieds.

 

[DiveNav]

Very good article!
Thank you for creating it.
I have included it as a link in our online class Introduction to Dive Computers

 

[Lake Hickory Scuba]

Awesome article, and definitely agreed that all new divers need to read this. On our channel we post videos of different scuba tips to help new and old divers out. One in particular was on planning dives using tables even if you use a computer. Scuba Tip Planning your Dive - YouTube For the majority of divers (that are not in the water 7 days a week like us), they don't realize just how often computers malfunction or batteries die. And when it happens, falling back on your original dive plan, not to mention aborting the dive is the only safe option there is. Being prepared for instances like that, carrying an extra set of gauges, and actually planning your dives, seems to be an afterthought of most new divers. I believe I'm going to print this article off and put it into all the student crew packs for any new students. Thanks for posting.

 

[drrich2]

A timely article. The bells and whistles of computers can be quite confusing to new divers. I believe a recent thread showcased this, with a diver apparently thinking he needed to set his computers F02 so it'd give a max. depth of 60 feet, if I understood his questioning properly. Which would mean a computer calculating on the assumption he was diving nitrox with a MOD of 60 feet, when he actually dove air.

As for having a backup, I prefer a backup computer to dive tables, though I own a copy of the PADI tables.

Richard.

 

[danhannan]

Thanks for posting this article. It is a good reinforcement of what I learned in my OWD course. I don't yet own a dive computer and am pretty adept with the eRDP and PADI tables, but when I do buy a computer I will heed the great advice

 

[cmdiver22]

Speaking from a recreational/OW point of view, and on #6, it has made me a better diver, since I need to know the water temprature, depth, and air remaining...constantly. It's a big deal where I dive, since 50F at the surface becomes <40F at 60'. I like to know if I'll be hypothermic in a wetsuit before the end of my dive when I'm at the bottom and below a thermocline. Also, since most of my murky dives are done in zero visibility, my ascent rate is deceiving since I have no reference, I need my computer to yell at me when I exceed 30ft/min. I also glue my eyes to it when I'm doing safety stops, since I'm not "advanced" enough to hold mid-water depths in zero vis with heavy swells without knowing my depth constantly.

I don't see the practicality of manually calculating a multi-level dive off a dive boat either, when all I know about the dive site is 1) the bottom depth under the boat, 2) how much air is in the tank, 3) previous SI. Your dive site is at the whim of the Captain/DM. Throw in pre-filled Nitrox tanks and fixed blends (31.8 or 33.2, pick one), and you've added even more fun. You options will be to either use the max depth off the table (if the bottom is 60', then plan the entire dive to 60', despite maybe only going to 40', then come straight up with a half-full tank), max depth/time for that Nitrox blend and 1.4 PPO2 limit, or doing it the PADI AOW/multi-level-diving way: rough table planning to the max bottom depth/time and dive to your computer as you go shallower.

I've made more pre-dive math mistakes than my computer has during dives, so I tend to err on whichever is the most conservative, whether it's the table, or my computer display. If I planned it badly, planned air/depth to stay under for 60 minutes, computer says I have 40 minute when I get there, I'll err on the side of the computer and dive 35 instead and figure it out what I goofed up on when I get back to the surface. All of this using the "ascend and call the dive" rule of thumb if something seems out of place, something flashes or alarms, or doesn't add up when I'm under. Tables only go so far, and are practically useless underwater since time moves along faster than my math speed with a pencil + bad vis + surge + shivering + 7mm gloves.

 

[AFdivedoc]

Speaking from a recreational/OW point of view, and on #6, it has made me a better diver, since I need to know the water temprature, depth, and air remaining...constantly. It's a big deal where I dive, since 50F at the surface becomes <40F at 60'. I like to know if I'll be hypothermic in a wetsuit before the end of my dive when I'm at the bottom and below a thermocline. Also, since most of my murky dives are done in zero visibility, my ascent rate is deceiving since I have no reference, I need my computer to yell at me when I exceed 30ft/min. I also glue my eyes to it when I'm doing safety stops, since I'm not "advanced" enough to hold mid-water depths in zero vis with heavy swells without knowing my depth constantly.

I don't see the practicality of manually calculating a multi-level dive off a dive boat either, when all I know about the dive site is 1) the bottom depth under the boat, 2) how much air is in the tank, 3) previous SI. Your dive site is at the whim of the Captain/DM. Throw in pre-filled Nitrox tanks and fixed blends (31.8 or 33.2, pick one), and you've added even more fun. You options will be to either use the max depth off the table (if the bottom is 60', then plan the entire dive to 60', despite maybe only going to 40', then come straight up with a half-full tank), max depth/time for that Nitrox blend and 1.4 PPO2 limit, or doing it the PADI AOW/multi-level-diving way: rough table planning to the max bottom depth/time and dive to your computer as you go shallower.

I've made more pre-dive math mistakes than my computer has during dives, so I tend to err on whichever is the most conservative, whether it's the table, or my computer display. If I planned it badly, planned air/depth to stay under for 60 minutes, computer says I have 40 minute when I get there, I'll err on the side of the computer and dive 35 instead and figure it out what I goofed up on when I get back to the surface. All of this using the "ascend and call the dive" rule of thumb if something seems out of place, something flashes or alarms, or doesn't add up when I'm under. Tables only go so far, and are practically useless underwater since time moves along faster than my math speed with a pencil + bad vis + surge + shivering + 7mm gloves.

I don't dive where you dive, so if your computer makes you a better diver there, you're the exception to my experience. The point is, be able to handle a failure of the sole instrument giving you your depth, time, ascent rate, inert gas/O2 exposure, and gas supply. Those are a lot of eggs in one basket, and it sounds like you dive in relatively demanding conditions.

I don't see the need to plan a multilevel dive off a boat either, unless the boat is anchored off wall, reef, or other item of interest in the shallows. The multilevel dives you are referring to are no-deco (although you can plan multilevel tec dives). If you're referring to the diver in Number 7, he inadvertently went into a significant amount of deco and had to do the staged decompression time, not a "multilevel" profile.

 

[Skittl1321]

I recently dove where the rental equipment included computers. The briefing, the computers were only mentioned as a means of keeping track of your 3 minute safety stop.

I had my own computer, which ran a much more conservative algorithm than the rental computer so it was interesting to compare. I got down to 7 minutes at one point, and the other computer was giving me like 20...

What was more scary interesting were the single day divers and their conversations on the boat after the dive. "What was the max depth you reached?" "Oh, I don't know- how can you tell that?" If they didn't know your computer had a depth gauge, did they have any idea it was also giving an NDL? These people weren't using tables...