Just joking around, sitting in interminable SF traffic, trying not to crash . . .
How important is a depth gauge as part of a reg set?
- Thread starter CycleCat
- Start date
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Just joking around, sitting in interminable SF traffic, trying not to crash . . .
OP
CycleCat
Contributor
ALL of them.
I realize I am a brand new diver. And I'm no mathematical genius. Maybe I am oversimplifying this. But if I plan to go in the water to 50 feet for 50 minutes, that will put me in Group G. If I dive anything LESS than 50 feet for part of those 50 minutes, I'm still Group G or better. Right? I'll just go with Group G to be safe. Am I misunderstanding how the dive tables work?
OP
CycleCat
Contributor
This whole thread started because I wondered if an analog depth gauge should be part of my setup in addition to the computer. I will be diving with a good ol' dive watch along with my computer because I LIKE dive watches. I've worn one since I was a teenager (early 80's). I'll lose bottom time that way but at a minimum, time in the water and max depth is all I need to know to use a dive chart, isn't it?
Yes, G or better.
I think the general point here is at that sort of depth, you'll run out of air before you'll run out of time. You've got 56mins at 18m, you'll be cold and bored by 45mins. But as John points out, if you go deeper to start your dive, you max out really quickly, especially the second dive.
The SS Yogala is in about 27m of water, give or take, laying on its side. The first dive you can get down to the sand, look at the mast laying in the sand, see the lower deck areas, then as you get to the end of the hull you come up shallower as you turn around. Then along the back side of the wreck you might be at 18-20m. On the second dive your NDL is running tight, so you stay well clear of the sand and sit much shallower along the deck and look at the fish life and sea snakes, but the end of that second dive you're well above the wreck, diving in the shoals of Maori Wrasse and Golden Travelly and hopefully some Manta Rays. You absolutely fly the computer, the second dive you watch the NDL clock as as the countdown gets small, you come up a few metres until you get some time back. You cannot level an airstrip with a bulldozer and you cannot do this type of diving on tables. Its not a sign of stupidity to dive the computer, you just need to be clear on what to do if you lose it.
A back up depth gauge is of zero value to me for this sort of diving, I would not buy one for me. They work, they're reliable, but I don't know anyone that does diving where it would add any value. If you computer fails on the first multi-level dive, you're out of the water based on tables. To use tables you would've needed to plan a multi-level dive, and dive that plan, to then safely know what you could do on a second dive. Consider the diving you are going to do, get equipment to support that.
I must say of I'm bored with the adage that common sense was common 'back in the day'. People were different, skills were different, life was different. My kids would struggle to make sense of a rotary dial phone, my mother-in-law can't set the temperature on her fridge. Learning is primarily driven by desire, exposure, opportunity and aptitude; it has much less to do with intelligence or the era you live in. We have progression charts of dive courses developed to address the failings of prior accidents, we have national archives full or workplace incidents and books shelves full of OH&S legislation based on retrospective review of fatalities caused by laziness and stupidity. Just make the best decision you can and review that decision continuously, never be afraid to call a dive or sell gear that isn't working for you.
A multi-level dive is where you spend different times at a variety of depths. If you are using the tables, you must calculate it as if you had spent the entire time at the deepest depth. In the reference I made above, my maximum depth was at 92 feet, which must be rounded to 100 feet using the tables. With nitrox 32, that gives a maximum time of 30 minutes at that depth, and that would be my maximum bottom time using tables, no matter how much time I spent at shallower depths. In the dive I mentioned, although I hit a maximum depth of 92 feet, most of the dive was considerably shallower. With tables, it does not matter. WIth computers, it matters immensely, because they constantly recalculate your dive. In my case, I was able to dive for 69 minutes and stay well within the computer's limits. That was the first of 3 dives I did that day. After that, I did 59 feet for 65 minutes and 72 feet for 64 minutes. Not one of those dives would have been permitted if I had been using tables.
I have on a number of occasions on NDL dives gone to depths in the 100 foot range to see something specific and then ascended to shallower depths, finishing the dive in the 80 minute range, several times the limit imposed by a strict table calculation.
OP
CycleCat
Contributor
I guess that is what this boils down to... maybe what I didn't say clearly to begin with. I'm not going into the water before I know clearly what is my max time for my max depth according to the table. Then if the computer graciously grants me extra time... GREAT! But if it shuts down, I know my limit based on a watch and a dive table.
What if it shuts down during the time period that is after what the dive table says you are okay and you are at some depth above your deepest depth? You’ll have to abort and surface safely. When you surface you’ll have an elapsed time on your watch and a max depth on your gauge that could be well outside the NDL for the table. So to be safe, you’ll have to wait 24 hours. It’s the exact same as if you had no dive table and no gauge and no watch.
OP
CycleCat
Contributor
You are right. Not a scenario I had thought of. Obviously, when I actually start getting some dives under my weight belt I will be better prepared for the many ways a dive can go sideways. Nevertheless, my solution, as of last night, is to buy a console with a second dive computer, so hopefully I am covered.
Eric Sedletzky
Contributor
If you plan your dive based on tables then use a computer, then you’ll just basically be using the computer as a bottom timer, or else you’ll blow the tables.
Actually, figuring a dive on tables then using a computer won’t technically work from the very start because with tables the dive starts as soon as you begin to descend, and ends when you begin your ascent in which you are supposed to make a direct ascent to the surface or 15’ if you do the recommended SS.
All that time from the surface to the bottom when you start the dive on tables goes against your deepest depth.
Besides that, if you use a computer and pretend like it’s a tables dive, then your computer grants you some extra time beyond the NDL of the table (which it most likely will) then you’re violating the table and are now doing a computer dive. If you use up the extra BT that the table didn’t give you and your computer just happens to crap out when you’re way out from a table NDL then there is no way you’re going to salvage your dive day on tables because you’d be so far off. What pressure group would you pick? Would you be able to figure out how much deco to do trying to resume a failed computer dive with tables?
If you want to cheat the tables and pick a lesser pressure group thinking that it’s ok then there’s nothing stopping you, it’s a free world. But I don’t recommend it.
If you want to dive tables then dive tables.
If you’re into computers then go that route and get a backup computer.
The two systems don’t jive.
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