this thread is a bad idea
Question Dive planning exercise, please check my work
- Thread starter Cthippo
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johndiver999
Contributor
Why because if you don't know; don't ask?
It is a dive to recreational depths, and this is the advanced scuba section. If anything, someone my throw down a red flag when the OP casually mentions deco (for a few minutes), but I interpreted that more as a contingency in the dive plan, rather than the actual plan.
Knowing how to deal with accidental, or unplanned deco for a few minutes should be within the recreational discussion, as long as it is not planned, right? Or is it the diving over 100 feet on air, not something that should be discussed?
DiveLikeAMuppet
Contributor
Casual recreational depth? Sure, in Egypt, warm water, infinite viz.
There is nothing wrong with deco. 10 mins of backgas deco on a single cylinder is fine, worst case you would need to breathe O2 for a bit back on the boat.
What’s wrong is a bounce dive to 40 meters/120 feet in what I presume is fairly cold, potentially dark place and all the contingency planning around it that is not just about picking the right gas and staying within the magical no stop (I hate “no decompression”, every dive is a deco dive) limit.
AOW here in the Great Lakes is a common dive to these depths, with single tank, including just air (though there is a better nirtox mix if your training allows it)....
You don't get to see much or have much bottom time, so that alone explains that this type of diving is best done with advanced training, but it can be done within recreational limits...
You don't get to see much or have much bottom time, so that alone explains that this type of diving is best done with advanced training, but it can be done within recreational limits...
DiveLikeAMuppet
Contributor
The problem is, if I run the numbers, I get maybe 15 minutes of no-stop dive with 28% nitrox at 36 meters/120 feet with GF55/85. It would take me about 3-4 minutes to descend and settle on the bottom. I would obviously want to leave 2 minutes earlier, so that’s at maximum 9-10 minutes at 36 meters diving tables. With a computer and aggressive settings, you could stretch it to 15 minutes total bottom time?
Not much time to do anything - a little swim and done, and you can’t swim too fast at 36 meters/120 feet to avoid narcosis. You pay for it with half a day, possibly a full day of “work”. That’s why I suggested doubles and some deco, at these depths it makes diving so much more worthwhile.
OP
Cthippo
Contributor
I was looking at the deco not so much as part of the plan but to be sure I was reading the table right.
That's not how tables work. Bottom time ends when you leave the bottom. It is bottom time, not underwater time.
DiveLikeAMuppet
Contributor
And? So if tables give me 15 minutes bottom time, I still need to allocate some time for descent and need to leave a bit early. Yes you teleport yourself to the bottom/drop like a rock and you could execute a perfect 10 (or 20, depends on the table) meters per minute ascent right on the 14:59 mark but as a prudent recreational diver who want needs to avoid mandatory deco stops, you want to leave a earlier.
Nah. The BT starts when you leave the surface. No need to leave the bottom early, you are already conservative.
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