One more near-miss

[Rick Murchison]

In this thread I discussed some basic gas planning methods for recreational divers that are pretty easy.
While I don't use the term "Rock Bottom" (I think somebody else owns that ) I think that's a good way to go as well, if you prefer.
Rick

 

[K_girl]

I was surprised to hear that you started your ascent from a 100+ dive with only 500 pounds of air. I've signed many waivers that says you must start your ascent with 1,000 pounds of air. One outfit I dove in Key Largo said you had to be back on the boat with at least 500 pounds or they would not let you dive again (we called them the dive Nazi's). I've set a rule of thumb for myself to start my ascent, and it is going to be different depending on your air consumption, but it works for me:

30 ft or less - 500 lbs
40-50 feet - 600 lbs
50-60 feet - 700 lbs
70-80 feet - 800 lbs
80-130 - 1000+ lbs

Typically for me, since I am an average female and my air consumption is really very good, I find myself low on no-deco time long before hitting my remaining air time on deep dives, so my attention really gets focused on the remaining no-deco time on those deep dives. I would not consider 500 pounds enough air for myself to ascend safely from a depth of 100+ feet, even though my air consumption is really good. I dove once with two guys who brought an extra tank to share between them so they could stay down with me while I was on a single alumn 80.

If you find yourself in a strong current and need to conserve air, just get a normal swimming position, turn yourself into the current, focus on a fixed point and kick in a relaxed manner, just enough to maintain your position. If it's a truly ripping current, perhaps it should have been a drift dive.

K..

 

[jeckyll]

K_girl:

Do you buddies have air consumption as good as you? Starting an ascent at 1000 if you are over 100, that might get very tight if you have an OOA buddy at that point who maybe stressed and breathing hard

 

[K_girl]

Usually, on a deep dive, my no-deco limit becomes more critical than my remaining air - that's why I listed it 1000+. For instance, if I'm diving over 100 feet, I am typically going to come close to my no deco-limit with a lot more than 1000 pounds. Of course, I am still going to watch the gas, but the no-deco limit becomes more critical for me. For instance, when I dove the Blue Hole in Belize, at a depth of 137 feet. I had to start my ascent to avoid the no-deco limit and I had about 1800 pounds of air left on an alum 80. That's just how it typically works out for me, personally. One of the benefits of being smaller, less air consumption. I dive high-pressure steal 100's at home here in Northern California so I can get similar bottom time that I get in warm water on alum 80's. Diving a dry suit with a lot more weight and colder temps makes a huge difference, but I can use the same gas management plan I use for warm water in cold water with the bigger tank.

K..

 

[WyCal]

One thing that hasn't been mentioned, is that if you find yourself low on air down-current from the line that got you to the divesite, doesn't mean you need to spend the rest of your life getting back to that line for your ascent. You can always go up another line, and if need be, go up without a line, inflate your signal sausage and wait for the boat to come pick you up.

 

[ShakaZulu]

....Wreck penetration, even in a wide open, holes everywhere is really dangerous with a good current at 100'......

So true....thanks for making me think of this.

 

[tracydr]

A lot went wrong on this dive and it seems like the OP learned a lot. The thing it seems like he may not have recognised is that he shouldn't have made his second dive. As someone else stated, he should have gone on pure O2, stayed out of the water for 24 hours and thanked his lucky stars he didn't ended up in a chamber. I think he missunderstood his computer. He was in deco mode and didn't do the 5 minute required stop. Very dangerous but in that instance couldn't be helped. Live and learn.