Diving with gradient factors for a new recreational diver
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scubaozy
Contributor
Blackcrusader
Contributor
OK I read all 16 pages of the thread before answering. I've been diving 3 plus decades. I do recreational diving ( deco dives I also consider recreational some think technical ) Firstly what dive computer do you have? Make sure it has GF as some computers like Suunto do not. I use a Shearwater Perdix as I can gas plan dives for fun. I do not gas plan recreational dives as a matter of course. I may do a gas plan for the fun of it to see if my air consumption is close to what the planner would predict. Then again do you know your RMV or Sac rate? If not it's not really relevant to what you were asking. Learning buoyancy and correct weighting so that you can control it using your lungs is more important.
For me any dive that does not exceed NDL limits regardless of depth I count as a recreational dive. That is me others will have different opinions on that. On many of my dives the last part of the dive will be along a reef or on top of a reef. So I may spend the last 15 minutes of the dive at 5m depth or less taking photos and video. Most computers allow you to choose the setting for NDL dives. If you are worried about DCS then choose the most conservative option. I use my Pedix in Tec mode not recreational mode as there are more features in Tec mode. I read the manual many times and spend several hours changing settings and doing gas planning for fun of it.
I do vacations where I do 40 plus dives in two weeks every couple of months when I can. I dive mostly on air sometimes on nitrox. Never had a DCS issue since my first dive in 1986. I never really think of it either. Multiple stops are not a requirement for NDL multi level dives or even square dives. Most recreational dives are multilevel dives. Mine are mostly to 100 feet depth or deeper and sometimes to 130 feet. I try to make sure from my deepest part of the dive to have a few minutes to NDL. On many dives that are shallow with say 60 foot max depth getting to NDL is not the issue for many it is having enough gas to get close to NDL.
As people wrote you are really overthinking about GF and DCS. It's good to be concerned and wanting to understand. I would just go out and do more diving. I often get paired with instabuddy divers. It's not a bad thing. Talk to them about your expectations. I often dive with vacation divers who have no dive computer so they will just follow me. In these cases I tend to make sure max depth is around 85 feet. Do we need to do extra stops? No. If you do a slow ascent along the dive then you get the benefit of not needing any extra stops for NDL dives. You could practice doing 15 feet for 5 minutes then 9 feet for 5 minutes. I set my safety stop time on my dive computer to 5 minutes from default 3 minutes.
PS I also do deco dives and this is where GF is more critical. You can see my Perdix is set at 45/95. It allows me longer times to NDL than say 45/85 or 45/70. If I have a dive partner using a Suunto I have to make sure they do not exceed NDL and the two computers will have different readings. So make sure you look at your dive partners computer to see their NDL as people do not stay exactly at the same depth together during a dive. You may also find a buddy that does not have a dive computer.
Blackcrusader
Contributor
I would recommend you look at the Shearwater Peregrine. I use the Shearwater Perdix which is more expensive but also has some functions the Peregrine does not. Recreational divers don't need these functions. This video is one I took just to show settings on my dive computer. I am diving on air, max depth was 38.2m but it really shows that my alert setting to NDL starts at 4 minutes to NDL. I can change that setting. Some dive centers ask you to not get to less than 5 minutes to NDL for their recreational dives. Some allow you to have less time to NDL. It is really a matter of choice for you as a certified diver. Once in the water you are really responsible for yourself. Even when diving with a buddy I always consider myself to be alone and to regularly monitor my air and NDL and depth. That's is on me alone. I will also monitor an instabuddy whereas my regular dive buddies we check each other from time to time but not as often as someone I do not know who is not so experienced. Remember also as a buddy you have the right to ask another diver for their air and also to look at their dive computer. Sometimes it's good to have your computer and your buddy's computer to look at and compare the readings.
Blackcrusader
Contributor
I took this video to show some divers who thought they had to rush to the surface that all they needed to do was make a very slow ascent and they would see their NDL time increase. Oh they are like you mean I don't need to rush to the 5m safety stop? I ask them who told them that? I have seen it also.
@boulderjohn looked into it one, IIRC it included the guy who did make it to the surface, climbed on board, sat down on the bench, then had a heart attack.
To be specific...
After yet another post about the percentage of divers who die without dropping weights, I went through several years of DAN fatality studies, and I am pretty sure that everyone of them who died died with their weights on. It did indeed include a guy who had a heart attack after climbing onto the boat after the dive. I never saw a single case in which there was even a hint that the diver attempted to reach the surface and failed because of a failure to drop weights. I found a lot of sudden cardiac deaths and other events where people could not have dropped weights, and I found even more cases where people successfully reached the surface and died after that for some reason.
I did find that in fewer than 10% of cases, a lone victim was found after a search with no clear indication of the cause of death. It is possible that dropping weights could have been a factor in some of those deaths.
That one's called false causality aka "correlation is not causation". The case of 80% of recorded DCS instances among rec divers being within the limits is more likely "sample bias".
Correct. I have yet to encounter a single case in which we can say confidently that a diver in distress tried to surface and failed to do so in a situation in which dropping weights was an option that was not attempted.
There was a case in Florida in which the diver intentionally overweighted himself as a strategy for hunting lobster. He was wearing a brand new BCD he evidently did not understand, and when he ran out of air, he could not figure out how to release the weights. (My guess from reading details is that he had a Zeagle and put the weights in the wrong pockets.) Another diver tried to help, but she had rented a regulator with no alternate air source, so they had to use buddy breathing. Both drowned.
badelaar
Registered
How was this table created ? I am interested in generating some of the buhlman NDLs for the GF factors in between.
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