First dive at 40 meters - Newbies recreational

[KenGordon]

US navy NDL is in fact 8 minutes at 40,5. But it is only at 58 m that it is 5.

Different tables and computers use different assumptions. For example the navy tables assume fit young men and probably direct on site access to a chamber. They may also be prepared to bend more people than SSI. In general tables etc have a target probability of bending people which is not zero. Do the same NDL dive 1000 times and see how many bends happen. The navy ones will have a higher number than then SSI one. Other differences include the definition of what the NDL time is, does it include the ascent? How fast is the descent, the ascent etc etc.

BTW I think you are being somewhat beaten up unfairly on this thread. My general advice would be to go and get gentle experience and avoid unnecessary deep dives. Get your planning skills so your 25m dive turn out nice and smooth and to plan and gradually go deeper. Get so you are happy diving with your buddy and not at all relying on some random DM or instructor. One way of reading your initial post is that ALL your dives have been with these same people and none independently. That would be a bad plan. You may be unconsciously using them as a crutch.

Finally, give things time to sink in and be understood.

 

[KenGordon]

Some quotes... They are at 40m with 1min to NDL. My other point is that he sees 1m to NDL but that as the computer does not show seconds he could show 1m to NDL and only have 15 seconds left to exceeding NDL. He has to ascend and is he also watching his NDL at same time?

It must have been 30 seconds that we are flipping upwards and we only moved from 40 to 37

I fought the urge to inflate our BCDs (we are still breathing and we have air so there is no immediate emergency) and I made a very quick calculation (worst case scenario, we consume 5 times our SAC. 5x11 l/min round to 12, it is 60 l/min. with 150 bar that is 1800 liters, we have 30 min so no need to panic). So we continued to fin. Then, the computer again. Stop at 20 meters: 2 minutes

At this point, I would have been happy to be at 20 meters but I realized that I was at 28. Relief. We continued finning calmly and at about 25 meters, we saw the most magnificent reef we had ever seen. Wonderful colors but mainly yellow. Never seen such a beautiful scenery even at the Louvres. My wife released my hand grip and we swam towards the reef as there was no current there. I decided that we would do the stop there and inform the DM. The DM was slightly above us, still in control. I don't know how long we stayed there but probably more than 2 minutes.

Then the computer said: 12 meters - 2 minutes stop.

These are not real stops. He can ignore them.

You need to carefully read the manuals for the computers which insert deep stops and understand the differences between real stops, ie mandatory stops due to exceeding nitrogen supersaturation, and deep stops introduced by rule of thumb, like Pyle stops. The computers generally have some rule along the lines of a minute at half max depth, then a minute at half that depth. These may be regardless of any actual stops due or time at depth, so the same for a bounce dive as a 40 minute bottom time.

http://www.aqualung.com/ca/technical_library/i750TC_owners_manual_EN.pdf See the bottom of page 20. In this computer’s case the deep stops are turned of if there are real stops, so for sure he had no deco.

 

[Blackcrusader]

One way of reading your initial post is that ALL your dives have been with these same people and none independently. That would be a bad plan. You may be unconsciously using them as a crutch.
Finally, give things time to sink in and be understood.

Why Couples Training (Sometimes) Sucks - Full Version

 

[KenGordon]

Why Couples Training (Sometimes) Sucks - Full Version

It is the DM etc I consider the issue. Always diving as a couple less so.

 

[Dody]

Different tables and computers use different assumptions. For example the navy tables assume fit young men and probably direct on site access to a chamber. They may also be prepared to bend more people than SSI. In general tables etc have a target probability of bending people which is not zero. Do the same NDL dive 1000 times and see how many bends happen. The navy ones will have a higher number than then SSI one. Other differences include the definition of what the NDL time is, does it include the ascent? How fast is the descent, the ascent etc etc.

BTW I think you are being somewhat beaten up unfairly on this thread. My general advice would be to go and get gentle experience and avoid unnecessary deep dives. Get your planning skills so your 25m dive turn out nice and smooth and to plan and gradually go deeper. Get so you are happy diving with your buddy and not at all relying on some random DM or instructor. One way of reading your initial post is that ALL your dives have been with these same people and none independently. That would be a bad plan. You may be unconsciously using them as a crutch.

Finally, give things time to sink in and be understood.

Thank you for your advice and encouragement. I have really appreciated all the comments here. I embraced scuba diving with a vengeance and I am usually a very quick learner. This of course does not come without mistake but the plan is not to do any life threatening mistake. I won’t pretend that I am an experienced diver with my less than 40 dives but one cannot expect a newbie diver with 30 dives a year to progress at the same pace as one with 40 dives every two months and hopefully over 100 dives a year. Now, it true that I have never dived just with my buddy. I have always been with an Instructor or a DM even when I was leading. But this is another proof that I am not a brainless risk taker. I have read on SB stories about people who considered that they were completely in control right after OW. Some even started diving solo. That’s their rhythm. I wouldn’t do that. But planning and executing several dives between 30 and 40 meters, I think I can do it (I got sole valuable intel in the last 2 days )... with the presence of a more experienced diver... for now.

 

[Dody]

Ok i learned to breath myself buoyant.
After 1m the expanding air is adding to that effect.

I just think its not a good advice to a new diver to use the bcd as a elevator. I saw to many kork to the surface.

Then ofc (some) rules are there to break it. But only after learning them.


Best practice is in both ways to be buoyant.
And not to swim up.
But swimming up is not "wrong" in rec diving, especially as beginner it might be easier.

As a newbie, I tend to agree with Raphus. The reason why I fin to go up is that it usually does not require much effort and that it is easier to control. Using the BCD, it happened to me that I overshot the safety stop for example and ended up almost at the surface. If I start finning from let’s say 20 meters or even 30, I empty my BCD (not completely) first, I fin up slowly and all I have to care about is releasing air if my speed increases too much as I ascend. Then, as I reach 8 meters, I stop finning preparing to adjust my BCD in order to be neutrally buoyant at 5 meters. I only inflate my BCD at the beginning of the ascent if I feel my fin up is requiring to do some exertion. And I should not be overweighted as I dive with 4 to 5kg. I am 1.78 m for 70 kg.

 

[Sifossifoco]

I just wanted to say that you did well! Yes, you took some (low) risks and a catastrophic chain of events could have had you in some serious trouble, but at the same time that's life, you did your best planning (which was better than what most of us did in our first 40 m dive...) and wanted to have a quick look at how it is down there. Now you have learnt a lot and you know that you need a reason to return to 40 m or deeper. You will be better able to judge if the reason is worth the effort when the moment comes. All the best for your future dives, and don't go crazy over your SAC rate, you sound like somebody that will end up diving a rebreather anyway

 

[KenGordon]

Thank you for your advice and encouragement. I have really appreciated all the comments here. I embraced scuba diving with a vengeance and I am usually a very quick learner. This of course does not come without mistake but the plan is not to do any life threatening mistake. I won’t pretend that I am an experienced diver with my less than 40 dives but one cannot expect a newbie diver with 30 dives a year to progress at the same pace as one with 40 dives every two months and hopefully over 100 dives a year. Now, it true that I have never dived just with my buddy. I have always been with an Instructor or a DM even when I was leading. But this is another proof that I am not a brainless risk taker. I have read on SB stories about people who considered that they were completely in control right after OW. Some even started diving solo. That’s their rhythm. I wouldn’t do that. But planning and executing several dives between 30 and 40 meters, I think I can do it (I got sole valuable intel in the last 2 days )... with the presence of a more experienced diver... for now.

When it is possible I would suggest getting away someplace with a good selection of shallow sites where you can look after yourselves without too much risk. Somewhere like Marsa Shagra Marsa Shagra Village, Marsa Alam, Red Sea where you can either dive with a DM or as a buddy pair once comfortable. There are excellent reefs immediately there and you can choose your depth. This is literally walk up, grab a cylinder and jump in if you like.

 

[boulderjohn]

Deep Stops in Recreational Diving

This article that I published a while ago summarizes the evolving thinking on deep stops in decompression diving. The quick summary is that several decades ago, several people published theories and even created decompression algorithms (like RGBM and VPM) that favored decompression stops that were much, much deeper than the ones in use by the accepted algorithms of the time, including Buhlmann. This practice became all the rage and was almost universally accepted by the technical diving community, despite the fact that it had never been tested. As it began to be tested, though, doubts were raised, because the testing was not supporting the practice. The testing suggested that those stops were too deep and were contributing to a detrimental loading of nitrogen in slower tissues. Today, the trend is very much away from those very deep first stops, with stops that are still a little deeper than the older models but nowhere near as deep as the practice in the heyday of deep decompression stops.

When deep decompression stops were all the rage in decompression diving, people wondered if they should be incorporated into recreational diving as well. A couple studies in the early 2000's suggested a benefit, but those studies are not well-regarded today. As an agency, NAUI adopted the practice, probably due to the strong influence of Bruce Wienke, who was a key member of the NAUI Technical Training Division’s Technical Advisory Group from its inception. Wienke devised the RGBM algorithm that strongly favored deep decompression stops, software that was adopted for Suunto recreational computers and some others. To the best of my knowledge, Wienke was still a deep stop advocate until his death earlier this year.

Deep stops in recreational dives are controversial. DAN America does not not endorse them, and it chief publication on the issue is a discussion of 4 experts, with three of the 4 saying not to do them. The one who said they might be OK is one of the authors of one of the studies mentioned above that are not now highly regarded. DAN Europe endorses deep stops for recreational diving, but the last time I checked they cited no studies in support of that endorsement. DAN Europe also seems to favor deep stops in decompression diving as well, despite the fact that there is no real supporting evidence. They recently published an article with a title promising fresh new evidence supporting deep stops in decompression diving, but although the article did say those deep stops were good, the only evidence cited was two 15+ year old discredited articles on recreational deep stops. I know of no studies whatsoever supporting the use of deep stops in decompression diving.

In writing the article above on deep stops in recreational diving, I got significant help from Dr. Simon Mitchell. I then wanted to write another article on deep stops in recreational diving, but Dr. Mitchell declined to participate, saying there was not enough evidence upon which to draw a conclusion, and he therefore did not have an opinion. I forged ahead on my own, looking at all the evidence I could find, and I concluded that there was not enough evidence upon which to draw a conclusion, and I therefore do not have an opinion. What I concluded was that there is a major difference between ascents in a decompression dive and ascents in a non-decompression dive. In a decompression dive, if you linger on the ascent, it clearly has a detrimental effect that must be dealt with via stop time later in the ascent. In a non-decompression, recreational dive, lingering on an ascent does not seem to have that same issue; you can take your time on the way up and still only need to do at most a typical safety stop. Is there a benefit to lingering at some depth along the way? I don't know. I do know it will be hard to explain the difference between a 2-minute deep stop at half your maximum depth and a 20-minute extension of your dive time at half your maximum depth while doing a multi-level dive.

 

[boulderjohn]

As a newbie, I tend to agree with Raphus. The reason why I fin to go up is that it usually does not require much effort and that it is easier to control. Using the BCD, it happened to me that I overshot the safety stop for example and ended up almost at the surface. If I start finning from let’s say 20 meters or even 30, I empty my BCD (not completely) first, I fin up slowly and all I have to care about is releasing air if my speed increases too much as I ascend. Then, as I reach 8 meters, I stop finning preparing to adjust my BCD in order to be neutrally buoyant at 5 meters. I only inflate my BCD at the beginning of the ascent if I feel my fin up is requiring to do some exertion. And I should not be overweighted as I dive with 4 to 5kg. I am 1.78 m for 70 kg.

What Ralphus describes and you endorse is the standard practice advocated by nearly all agencies teaching recreational scuba. Done properly, it gives the diver the maximum control over the ascent. Many more advanced divers , especially technical divers, use a different technique, but there is not much an advantage, if any, for recreational diving.

When you begin your ascent, you should be neutrally buoyant, so the need to kick to start the ascent should be very minimal. In order to maintain control of the ascent, you will need to vent some of the expanding air out of the BCD from time to time, or else you will become too buoyant and will ascend too quickly. The need to do this and the difficulty in doing it depend upon the amount of weight you are carrying, which can in turn depend upon the thickness of your wetsuit. If you have a thick wetsuit, you need much more weight at the shallowest portion of the dive than you do at depth, when the suit is compressed. At depth that weight is more than you need, so you must have extra air in the BCD to compensate. If you have a thinner wetsuit and are overweighted, the same thing will be true--you will need extra air in the BCD to compensate. If you have that extra weight, you have to be careful not to vent too much air as you ascend, because if you do, you will find it much harder to kick your way up--which evidently happened on this dive. If you find that happening, then you will want to add some air back into the BCD, but adding air to the BCD during ascent is usually neither desirable nor necessary.