"Correct Weighting" Identified as #1 Needed Improvement in SCUBA Diving
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My web site is out of date, and it needs a lot of work. The man I paid to do it fell down on the job.
What I said was that teaching in neutral position does not take any more time than teaching on the knees. When I was doing that, I was working for a dive shop (still named on the web site), and I had the same time to teach the same classes as all the other instructors working for that shop. The cost was the same whether you got me or one of the others.
I stopped doing OW instruction in my old age, and I now only do technical.
More information....
If you read the article I attached a little while ago, you will see that it was cosigned by a number of other people. Some of them were colleagues in the shop I was with back then. One of them is the man who was then the Course Director who managed the instruction in the shop. I checked with him as I experimented to make sure I was not breaking standards. When he saw how well it worked, he required that all the instructors in the shop adopt that methodology. They did not make any changers to class schedules when he did that.
If you read the article I attached a little while ago, you will see that it was cosigned by a number of other people. Some of them were colleagues in the shop I was with back then. One of them is the man who was then the Course Director who managed the instruction in the shop. I checked with him as I experimented to make sure I was not breaking standards. When he saw how well it worked, he required that all the instructors in the shop adopt that methodology. They did not make any changers to class schedules when he did that.
Remember that the average person has 13 pounds of lift capacity in the lungs. If the diver is close to neutral at mid breath, they'll have -+ 6ish pounds of authority on tap to ascend or sink on demand. This is the average, nothing extraordinary.
A person using the whole of their lung capacity to avoid sinking is not neutrally buoyant in a practical diving sense. For actual diving you need to be able to pay attention to stuff other than buoyancy without losing control. Part of the point of slightly tricky midwater skills such as DSMB deployment is that they show whether a student is actually neutral or just maintaining their position in the water by trying really hard. If when they stop trying they sink they were not neutral.
Also, if you are relying on quite full lungs to stay neutral, actually ascending is somewhat more risky if you are trying to keep full lungs on the way up. So to avoid that should the diver go vertical and fin up? Now the bottom is being pummelled by wash.
Here we are just talking about going up and down 10 or 12 feet in a pool. It is a transient maneuver. Inhaling and exhaling to do that kind of transient is just an exaggeration of the diver's normal breathing, and very easy to do.
I've measured my forced vital capacity. It is slightly larger than the average person, displacing about 16 pounds of water (according to a google search, average is just over 13 pounds). I can't and don't use all of that to maintain buoyancy, but I can use most or all for transient shifts. At the practical limit, I figure that I can tap about half of that vital capacity (8 pounds) for buoyancy control, and I'm very comfortable maintaining about a 6 pound shift over the course of a dive without feeling like I'm trying.
I've been doing this awhile now, and the breathing patterns have become automatic to the point to where I rarely think about it when I'm diving. This 6 to 8 pounds of automatic buoyancy control is more than enough control to execute a warm water recreational dive. When the breathing patterns are automatic, a diver's buoyancy during the dive can also be automatic if they are weighted such that the buoyancy variations during the dive fall within that control range. The diver would never touch the inflator hose on the BC; there would be no need.
Bob DBF
Contributor
The average male has a total capacity of 6 liters in their lungs which is 12.12# of lift total. The vital capacity, the largest volume of air that can be expelled from the lungs after taking the deepest breath, is only 3 to 5 liters ( 6# to 10# ) limits the volume used for variable buoyancy and breathing. Although this is enough to execute a warm water recreational dive, it gives an overly optimistic assessment of a student's abilities based on your personal abilities.
Although I started diving without a BC, and occasionally still do, I don't think that starting without a BC is a good idea with a lot of the students having marginal water skills. If instruction started with swimming, snorkeling, freediving, and then progressing to SCUBA, as it was when I learned, it would be a natural. As it is, diving without a BC is now an advanced skill.
Bob
6 liters is 6 kg of distilled water at 4 C, by definition. That is 13.23 pounds. Salt water will be heavier by about 2.5%, but warm water will expand. I think the salt wins out though.
"Average density at the surface is 1.025 kg/l. Seawater is denser than both fresh water and pure water (density 1.0 kg/l at 4 °C (39 °F)) because the dissolved salts increase the mass by a larger proportion than the volume."
When I tested, which I have only done once, it seemed everyone else testing (combination of men and women divers) was coming up in the 5 to 7 liter range. I thought the average VC was 6 liters, as I had seen written in many places that the average lung capacity for humans is 6 liters.
mattia_v
Contributor
I'm oversimplifying here, but for an average man, you're looking at the following:
- Average vital capacity is about 5 liters. This is the maximum amount of air that can be exhaled after maximum inhalation.
- Average lung volume is about 6 liters, including about 1 liter of dead space
- A normal, full inspiration (without addressing the functional residual capacity you have) is around 3L, + 0.5L of tidal volume.
Basically, if you're breathing normal but deep/full breaths (not as deep as possible, just full, deep breaths), you'll have about 3.5L to play around with, and the ability to suck up another 1.5 or so, at which point your lungs 'max out', and you can't exhale the final litre or so (residual volume). You can't really increase your long volumes (genetic and based on your height/size), but you may be able to more efficiently recruit your functional reserve capacity (better control / strength in respiratory muscles, increasing thoracic compliance, perhaps). Good freedivers may skew towards higher values because their physiology makes them more suited for it, but it's not really going to be a training effect.
- Average vital capacity is about 5 liters. This is the maximum amount of air that can be exhaled after maximum inhalation.
- Average lung volume is about 6 liters, including about 1 liter of dead space
- A normal, full inspiration (without addressing the functional residual capacity you have) is around 3L, + 0.5L of tidal volume.
Basically, if you're breathing normal but deep/full breaths (not as deep as possible, just full, deep breaths), you'll have about 3.5L to play around with, and the ability to suck up another 1.5 or so, at which point your lungs 'max out', and you can't exhale the final litre or so (residual volume). You can't really increase your long volumes (genetic and based on your height/size), but you may be able to more efficiently recruit your functional reserve capacity (better control / strength in respiratory muscles, increasing thoracic compliance, perhaps). Good freedivers may skew towards higher values because their physiology makes them more suited for it, but it's not really going to be a training effect.
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