"Correct Weighting" Identified as #1 Needed Improvement in SCUBA Diving

[wetb4igetinthewater]

There are some instructors who get their people in mid water right from the start. I am not one of them, in part because I have been traditionally very limited by the shop where I worked in terms of the equipment and weights I could use. The other reason is that the start of the class is in the shallow end of the pool, and there is barely enough room for the student to be in mid water. For the first dive in the shallow end of the pool, I have the students lie down on the bottom and put just enough in the BCD so that they rise and fall gently when they inhale and exhale. Their legs or fin tips gently touch the floor, spread comfortably apart. Since I have them pretty close to correct weighting at this point (the true weight check comes later), they don't need much air in the BCD at all. It is important that they be in horizontal trim to the greatest degree possible, so I do not want them in a 45° angle at all. Anyone can do this--it is, in fact, easier then getting them to kneel properly.

Once in that position, the skills go oh-so-much-more-easily. Think, for example, of the reach method for regulator recovery. On the knees, the students are actually tipped backwards a little so they don't fall on their faces. The tank is pulled down and away by gravity. Most cannot reach the regulator, so we end up adding a step that is not necessary in real life--reaching back with the left hand to lift the bottom of the tank so the top gets close enough to reach. When the diver is horizontal instead, gravity puts the top of the tank by the student's neck, and the regulator hose lies right behind the ear, in easy reach for anyone. The skill is completely with ease. All of those first skills are easier and more like real diving in that position.

Once we reach the deep end of the pool, we do all skills in mid water. One of the reasons the whole session does not take as long is that traditionally the most time consuming parts are the later buoyancy exercises. When students have been neutrally buoyant from the start, they get those done much more quickly.

Fortunately, the pool we rent (2 nights back to back with 3-hour pool sessions), there is more than enough room at the shallow end (about 4 feet of depth) for even a large class (more than one instructor). Weights can be an issue, so I bought off ebay 10 1-lb weights and 10 2-lb weights (for about $100) that can go onto a belt (I bought some inexpensive plastic buckles off DGX and bought some 2" webbing from a local fabric store). There are some weight belts with pouches, but not enough to go around. Some people, especially if they bring their own wetsuit to the pool, need the weight belts with permanent soft pouches attached (6, 8, 10, 12, and 16 lb'ers). So I think I have proper weighting down for a class of 8 with 2 instructors. So logistically, because I can go mid water from the beginning, I do so. And I'm happy with the improved results.

 

[dmaziuk]

So having that person lay face down in the water, reg in the mouth, and handing them weights until they float midwater didn't work?

I can go all the way up in the 12' pool just taking a full breath. That's something you need to learn => extra time.
My wife was so anxious on the 1st day she dropped the weight belt at least once trying to adjust the BCD (pulling on the wrong buckle).
2 of them couldn't swim at all, though they don't count as they didn't get to the skillls part.

 

[TMHeimer]

I like this question, so I will have a go at it.

I will say no, at 100 feet it would probably not be possible to put enough air in your lungs to neutralize the buoyancy shift in a 7mm wetsuit to 1/4 thickness.
Assume for simplicity starting neutral on the surface; as an example, me....
My 7 mm wetsuit (farmer john & jacket, so double thickness on the torso), when new, had a buoyancy of +20 lbs;
So compressed to 1/4 its buoyancy would be +5 lbs, so a buoyancy shift of -15 lbs.
Average adult male lung volume is 6 liters (which mine are) = 13.2 lbs buoyancy; but the original neutral buoyancy at the surface include residual lung volume, so really only about +10 lbs lung volume to get neutral with at most.
So with full lungs, I would still be at about 5 lbs negative on the inhale; and on an exhale, about 15 lbs negative.
So no.

Also, having done a 100 foot dive in this gear configuration, these calculations look about right, and I found that I do need the BC to get neutral. But, dropping 5 lbs would put me neutral on the inhale, and dropping 15 lbs would put me neutral on the exhale.

Depends on the gear though: If the question were, can a properly weighted diver in a 3mm shorty get neutral at 30 feet by breathing, the answer would be, yes.

That last sentence is about what I figured. Maybe this is how they dived back then?

 

[wetb4igetinthewater]

I can go all the way up in the 12' pool just taking a full breath. That's something you need to learn => extra time.

With no air in your BCD? That's a set of lungs you have!

My wife was so anxious on the 1st day she dropped the weight belt at least once trying to adjust the BCD (pulling on the wrong buckle).
2 of them couldn't swim at all, though they don't count as they didn't get to the skillls part.

Some people are best served by a private class.

 

[dmaziuk]

With no air in your BCD? That's a set of lungs you have!

I swim. But no, "mid-water" for 12 feet is 6. I'm not going to stop ascending when I start exhaling and 6 feet of water just isn't far enough.

 

[boulderjohn]

I'm not going to stop ascending when I start exhaling

Why not?

 

[dmaziuk]

Why not?

There's this thing called inertia.

PS. If there wasn't, I wouldn't be able to float on my back either because my face would be underwater the moment I start exhaling and then I'd inhale water and drown. Which isn't happening to me about 3 times a week.

 

[boulderjohn]

There's this thing called inertia.

PS. If there wasn't, I wouldn't be able to float on my back either because my face would be underwater the moment I start exhaling and then I'd inhale water and drown. Which isn't happening to me about 3 times a week.

Maybe I am not understanding what you said.

I do a demonstration in every OW class I teach in which I go from the bottom of the pool to the top and then back to the bottom again using nothing but my breathing. I can stop at any time and hover, and that is part of the demonstration.

What are you doing that is different?

 

[dmaziuk]

Maybe I am not understanding what you said.

I do a demonstration in every OW class I teach in which I go from the bottom of the pool to the top and then back to the bottom again using nothing but my breathing. I can stop at any time and hover, and that is part of the demonstration.

I have no doubt that you can do that, I questioned your assertion that you can get OW students doing it at no extra cost.

Like I said, this is based on one OW class of 8 people, it's very representative, and I'm talking out on my Alternative Sound Source hole here.

 

[boulderjohn]

I have no doubt that you can do that, I questioned your assertion that you can get OW students doing it at no extra cost.

Like I said, this is based on one OW class of 8 people, it's very representative, and I'm talking out on my Alternative Sound Source hole here.

Well, I guess you know much better than I do what happens in my classes. That's the kind of thinking that allows people to reject innovation in all kinds of areas. If you know ahead of time that something can't be done, you have a good reason not to try.