This thread did perhaps not start very well, and at some point it derailed a bit.
But in the end it resulted very informative for me and here I want to thank the contributors.
English is not my mothertongue, and this thread exposed the need of proper technical terminology for describing the various physical phenomena involved in buoyancy, rotational force balance, attitude (in both of his meanings), passive and active trim (or static and dynamic, if you prefer).
I apologize for when I did use some terms improperly.
I also apologize if, when describing how was my first-level basic training in the seventies, I gave the impression of advocating that such a paramilitary traing approach was the good one, which should be used also today.
Actually my position was exactly the opposite.
I was one of the few CMAS instructors who pushed for shortening the first basic course from 6 months to 4 weeks.
The other one was Gianni Bertieri.
Together we shaped super-short basic diving courses to be taught in holiday resorts, in two weeks in villages in the Mediterranean, and in just one week at Maldives.
Of course, shortening the training so much, the ARO training had to be suppressed, together with the long exercises about buoyancy and dynamic trim control.
On the other side, the equipment of the time (an heavy 15 liters steel tank on the back, and an horse-collar BCD) made it very difficult to get the coincidence between mass and volume centers. All divers were invariantly feet-heavy.
So what we were teaching, in such short courses, was a subset of dynamic trim control based on two concepts:
- neutral buoyancy (not negative)
- proper finning technique
This allows to swim horizontally, or even with fins slightly above the body, creating the rotational momentus which counter-balance the uneven weight distribution.
But as soon as the diver stops finning (I do not use the word kicking by purpose) he comes back almost vertical.
It was not possible to do anything better in a short time and with that sort of equipment.
Of course nowadays we can do better, and I agree that, particularly with beginners, providing them with properly balanced equipment is the way to go.
Unfortunately I still see many divers who are still strongly unbalanced.
So I agree that the first goal in a basic course is to get the students properly balanced.
Starting there, the trim control will come easily with some experience and some guidance.
The completely opposite training I had in 1975, with a strong weight unbalance and the need to learn powerful active trimming control techniques, is definitely an obsolete approach.
I did just find useful to explain how this was the standard here in Italy for basic scuba training in the seventies.
Rebreathers were the most common scuba systems in diving schools. It was not "technical training". It was considered more basic than using an OC system...
