"Buoyancy and trim" stability: physics principles behind it

[Bernie_U]

I doubt that there is much more to buoyancy & trim than adding or removing weights first until you got the optimum amount, then distributing your gear a little head-wards or toe-wards until you can maintain the horizontal trim effortlessly.

But nevertheless, let me add two footnotes to this thread:

1. The is no such thing as 'diving physics' or 'mechanics of diving': Regular physics does the trick. Just take a standard book for university students on that matter and you get a basic physics and mechanics knowledge that works everywhere. You can apply it to your car (dynamics) or your house (static problem) or even underwater swimming.
2. On YouTube, a female physicist recently explained the difference between science and opinion. The article "Just a Trim" appears to be factually, but when you look closer, it is just opinion. There is nothing wrong with opinions, but don't confuse them with facts. Some people claim that there is just one way of diving that fits all, but I am with Angelo in this: in a strong current, I don't want to mimic a parachutist. (This is my opinion, not a fact )

 

[The Chairman]

I would disagree. The physics remains the same, but the applications are unique. Diving has its own peculiarities that are not obvious to most people. Divers often overlook the importance of Archimedes principle in achieving trim, just as you seem to have done. If you don't 'get it' in regards to having to deal with both weight and buoyancy, then you're in for a lot of frustration and subpar trim. Without proper trim, the thrust angle is all wrong, causing major complications to being perfectly neutral without constantly fiddling with your BCD.

To reiterate, it's not that the physics is different, it's that it's applied a bit differently.

 

[Angelo Farina]

As an instructor I did find that usually those with a degree in physics are the worst students for the theory of diving (physical laws, etc.).
The way physics is taught at high school and at the university is not the way useful for a diver.
Being able to write differential equations, with proper boundary conditions, and to solve them with advanced calculus, is of no value underwater.
I happen to be also a professor of Applied Physics at the University of Parma, and so I know very well how the same physical laws must be taught in a diving course and at an university course...
Yes, the physical laws are the same: it is how you use them which is entirely different...

 

[MichaelMc]

Stability is two fold: Gear balance and skill. The closer your gear is balanced, the less skill you need to be trim. With back mount scuba, there is always skill needed. The weight is on top of the buoyancy, so there has to be some balancing done and that takes skill. When you go to something like sidemount, you put the weight below the buoyancy, so less skill in balancing is needed.

You can make yourself front-heavy in back mount. An Al80, AL plate, THICK wetsuit, and LOTS of lead on the front will do it. I did that early on in my recent diving. Any time I rolled myself to the side gravity would strongly pull me back to front down. It is just physics and enough neoprene to give you enough lead to play with.
(By thick wetsuit I mean a new 20/10 farmer john beavertail, worn in a normal pool to shake out that setup.)

I argue you could model a diver, it would just be very complex. Density models of all the dive gear plus MRI of the diver plus some modeling of breathing. Possible but complex and expensive.

 

[Bernie_U]

Teaching university stuff to SCUBA students is not my point. I am just saying: Don't search SCUBA books for scientific explanations about buoyancy and trim. Go for the scientific literature to find the answers to scientific problems. In my opinion, the better approach to address the problem of the TO is trial & error and asking the buddy after dive.

I really doubt that teaching divers in physics was of great benefit. Hence, I appreciate that PADI, SSI and other agencies have removed most equations from the textbooks and make use of video clips and animations to teach theory.