THE "PERFECT ( being horizontal ) TRIM" HOAX
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It's quite funny to read all the instances where "perfect trim" is being challenged.
Maybe "perfect NEUTRAL trim" would be more appropriate?
Maybe it's the most versatile orientation to start from? Streamlined travel at a constant depth? Most efficient position to spin around? It seems natural to me but I don't strap a tank to my back either.
Maybe the obsession isn't the position, it's the level of control? This is my focus, for me, for those I'm with and for the environment we're in.
A favorite maneuver of mine to drop out of the current, over a ledge, to take a look or just pause, is to empty my lungs and do a front flip/half twist requiring little input and no effort. Probably not DIR though.
Hone your abilities or not, just don't exceed them. Endangering yourself, others or the environment is completely unacceptable.
Drifting is the best!
You can do it while exercising great precision or you can just hang like debris in the water. Worry about you and yours.
Cheers!
Maybe "perfect NEUTRAL trim" would be more appropriate?
Maybe it's the most versatile orientation to start from? Streamlined travel at a constant depth? Most efficient position to spin around? It seems natural to me but I don't strap a tank to my back either.
Maybe the obsession isn't the position, it's the level of control? This is my focus, for me, for those I'm with and for the environment we're in.
A favorite maneuver of mine to drop out of the current, over a ledge, to take a look or just pause, is to empty my lungs and do a front flip/half twist requiring little input and no effort. Probably not DIR though.
Hone your abilities or not, just don't exceed them. Endangering yourself, others or the environment is completely unacceptable.
Drifting is the best!
You can do it while exercising great precision or you can just hang like debris in the water. Worry about you and yours.
Cheers!
MichaelMc
Working toward Cenotes
This ^^^^^^^. Neutral trim is the most versatile. Center of mass close to center of volume. It protects the bottom from divers by removing a default orientation of fins down.
I do not think the people bicycle kicking down the reef want to be doing that. They are doing it because they are not set up for gravity to do anything other than put them fins down, kicking up the bottom. They may not care, but it is unlikely their plan. They may not care as they were initially set up tail heavy and so not educated to not kick up the bottom as it would be a very frustrating exercise for the instructor who was responsible for their gear's fins down weight distribution.
The big picture risk is not well-trained divers needlessly floating mid-water in a horizontal orientation instead of inverted, lotus or cartwheeling.
The big picture risk is divers kicking up and destroying the bottom because they are fins down as gravity put them that way. And of their depth and buoyancy control being terrible as a result. Telling them horizontal orientation is not a big deal gives them an excuse to not fix their s***, and for their instructors as well.
Fixing their s*** means distributing their weight so gravity does not dictate their orientation in the water. If their gear does not allow that, get gear that does, or add pockets high enough so they can. If they can not add pockets high enough to do that, get gear that lets them.
KDAD
Contributor
Perfect trim? When appropriate for the dive, which is a lot of them, or when I want to show off, again, which is a lot of them.
Body position all over the place? When I want to actually see something or am really relaxed and just want to enjoy the dive. Oh, and show off those special skills, too.
Body position all over the place? When I want to actually see something or am really relaxed and just want to enjoy the dive. Oh, and show off those special skills, too.
You must be an optimist. I expect people bicycle kicking are doing it because nobody ever taught them to swim properly. Same goes for trim: in the pool it's very easy to see people doing front crawl with their heads out of the water on inhale for 3/4 turn, and their legs barely bicycle-kicking at 45 degree angle down, and those who pretty much lay flat on the water and side-breathe through the corners of their mouth.
Of course having the center of gravity coincident with the center of Archimedes' buoyancy force allows the diver to get any orientation easily, and keeping it with little effort.
However I do not call this as "having proper trim control".
You do not need good control if you are in such favourable case of lack of rotational forces. It is just too easy...
When I was taught trim control, in 1975, it was using the ARO rebreather.
This is chest mounted. The amount of gas in the counterlung affects both buoyancy and trim.
If you set the buoyancy to be neutral, generally the natural attitude you get is facing up...
So we were trained to DYNAMIC trim control.
We had to accomplish a number of tricky exercises assuming different attitudes: horizontal, vertical, head down walking with hands on the bottom of the pool, performing horizontal and vertical 360-degrees rotations, etc.
For controlling the trim dynamically you had to use breathing, fins and hands (mostly with the famous "opposition" movement).
When you get full dynamic trim control (even when the gravity center is signicant offset from the buoyancy center) you are free to assume any attitude and to keep it indefinitely, either howering in a fixed position or moving in any direction, and directing the water being pushed away of you in such a way that it does not raise silt.
No particular trim was called "perfect", as we were trained to assume wathever trim was the more appropriate for the environment and the activity being performed...
However it was not easy. The first course was 6 months long. The second and third ones were 3 months long, and each year you were allowed to make just one, so I completed my training in 1977.
And I was not perfect yet.
At the first instructor course, in 1978, I did not pass exactly on one of these exercise about trim control with the ARO, so I had to repeat the exam after further training...
However I do not call this as "having proper trim control".
You do not need good control if you are in such favourable case of lack of rotational forces. It is just too easy...
When I was taught trim control, in 1975, it was using the ARO rebreather.
This is chest mounted. The amount of gas in the counterlung affects both buoyancy and trim.
If you set the buoyancy to be neutral, generally the natural attitude you get is facing up...
So we were trained to DYNAMIC trim control.
We had to accomplish a number of tricky exercises assuming different attitudes: horizontal, vertical, head down walking with hands on the bottom of the pool, performing horizontal and vertical 360-degrees rotations, etc.
For controlling the trim dynamically you had to use breathing, fins and hands (mostly with the famous "opposition" movement).
When you get full dynamic trim control (even when the gravity center is signicant offset from the buoyancy center) you are free to assume any attitude and to keep it indefinitely, either howering in a fixed position or moving in any direction, and directing the water being pushed away of you in such a way that it does not raise silt.
No particular trim was called "perfect", as we were trained to assume wathever trim was the more appropriate for the environment and the activity being performed...
However it was not easy. The first course was 6 months long. The second and third ones were 3 months long, and each year you were allowed to make just one, so I completed my training in 1977.
And I was not perfect yet.
At the first instructor course, in 1978, I did not pass exactly on one of these exercise about trim control with the ARO, so I had to repeat the exam after further training...
Whenever I chat with scuba students about trim and buoyancy, I show them a couple of things I've found on the 'web. This pic is taken from the slide presentation here (http://www.nasa-klass.com/Curriculum/Get_Oriented 2/Solid Rocket Boosters/PRES_SRB.pdf). Whatever my gear configuration, I want to be able to move as easily as these divers, especially the videographer.
rx7diver
rx7diver
MichaelMc
Working toward Cenotes
@Angelo Farina,
The base goal is open circuit divers not kicking up or destroying the bottom and safely enjoying their dive. The casual diver is unlikely to be motivated enough for your year-long class nor to spend their dive constantly pushing with hands and feet to fight gravity's rotation. As impressive as it is to fight gravity for the entirety of every dive, or as necessary as it may be with your rebreather or with heavy tech gear. But this is the basic forum.
So yes, the more assured approach is to have their gear set to make it easy. As they will not be doing the hard approach for long at all. (Whether that counted as 'proper trim control' in your rebreather class or not.)
And as impressive and useful as those active rotational thrusting techniques are. And as useful as they would be on top of a body that gravity was not trying to put in some unhelpful orientation.
I agree no particular orientation is perfect for all circumstances. Divers should assume the orientation that best fits the current need. Neutral trim (coincident mass and volume) makes assuming any orientation the easiest. So I argue neutral trim is the key for getting casual divers to adapt productive orientations. As without it, the work is too much for them, so they will just let gravity rule. They are not graduates of your year-long rebreather training and the evidence shows that they do let gravity rule their orientation.
The base goal is open circuit divers not kicking up or destroying the bottom and safely enjoying their dive. The casual diver is unlikely to be motivated enough for your year-long class nor to spend their dive constantly pushing with hands and feet to fight gravity's rotation. As impressive as it is to fight gravity for the entirety of every dive, or as necessary as it may be with your rebreather or with heavy tech gear. But this is the basic forum.
So yes, the more assured approach is to have their gear set to make it easy. As they will not be doing the hard approach for long at all. (Whether that counted as 'proper trim control' in your rebreather class or not.)
And as impressive and useful as those active rotational thrusting techniques are. And as useful as they would be on top of a body that gravity was not trying to put in some unhelpful orientation.
I agree no particular orientation is perfect for all circumstances. Divers should assume the orientation that best fits the current need. Neutral trim (coincident mass and volume) makes assuming any orientation the easiest. So I argue neutral trim is the key for getting casual divers to adapt productive orientations. As without it, the work is too much for them, so they will just let gravity rule. They are not graduates of your year-long rebreather training and the evidence shows that they do let gravity rule their orientation.
Michael Phelps will do a great job kicking up the bottom if gravity rotates his hips way below his shoulders. A proper kick would be great, and a frog kick is very useful and smooth. But of no more use to the bottom if it is still directed down at the reef.
The Chairman
Chairman of the Board
I think educators do just fine. I bet the OP never heard an instructor say you must be in trim ALL the time. It's a natural reaction when you see something you can't do, to vilify it and take it out of context. I make a point for all my students to be vertical at their safety stop so they can leisurely spin and check for oncoming traffic: boats and/or critters. It's all about situational awareness and not silting or touching the bottom.
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