dumpsterDiver
Banned
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That is a very cool story. I have gotten stuck a few times under natural rock ledges. The analogy of the tank acting like a ratchet within the "cave" is perfect. It took me a while to understand exactly how a tank (itself) acts as a rachet:
Based on my personal observations: The diver entering the hole has his head down slightly and as the passage gets more narrow (vertically) the bottom of the tank begins to scrape along the roof. Eventually, as the hole gets smaller, the TOP edge of the BOTTOM of the tank will be scraping along the roof. As long as the diver is moving forward (due to the slight head-down angle of the tank) the tank will continue to slide forward across the ceiling easily.
At some point the diver may decide that they are starting to really feel some downward pressure from the tank contact with the roof. Now the diver may decide that they can not proceed and must therefore just back out the way they came in.
This is when it gets fun, as the diver tries to back out, the bottom of the tank can slip upward into a small recess in the ceiling. Now when trying to back up, instead of just sliding, the TOP edge of the BOTTOM of the tank gets stuck in the recess or lip. Now when trying to back up, the bottom if the tank is just forced further upward and the front of the tank is forced downward.. Exactly like a ratchet.
The harder the diver pushes backward, the more the tank will be rotated and this will push the diver’s face into the bottom. In other words, because the top edge of the bottom of the tank is caught in a lip, all the energy the diver exerts pushing backwards will serve to rotate the head slightly downward, rather then allow the tank to slide backwards, This makes the entrapment feel even tighter.
I'm nor sure I can explain it well, but the harder you try to back up, the more the tank rotates (maybe only an imperceptible inch) and this crushes you down. The OP diver "rolled out" of this constriction, but I have been stupid enough to get stuck in a hole that had no room for a roll. The only way that I have been able to extricate myself in this type of situation is the following:
The tank needs to be moved just enough so that the top lip of the bottom of the tank is removed from the recess; this requires rotating the tank on the longitudinal axis.
You need to dump all the air from the BC to get as heavy as possible.
Push the hips downward (pelvic thrust). (Get your butt down)
Then reach back and grab the outside portion of waist strap (or cummerbund) of the BC and PULL the butt end of the tank DOWNWARD and then try squeeze just an inch or so forward.
This hopefully will free the tank bottom from the lip or recess and now the diver should be able to move backwards as long as he keeps the tank angled with the valve upward and the hips smashed into the bottom.
It is much easier to show with props, but you can simulate the action by holding your hand outstretched palm down, fingers spread.
Hold a soda can vertically upside down on the bottom of your pinky.
The soda can represents the tank and the fingers, and gaps between the fingers, simulate the ceiling which has the recesses in it
Now rotate the soda can so that the top is moved toward the thumb.
Rotate until the can is just slightly angled with the front downward and hold in this angle. The can is nearly horizontal (maybe 5-10 degrees)
Now while continuing to push the can upward into the pinky, slide the entire can forward across the fingers toward the thumb. You will see that the can bottom slides easily forward and just easily bumps across the gaps between the fingers due to the angle of the can (scuba tank).
Then try to push the can backwards, while keeping the same slight downward angle. Try to exert force on the can upward to press it hard against the fingers. As you attempt to push the can backwards (toward the pinky); the bottom of the can will get wedged into the gap between the fingers, once this occurs, as you push backwards (and upwards) the can will tend to rotate pushing the front of the can downward. The can will not slide backwards because the can is being rotated.
Based on my personal observations: The diver entering the hole has his head down slightly and as the passage gets more narrow (vertically) the bottom of the tank begins to scrape along the roof. Eventually, as the hole gets smaller, the TOP edge of the BOTTOM of the tank will be scraping along the roof. As long as the diver is moving forward (due to the slight head-down angle of the tank) the tank will continue to slide forward across the ceiling easily.
At some point the diver may decide that they are starting to really feel some downward pressure from the tank contact with the roof. Now the diver may decide that they can not proceed and must therefore just back out the way they came in.
This is when it gets fun, as the diver tries to back out, the bottom of the tank can slip upward into a small recess in the ceiling. Now when trying to back up, instead of just sliding, the TOP edge of the BOTTOM of the tank gets stuck in the recess or lip. Now when trying to back up, the bottom if the tank is just forced further upward and the front of the tank is forced downward.. Exactly like a ratchet.
The harder the diver pushes backward, the more the tank will be rotated and this will push the diver’s face into the bottom. In other words, because the top edge of the bottom of the tank is caught in a lip, all the energy the diver exerts pushing backwards will serve to rotate the head slightly downward, rather then allow the tank to slide backwards, This makes the entrapment feel even tighter.
I'm nor sure I can explain it well, but the harder you try to back up, the more the tank rotates (maybe only an imperceptible inch) and this crushes you down. The OP diver "rolled out" of this constriction, but I have been stupid enough to get stuck in a hole that had no room for a roll. The only way that I have been able to extricate myself in this type of situation is the following:
The tank needs to be moved just enough so that the top lip of the bottom of the tank is removed from the recess; this requires rotating the tank on the longitudinal axis.
You need to dump all the air from the BC to get as heavy as possible.
Push the hips downward (pelvic thrust). (Get your butt down)
Then reach back and grab the outside portion of waist strap (or cummerbund) of the BC and PULL the butt end of the tank DOWNWARD and then try squeeze just an inch or so forward.
This hopefully will free the tank bottom from the lip or recess and now the diver should be able to move backwards as long as he keeps the tank angled with the valve upward and the hips smashed into the bottom.
It is much easier to show with props, but you can simulate the action by holding your hand outstretched palm down, fingers spread.
Hold a soda can vertically upside down on the bottom of your pinky.
The soda can represents the tank and the fingers, and gaps between the fingers, simulate the ceiling which has the recesses in it
Now rotate the soda can so that the top is moved toward the thumb.
Rotate until the can is just slightly angled with the front downward and hold in this angle. The can is nearly horizontal (maybe 5-10 degrees)
Now while continuing to push the can upward into the pinky, slide the entire can forward across the fingers toward the thumb. You will see that the can bottom slides easily forward and just easily bumps across the gaps between the fingers due to the angle of the can (scuba tank).
Then try to push the can backwards, while keeping the same slight downward angle. Try to exert force on the can upward to press it hard against the fingers. As you attempt to push the can backwards (toward the pinky); the bottom of the can will get wedged into the gap between the fingers, once this occurs, as you push backwards (and upwards) the can will tend to rotate pushing the front of the can downward. The can will not slide backwards because the can is being rotated.
