? about underwater swims

[kraknos]

Hey everyone, I just have a question about the 50m underwater swim. I can already complete the swim myself but I was wondering about something i seem to hear often. From several different places I've seen/heard the key to the underwater swim is to 'get deep and stay deep'. Personally when i do it Im close to the surface (2-4ft deep range), is there actually any reason to go deeper? Thanks in advanced to any responces.

-Lou

[jp116]

The deeper you go, the faster you will swim.

[SR1077]

The deeper you go, say 10 feet. Your lungs become more compressed because of the pressure of the water bearing down on you. There for you are able to hold your breathe longer and swim faster. Only thing that is stopping you is fear.

[ebriggs]

i scuba dive and i can state this as a fact that the deeper you dive the more air you consume. i dont know if it carries over to free diving like that but i would assume it would. and i believe the true reason is because the deeper you go the less bouyant you are and the less energy you expend trying to stop from surfacing.

[dive doc]

Guys,

This is another excellent case of, if you don’t know … don’t guess!!!

Extended underwater swimming is very dangerous and it is DEFINITELY not recommended to do this while swimming alone and without proper supervision. There is a very good reason that you have a BUD/S instructor swimming above each candidate on the return leg of the 50m swim, as going unconscious under the water as you come near the end of the swim is a real possibility for some. Im open to correction on this from the guys that have been through BUD/S, but as far as I know a couple of guys (if not more) pass out under water during the 50m underwater swim evolution in almost every BUD/S class.

The reason going deeper during the underwater swim (especially the early part) is so beneficial is that even a change in depth (aka pressure) of even 10 feet increases the pO2 (partial pressure) of oxygen within the body. This is a fundamental of diving with oxygen that must be understood as well. 21% oxygen at the surface is the same as 21% oxygen at 100 feet. However, the partial pressures are dramatically different. After this depth you can begin to suffer what is called oxygen toxicity.

However, in the case of the underwater swim, going deep early raises the partial pressure of oxygen within the body and gives the “semblance” of having more air and stops the hypoxic drive from increasing levels of CO2 from kicking in as quickly. However, VERY importantly as you finish the level of oxygen in the body will be slightly lower, you will also decrease the partial pressure of oxygen as your depth decreases. This will result in consequential rise in the level of CO2 and your body’s physiological mechanism will kick in and can contribute to what is called “shallow water blackout” where the level of CO2 can rapidly rise and overcome a swimmer and cause them to rapidly go unconscious. You will not be aware of this!

This is a dangerous evolution and 50m underwater swims (especially deep) should never be attempted alone.

Best of luck.
DD

[infantry_scout]

For me, swimming a little deeper helps because when I get to the point where I'm ready to surface for air, my ascent takes a little bit longer because I'm deeper, so I'm able to get a few more meters out of my underwater swim. If I was near the surface, I might swim another 1/2 a meter or a meter before re-surfacing. Of course, like Dive Doc stated, don't go too deep, and never without a buddy or lifeguard, but you shouldn't do any kind of swimming alone anyways.

[kraknos]

Thank you DD, you were (as usual) extremely informative.

[dive doc]

No worries Kraknos, just trying to help out.

Best of luck.

[PaulieP]

What kick and stroke does everyone do for the their underwater?

I do a scissor kick and a modified breast stroke that turns into a sort of "triangle pushup" push along my body with my hands once they break past the shoulders.