35ish dives in, started to panic, had to abort - still causes some concern

[mattia_v]

I had a similar scary dive (chop, foam, unable to descend, lost my group, on rental gear; dive 30-ish). I was fatigued and tired out but it was hyperventilation that got to me - the crappy rental reg felt like it was force blowing a lot of air in, so with the stres I was shifting out excessive volumes of air at fairly low depths leading to low CO2. Blew through my tank in 15 minutes, finished the dive on the DM’s larger tank and octo. Next dive I did a few months later in dark low vis water triggers mild panic, so I ascended and waited a bit, got my resting under control, updated my buddy, and pushed through and it went fine. I’m glad I got back in the water, not sure I’d still be diving if I hadn’t.

a minor nitpick on terminology: dyspnea just means shortness of breath. It’s not a medical issue per se. Exertion causes dyspnea. Hyperventilation (where you offload more CO2 than you produce, which may be due to stress or excess of exhalation/‘poor’ breathing technique due to over exertion) also leads to dyspnea.

The issue at depth (from my understanding) is the pressure on the airways and density of the gas, which reduces effective ventilation and thus CO2 off-gassing. On the surface, it’s pretty much impossible for a healthy individual without an obstructive lung condition to develop elevated CO2 levels. It’s very easy to get them too low if you try hard enough. I think most beginner divers generally never think about normal breathing until they get in the water, and then start doing weird things. Singers and yoga practitioners (or others with hobbies that involve breath control) will be more used to even, controlled breaths and full (but not forced) exhales that are generally slower than the inhale.

 

[АлександрД]

We were trained to swim with different types of fins and with different kicking methods according to the requirements, and for strong currents the recommendation was to use long free-diving fins, and to use the "free diver" kicking technique: slow, ample, without flexing the knees, and making the long fins to flex both upwards and downwards, so that both movements of the leg (up and down) produce an active thrust during both actions. This way of kicking, using those long, flexible fins, is not "natural", you have to learn it, and it takes a couple of months going to the swimming pool for 2-3 hours per week, under the guidance of a fin-swimming instructor.

Which fins are good for strong currents

Also fins, and the other parts of your equipment, are also important: when diving in open water and with strong currents, all your setup must be very hydrodynamic and streamlined, for minimizing drag and making easier to penetrate the water. The ideal would be to become as hydrodynamic as a free diving recordman. Look for their videos on Youtube, you will see how they move gently, with minimal wast of energy, always keeping their body perfectly aligned with the direction of motion, without anything protruding from the shape of the body.

.. it looks like you have bring here picture of the SideMount diver, as illustration of this description...

My solution: reading up on and practicing breathing techniques above water

Controlling and reducing air consumption
Here I`d described some such technics. It helps me much.

Antiofftopic: Universal rule: Stop. Think. Do.

 

[Angelo Farina]

.. it looks like you have bring here picture of the SideMount diver, as illustration of this description...

While side mounted doubles are definitely more streamlined than back mounted doubles, in really strong currents (in Maldives' channels) what I did do, when in need to swim against the current, was going "no mount", bringing the single tank in your hands in front of you, as in underwater-velocity competitions:

Side-mount, as used for cave diving, is usually more tailored to get a perfect control than to get maximum speed against current. Hence side-mount divers are usually keeping a poor hydrodynamic trim, something like this, which is indeed sub-optimal:

Notice the knees too much flexed (the legs should be almost perfectly extended, straight), the frog-kicking instead of the powerful free-diving kicking, the fins short and rigid, and the arms only partially stretched forward and kept wide apart, causing a lot of friction. It is still much better than with backmount, indeed:

This is really horrible and not efficient.

See here instead the proper style for maximum speed against current:

Add a small tank in your hands, no BCD, and there you are for very strong currents...