Evan Gatehouse wrote:

Rosalie B. wrote:

Some people can do quite well free-diving. My SIL does this for the
lobster season in FL, and can stay down for a considerable time. Even
I can dive on the prop and do some work on it if I wear fins. It is
not that hard if you practice and it makes a reasonable workout. The
only time I can't do too much is if the water is cold - I can't stay
in too long in cold water, and if I wear a wet suit, I am too buoyant
to stay down.

It sounds to me like the guy in Costa Rica didn't have a dive flag or
take appropriate safety measures - like having someone watching.

It was reported in Lat 38's Electronic Latitude that he was
the victim of shallow water blackout, not having a boat
above him.

That sounds more reasonable. After all - if the power boat wasn't
there when he went down there, the power boat would be moving - he
wouldn't be caught under it although he might be cut up.

Shallow water blackout occurs when you hyperventilate too
much before a freedive, and then when down, you run out of
O2. Your body uses increasing levels of CO2 to tell you
when to breathe, and hyperventilating reduces blood CO2. So
you don't get the urge to breathe, and pass out underwater.

I've come close a few times (black spots as I come up).
Now I only ever hyperventilate 3 deep breaths before a dive.
Diving with a buddy close by might save you, but by the
time they notice a problem you might be 20' deep and sinking...

In my case, I wouldn't sink I don't think. Even when I breathe out as
far as possible, I still float. I might come up under our boat
though. So having Bob in the dinghy watching (and in cases when I
would do this, the water would be clear enough to see me - our prop
isn't that far down) would be a help.

It reduces my bottom time slightly but I feel a lot safer

I've never been that close to blacking out. Or if I was, I didn't
have any warning like black spots.

grandma Rosalie