"Terry Spragg" wrote in message
...
Well, once a month I take a swim with a wire brush, take a few
deep breaths and the see how long I can stay underwater
hanging on to the prop shaft. But then I'm in warm water
(never less than 18C) and it's clean and clear.

hmmm... Ever thought of attaching a regular snorkel to some
larger hose? Vacuum hose is great with a float at the loose
end. You can stay down a lot longer. Some of the co2 you exhale
will get re-inhaled each time.

How about a y fitting from the snorkel to two vacuum hoses, the
float
on one would have a caged ping pong ball for an outflow only
and the float on the other would have a soft sprung flapper for
an
inflow only??

All you need is an exhalation valve at the mask, and an iron
lung to enable you to suck air below about 4 feet. Try it, just
suck in through the mouth using a harden hose and exhale through
your nose.

OK. Full story. Snorkel is attached to a long hose which goes up
to the deck. Mask covers nose and eyes only. I breath out through
the nose (which then bubbles out through the edges of the mask,
good one way valve) and breath in through the snorkel. No need for
any balls (unless the alligators are hungry). I've scrubbed a
whole bottom this way.

But I don't recommend anyone doing this unless they do some
shallow water practice first, sitting in a pool. Ask a friend (!)
to disconnect/block/duck the hose end into the water at random
times to familiarise yourself with recovery routines. Then do this
deeper. The purpose of these practice sessions, which you should
do several times, is to get the feel of an imminent mouthful of
water coming down the line, and develop routines to reduce your
panic levels when it happens. Otherwise, feeling that gurgle in
the pipe when you've just breathed out is quite a downer . . .
don't ask.

Oh, and have someone on deck looking out for you, with a bit of
string to give you a couple of tugs if you should quickly come up
for some reason.

JimB