Rick wrote in message link.net...
Jim Richardson wrote:


2) The pressure at say, 7 feet depth, is about 1.5 atmospheres,

The pressure at say, 7 feet depth, (in seawater) is about 3 psig. It
would take another 9 feet to reach 1.5 ats.

Seawater pressure increases at around .445 psig per foot.

Rick

I do use a mask and snorkel to work on my prop. I even use it to work
on my keel and I just dive down and hold my breath. Its not a
problem. Sometimes when I dont want to dive down, I use a long
handled edging tool to reach the keel, works for the prop too.

I've wondered about the small bottles of compressed air complete with a
mouthpiece that emergency crews might carry.
Not sure if they are for 'fire' use or to revive a patient.
Could they be used for Lloyd's application?

I've wondered about the small bottles of compressed air complete with a
mouthpiece that emergency crews might carry.
Not sure if they are for 'fire' use or to revive a patient.
Could they be used for Lloyd's application?

Glenn Ashmore wrote:

One atmosphere of pressure (14.7 psi) is 33 feet of seawater. THe .445
is correct but your math is wrong. 1.5 atmospheres would be about 50
feet.

One atm is 14.7 psia, it is a measure of absolute pressure. Itis the
pressure at the surface of the water. Pressure at 33 feet depth is 2
atmospheres absolute or 14.7 psig or guage pressure.

To obtain a pressure of 1.5 atmospheres (a measure of absolute pressure)
you would have to descend to around 16 feet. The guage pressure at that
depth is about 7 psig.

The pressure at 7 feet may be described as around 3 psig or 17.7 psia.
It is not by any measure 1.5 atm.

Rick

Glenn Ashmore wrote:

One atmosphere of pressure (14.7 psi) is 33 feet of seawater. THe .445
is correct but your math is wrong. 1.5 atmospheres would be about 50
feet.

One atm is 14.7 psia, it is a measure of absolute pressure. Itis the
pressure at the surface of the water. Pressure at 33 feet depth is 2
atmospheres absolute or 14.7 psig or guage pressure.

To obtain a pressure of 1.5 atmospheres (a measure of absolute pressure)
you would have to descend to around 16 feet. The guage pressure at that
depth is about 7 psig.

The pressure at 7 feet may be described as around 3 psig or 17.7 psia.
It is not by any measure 1.5 atm.

Rick

"GA" == Glenn Ashmore writes:

GA It would be extremely dificult if not impossible to breath through a
GA hose at surface pressure if your lungs get more than 2 or 3 feet under
GA water. The difference at 3' is only about 1.5 pounds per square inch
GA but the water is pressing on a couple thousand square inches of lung
GA surface.

The real problem is the "dead volume" in your snorkel. You will be
inhaling your own breath over and over again.

snip

--
Strange attractors stole my wife

"GA" == Glenn Ashmore writes:

GA It would be extremely dificult if not impossible to breath through a
GA hose at surface pressure if your lungs get more than 2 or 3 feet under
GA water. The difference at 3' is only about 1.5 pounds per square inch
GA but the water is pressing on a couple thousand square inches of lung
GA surface.

The real problem is the "dead volume" in your snorkel. You will be
inhaling your own breath over and over again.

snip

--
Strange attractors stole my wife

"Lloyd Sumpter" wrote in message
news
Hi,

Whenever I need to work on my prop, etc. underwater, I've just slapped
on the mask and fins and held my breath. But I've always wondered: why not
rig up a hose arrangement to be able to breathe? We're not talking 50-ft
depths here, so I'd think it would be pretty safe. Perhaps some kind of
non-collapsable hose on the end of a snorkel?

Does anyone do this? Why or why not?


Take a look at the hookah equipment, cheap and cheerful, but recommend you
do a dive training course before use.

http://www.akmining.com/dive/systems.htm

garry

"Lloyd Sumpter" wrote in message
news
Hi,

Whenever I need to work on my prop, etc. underwater, I've just slapped
on the mask and fins and held my breath. But I've always wondered: why not
rig up a hose arrangement to be able to breathe? We're not talking 50-ft
depths here, so I'd think it would be pretty safe. Perhaps some kind of
non-collapsable hose on the end of a snorkel?

Does anyone do this? Why or why not?


Take a look at the hookah equipment, cheap and cheerful, but recommend you
do a dive training course before use.

http://www.akmining.com/dive/systems.htm

garry

We met an interesting and inventive guy on our trip through the Panama Canal
who dealt with this by making his own electric hookah -- take one Jabsco
diaphragm bilge pump, attach hose and a SCUBA mouthpiece and presto, you
have cheap device that will work down a few feet. You want a diaphragm bilge
pump, not a pressure water pump, because the former is relatively high
volume, low pressure.

We used a "real" hookah from Brownie for work on the boat. Vast overkill.

For Fintry, I'm thinking about using a commercial oil-less compressor
(Porter Cable, for example) which will run air tools and, through a filter
(same filters we use on our tank-fill compressor) drive a low pressure hose
for use down to ten feet or so.


--
Jim Woodward
www.mvFintry.com



..
"Lloyd Sumpter" wrote in message
news
Hi,

Whenever I need to work on my prop, etc. underwater, I've just slapped
on the mask and fins and held my breath. But I've always wondered: why not
rig up a hose arrangement to be able to breathe? We're not talking 50-ft
depths here, so I'd think it would be pretty safe. Perhaps some kind of
non-collapsable hose on the end of a snorkel?

Does anyone do this? Why or why not?

Lloyd Sumpter
"Far Cove" Catalina 36