Propellers

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cool_hardware52:
Would it be possible to create this low pressure area without creating any vapor? Seems unlikely.

Tobin

But so what? As in the bicycle pump analogy, the creation
of vapors doesn't really impact the creation of the vacuum
-- it just keeps it from being a perfect vacuum. I just
like to be clear on it because some people think that
if the vapor weren't created, it won't be possible to pull
back the piston -- that the piston can only be pulled back
because the vapors alleviate the pressure. This simply
isn't so. The vapors are a artifact to the process.

In an exaggerative analogy, it would also be unlikely to be
able to cavitate without perturbing the earth's wobble
on her axis, since the earth's mass is being redistributed,
that doesn't tie earth axis wobble by definition to
cavitation.

Another analogy would be to consider the water replaced with
a bunch of ball bearings. If you put a prop in there and
spin it hard, you'll get cavitation, even if a couple ball
bearings do fly through the cavity. Now repeat the whole
thing in a vacuum. Those few ball bearing flying through
the cavity isn't what allows the void to be created.
They're part of the story, but not part of the definition
of the cavitation.

Regards,

--Mike
 
Gotta throw this into the mix. A poster way back on page three mentioned it...

"Huh? The hunt for the Red October and other sub footage does show bubbles coming off of the props."

Note: The submarines in "the Hunt for Red October" are models suspended in a smoke filled "room". Any bubbles emitting from the props had to be added digitally. I always caution my students, "don't get your science from Hollywood. Anything is possible in movies."
 
Okay, I'm not attempting to hijack the thread, but you gotta see this. In one of the photos in Panama Mike's recent post, it shows presumably Navy divers working at replacing a prop. I found it interesting that they fly the proper dive flag and all, but LOOK AT THE DIVER ON THE BOAT!
I can hear the screams now...MOF!!!

Now, now...please refrain from arguing, and don't flame me!
 
Gary D.:
Here is an example of a new screw and a small screw with cavitation.:wink:

http://www.scubaboard.com/gallery/showphoto.php/photo/9991/cat/500/ppuser/2714

Gary D.

Nice pics.

I used to work in the construction business, and we did some projects at the Long Beach Naval Ship Yard on Terminal Island in LB CA. It's sadly no longer there. It was a fasinating facility. Everything on a grand scale.

One our projects was a fire protection retrofit of the "Prop Shop" and the Propeller Shaft rebuilding Building.

Hollow Propeller Shafts you could walk down the center of. Lathes that you climbed up and Rode On.

The Prop Shop was filled with guys welding up the damage on the individual blades that were then fitted to huge hubs. Many were variable pitch. Single blades 15-20 ft tall.

Very interesting place if ships and the sea intrique you.

Tobin
 
Guba:
Okay, I'm not attempting to hijack the thread, but you gotta see this. In one of the photos in Panama Mike's recent post, it shows presumably Navy divers working at replacing a prop. I found it interesting that they fly the proper dive flag and all, but LOOK AT THE DIVER ON THE BOAT!
I can hear the screams now...MOF!!!

Now, now...please refrain from arguing, and don't flame me!

I can say these aren't presumably Navy Divers replacing the Screws. I'm in that group on this job. Props are on movie sets. :wink: I'm pleased that you approve of the flag but the MOF is only a SPORT thing. Get the AED ready before you open this one. :D http://www.scubaboard.com/gallery/showphoto.php/photo/35319/cat/500/ppuser/2714

Gary D.
 
And the REALLY interesting thing is.. All i need to know about props while diving is how it sounds underwater so i dont submerge into one :p
 

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