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Message no. 1
From: lordmountainlion@***.rr.com (Scott)
Subject: Cavitation
Date: Sun, 30 May 2004 05:32:06 -0600
'Would you MIND not shooting at the thermonuclear weapons please?'

2) at deeper depths, you have higher ambient pressures, which lead
to less cavitation. Most proprellers (there are exceptions) are
designed to
operate at peak efficiency when there is no cavitation (as the state
change
creates vapor, which is compressible, which in turn wastes thrust unless
carefully accounted for). Hence, you are operating in a regime at which
your propeller is cranking at peak performance.

Marc
[>] Do me a favor explain cavitation. Ever since crimson tide I been
wonder what the hell it means to cavitate to avoid a torpedo.

Scott
Message no. 2
From: matryoshka_01@*******.com (Danyel Woods)
Subject: Cavitation
Date: Mon, 31 May 2004 12:57:59 +1200
>Date: Sun, 30 May 2004 05:32:06 -0600
>From: "Scott" <lordmountainlion@***.rr.com>
>Subject: Cavitation

>'Would you MIND not shooting at the thermonuclear weapons please?'
>
>2) at deeper depths, you have higher ambient pressures, which lead
>to less cavitation. Most proprellers (there are exceptions) are
>designed to
>operate at peak efficiency when there is no cavitation (as the state
>change
>creates vapor, which is compressible, which in turn wastes thrust unless
>carefully accounted for). Hence, you are operating in a regime at which
>your propeller is cranking at peak performance.
>
>Marc
>[>] Do me a favor explain cavitation. Ever since crimson tide I been
>wonder what the hell it means to cavitate to avoid a torpedo.

Speaking as an armchair expert:
Submarines emphasise stealth in all their operations, especially so the
Ohio-class SSBNs like in 'Crimson Tide'. As typical submarine operating
depths, cavitation is a product of a high propeller speed or a sudden
increase therein; since cavitation is very, very noisy, standard procedures
say that unless specifically ordered to do so, you don't cavitate when
accelerating. However, if you need the speed more than you do the stealth,
you order propulsion to 'cavitate', or pour on the gas and to hell with the
noise.

-> Danyel
Who hopes he got this right enough and didn't steal Paul's thunder

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Message no. 3
From: lordmountainlion@***.rr.com (Scott)
Subject: Cavitation
Date: Sun, 30 May 2004 19:21:57 -0600
>Date: Sun, 30 May 2004 05:32:06 -0600
>From: "Scott" <lordmountainlion@***.rr.com>
>Subject: Cavitation

>Marc
>[>] Do me a favor explain cavitation. Ever since crimson tide I been
>wonder what the hell it means to cavitate to avoid a torpedo.

Speaking as an armchair expert:
Submarines emphasise stealth in all their operations, especially so the
Ohio-class SSBNs like in 'Crimson Tide'. As typical submarine operating

depths, cavitation is a product of a high propeller speed or a sudden
increase therein; since cavitation is very, very noisy, standard
procedures
say that unless specifically ordered to do so, you don't cavitate when
accelerating. However, if you need the speed more than you do the
stealth,
you order propulsion to 'cavitate', or pour on the gas and to hell with
the
noise.

[>]So you try to outrun the torpedo which is homing in on your sounds
produced by the propellers cavitations. That would explain the turning
and noise makers in the knuckles to draw off the sound homing torpedoes
from the propellers cavitations.


Scott

'Would you MIND not shooting at the thermonuclear weapons please?'
Message no. 4
From: nightgyr@*********.com.au (GreyWolf)
Subject: Cavitation
Date: Mon, 31 May 2004 12:13:15 +1000
> [>]So you try to outrun the torpedo which is homing in on your sounds
> produced by the propellers cavitations. That would explain the turning
> and noise makers in the knuckles to draw off the sound homing torpedoes
> from the propellers cavitations.

Id assume the theory being to crank out as much relative distance.. then if
the torp still decides to go for you rather than the first noisemaker, make
the sharp turn under power, and drop a Nmkr then cut the power so the Nmkr
is the only thing for the torp to home in on while you go off at a tangent
out of the blast radius... hopefully... well, makes sense to me.

Greywolf
Message no. 5
From: ShadowRN@********.demon.co.uk (Paul J. Adam)
Subject: Cavitation
Date: Tue, 1 Jun 2004 11:40:20 +0100
In article
<!~!UENERkVCMDkAAQACAAAAAAAAAAAAAAAAABgAAAAAAAAAOt4fGdQeokS2jD6QUMhyasKAA
AAQAAAAtrF22U1n0kiOcS0ZTXGugAEAAAAA@***.rr.com>, Scott
<lordmountainlion@***.rr.com> writes
>[>] Do me a favor explain cavitation. Ever since crimson tide I been
>wonder what the hell it means to cavitate to avoid a torpedo.

You don't "cavitate to avoid a torpedo" - Crimson Tide is a veritable
"how not to do it" of submarine warfare.


Cavitation occurs when the pressure on the back of your propeller drops
enough that vapour bubbles form (the 'cavities' of its name). The harder
you drive a propeller, the larger a pressure difference you create -
that's what pushes you along. But above a certain point, the water and
the dissolved gas in it starts to break down and bubbles form, then
collapse. (Think of it as a sort of wheel-spin: put too much power
through a tyre and it loses grip, too much power through a propeller and
it cavitates. However, cavitation doesn't have the same loss of driving
effect)

The imploding bubbles produce serious local stress points, and can erode
your propeller quite badly (perhaps also where 'cavities' come in: a
propeller that's cavitated badly for a while will often be pitted and
eroded). They also make *noise*: cavitation experiments in a university
lab usually sound like a soft rising electric whine (as the pump spins
up) and then the most Godawful racket, like handfuls of gravel in an
electric blender, when the blades start to cavitate.

Cavitation is bad because it's noisy and because it can eventually
damage the propeller. Submarines in particular try very hard to avoid
it, because it's a huge "HERE I AM! COME AND KILL ME!" sign. However, if
there's an incoming torpedo already, the enemy *knows* where you are,
and briefly cavitating to get some extra speed might let you get away
from the weapon.


--
Paul J. Adam
Message no. 6
From: cmd_jackryan@***.net (Phillip Gawlowski)
Subject: Cavitation
Date: Thu, 03 Jun 2004 11:17:48 +0200
On Tue, 1 Jun 2004 11:40:20 +0100, Paul J. Adam
<ShadowRN@********.demon.co.uk> wrote:


[cut_correct_info]
> Cavitation is bad because it's noisy and because it can eventually
> damage the propeller. Submarines in particular try very hard to avoid
> it, because it's a huge "HERE I AM! COME AND KILL ME!" sign. However, if
> there's an incoming torpedo already, the enemy *knows* where you are,
> and briefly cavitating to get some extra speed might let you get away
> from the weapon.

Of course, you deeper a sub dives, the higher the speed without
cavitation, as the pressure prevents what you mentioned in your previous
post.

--
Phillip Gawlowski
Bastard GameMaster From Hell (Der Meister) and General Idiot

"Anything worth shooting once is worth shooting twice."
- Col. Jeff Cooper, USMC (Ret.), regarding combat handgun training

Further Reading

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