[OT] Navy releases photos of U.S.S. San Francisco

Pat Flannery wrote:
They never turn on their active sonar unless they have to; if they are
in what they think is unobstructed water they will maintain silence if
at all possible for the sake of stealth.
One odd thing though; the first-hand account stated that they were going
pretty fast- he said something like "as fast as we can at 500
feet"...which might suggest that the were going at the maximum speed
they could without their propellor cavitating and producing
sound....given that the water pressure increases with depth, I wonder if
cavitation vacuum bubbles are less prone to occur at depth than near the
surface, and the deeper you go the higher your propellor RPM (and speed)
can be?

Modern subs are actually faster under the surface than on
it, since that's where they're designed to do the majority
of their travel, and their hulls are shaped accordingly.
Though, yes, cavitation does drop with depth.


In the book "The Hunt For Red October" they mention a "mass detector"- a
device that picks up gravitational anomalies near the sub and allows
navigation around subsurface obstacles without the use of sonar.
[snip]
and if San Francisco was equipped
with such gear, then it should have shown something as they approached
the seamount. Maybe by the time they realized it was there it was too
late to turn sharply enough to completely avoid it, like the iceberg in
the case of the Titanic

That would be the gravimeter. They're not, strictly speaking,
secret devices, as many organizations and companies operate them
for varying purposes. For example, measuring tidal forces,
detecting various mineral or petroleum deposits, etc. It does
seem odd, though, an undersea mount definitely falls into the
class of things you'd think they could spot from a mile away.
Those boats are also pretty danged manouverable, it's hard to
see how this sort of thing could have happened.

On Mon, 31 Jan 2005 03:00:40 GMT, (Henry Spencer)
wrote:

Trouble is, all that technology doesn't change the fact that it's pretty
damn dark 500 feet down. There basically isn't any way you can detect
what's right in front without illuminating it yourself -- with light,
sound, or whatever -- and it's hard to do that and still remain stealthy.
So subs emit only when they have urgent reason to.

....Well, guess that *really* makes the Seaview a technical
impossibility :-(

OM

--

"No ******* ever won a war by dying for | http://www.io.com/~o_m
his country. He won it by making the other | Sergeant-At-Arms
poor dumb ******* die for his country." | Human O-Ring Society

- General George S. Patton, Jr

On Sun, 30 Jan 2005 17:11:03 -0600, Pat Flannery
wrote:

I still want to know if he's got those submariner propellors* tattooed
on his butt.

....Actually, he has anchor and chain tattooed on his...no, wait. I
won't stoop that low :-P

OM

--

"No ******* ever won a war by dying for | http://www.io.com/~o_m
his country. He won it by making the other | Sergeant-At-Arms
poor dumb ******* die for his country." | Human O-Ring Society

- General George S. Patton, Jr

Pat Flannery wrote:

given that the water pressure increases with depth, I wonder if
cavitation vacuum bubbles are less prone to occur at depth than near the
surface,

That's correct. The deeper you are, the faster you can go without
cavitating.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

(Henry Spencer) wrote:

In the book "The Hunt For Red October" they mention a "mass detector"- a
device that picks up gravitational anomalies near the sub and allows
navigation around subsurface obstacles without the use of sonar.

Not quite -- the device in the book detects small changes in the local
gravitational field, which can be compared against a gravity *map* to
navigate accurately in a *mapped* *area* without sonar. It's a navigation
system, not a way of sensing what's ahead; it wouldn't help you avoid an
unmapped obstacle.

(Such devices really do exist, but whether they are useful and practical
for submarine navigation is not obvious.)

They were originally baselined into the D5 navigation system, but
after a decade plus of work, they were abandoned.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

"Christopher M. Jones" wrote:
It does seem odd, though, an undersea mount definitely falls into the
class of things you'd think they could spot from a mile away.

Next time you are at the beach, try and look a mile away through the
water. Then ponder the lack of windows on a submarine.

Those boats are also pretty danged manouverable, it's hard to
see how this sort of thing could have happened.

Hmm... No way to see outside, and the bottom of the ocean is..
'poorly mapped'.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

On Mon, 31 Jan 2005 06:52:01 GMT, (Derek Lyons)
wrote:

That's correct. The deeper you are, the faster you can go without
cavitating.

....Which is why Navy regs prohibit allowing Dick Cavitt onboard any US
sub while on manouvers.

OM

--

"No ******* ever won a war by dying for | http://www.io.com/~o_m
his country. He won it by making the other | Sergeant-At-Arms
poor dumb ******* die for his country." | Human O-Ring Society

- General George S. Patton, Jr

OM wrote:
On Mon, 31 Jan 2005 03:00:40 GMT, (Henry Spencer)
wrote:


Trouble is, all that technology doesn't change the fact that it's pretty
damn dark 500 feet down. There basically isn't any way you can detect
what's right in front without illuminating it yourself -- with light,
sound, or whatever -- and it's hard to do that and still remain stealthy.
So subs emit only when they have urgent reason to.


...Well, guess that *really* makes the Seaview a technical
impossibility :-(

OM


Well... at least until the Navy quits slacking off on their
implementation of "virtual backlot technology"...

On the other hand, do we really want to be able to see all of the
ball-eyed kelp monsters that Irwin Allen predicted? Bad enough to see
them during the initial run...

--
Reed Snellenberger
GPG KeyID: 5A978843
rsnellenberger-at-houston.rr.com

Henry Spencer wrote:


(Such devices really do exist, but whether they are useful and practical
for submarine navigation is not obvious.)



Triton found some correlation between hers and their search sonar (their
fathometer was on the fritz) as far as what depth of water they were
traversing... the big problem is that the sea bottom and its topography
can be made out of substances of different density (silt, limestone,
basalt, granite, etc.), and there are local areas of gravity anomaly due
to the underlying geologic structure- and both can throw of the readings
on the device. But if you had one of these near the stern of the sub,
and one near the bow, then you should get a reading of some sort if you
approached a steeply-sloped seamount, such as the sub apparently hit
-based on the damaged area- because of the different degree of
gravitational attraction at the two ends of the sub as the seamount was
approached. The degree of difference and its rate of change at the two
ends of the sub could give you the approximate distance to the seamount
ahead of you.

Pat

OM wrote:

...Well, guess that *really* makes the Seaview a technical
impossibility :-(



Of course she had her bow floodlight.
You know how you fish for squids? You hang lights in the water to
attract them; now if only Admiral Nelson and Captain Nemo had known
that, they both could have saved themselves a great deal of trouble.
On the Microsoft Encarta Virtual Globe '99 the whole Sea Of Japan is lit
up on the night view by the illumination of the squiding fleets.

Pat