On Mon, 17 May 2010 20:27:16 +0000, Larry wrote:

"Steve Lusardi" wrote in
:

Subject: Gyrocompass bearing a bit jam
From: "Steve Lusardi"
Newsgroups: rec.boats.electronics

Less than 1/2 a degree true on the equator. They start getting less
accurate beyond the 70th parallel and the bearing will shift a bit at
speed above 30 knots vessel speed. Today's modern gyro compasses all
have two gyros within the gyrosphere whose planes are offset by
typically 90 degrees to make accuracy better above the 70th. They
don't like acceleration much and high ROT numbers, but the high ROT
(higher than 20 degrees per sec) is mostly the limit on the repeater,
not the gyro. Of course digital bearing displays have no ROT limit.

Historically, gyro compasses has been considered the most significant
weapon innovation of WW1. With the advent of long range naval guns and
steel ships, the magnetic compass was almost useless. The big
disadvantage is the high cost. Today, the same accuracy can be
achieved with satellite compasses with no latitude or speed
limitations at a much lower cost of both acquisition as well as
life-cycle cost. Steve


My GPS tracks me down the exact lane I'm driving 70mph down any Interstate
highway for hundreds of miles....changing lanes on the Virtual Earth
satellite combo map/photo when the car does, pointing in the EXACT
direction I'm going or we'd be drifting out of that lane in a hurry.

Assuming the vessel is in MOTION, that'd be lots more accurate than 1/2
degree true....tracking within a foot for 500 miles....wouldn't it?

I fail to see the point of the archaic mechanical gyro compass.

How does the inertial navigation system, used on submarines, work? Or
are they outmoded?

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

Bruce wrote in
:

How does the inertial navigation system, used on submarines, work? Or
are they outmoded?

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)


Sorry, that's classified.

--
Creationism is to science what storks are to obstetrics.

Larry

Not for aircraft anymore Larry. Maybe it was at some point in the past, but certainly not now. Basically there are a series of
gyroscopes mounted on a common platform in 3 axis. These measure acceleration in pitch, roll and yaw. These are fed to a computer
system where these a computed with a very accurate time source to determined distance travelled. Effectively, these are very
accurate dead reckoning systems. Obviously, error accumulation over both time and distance is their weakness and from time to time
must be reset from another position source. Their big advantage is they need no radio signals to function, so they are stealthy.

Also Larry, you may be confusing GPS systems with satellite compasses. They do not work the same way. Satellite compasses work by
positioning 2 or more GPS receivers at fixed, accurately positioned distances from each other and the receivers then use only the
signal carriers and do phase comparison to determine the bearing of the centerline of the ship. No satellite intelligence is used
in the system. Therefore no motion is necessary. Bearing info from GPS systems in comparison is extrapolated track data.
Steve

"Larry" wrote in message ...
Bruce wrote in
:

How does the inertial navigation system, used on submarines, work? Or
are they outmoded?

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)


Sorry, that's classified.

--
Creationism is to science what storks are to obstetrics.

Larry

In article ,
Larry wrote:

Bruce wrote in
:

How does the inertial navigation system, used on submarines, work? Or
are they outmoded?

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)


Sorry, that's classified.

Laser Ring Gyros, with Military Stream GPS fixes, periodically, to reset
long term accuracy.....