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reverse? - real subs?

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Postby petn7 » Thu Jul 03, 2003 1:06 am

i know this proabaly sounds dumb, but real military subs can go in reverse, right? if they do, is it by their main propeller or by thrusters/mini propellers?
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Postby BoomerFunker » Thu Jul 03, 2003 3:32 am

Not dumb at all!

Subs will use the main propeller (called a "screw") for both ahead and astern movement. I'm sure a current or former "nuke" could explain it in serious detail but the simple answer is the boat uses a clutch mechanism to disengage the shaft from the reduction gears and reapply steam and the gears to begin spinning the shaft the other way. A boat will shake as the excess foward momentum is worn down and reverse speed is gained and this period is called "backing down"
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Postby Robse » Thu Jul 03, 2003 2:46 pm

Hi y'all

I don't know if the following is already in active use, but I'd imagine it'll work:
Wouldn't it be better to control the pitch of the propeller blades, and thus reversing the force, without reversing the actual propeller and shaft etc? (Like airplanes do..)

This would also enable the crew to minimize the cavitation as described in previous add, by simply trimming the pitch to the most effective point. Cavitation noises are coffee and cake to any live passive sonar in the area... :)

IF someone needs it, then a full, quick reversal of the pitch (without thinking about noise) offers quicker 'reversal' cause U wouldn't have to wait for the propeller and shaft etc. to stop before engageing reverse. Quick reaction must be the number one goal in case of an emergency stop.

...just a few thoughts.
Yours Sincerely, Robert Holsting, Denmark
1/81 SSBN Ohio Class scratch builder, more at www.robse.dk

"Never be afraid to try something new; remember that it was amateurs who build Noah's Ark, and professionals who build the Titanic"
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Postby wlambing » Thu Jul 03, 2003 5:06 pm

Gents,
The screw is controlled purely by the throttles on US boats. If you're steaming ahead and want to stop or go in reverse, the ahead throttle is shut and the astern thotle is opened. This is done simultaneously, in a very smart and military manner! The kid on the wheels is usually a pretty sharp dude, even if he is an Electrician's Mate!
Controllable pitch screws are not used by the USN for many reasons,SubSafe and arrangement issues among them.
Take care,
Bill
"If you ignore the problem long enough, it will go away. Even flooding stops eventually!"
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Postby Robse » Fri Jul 04, 2003 6:37 am

Thanks for setting that straight, Bill. I guess a pitch prop. IS more fragile than a fixed prop, so I see your point / reasoning.
Also, I'm sure too that every hand onboard is, as you say, pretty sharp. Anything less would endanger the hole integrety of both sub and crew. :)
Yours Sincerely, Robert Holsting, Denmark
1/81 SSBN Ohio Class scratch builder, more at www.robse.dk

"Never be afraid to try something new; remember that it was amateurs who build Noah's Ark, and professionals who build the Titanic"
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