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Marc and Carsten,
I think redundancy would be nearest and dearest to my heart, especially
when being the first to attempt a transit under the Arctic ice cap. On the
single-screw diesel-electrics, they nevertheless had two or three diesel engines
and likewise multiple electric motors. On American nuclear subs (single
reactor), I'm not aware of any of them ever having to shut down. They are
extremely reliable. The Soviets have had that problem.
On modern military subs, low noise signature is obviously a very high
priority and the single, center-line screw has it all over the twin screw.
In one of the Albacore's refits, they installed concentric, counter-rotating
screws as an experiment, but I don't know the results.
Despite having twin screws, the huge Typhoons are very quiet. At that
size, a single screw would have had to be so large (resulting in higher tip
speeds) or turn at a faster rpm. Either one would have increased the noise
level.
Fortunately on our little subs, we're not trying to be silent and sneaky;
we want EVERYBODY nearby to know we're there.
Jim
In a message dated 9/26/2010 8:19:31 A.M. Central Daylight Time,
piolenc@archivale.com writes:
A
single, central screw is definitely going to win the efficiency
contest; a
single screw centered in an (almost) axially symmetrical wake
will have
much higher propulsive efficiency than any other configuration
- see
"wake-adapted propeller" or "wake-immersed propeller."
I was wondering only
about operational considerations, as touched on by
another poster. Things
like redudancy, being able to maneuver in tight
places by going ahead on
one shaft and astern on the other, etc.
Best,
Marc
Archivale
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On 9/26/2010 7:46 PM,
JimToddPsub@aol.com wrote:
> Marc,
> During the development of the
USS Albacore in the 50s (not to be
> confused with the WWII sub of the
same name), they did extensive
> hydrodynamic and wind tunnel including
twin-screw vs single screw
> design. Single screw was the winner and
became the standard ever after.
> The Albacore was primarily a test bed
and was most noted for being the
> first with the tear drop shaped hull
which also became the standard. The
> Albacore is now a museum near
Jon's stomping grounds in Portsmouth, New
> Hampshire.
> The only
subsequent military sub I'm aware of with twin screws is the
> Soviet
Typhoon class, but that sucker has twin parallel main pressure
> hulls
as well and a beam of 75 feet!
> Jim T
> In a message dated
9/25/2010 10:52:34 P.M. Central Daylight Time,
> piolenc@archivale.com
writes:
>
> Interesting. I wonder if subsequent
operational experience confirmed
> Kittredge and
company in their condemnation of single screws, or not.
>
>
Marc
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