Kort nozzles

[Rick Lucertini <empiricus@sprint.ca>]

> Kort nozzles are basically propeller shrouds.  They increase the efficiency of
> the propeller and --

I believe that the nozzle reduces spillage off the ends (outside arc) of the blades and redirects the
flow into thrust.

Unlike air, which is highly compressible, water can only be redirected and not really influenced to
change density - at least not at the forces we're dealing with.  A shroud on an aircraft will, besides
redirecting flow, compress air as it enters the shroud.  As it compresses, it becomes denser.  The
aircraft engine's fan blades have something to "chew" on and efficiency increases.

Korts can also act as rudders.  The combination of redirected thrust and the port and starboard arcs
of the shroud, acting as dual rudders, increases the efficiency of stearage.

I know there's been some question about all this Kort business.  Is it really efficient u/w?  Once the
benefit of fluid compression is eliminated, then . . .

Evidently some builders are happy with them because they turn up.  Perhaps for vessels where steerage
is more important than fuel consumption?  Korts add parasitic drag.

Rick



Rick Lucertini
in Vancouver, Canada
empiricus@sprint.ca

"To a rational being it is the same thing to act according to nature and according to reason."

    Marcus Aurelius Antoninus, 121 - 180 a.d.