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Kort Nozzle
Hello All:
A very important area of psub design has to do
with propulsion. The ideal is low speed and high thrust. Low speed
because visibility is poor in most waters. High thrust to quickly maneuver
out of harm's way. To my knowledge, nothing serves these requirements
better than a kort nozzle. Having looked over the available information on
the web, here are my conclusions:
Kort nozzles increase low-speed thrust over
typical stand alone props. They are used extensively on tugboats and other
work vessels requiring a great amount of thrust for push and pull.
The increased thrust is
transferred to the craft's hull via the nozzle as apposed to delivering
increased thrust via the shafting ie. seals, bearings, motor, motor mounts,
hull.
The prop blades are constructed in such a way as to have
minimal clearance to the nozzle's surface to reduce turbulance and drag.
Their purpose is to pull water through the nozzle.
The nozzle has a cross-sectional airfoil shape not unlike a
jet or rocket exhaust nozzle, or an airplane wing's lifting surface with the
upper wing surface on the inside of the nozzle. Water enters the nozzle
and is high-pressure constricted, and leaves the nozzle low-pressure
expanded producing forward thrust through increased velocity.
To my mind there must be three all important variables
involved in designing a kort system:
1) Airfoil shape
2) Prop pitch/diameter
3) Position of prop for/aft within the nozzle
It's all very interesting. I found one web page that
said the reason there is not much info on korts is because most of it is
classified. Can anyone of you provide additional information? I look
forward to your replies.
TTYL,
Big Dave