Page 34The Kort Nozzle

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The Kort Nozzle is a certain way of increasing the speed of the boat by about 10%

It improves the efficiency of the propeller.

The blade of the propeller pushes water away and behind the boat.
The water flows onto the leading edge of the blade and the middle of the blade pushes
the water back and away.
Some water will escape and slip off the trailing edge of the blade.

Also, some water will escape and slip off the outer edge of the blade.

If the outer edge of the blade is encased in a tube, then water cannot escape in that direction.
This unwanted flow – and energy waste – is prevented.
The efficiency of the propeller is increased.

Why aren’t Kort nozzles fitted to all boats?
Because it only works for boat speeds below 11 or 12 mph.
Thereafter the drag generated by the nozzle outweighs the efficiency gain.

So tow boats, and tugs very often use Kort Nozzles
And how about inland water craft which are limited to 5 mph?