High speed propeller duct (15-20 knots)

I came across this article regarding propeller ducts optimized for higher speeds than a conventional Kort-nozzle.

The article claim that the HR-nozzle (and the Rice-nozzle) seems to give the same benefit of the Kort-nozzle at lower speed, without adding significant drag at speeds over 14 knots, which is the problem with the Kort-nozzle, designet for low speeds.


What do you think?

Yes, Rice-nozzle is faster. It’s easy to understand from this picture: https://gcaptain.com/wp-content/uploads/2012/03/Screen-shot-2012-03-02-at-12.55.58-PM.png

Yea. Came across same picture, and decided to redaign PMs duct with a Rice nozzle design.

Can someone explain to me, why a simple straight tube is less efficient than a profiled tube? I understand that i can modify the effective velocity the propeller sees, e.g. by tapering the diameter or adding a profile, so i can get more thrust for a given propeller diameter at low velocity.
Also i understand, that adding a duct will improve efficiency because there is no dedicated wing tip effect.
But why is there a profile needed at all? Won’t any profile thicker than needed for mechanical stability will produce more drag at high velocity?

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The answer is easy: Water does not flow straight into the pipe, but always from the side. The jet of water is obstructed by the engine, shaft, tube holders and propeller hub.

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How thin can this rize nozzle be practical? Is it scientifically backed? Or is it just an experience? How sleek must this rize nozzle be to add the lowest drag at medium and high velocity?

I am preparing a drawing of the propulsion system (direct drive with outrunner) that will solve all the important issues. Next week, I will create a new topic in the “Propulsion System (Motor, Gears)” section.


Interesting, do you design this type stuff professionally?

Hi Jezza, I specialize only in hydrodynamics. I looked at your theme Jezza’s Build (slow), nice drive. You just need a quality propeller and add a pipe.