Ludwig Kort applied for a patent for a Kort nozzle in 1938, so I wouldn't exactly classify this idea as an emerging technology. That said, Kort nozzles can provide a 25-30% improvement in thrust at low speeds, the shrouding causes extra drag that negates their advantage at speeds over 10 knots. These devices may not provide much of an increase in speed over un-ducted blades, but they will be able to move heavier boats, which may be an advantage after adding 1000 pounds of batteries to electric conversions.
Fair winds,
Eric
1964 Cheoy Lee Bermuda 30 - Serenity
Marina del Rey, CA
--- In electricboats@ yahoogroups. com, James Graham <osirissail@ ...> wrote:
>
> Here is a video showing the Kort Nozzles on a tug boat. Notice the shape of the propeller inside the nozzle. The maximum blade width is right at the interface of the nozzle and the propeller. Using a standard propeller that has not been modified in a Kort Nozzle shape is worse than no Kort Nozzle at all. The increases thrust at low speeds comes from being able to eliminate the 20-25% of the prop blade tip that is inefficient and using the nozzle to contain any off-tip water flow. For the same diameter propeller, the Kort Nozzle prop can have significant more surface area interacting with the water resulting in greater amounts of water being moved which equates to more power.
> http://www.youtube. com/watch? v=QdSH6SBl5hY
>
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