Kort Nozzles

[lockhughes]

If you don't know what these are, here are a few links:

http://www.vhby.com/kortnozz.htm
http://www.qis.net/~jmgraham/advantag.htm
http://www.electriclaunch.com/driveso_rt.html
http://powerandmotoryacht.about.com/library/weekly/may02/aa051302g.htm
http://www.5throw.com/brtmarine/propellers.htm

Question is, if these are so great, why aren't we all using them???

My particular interest (apart from efficiency gains) is whether a Kort nozzle would help or hinder if the prop has to deal with a lot of weeds...

It seems to me that if a *steerable* kort nozzle (instead of a rudder, the rudder shaft ends with a kort nozzle, so turning the "rudder" steers the boat by directing the stream from the prop to port or starboard) would offset the additional drag incurred with the Kort with drag saved by going rudderless?

It would be nice too, of course, to be able to kick the stern around while the boat is dead in the water ( I'm talking inboard electric motor here, not steerable outboard, and sheltered waters with a 6 knot max. speed limit... so bigger prop, slower revs.)

I see that Elco and the Reservoir Runner (electric outboards) both use a Kort Nozzle...

Lock

[BrettM]

In a nutshell, nozzles work best at slow speed and are very good at producing bollard pull. Hence their use on tugs, trawlers and craft of the like.
Brett

[duluthboats]

This mightbe of some interest.

http://www.boatdesign.net/forums/showthread.php?s=&threadid=418&highlight=kitchen+rudder

Gary

[lockhughes]

Originally posted by duluthboats
This mightbe of some interest.
http://www.boatdesign.net/forums/showthread.php?s=&threadid=418&highlight=kitchen+rudder
Gary
Thanks Gary. yes, I did see that thread. It's the claims about fuel economy that caught my eye. My narrow interest is a 40-ppl passenger ferry on sheltered waters, running at a standard 6kts on a fixed schedule, electric propulsion.

I gather that a Kort (Rice, whetever) is best optimized for a narrow range of certain conditions. Hence the optimism.
I assume that (diesel/gas) fuel economy translates as shorter re-charging times, smaller battery farms, whatever.
L

[lockhughes]

Here's a quote about the Kort, from the Reservoir Runner pages
at
http://www.qis.net/~jmgraham/resrun.htm

Reservoir Runners incorporate a ducted propeller system or Kort Nozzle. A Kort Nozzle features a hydrodynamically shaped duct, enclosing a high thrust propeller, to minimize turbulence losses and produce exceptional thrust and efficiency. The efficiency of a Kort Nozzle can be 50% to 70% higher than an open propeller on an electric boat, producing boat speeds 15% to 20% greater without using additional power from the batteries! At a given boat speed, run times are extended 50% to 70%. The propeller is also protected against hitting stumps and rocks, is safe around swimmers and won't tangle fishing lines.

... so, what am I missing?
L

[lockhughes]

this just keeps getting better and better...

http://www.karvi.com/technology/tech-speednozzle.htm