Kort Nozzles

Discussion in 'Boat Design' started by lockhughes, Jul 4, 2002.

  1. lockhughes
    Joined: Jun 2002
    Posts: 110
    Likes: 3, Points: 0, Legacy Rep: 27
    Location: Wards Island Toronto north shore, Lake Ontario

    lockhughes ElectricGuy

    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
     
  2. BrettM
    Joined: Apr 2002
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    Location: Australia

    BrettM Senior Member

    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
     
  3. duluthboats
    Joined: Mar 2002
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    Location: Minneapolis,MN, USA

    duluthboats Senior Dreamer

  4. lockhughes
    Joined: Jun 2002
    Posts: 110
    Likes: 3, Points: 0, Legacy Rep: 27
    Location: Wards Island Toronto north shore, Lake Ontario

    lockhughes ElectricGuy

    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
     
  5. lockhughes
    Joined: Jun 2002
    Posts: 110
    Likes: 3, Points: 0, Legacy Rep: 27
    Location: Wards Island Toronto north shore, Lake Ontario

    lockhughes ElectricGuy

    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
     

  6. lockhughes
    Joined: Jun 2002
    Posts: 110
    Likes: 3, Points: 0, Legacy Rep: 27
    Location: Wards Island Toronto north shore, Lake Ontario

    lockhughes ElectricGuy

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