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Author Topic: Prop size vs diameter of Kort Nozzle  (Read 5523 times)

westcoaster

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Prop size vs diameter of Kort Nozzle
« on: August 28, 2008, 11:27:04 AM »

Would appreciate your views as to the maximum diameter of propeller that you could realistically set up with a (nominally) 50mm Graupner steerable Kort. The actual inside dia is 51.52mm at a point 5mm in from the in from the end nearest the hull and it gently tapers to 50.55 at 15 mm in.
Another question - where is the best position for the prop relative to the length of the Kort - should it be in the middle or is it better at the hull end 5mm in. It's difficult to express this clearly, but I think you'll know what I mean
Best Wishes
Douglas
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boatmadman

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Re: Prop size vs diameter of Kort Nozzle
« Reply #1 on: August 28, 2008, 06:47:38 PM »

I set up my kort props so the centre of the blades run in the narrowest part of the nozzle and size them to get as little clearance as possible, they seem to work ok this way.

Ian
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DavieTait

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Re: Prop size vs diameter of Kort Nozzle
« Reply #2 on: August 28, 2008, 08:07:22 PM »

Can't do it that way in a steerable Kort though Ian. My thoughts would be to use the narrowest measurement and take 1mm off it to get the max safe diameter to run inside the kort to avoid the prop hitting the inside of the nozzle
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Martin [Admin]

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Re: Prop size vs diameter of Kort Nozzle
« Reply #3 on: August 28, 2008, 10:16:58 PM »

I think with steerable Korts, it is in the narrowest point of the Kort but uses and rounded tip prop.
 A couple of reference photos....








See also:
http://www.highlift-rudder.co.uk/03_products_content/03_kort_movie01.html
http://www.highlift-rudder.co.uk/03_products_content/03_kort_movie02.html


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westcoaster

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Re: Prop size vs diameter of Kort Nozzle
« Reply #4 on: August 29, 2008, 11:02:25 PM »

Ian, Davie and Martin
Thanks for your responses - all good stuff which will help me to ( hopefully ) set up a decent steerable kort arrangement on my new Nangee based tug
Best Wishes
Douglas
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Reade Models

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Re: Prop size vs diameter of Kort Nozzle
« Reply #5 on: August 29, 2008, 11:54:02 PM »


Amazing...

If anybody had suggested round tipped props in Kort nozzles to me before I saw this, I just wouldn't have believed them.

You live and learn.

Malc

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DavieTait

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Re: Prop size vs diameter of Kort Nozzle
« Reply #6 on: August 30, 2008, 01:28:40 AM »

Usually fitted to older boats Malc. A lot of fishing boats just stick a nozzle around the original prop until they can afford to have a custom prop made up
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Tugboat Andy

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Re: Prop size vs diameter of Kort Nozzle
« Reply #7 on: September 07, 2008, 01:25:05 AM »

Another thought regarding propeller placement. It is important to make sure that there is enough shroud extending behind the propeller to make sure you maximize your turning ability. My first boat with a kort nozzle has the propeller too far aft and when the kort swings side to side I do not believe I get proper turning thrust. That problem was solved on the second boat O0   
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-Martin-

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Re: Prop size vs diameter of Kort Nozzle
« Reply #8 on: September 14, 2008, 12:01:30 PM »

Clearance between prop and kort should be as little as possible to achieve the best effect and regarding the position of the prop relative to the length of the Kort, this is dictated by one thing only. The prop should allways be centered in line with the rudderstock of the kort to avoid the kort hitting the the prop when turning. This is probable not as important on models as the clerances proportionally is much bigger than in real life, but is is something to take into consideration.

The red line on the picture illustrates the centre of the rudderstock of the kort in relation to the prop.

Brgds

Martin
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Martin [Admin]

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Re: Prop size vs diameter of Kort Nozzle
« Reply #9 on: October 30, 2008, 09:26:52 PM »

You guys are doing it all wrong! I just found this....

http://uk.youtube.com/watch?v=PzjFEe47bzA
( Flowserve Thruster )


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toesupwa

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Re: Prop size vs diameter of Kort Nozzle
« Reply #10 on: October 31, 2008, 04:21:03 PM »

Something like....

The prop should be on the CL (rudder post position) of the Kort..

You will find that to turn the Kort, there will need to be a gap between the edge of the blades of the prop and the inner face of the Kort ring.
If the Kort was a fixed type, the gap would be reduced considerably...
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