Author Topic: Does anyone know the name of this girl? KEENOMA apparently.  (Read 16754 times)

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Toby

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Re: Does anyone know the name of this girl? KEENOMA apparently.
« Reply #15 on: August 24, 2018, 14:33:50 »
  Norm,

Great looking job!!  Very  neat and crisp.

Toby


des

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Re: Does anyone know the name of this girl? KEENOMA apparently.
« Reply #16 on: August 24, 2018, 15:34:28 »
Hi Toby

The Kort nozzles have an airfoil cross-section, usually thicker at the forward end and thinner at the outlet end (although there are some exceptions); flat in the area of the prop ring - the smallest internal diameter of the nozzle is in the region of the prop ring itself;  the nozzle then opens up slightly towards the outlet, thereby forming a venturi shape.  The outer surface is always tapered down, in a straight line, from the greater diameter of the leading edge, to the thinner diameter of the trailing edge;  this shape promotes laminar flow of the water over the outer surfaces of the nozzles.  (The nozzle is never partially flat and parallel, and partially tapered, as seen on some freebie model plans.)

There are two different airfoil shapes in common use for fixed or steerable nozzles (not sure about Schottel drives though) -

- one airfoil shape is used when thrust is most usually required in one direction only (usually forward) than the other - eg for towing over the stern, or pushing with the bow.  (I would think that this is the nozzle shape most likely to be used for Schottel and other ASD drives.)

- a different airfoil is used if the tug is of a type which can equally tow over the bow while travelling backwards, as well as towing over the stern.  This nozzle is not as efficient as the first when towing in the principal direction, but is more efficient in the "other" direction.

The internal diameter is never less than the tip diameter of the prop, so as to allow the prop to be withdrawn out the aft end (after the rudder has been removed).  In practice, some clearance is required, so in most model setups the internal nozzle diameter is usually 2-3 mm greater than the tip diameter of the prop - this makes for some interesting considerations when trying to source compatible props and nozzles from different suppliers, as some manufacturers of both state true diameters, and others state "nominal" diameters.

The nozzles are always set parallel to the shaftline - this is a matter of physics and fluid dynamics, as well as the need to maintain a constant propeller tip clearance within a narrow space.  Canting of the nozzles relative to the shaftline will decrease propeller tip clearance in one region, while opening it up in another, thereby resulting in vortices forming in the water flow through the nozzle.  If the shaftline itself is set running in or outboard, then the nozzles will be set accordingly.  Similarly, if the shaftline is set running upwards or downwards, then the nozzles will be set accordingly.  (I am currently working up working plans for a model where the prototype tug's prop shaftlines run both slightly downward, and slightly outboard.)

Hope this is helpful.

Des.

Toby

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Re: Does anyone know the name of this girl? KEENOMA apparently.
« Reply #17 on: August 24, 2018, 16:59:41 »
Hello Des!

Wow, what a lot of useful and interesting info.
Thank you.
I shall re- read it for kort nozzles are not something I have dealt with before and this all quite new.

Toby

Toby

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Re: Does anyone know the name of this girl? KEENOMA apparently.
« Reply #18 on: September 25, 2018, 10:32:22 »
Work on my model is progressing:

Keel primed and painted

the ice breaker bars at the bow added.... made and shaped in wood and coated with finishing resin...

Shafts in and  exit housing about them on the outside of the hull made by gluing a plastic washer to the shaft at the approoriate point and then filling behind with p38 filler and shaping  followed by a coat of resin.

Forecastle and hawse pipes and anchor housings installed.

Decks and bulwarks finished but for a few bulwark supports.

Diesel stacks made and painted and a few deck fittings organised.

Working on the wheelhouse structure and wondered if anyone had ideas about kitting out a fairly modern type of wheelhouse.  How have others improvised those various items of controls and electronic gadgetry.

Toby
« Last Edit: September 27, 2018, 17:06:46 by Toby »

sea monkey

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Re: Does anyone know the name of this girl? KEENOMA apparently.
« Reply #19 on: September 25, 2018, 21:23:38 »
Any photos?

Toby

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Re: Does anyone know the name of this girl? KEENOMA apparently.
« Reply #20 on: September 29, 2018, 01:29:02 »
 Have been trying to upload photos  but keep on getting error message.

des

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Re: Does anyone know the name of this girl? KEENOMA apparently.
« Reply #21 on: September 29, 2018, 04:16:15 »
Hi Toby

You'll probably find that the photos exceed the forum's file size limit.  There are a number of free utilities available from the web you can use to re-size the photo files, or I just use Windows Paint.  I know other members use Photo Bucket, but I don't know how this works.

Des.

Toby

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Re: Does anyone know the name of this girl? KEENOMA apparently.
« Reply #22 on: September 29, 2018, 06:10:00 »
Deck etc is just first coat of grey and yellow.
 A bit of tidying up to do.
« Last Edit: September 29, 2018, 06:31:44 by Toby »

Toby

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Re: Does anyone know the name of this girl? KEENOMA apparently.
« Reply #23 on: September 29, 2018, 06:12:06 »
.

Toby

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Re: Does anyone know the name of this girl? KEENOMA apparently.
« Reply #24 on: September 29, 2018, 06:16:23 »
 The arrows point to where plastic washers were glued on to the stuffing tube behind which filler used to shape the housing required.

olscuzbut

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Re: Does anyone know the name of this girl? KEENOMA apparently.
« Reply #25 on: September 30, 2018, 06:00:32 »
Looking very nice Toby.  Just wondering if you will experience any cavitation problems as it looks like your props will not be too far below the water line.  Or maybe that is just how it appears in the picture.  Will be watching for sea trials.

Norm

Toby

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Re: Does anyone know the name of this girl? KEENOMA apparently.
« Reply #26 on: September 30, 2018, 06:26:38 »
Norm,

I will have to look at that point you raise, when I return home.
I don't have the basic plan sheet to hand.

T