Model Boat Mayhem - Forum

Mess Deck: General Section => Tugs and Towing => Topic started by: Canada1 on October 16, 2009, 12:46:13 AM

Title: Kortz Nozzle help
Post by: Canada1 on October 16, 2009, 12:46:13 AM
Greetings all,
 I am just starting my first build (Nangee/MMM)-Twin screw config
as i am very new to this i was wondering if there was a rule of thumb in regards to positioning Kortz Nozzles
Thanx in advance
Title: Re: Kortz Nozzle help
Post by: BarryM on October 16, 2009, 08:49:21 AM
If you are talking about the position of the Kort nozzle relative to the screw, then look here  http://en.wikipedia.org/wiki/Kort_nozzle

The Kort is a venturi and the screw always sits at its throat. Remember the blade tips always match the radius of the Kort internally no matter whether it is a fixed or a steering Kort. Some Korts I've seen in model form use conventional round tip blades suitable for non-Kort use and these are entirely wrong.

If you are referring to where the whole Kort/prop assembly sits, then refer to the original or its GA plan.

Regards

Barry M
Title: Re: Kortz Nozzle help
Post by: Canada1 on October 16, 2009, 01:42:54 PM
thanks BarryM... that helps a great deal . although i haven`t been able to find tech. info on the original and my plan doesn`t show the kort nozzles on it
I guess what i was asking is there a specific spacing requirement between the two, obviously to allow turning. perhaps  a location in regard to the keel

Canada1
Title: Re: Kortz Nozzle help
Post by: BarryM on October 16, 2009, 01:50:53 PM
Ok I'm with you now. Driveline displacement from the centre line is down to the naval architects but as a rough guide I suppose that the shaft will be roughly midway between the side of the hull and the centre line. The outer edge of the nozzle will always be inboard of the hull side.
Have a look here. http://www.marinepropulsion.net/kort/nozzle.htm

Does that help?

Barry M
Title: Re: Kortz Nozzle help
Post by: Canada1 on October 16, 2009, 01:59:10 PM
thats the ticket .......thanks
off i go then to the workshop
Regards
Canada1
Title: Re: Kortz Nozzle help
Post by: portside II on October 16, 2009, 04:22:07 PM
I can understand the efficiency of having flat tipped blades on a kort /prop configuration ,
 that the water cannot drift over the blades and reduce power . But i have seen a picture on the net , maybe on here where the prop has rounded blades and is opperating with a kort.
My own tugs , which one is a twin screw nangee has rounded props in korts has plenty of thrust , the use of flat tipped blades is not a neccesity in my eyes, but thats  just me.
daz 
Title: Re: Kortz Nozzle help
Post by: chrise on October 16, 2009, 04:58:47 PM
I can understand the efficiency of having flat tipped blades on a kort /prop configuration ,
 that the water cannot drift over the blades and reduce power . But i have seen a picture on the net , maybe on here where the prop has rounded blades and is opperating with a kort.
My own tugs , which one is a twin screw nangee has rounded props in korts has plenty of thrust , the use of flat tipped blades is not a neccesity in my eyes, but thats  just me.
daz 

AND if your Kort is steerable then you cannot have fully square ends anyway unless your props are much smaller than your tubes. I have tried both ordinary props & fairly square ended ones & I agree that in model use the differences are small.
Title: Re: Kortz Nozzle help
Post by: BarryM on October 16, 2009, 05:02:09 PM
Props in fixed Korts will have flatter tips that props in steering nozzles (think about it) but at our scale there is unlikely to be any discernible propulsive effect. However, it's the look of the thing. Props intended to operate unshrouded simply look wrong in nozzles and are incorrect as a representation of the real thing. Surely it's a simple thing to get right?

Cheers,

Barry
Title: Re: Kortz Nozzle help
Post by: tolnedra on October 16, 2009, 05:35:20 PM
Have another look at your plans; I have MMM's Anglian Man, and also Gerhard, both of which show the positioning of the Korts on the plans, the stern view being the one to get your dimensions for the Korts from. Alternatively, send Bryan an email, I'm sure he'll help. I've phoned him on occasions to clarify things, and he's always helped. Admittedly it's easier for me to phone, could be a bit costly for you from Canada! Hope this helps.

Danny (the older one, another tug nut!)
Title: Re: Kortz Nozzle help
Post by: ministeve on October 16, 2009, 06:33:27 PM
hi Canada i do a lot of tug towing and have found that if your kortz are as far apart as you can without passing the outside of the hull lines works best for maneuverability when towing.
i too have a nangee part built please find attached photos of the hull

hope these help

ministeve
Title: Re: Kortz Nozzle help
Post by: ministeve on October 16, 2009, 06:35:13 PM
some more
Title: Re: Kortz Nozzle help
Post by: ministeve on October 16, 2009, 06:41:16 PM
last two
Title: Re: Kortz Nozzle help
Post by: poll on October 16, 2009, 06:49:31 PM
Hi  Steve,  Legs look good too. :-)) {-) {-) {-)

John
Title: Re: Kortz Nozzle help
Post by: ministeve on October 16, 2009, 07:06:58 PM
 :-)) thanks john :}
Title: Re: Kortz Nozzle help
Post by: Canada1 on October 16, 2009, 10:43:06 PM
most appreciated 
A newbie says thanks to all for the input
this forum has indeed proved invaluable
thanks again
Canada1
Title: Re: Kortz Nozzle help
Post by: daz on November 14, 2009, 03:43:30 PM
Hay Steve what size dia is the bow thruster on your nangee.
 :-))
Daz
Title: Re: Kortz Nozzle help
Post by: ministeve on November 14, 2009, 09:34:20 PM
if memory serves me right 28mm but on a polen hull i have used 40mm waste pipe how you getting on with her
Title: Re: Kortz Nozzle help
Post by: Mal X on November 18, 2009, 08:15:33 PM
round tip blade is wrong  <:( sod and damn it,  because i was going to use a standard 90mm 4 blader Rivado

this means i'll have to go to Prop Shop, oh well never mind.
Title: Re: Kortz Nozzle help
Post by: DickyD on November 18, 2009, 08:18:31 PM
I have round tipped ones on my tug, goes great.
Title: Re: Kortz Nozzle help
Post by: portside II on November 18, 2009, 08:40:40 PM
Oh no , that wasn't that can of worms been opened ?  :o .
there will be tears.
daz
Title: Re: Kortz Nozzle help
Post by: DickyD on November 18, 2009, 08:46:48 PM
Not from me daz, might make a difference on 1:1 but on this size I think not unless you are entering a show.
Title: Re: Kortz Nozzle help
Post by: portside II on November 18, 2009, 09:49:50 PM
No i didn't mean any one in particular Richard , we have been down this rocky road before regarding props in korts and whether the blades should be flat or round .
This depends on the boat in question , yes if you are going to build a model exactly to scale and the original draughtman's drawings show the prop/s with flat a edge then do so , but as photos have shown on here before that full size tug's etc have props with rould tip's .
as do other vessils .
I have recently married a 90mm rivabo 4 blade brass prop with a MMM 90mm sterable kort , even though they are listed the same size i have had to run the prop in the lathe  with a sanding block to reduce the dia by 3mm , this has resulted in the tips been slightly flat .
I think thats a tip(how to reduce the sise of a prop).
daz 
Title: Re: Kortz Nozzle help
Post by: Mal X on November 18, 2009, 11:28:32 PM
ok maybe it'll be alright, because 90mm is huge anyway; so it'll have loads of power, plus steer better than the normal set up
Title: Re: Kortz Nozzle help
Post by: portside II on November 20, 2009, 12:49:17 AM
You should be ok , i have a 90mm 4 blade round tipped brass prop in a MMM kort on my tug which has been running for the last four years .
Loads of thrust  , the only prob it the fit is realy tight and as the kort is only pivoted at the top there is a little movement which shows as wear marks on the inside of the kort .
daz
Title: Re: Kortz Nozzle help
Post by: Mal X on November 20, 2009, 04:16:28 PM
yes mine used to bang the Kort when steering hard to port/starboard as well
Title: Re: Kortz Nozzle help
Post by: boater12 on November 20, 2009, 04:21:45 PM
There is a forum based around tugs,

www.modeltugforum.com

Maybe there are some answers for you on there.

Boater12
Title: Re: Kortz Nozzle help
Post by: DickyD on November 20, 2009, 04:54:29 PM
There is a forum based around tugs,

www.modeltugforum.com

Maybe there are some answers for you on there.

Boater12
Dont want to go on there, all the rough get on there. ok2
Title: Re: Kortz Nozzle help
Post by: portside II on November 20, 2009, 06:52:48 PM
mine still does Richard , eventually something will wear away  {:-{ , my bets are on the prop to win  :} .
daz
Title: Re: Kortz Nozzle help
Post by: boater12 on November 20, 2009, 06:59:58 PM
Dont want to go on there, all the rough get on there. ok2

All the rough ? I am not sure what you mean, I have visited a few times and found it helpful but guess it depends what you are looking for.

Boater12
Title: Re: Kortz Nozzle help
Post by: DickyD on November 20, 2009, 07:07:07 PM
All the rough ? I am not sure what you mean, I have visited a few times and found it helpful but guess it depends what you are looking for.

Boater12
It was a joke Boater. :-))