Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: oldflyer2 on August 03, 2015, 11:12:18 PM

Title: To Kort Or Not To Kort ... That Is The Question
Post by: oldflyer2 on August 03, 2015, 11:12:18 PM
OK, I lusted after one for 20 years and never thought I would see one ... Mr Darby ... the brutish, big pulling power, back breaking, R/C tug boat that pulls people around lakes. I was given a hull and plans last week, and have made a start on the the hull ... it had one small crack.

Anyway, I have seen build threads and indeed, one can buy the current version from Harbor Models in California, with or without.

My question .., given the same motors, props, weight, ect., how much difference do korts actually make and would it be worth my while to turn a pair out of some aluminum I have under the bench?

Cheers

Tom
Title: Re: To Kort Or Not To Kort ... That Is The Question
Post by: morley bill 1 on August 04, 2015, 09:40:53 AM
Korts improve efficiency if you use the proper kort props with them they also provide a big improvement in steering .regards Bill..
Title: Re: To Kort Or Not To Kort ... That Is The Question
Post by: Pirate on August 04, 2015, 09:42:49 AM
 
If all other things remained the same!! You would see a 15 - 20% power increase as similar to when shrouds/korts were placed on motor canal barges. If you then invest in research as to the developing and modern kort nozzle, then expect another 10%, if you then use a kort prop of suitable type and size that allows for the minimum prop to inner kort wall gap, then another 10%. There will be many who borishly brag that this is not so or seen. I have been building and experimenting with such for a long time. Those who have followed suit have found more power in the right place and going astern prop walk virtually eliminated, except on steerable korts where a modicum of compromise has to be taken!!!

My advice, .... MMM nozzles, Prop shop prop. Any experimenting in a similar guise should see but improvement.
Wishing you well and looking forward to seeing your build log.

Pirate
Title: Re: To Kort Or Not To Kort ... That Is The Question
Post by: Pirate on August 04, 2015, 09:46:14 AM
PS.. Correction; kort prop adds 10% extra
Tugs rely on brute power at the right time and place, delicately controlled. Aim for the best.

Pirate
Title: Re: To Kort Or Not To Kort ... That Is The Question
Post by: Fastfaz on August 04, 2015, 10:34:23 AM
Hi,
   Without question go for a Kort nozzle and as Pirate says a close fitting Kort prop. I have a Lowgarth which is fitted with the steerable Kort nozzle that comes with the kit (tale there but not right now) and a Raebosch 75mm Kort prop, she tows really well and steers on a sixpence goes well backwards too. If you search for an article on screw direction in a twin screw boat the is a very good one by a working skipper really helpful, this guy knows his stuff and he recommends a fixed Kort with the right prop this works exceptionally.
    Pirate is spot on with using Prop shop propellers I have a pair that are going in 60mm korts in my Portgarth from MMM. At this time I am building a Norton Cross which has an MMM kort steerable kort and 5 bladed Prop shop kort prop. They are not cheap but are exceptionally well made. If I can find the rotation post I'll let you know, I'll also let you know how the NC behaves. Hope this helps.
     Cheers,
        Faz. :-)) :-)) :-)) :-)) :-)) :-)) :-))
Title: Re: To Kort Or Not To Kort ... That Is The Question
Post by: Tug Fanatic on August 04, 2015, 11:18:30 AM
Go with the kort.

I have never noticed any improved efficiency but the steering response is wonderful and it even works well as a zero power rudder particularly if you have a vertical blade (effectively a rudder) at the stern end of the kort.

I am always amused when I see reference to efficiency as the bits that really matter for efficiency, like prop design, are taboo subjects in scale model boats. I have tried to start discussion about blade design, number, pitch, diameter etc and how they affect efficiency but have never had much response as nobody seems to have done any real comparative testing. I guess that none of us own enough props!
Title: Re: To Kort Or Not To Kort ... That Is The Question
Post by: Calimero on August 04, 2015, 12:43:18 PM
Kort if you want.


But on a twin screw tug: independent control of both the motors and rudders.
Title: Re: To Kort Or Not To Kort ... That Is The Question
Post by: Tug Fanatic on August 04, 2015, 12:44:38 PM
Kort if you want.


But on a twin screw tug: independent control of both the motors and rudders.

I tried independent rudder control once with speed and rudder on a transmitter stick for each motor/rudder & it made my brain hurt!
For real low speed control I much prefer a powerful bow thruster and independent motor control.
Title: Re: To Kort Or Not To Kort ... That Is The Question
Post by: oldflyer2 on August 04, 2015, 02:04:35 PM
Thank You for all the replies and links.

Looks like I will play with making a pair of them for the time being. Ordering anything from the UK at the moment is cost prohibitive, although I am going to splash out and get a P94 controller from Action a bit later in the year.

Tom