Model Boat Mayhem

Mess Deck: General Section => Tugs and Towing => Topic started by: BigAde on February 13, 2010, 12:02:17 am

Title: BIG MISTAKE! What an idiot i am!
Post by: BigAde on February 13, 2010, 12:02:17 am
Hello all,

Today I bought a 70mm brass prop for a new tug that I am building from my local model shop! The problem I have is that the prop is exactly 70mm and now I need a kortz nozzle for it. I was planning on making my own out of some plastic pipe but I cannot fine some 70+mm pipe in B&Q and also the Kortz MMM sell are exactly 70mm so they will not fit!

does anyone know where I might be able to buy some 74mm pipe to fit my prop that I should of checked if I could get the pipe first! B&Q sell 68mm and I looked at all their differnt fittings but the prop will not fit, I tried!

Can anyone help??

Cheers

Adrian
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: HS93 (RIP) on February 13, 2010, 12:08:22 am
do you know anyone with a lath who can spin it up and fatten the tips to fit a commercial Kort.its only 2mm off the tips so very little loss off drive

Peter
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: BigAde on February 13, 2010, 12:20:28 am
do you know anyone with a lath who can spin it up and fatten the tips to fit a commercial Kort.its only 2mm off the tips so very little loss off drive

Peter

Thats a good idea! I would need to take off 4mm to fit a 68mm pipe! I never thought about spinning maybe even in a drill! at least then it will look more like a kotrz prop instead of the usual round normal prop!
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: toesupwa on February 13, 2010, 12:27:42 am
Thats a good idea! I would need to take off 4mm to fit a 68mm pipe! I never thought about spinning maybe even in a drill! at least then it will look more like a kotrz prop instead of the usual round normal prop!

I wouldnt spin a prop in a drill and try to remove some material off the tips of the blades.. if i were you!... blades have a habit of coming off the 'boss' at speed when you are trying to machine them...  :embarrassed:
Unless you can hold them in a lathe and GENTLY (0.02" per cut) remove material, you would be better off making the kort to fit the prop...

My 'how to' make a kort on RC Groups..
http://www.rcgroups.com/forums/showthread.php?t=1025555
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: BigAde on February 13, 2010, 12:35:49 am
I wouldnt spin a prop in a drill and try to remove some material off the tips of the blades.. if i were you!... blades have a habit of coming off the 'boss' at speed when you are trying to machine them...  :embarrassed:
Unless you can hold them in a lathe and GENTLY (0.02" per cut) remove material, you would be better off making the kort to fit the prop...

My 'how to' make a kort on RC Groups..
http://www.rcgroups.com/forums/showthread.php?t=1025555

Wow that is an ace tutorial but I do not have the tools to make my own like that hence using some simple plastic tube to the correct diameter.
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: sinjon on February 13, 2010, 06:47:07 am
Would it not be possible to build up a tube to the right diameter, then lay up fibre glass ?

Colin
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: FullLeatherJacket on February 13, 2010, 07:43:31 am
Idiot's contribution - what about cutting a slot lengthwise along a piece of 68mm tube and inserting a 19mm-wide sliver of the same material to increase the diameter out to 74mm? It won't be exactly round then but the difference won't be noticeable. You can buy a suitable adhesive for plastic drain pipe from the same source.
Suit yourself.
FLJ
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: funtimefrankie on February 13, 2010, 08:43:20 am
that's about 3 inches, What about a paint tin or large soup tin,  shaped with filler...or even a small bucket :-))
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: Tom@Crewe on February 13, 2010, 08:46:27 am
Spray can top. They come in all shapes and sizes, take your ruler when you help wife with the shopping.
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: Airsparks on February 13, 2010, 09:21:28 am
 Have you tried brass tube from a plumbers merchant.

My korts are 50mm brass tube supplied by Mobile Marine Models. If all else fails ask Brian at MMM

    Alastair
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: Colin Bishop on February 13, 2010, 10:46:01 am
If you can find a round former of the right size you could try laminating the nozzle with layers of thin styrene sheet. Once you have built it up to a decent thickness and it has fully dried it should be pretty tough.

Colin
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: norry on February 13, 2010, 12:03:18 pm
...Hi Guys...

Measure a Sooup Tin...Its about 75mm Just Right for a 70mm Prop...

If you use the Medium size Bean Tins, Then you have the correct length as well...Just build the outside up with P38...

But Remember... Beanz Meanz Heinz...Norry...

Title: Re: BIG MISTAKE! What an idiot i am!
Post by: chrise on February 13, 2010, 12:20:55 pm
...Hi Guys...


I use the Medium size Bean Tins, Then you have the correct length as well...Just build the outside up with P38...

Do you mean that your Korts are no more than a layer of P38? I would not have thought it strong enough unless very thick so how thick does it need to be & do you have a trick for getting a nice smooth outside surface? This would offer alternatives to the never ending search for plastic tube!

For your top & bottom pivots do you just use roughened brass rod or do you solder spreader plates to your rudder shaft to spread the load?
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: Colin Bishop on February 13, 2010, 12:58:46 pm
I think Norry meant to use the tin as the base and build up the shape with P38.
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: Bryan Young on February 13, 2010, 03:40:31 pm
Just in passing, fairly recently I (jokingly) suggested to the guy (Turkish?) who is making his own nozzles that for all the world the end result looked just like a Fray Bentos steak and kidney pudding tin. These tins are very robust and mor "solid" than your usual food tin.
The contents are pretty good also, so a trial may be worth the effort!. BY.
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: chrise on February 13, 2010, 04:50:10 pm
I think Norry meant to use the tin as the base and build up the shape with P38.

Pity. I had hoped that Norry had found something new.
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: norry on February 13, 2010, 06:04:28 pm
...Hi Guys...
It seems that Chris E has found something new... A cheeky way of twisting words...

How to take a posting made by one member of the Forum, Change the Wording of that Posting, Then use it as a quote from the original posting...

I never stated that that I use Bean Tins to make Kort Nozzles...
I suggested that they could be used to make Korts in a Lower Budget build...
All my tugs are built for Tug-Towing and have been fitted with proper Factory Made Korts...

...Best Regards...Norry...
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: andywright on February 13, 2010, 08:51:36 pm
I would buy a MMM kort, and shape the blades to fit, it is possible to do this by hand or with a dremel, bare in mind to keep the prop balanced, it you bought the Kort you could use this as the template,
Andy
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: craftysod on February 13, 2010, 09:11:16 pm
Get a kort from MMM and just sandpaper a couple of mill out of it 
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: HS93 (RIP) on February 13, 2010, 09:16:58 pm
what make off prop is it ? and what part of the world are you in ?  ( roughley)

Peter
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: captain ron on February 13, 2010, 10:11:51 pm
What about a plastic beaker.It is tapered so you could remove a section anywhere along its length to vary the diameter.You could also use it as a mould to make your own.Tupperware also do tapered storage containers that would probably suit.

Ron
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: poll on February 14, 2010, 09:14:57 am
You could try the sleeve that couples the 68mm pipes together.

John
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: DARLEK1 on February 14, 2010, 01:39:17 pm
A plant pot? There has got to be one the right size somewhere!
 Paul... :-)
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: BigAde on February 14, 2010, 02:26:01 pm
WoW what a massive response!

Sorry I cannot reply to all of them but here goes:

I got my prop and swiftly went into my kitchen cupboards and found said bean tin and WOW they are perfect size BUT then thought on, If i cut the top and bottom off it would then be too flimsy, putting fiber glass around it would be a pain to sand to the correct shape!

I tried finding a 68mm pipe fitting which should be bigger but could not find what I needed for the job of the correct size, I might have to go to Jewsons!

I am going to look in ASDA for a plastic cup which might just well do the job!!! Excellent idea!!!!!!

I dont fancy buying a Kortz from MMM as this boat was ment to be a budget build and so far I have probably spent the best part of £150 just trying to get a running hull with no decking or super structure!

I am trying to get this boat running for the Ellesmere Port boat show in a few weeks so I have a second tug for towing!!!

Right I am off to ASDA!!! keep you all posted
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: portside II on February 14, 2010, 05:01:51 pm
Just going back to fitting the props in mmm korts , i had the same problem with a 90mm prop and a mmm kort .
There was an idea of pitting the prop in a lathe or drill and trying to machine some material off , this can be done as i did it by putting the prop on a shaft and either using a drill or a lathe if you have one , and a piece of emery/glass paper to reduce the diameter .
This is an easy job and within 5 mins of stop and starting the prop was a good fit with ablut 1mm clearance .
it worked for me.
daz
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: BigAde on February 14, 2010, 08:28:40 pm
Well my trip to ASDA could not have gone better! A small plastic pot exactly 74mm and for only 80p. This kortz must have cost me about £3 in total!!!

Title: Re: BIG MISTAKE! What an idiot i am!
Post by: captain ron on February 14, 2010, 10:56:22 pm
Fantastic glad you got sortied.Thats what the forums about.we're all here to help.

Ron
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: Den the tug on February 17, 2010, 05:55:57 pm
Hey Troops,
Friend of mine made korts out of yoghurt tubs, skined with balsa and sealed.
 Absolutly brilliant, the power produced from the car heater motor to the 70 mm prop beats my twin 850 motors to 40mm ready made props and korts.
Thats the way Ill go next time.
Den :-))
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: chrise on February 18, 2010, 10:50:21 am
Well my trip to ASDA could not have gone better! A small plastic pot exactly 74mm and for only 80p. This kortz must have cost me about £3 in total!!!





Are you planning a bottom bearing & to shorten the nozzle so that it is not quite as vulnerable?
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: andywright on February 18, 2010, 04:48:45 pm
Hey Troops,
Friend of mine made korts out of yoghurt tubs, skined with balsa and sealed.
 Absolutly brilliant, the power produced from the car heater motor to the 70 mm prop beats my twin 850 motors to 40mm ready made props and korts.
Thats the way Ill go next time.
Den :-))

Large props are allways more efficient than small props, I used a single 70mm on my Nangee rather than twin 55mm. She steers brilliantly, especially as the Kort is steerable.
Andy
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: andywright on February 18, 2010, 04:55:13 pm


Are you planning a bottom bearing & to shorten the nozzle so that it is not quite as vulnerable?

There will be less drag on a shorter Kort, both from moving through the water and also from the thrust of the water travelling through the Kort, modern day korts are very short. I would go to half or less. And fit a bottom bearing to stop any vibration, and protect the kort from damage ie being knocked.
http://www.kortpropulsion.com/kort_nozzles_propellers.htm

I the one shown is fixed, but they are all similar.
Andy
Title: Re: BIG MISTAKE! What an idiot i am!
Post by: BigAde on February 20, 2010, 08:23:24 am
There will be less drag on a shorter Kort, both from moving through the water and also from the thrust of the water travelling through the Kort, modern day korts are very short. I would go to half or less. And fit a bottom bearing to stop any vibration, and protect the kort from damage ie being knocked.
http://www.kortpropulsion.com/kort_nozzles_propellers.htm

I the one shown is fixed, but they are all similar.
Andy

I was thinking about shortening the kortz, but I will see how it performs first then adjust with a dremmel later!