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[npomeroy]

I'll be looking for two 50mm props for my tug. I like brass/bronze as it looks the part. Locally I can get SAB brand which I don't see on an international search. I bought one already and it seems to be made with sheet-brass blades fastened between the end cone and a short sleeve: https://www.rcnz.co.nz/categories/boat-and-yacht-accessories/boat-propellers/sab-brass-3-blade-prop-50mm-m4-rh/
The blades bend easily. On a website it looks similar to the Raboesch brass props. Are they similar construction or cast?


Also there will be a L and R one and will need to reverse. Is a lock nut usually sufficient to prevent unwinding on reverse or is glue or solder used? I have a little gas solderer and could use that to melt solder into threaded join.


Cheers
Nelson

[ChrisF]

I have a Roboesh 3 blade and the blades are soldered on and is well made. It is only 30mm dia though and so no bend in the blades.

I'd be concerned about those SAB ones though. 50mm is still not a big dia and they shouldn't bend easily.

We are lucky in the UK that we have Prop Shop as well and theirs are cast. They do a great range - I guess postage would be a problem? Be worth inquiring though.

As regards retention a locknut is commonly used but on a bigger model you could drill and tap for a grub screw in the prop and file a flat on the prop shaft.

Chris

[npomeroy]

Thanks Chris. Those look good. Here we are reconciled to shipping costs from overseas.
N

[Akira]

You may want to look at George Sitek's props. They are right up there with the Prop Shop.http://gsitek-props.co.uk/

[npomeroy]

Thanks for the suggestions.

The GA drawings show 3-bladed props in the kort nozzles in which the blades are wide: they occupy a large part of the disc area, but have rounded tips. So the Prop Shop kort props are more square-tipped and do not show as available in 3-blade. It seems the "standard scale" prop shapes at both Prop Shop and George Sitek's are the nearest to the scale outline.

Although my ESC's seem to have good low-speed control, I am a bit concerned to not have too much thrust - i.e. to have realistic scale speed. Prop Shop show pitch figures that all seem about 1:1 to the diameter. Are any particular prop styles usually done with a finer pitch?

Cheers
Nelson

[roycv]

Hi just some info from the late Towboat Joe ex Towboat Captain and model maker of said boats.
He said that full size experience was that originally Kort nozzles had the squared off tips associated with the nozzles.  However, on the Mississippi and Ohio river systems there are many loose logs in the waterways.  With the squared off tip propellers the logs would jam up in the Kort.  He said that they reverted to round tip propellers as these would chew up a log and spit it out and not cause a hold up.

I had wondered why they pushed the barges rather than pull them.  The reason is simple as the original tow boats had stern wheel power which would have produced a backward surge of water straight into the barges, so they pushed them instead.
Regards
Roy

[Akira]

Nelson, I would not be concerned with too much power, just the opposite. It is easy enough, especially with the current radios in use, to dial down the thrust and speed.  Please also remember, that Kort nozzles are wonderful for increasing thrust in one direction, but when reverse is applied, the props are much less efficient than than non nozzled props. The only way around that is to use a Z drive with a nozzle, being able to swivel 360 degrees.

[npomeroy]

Thanks for the comments all.  I've ordered a pair of 2.2" "Standard Scale" 3-bladed from Prop Shop. The international postage was quite reasonable, and I'm in no hurry. See my other thread here https://www.modelboatmayhem.co.uk/forum/index.php/topic,69311.0/topicseen.html for the project.

Nelson