Prop Mods Questions

[goldendesign04]

I got a new assortment of props today, Thanks steve!
I bought a few just on the theory that I cant find the prop that I want so I will modd one to my specification. So that means I have a few questions;

1. When cutting down the overall diameter, is there a limit you can do this say for arguments sake a x632 can you take it down to 28/29 mm with out an adverse effects?

2. How do you calculate the new pitch of a prop after you reduce the diameter?

3. On a lifting prop like a 1732 can it be bar-cut or the like to reduce strain on the motor when spooling up?

Thanks for whatever input you can give
-Wayne

[goldendesign04]

Id also say if there are any sites out there that go over the specifics of mdding props an why they are done Id be appreciative to know.

-Wayne

[ReddyWatts]

http://www.rcprops.com/TechNotes/rcprop_tech_info.htm

http://rcboat.com/prop.htm

http://www.rbbi.com/folders/prop/propcalc.htm

http://sites.mercurymarine.com/portal/page?_pageid=126,48572,126_49259&_dad=portal&_schema=PORTAL

[domwilson]

Good Links.

This one will help too.

http://www.modelpowerboat.com/Improving_your_Propeller

[Flying Scotsman]

I got a new assortment of props today, Thanks steve!
I bought a few just on the theory that I cant find the prop that I want so I will modd one to my specification. So that means I have a few questions;

1. When cutting down the overall diameter, is there a limit you can do this say for arguments sake a x632 can you take it down to 28/29 mm with out an adverse effects?

2. How do you calculate the new pitch of a prop after you reduce the diameter?

3. On a lifting prop like a 1732 can it be bar-cut or the like to reduce strain on the motor when spooling up?

Thanks for whatever input you can give
-Wayne

Question 1. If all and that is the key, dimensions are reduced proportianly. Should not be a problem
Question 2. If done properly. See above. The same formula applies ie 1.4 or 1.6 X diameter.
Question 3. I have no idea.
Douggie

[lonewolf]

Im not sure where you knowledge level is with props, the basic bsp is pretty basic. After that there are mild cuts that can be done fairly easy. Next is bending and cupping at this point it get pretty involved. You will need a pitch guage clay Pliers balls mallets callipers. and a few pads of paper to keep track of each adjustment. There is a reason that there are only a few "good" prop guys out there. Now if your experienced in prop working and need tools i can help there. I appologise if you are experienced in props, and already knew this.... Id be glad to help i might learn something... Dave

[goldendesign04]

Thanks for all the answers guys. It really helps me gain a better understanding of working with props of this size.

lonewolf Ive worked on large props for classics ie large 40+ wood chriscrafts, egg harbours an the like when I worked for a boat dock in MI on the clinton river, but that was all large dia 4 an even 5 bladed submerged drives an as you can guess completely irrelevant to surface drive high speed applications. BUT, an theres always a but... I do have quite a selection of handy tools I could use given my current proffesion as a custom jeweler. I have plenty of pliers with ball an cup nylon ends, a small forming mallet in brass, nylon, and rawhide as well as a few nifty dapping tools that would come in handy. Plenty of clays, waxes, polshes an a great diamond hone set as well as a powered dia. hone wheel.
Pitch guage I have as well as a plethora of different calipers.
So I believe I have the tools an the capability to form the metal (since metal forming is a daily occurance) I just need a few books or sites that get a little more indepth in the science of forming props an expected results.
Ive even been toying with designing an casting my own props since I have those facilities available too me also. Been throwing around a few metals combinations that might yield a stronger cast thats also easier to sharpen an way less toxic. I could go into more depth but unless youve studied metalurgy and/or chemistry it can be a little daunting.

-Wayne

[goldendesign04]

dang I did ramble a bit...lol But thanks again all an if any of you could point me to a more indepth explanation of prop working I would be greatly appreciative

-Wayne

[domwilson]

Hey Wayne,

Try this link.

http://forums.radiocontrolzone.com/showthread.php?t=195465

[lonewolf]

I cant find the link but its to a site call shark racing team. I have found alot of info there and also a downloadable sheet with all the pitch ratios and hoe to make your own pitch guage I did works great cost less than 20$ to make.]
They also go into copying props casting. Alot of info there look around under the diy areas tips and hints.. Ill keep trying to get the link unless you have already found it. Best way to find out what makes a certain prop react a certain way mod it test it document mod again test again document lol
Good luck Dave

[obrien]

Cutting down the diameter won't change the pitch. The pitch should stay the same reguardless of diameter.

However, you can probably scale this theory down to our scale props.

On a full size boat, a 1" change in pitch will usually give a 200 rpm change on the motor.

1" change in diameter will have the same affect as a 2" change in pitch.

hopefully that makes sense.

Lest say you are running a 15" x 26" prop. Thats 15" diameter x 26" pitch
and the motor will pull that prop to 5000 revs.

if you go to a 15 x 27 that will change to 4800 revs

or if you go to say a 16 x 26, that should give you 4600 revs.

Now these numbers will certainly be effected by the slip rate and setup of the boat.