changing propeller rake?

[Fastjeff57]

..."Surely to change rake you would have to take the blades off and weld them back on "

Yeah.... That's how I'm forced to make them for my Franken Mercs. Mr. Hill would gasps at doing it that way, but...

jeff

[phillnjack]

I dont think people realise that when a cast prop is cut through you can see material that is not exactly uniform.
it dont matter who makes them, if they are cast there Will be a certain amount of flaw in the material.
Now to take off a cast blade and change its rake it will have to be welded, the weld can be as strong in some
cases stronger than the original metal, but not the metal surrounding the weld.
This is where sometimes a repaired prop can fail, when the metal either side of the weld gives way due to
structure of the metal changing from its original cast process.
I can see its ok for a bit of the propeller being taken away, but to change the rake is to change the whole blade angle
not just the angle of the trailing edge.
This would also change the pitch completely and probably upset the whole way the blade works.

i dont think i would like to have a prop that has been through such a process unless it was done back at the
foundry where it was made.
They would be the only ones to understand the actual metalurgy of that particular propeller.

i think i would look for a different prop, as if your not happy with it now, you would have no way of knowing
what its gonna do once everything is completely changed.
and is it worth the risk of a dangerous propeller !!!!!!!!!!!!!!!!!!!!!



phill....

[Ron Hill]

I've actually never gone to Propeller School. O.F. Christner was one of the greatest outboard engine men of my time, but he called himself a welder. I frequently say, "I don't know that much about propellers! I do know if you get a good one, you keep it...You don't get a 'COPY' or one like it." We have recently spent almost 50 grand at Hill Marine Products trying to improve our already great Signature Propellers. We have known for quite sometimes, that of our propellers were better than others. For example, our 19 pitch Pleasure Five Blade will run the *** end off a Mirage 21 three blade. Out 19 is 2-3 MPH faster than a Mirage 21, holds the boat on plane better, keeps the boat on plane better and gets better gas mileage. Signature Pleasure 21 runs about the same as our 19, and planes slower. With our new machines we are getting so scientific we could go crazy!

Anyway, every propeller that Hill Marine makes and sells as Signature Propellers has been tested by either myself or my son, Chad Hill. The way we gets propellers to work, is with a hammer and grinders and test, test and test. My dad used lipstick on his props, we use a gps/computer....and "Seat of our pants". The hardest part for us has been once we find a very good propeller is making a very good copy. Our new scanner, has been doing some amazing stuff for us and CNC mills do some amazing mold making.

Getting to rake. I sold Rod ZaPF A 6 LITER INBOARD HYDRO PROPELLER PROBABLY 35 YEARS AGO. IT WAS A 19 SPLINE MERCURY CLEAVER WITH 15 DEGREES OF RAKE. GEORGE LOCKHART TOLD ROD HE COULD CHANGE THE RAKE TO 25 DEGREES. I told Rod to swend it to him, as I couldn't add 10 degrees of rake to that 15 degree rake prop. Well, when it came back it was 25 degrees. We looked it over and finally figured out that George had heated that prop to a very high temperature, then belt the blades. It was a beautiful job.

It wasn't long after that I started studying stainless steel and with the help of Tim Soares and his "ROSE BUD" tip on his torch, I started bending stainless steel every which way I could.

I started this post saying I'd never been to Propeller School and I haven't, but I define RAKE as the flat spot on the blade, when you straight edge goes through the middle of the prop shaft.

So, let's look at a couple of props:

1. Pictures 1,2 and 3...An old ZERO RAKE BRASS prop...As stated above somewhere, cup increases the rake... Flat part of the blade...zero degrees RAKE. Cupped are 10degree RAKE.

2. Pictures 4-5 Chopper, with 22 degrees of rake, roll the tip, goes to almost 30 degrees. Little boats usually need all the bow lift they can get, so I roll a bunch of RAKE in the blade...

3. Inboard three blade....Most inboard props, I see, just throw the water off the blade, I rolled this 11 X 15 left and it runs faster than almost every two blade inboard prop we've tested.

4. New "TOP SECRET" pitch gauge...$27,000 BUCKS WORTH........THIS MAY BE THE ONLY PICTURE OF THIS GAUGE, AS MY SON MAY KILL ME....

SO, CAN RAKE BE CHANGED? I MY OPINION, SURE! And you don't have to take the blade off to do it...

[Fastjeff57]

Thanks for confirming what I have suspected about the effect of rake. You sure know props!

Jeff (the beginner)

[phillnjack]

well the above statement seems a bit strange in many ways to me.
the way it reads is that by heating a blade you can just change the rake !!!!

well that dont exactly ring true.
Lets say a 13 inch diameter 21 pitch and 15 degrees of rake.

Now if you just heat the blade to change the rake where is the diameter comming from and the pitch !!!!!
the blade will obviously be totaly different from what it originaly was.
Blade area will surely be affected as well !!!!!!!!!!

By altering the rake you have to change each place the blade comes from(the hub) yes ?

So by heating the blade to the point of being able to bend it so much it would of structuraly changed the metal.
The metal takes on a certain hardness in the casting process, and re-heating will surely not keep its strength,
especially if its heated so much as to be almost liquified to change the rake.

Unless im not understanding the usa version of rake.

to me the rake is determined by where on the hub the blades are attached and where the tip of the blade is.
If a prop has its blade starting 1 inch back from rear of blade and is heated to take theis back further, the metal
must be molten metal to get to this state.
If a prop is cast it is molten metal to begin with, but by heating the metal a second time there is almost
an impossible chance of the metal ever being the same molecule structure from my understanding of metal and
its temper (hardness/flexibilty).

Every piece of metal that is cast will have a flaw somewhere,it might be very small and it could be pretty bad
depending on the care and metals used in the casting process.
But to weld a cast prop you can never tell how good the surrounding area is without x-raying the metal for the
porous state of the metal before and after the welding has taken place.

this is my view on welding cast metals, maybe ive been tought about welding and molten metals completely wrong.

just my opinion.

phill

[Fastjeff57]

As cast stainless steel is not that hard, so heating it up will not remove much (if any) hardness. Unless overheated, the metal will return to its original state.

Jeff

[phillnjack]

Ive just read the ron hill post above
it seems his version of propeller rake and my version of propeller rake are totally different.

All the prop books ive ever read and every picture ive ever seen about rake explains its the angle of the blades.
Nothing at all to do with cupping a blade.
cupping increases pitch not rake.
To put it in simple terms, Cupping to my mind is realy just a massive amount of pitch in a very small area on
the trailing edge of the blade.
this must be where some parts of the usa is totally different to the rest of the world.
obviously two different languages on props.
now you see why i said you have to take the blades of the hub, or atleast move them on the hub.


phill

[phillnjack]

As cast stainless steel is not that hard, so heating it up will not remove much (if any) hardness. Unless overheated, the metal will return to its original state.

Jeff .................................

No that is wrong, as soon as you apply heat to any metal you will change its molecular structure,and hardness.
not always a dramatic amount,but it will change for sure.
Sometimes certain metals are taken to particular temperatures and then go through a hardening process.

Now if the stainless prop has not gone through any process of hardening the cutting edge just how good is it.


phill

[Ron Hill]

I've been told, that stainless doesn't change much unless you heat it for a long time.

Pop Smith used to change my 6 3/4 Kamics to 7 inches by heating them an "DRAWING THEM". Pop ran a heat treating forge before he became THE MASTER PROPELLER MAKER. Pop Smith added a ton of rake to my runabout wheels, until I built my own boats. Then, I ran ZERO rake props.....I was fast a hell, but always out of control!

Like anything, getting your "DUCKS" lined up helps. If you have you pitch block ready, you heat the whole propeller and bend it, maybe with a press to the shape you want. If you figure you have changed the metal's structure, you can re heat treat.

I'm sorry my pictures weren't clearer, but holding the rake gauge, the prop and the camera ain't easy.

Pitch is how far a screw moves with one turn...(raise over run). Rake is the angle that the blade is in relationship to the hub. It has nothing to do with pitch!

ADD:

Most of the heat treating we do for propellers is to make them softer, not harder. As cast is about as hard as you get. Solution aneal/aging is to soft props. A soft prop has mor elongation, meaning it will bend before it breaks!

[Bill Van Steenwyk]

I knew a guy one time, used to ask his wife for sex. When she would say yes, he would argue with her and tell her she really did not want any.

End result, he got very little of what he was asking for, especially when he called her stupid and thick for answering him.

He soon learned how to both ask her for a favor, and get what he asked for without offending or running the risk of being "cut off".