Prop rake measurements.

[Terry Keeley]

Been thinking about how to check rake angles and poking around found these two pictures:

I also contacted Lohring Miller as I knew he had some some work on this. I came up with the idea of dropping an indicator on the blade and moving it out a certain x-y distance until it reads zero again and using trig to calculate the angle:

After figuring out what Lohring did I mounted the prop vertically and just read the indicator and calculated it that way. This old "09" series has zero rake, the indicator doesn't move from tip to root:

Surprising (to me anyway) this 1667 had about 17*:

Turns out the 21 series I've been running on my SAW boat has about 12*. I might havta cut up a 16 series next.

 

[charles siler]

Terry man you making up for that lost time in the hospital! lol and make us all prop wizards. I like it and it gets the justice going...

 

[David Ashcroft]

Terry rake can be altered by cupping as you would know..

 

[Terry Keeley]

Terry rake can be altered by cupping as you would know..

Not sure about that? Cup increases the pitch for sure but the angle the blade is attached to the hub?

 

[David Ashcroft]

That is true however i believe slight cuppinig can can adjust lift which is associated with rake..

Mark.Andy.Aaron would know

 

[Eric Canto]

Adding cup ONLY, would not change rake. That being said, I'm sure that many people have inadvertently changed the rake at the spot they were modifying cup. Of course, some folks have done this on purpose as well.

 

[Eric Canto]

Terry, the 1667 should not surprise you. You watched me use 1667's that I borrowed from you lakeside to run almost 100mph with a heat race set up and worn out engine.

 

[John Beardslee]

Terry rake can be altered by cupping as you would know..

Not sure about that? Cup increases the pitch for sure but the angle the blade is attached to the hub?

If you cup the trailing edge it will increase pitch, if the trailing edge is perpendicular to the bore. If the trailing edge is slanted toward the rear it will increase the rake slightly. If you cup the edge of the ramp (edge from the tip down toward the nose you will increase the rake more and it's easier to see the results of increases in positive rake on the hull set up.

Thanks, John

 

[Terry Keeley]

Terry, the 1667 should not surprise you. You watched me use 1667's that I borrowed from you lakeside to run almost 100mph with a heat race set up and worn out engine.

Oh ya, forgot about that.

I just didn't expect an "old" heat racing prop from Tom Prezentka to be such high rake, thought higher rake angles were a new thing. I'll havta check some "old" 14 series and others now.

I was thinking about modifying my fixture to increase rake angle but instead I can just cut a 16 series to get 17*.

Or I guess I could just try one of Jim's "game changers", but that would be a buzz kill for all this fun.

 

[dwilfong]

Time to let go and move up to the present day.

It will only hurt if you do it slowly.

The 2717-19-38 is a killer prop.

 

[charles siler]

Time to let go and move up to the present day.

It will only hurt if you do it slowly.

The 2717-19-38 is a killer prop.

Remember it’s a hobby.

 

[shoboat]

Terry,

To make a 1600 Octura propeller have more rake you will have to cut the blades off the hub

and braze them back on at the rake angle you are looking for. Cutting the trailing edge of the

propeller does not change the rake of the propeller blade. Remember the rake angle is determined

by the angle that the blade is attached to the hub.

As far as the "buzz kill" just be careful breathing the metal in the molding and casting process.

The best thing about the newer ABC propellers is you can find out what diameter your set up likes

first, and then you can go up or down with the different pitch ratios that Jim offers. The correct

diameter on your set up is really one of the most important things you can do for better performance

out of your motor and pipe combinations.

Have A Fun But Safe New Year,

Mark Sholund

 

[Terry Keeley]

Terry,

To make a 1600 Octura propeller have more rake you will have to cut the blades off the hub

and braze them back on at the rake angle you are looking for. Cutting the trailing edge of the

propeller does not change the rake of the propeller blade. Remember the rake angle is determined

by the angle that the blade is attached to the hub.

As far as the "buzz kill" just be careful breathing the metal in the molding and casting process.

The best thing about the newer ABC propellers is you can find out what diameter your set up likes

first, and then you can go up or down with the different pitch ratios that Jim offers. The correct

diameter on your set up is really one of the most important things you can do for better performance

out of your motor and pipe combinations.

Have A Fun But Safe New Year,

Mark Sholund

Yup, roger that. I'd mount the 1667 in my prop fixture, cut out the hub, rotate the blades to the new pitch then braze in a new hub. Then it's off to the casting shop.

I'd have one of my "3362's" but with 17* of rake instead of the 12* of the 21 series.

Double roger that, it takes all of about 30 sec to melt the 55g of BeCu to do a prop, I have my 4500 CFM spray booth fan running and a good charcoal mask. My exposure is very limited.

You be careful with all those props you're finishing...

 

[Terry Keeley]

Time to let go and move up to the present day.

It will only hurt if you do it slowly.

The 2717-19-38 is a killer prop.

Remember it’s a hobby.

Where's the "like" button?

 

[Andy Brown]

Hi Terry,

Your top photo with the Straight edge is the correct way to find the rake line. The straight edge must fit flat into the blade to be on the rake line.

If there is concave or convex between the blade surface and the straight edge then the straight edge is not on the rake line. Just rotate the straight edge until it fits continuously flat against the blade. Some blades will not fit perfect against the straight edge but will have hills and valleys.

You could scribe a line along the straight edge once you find the rake line then use your indicator to measure the actual rake.

You will find that the rake of the Octura 1600 and 2100 are about the same.

I think you will be shocked to see how much rake they have. It is much more the 12 and 17.

The Octura V900 props have variable rake. You can move the straight edge from the trailing edge of the V900 to the leading edge

and see how much the angle of the straight edge must increase to stay flat to the blade as it moves forward to the leading edge.

I don't remember exactly off the top of my head, but the T.E rake is around 10 degrees and the L.E rake is around 35 or 40 degrees.

Keep up the good work Terry!

 

[Terry Keeley]

Hi Terry,

Your top photo with the Straight edge is the correct way to find the rake line. The straight edge must fit flat into the blade to be on the rake line.

If there is concave or convex between the blade surface and the straight edge then the straight edge is not on the rake line. Just rotate the straight edge until it fits continuously flat against the blade. Some blades will not fit perfect against the straight edge but will have hills and valleys.

You could scribe a line along the straight edge once you find the rake line then use your indicator to measure the actual rake.

You will find that the rake of the Octura 1600 and 2100 are about the same.

I think you will be shocked to see how much rake they have. It is much more the 12 and 17.

The Octura V900 props have variable rake. You can move the straight edge from the trailing edge of the V900 to the leading edge

and see how much the angle of the straight edge must increase to stay flat to the blade as it moves forward to the leading edge.

I don't remember exactly off the top of my head, but the T.E rake is around 10 degrees and the L.E rake is around 35 or 40 degrees.

Keep up the good work Terry!

Hey Andy:

I did check several areas of the blade to come up with an "average", the fillet in near the hub skewed the measurements and down near the tongue things got a little funky. When I got away from the root fillet tho I could move up and down along the hub almost anywhere and get the same indicator reading moving out radially along the blade.

I understand what you mean by placing a straight edge flat on the blade like in the first photo, but I found you could move the straight edge at that same angle along the hub and it will stay in contact for the most part. As you say there are little "hills and valleys" but on average near full contact is made. I guess this is true only if the rake angle is constant, I haven't looked at a variable rake prop like the "V" series.

Not sure how you're getting your numbers on the 16 & 21 series, Lohring & I both got about 12* for the 21's. The 1667 as I measured it had a bunch more rake and now that I can visualize it I can actually "see" it just looking at the prop.

 

[Tom Foley]

I tried to post a page from mercury marine on Rake showing their ET series props that I have several of that have varying rake but for some reason I cannot "paste " anything on this site or quote anything . Great topic Terry , Andy and others .

 

[Timbo Whalen]

I tried to post a page from mercury marine on Rake showing their ET series props that I have several of that have varying rake but for some reason I cannot "paste " anything on this site or quote anything . Great topic Terry , Andy and others .

Hi Tom- is this what you were trying to post?... attached... Also, Merc has a 6 part Prop School thread-

http://www.mercuryracing.com/prop-school-part-1-introduction/

http://mercuryracing.com/prop-school-part-2-terminology/

http://www.mercuryracing.com/prop-school-part-3-blade-rake/

http://www.mercuryracing.com/prop-school-part-4-blade-cup/

http://www.mercuryracing.com/prop-school-part-5-blade-efficiency/

http://www.mercuryracing.com/prop-school-part-6-slip/

Hope that helps-

tim

 

[Tom Foley]

Thanks Tim .

 

[Timbo Whalen]

Thanks Tim .

Anytime, Tom...hope it was of some help.

tim