Prop Technical Discussion

[Marty Davis]

I added a post to another specific post and thought that we should start a new thread.

APPLES TO APPLES

Let's talk on the same level with pitch measurement.

I use a Steve Woods Pitch Gauge and the way that I measure my props is with the First and Second Steps on the gauge. On mine the first step is .072" and the second step is .134". This gives me the cup and the root pitch further down the blade. For my H32 the measurements are 8.25 degrees at .134" and 3.75 degrees at .072" Oh, I forgot, I use .134" on the tongue area of the prop.

Not quite sure why the blocks on my pitch gauge were different that what Steve indicates on the instructions, but mine are .072" and .134" on the first 2 steps. Guess it would be good for those using that gauge to measure their steps.

What do others do in their measurement systems? If many others use a different method, please post and I will try to give my measurements in the consensus method.

It sure would be nice if most people used the same system. I am willing to change if I am doing it different than most.

Andy, Mark ?

 

[Marty Davis]

Variance between Root Pitch (COB) and Cup (Pitch at the Tips)

I have often wondered what the best props that people run have, as a percentage relationship between Root Pitch and Cup.

For example I bought a blade at Charleston a couple years ago that was a prop that Andy had made and modified for Bob Bjorkman (his Borther-in-law) who was a very good boater in Florida over the past 10 years or so. This prop was documented using a Wood Prop Gauge when I was doing a lot of documentation of my best props.

I put this prop on my new Cougar 67 and I am convinced that it was running at or slightly over 90. I have had a lot of props over the years and this one was special. It had a cup to root pitch increase of 15.4%. Looking at my best props for .21's, .45's and .67's I do not have any props that have that high a ratio (close but not that high). Most of my best props are in the 9 - 11% range.

Would be interested in hearing what others have found in this relationship.

I helped a friend get his new .21 JAE ready for Charleston and we tested probably a dozen props. 6 were at 80mph or better. These props had a ratio of 8.5 - 14 (S15 was only one at 14, that I ran 86 with on my heat race boat several years ago). All of this is making me believe that I have left a lot on the table with props by not using enough progression between root pitch and cup.

The super prop that Andy did for his B-I-L had a fairly modest root pitch and a ton of tip pitch (and a ratio of over 15%).

I really like props that will mill well and have great acceleration off the turns and wonder if this high a ratio is something that takes away from that a ton.

I guess a conclusion of methods discussed in the first post in this topic is necessary, in order to be able to compare this ratio. Guess we need to address that, BEFORE the percentage increase in pitch can be analyzed.

I am SURE that for SAW that these ratios will be different..... ???

Thoughts...... :blink:

 

[Marty Davis]

I guess FIRST OFF, how do you measure root pitch (COB - center of blade) and Cup?

Lets assume for this discussion that everyone is using the Woods Pitch Gauge so that we can compare notes using the same device.

I realize that several use the Depth Micrometer Gauge, but we can discuss that seperately.

 

[mtruex]

I added a post to another specific post and thought that we should start a new thread.

APPLES TO APPLES

Let's talk on the same level with pitch measurement.

I use a Steve Woods Pitch Gauge and the way that I measure my props is with the First and Second Steps on the gauge. On mine the first step is .072" and the second step is .134". This gives me the cup and the root pitch further down the blade. For my H32 the measurements are 8.25 degrees at .134" and 3.75 degrees at .072" Oh, I forgot, I use .134" on the tongue area of the prop.

Not quite sure why the blocks on my pitch gauge were different that what Steve indicates on the instructions, but mine are .072" and .134" on the first 2 steps. Guess it would be good for those using that gauge to measure their steps.

What do others do in their measurement systems? If many others use a different method, please post and I will try to give my measurements in the consensus method.

It sure would be nice if most people used the same system. I am willing to change if I am doing it different than most.

Andy, Mark ?

marty,

my steps are different also, .068 .062 .060 .059 i use the 1/16 step for all my measurements becuase the chart is calculated for 1/16..

not sure if its the right way or not, but at least its consistent for me...hard to compare numbers though like you say..i know i have got props from others and i get different numbers when i measure them..

i guess all that really matters anyway is that you have your own consistent way of doing it..

 

[Marty Davis]

I added a post to another specific post and thought that we should start a new thread.

APPLES TO APPLES

Let's talk on the same level with pitch measurement.

I use a Steve Woods Pitch Gauge and the way that I measure my props is with the First and Second Steps on the gauge. On mine the first step is .072" and the second step is .134". This gives me the cup and the root pitch further down the blade. For my H32 the measurements are 8.25 degrees at .134" and 3.75 degrees at .072" Oh, I forgot, I use .134" on the tongue area of the prop.

Not quite sure why the blocks on my pitch gauge were different that what Steve indicates on the instructions, but mine are .072" and .134" on the first 2 steps. Guess it would be good for those using that gauge to measure their steps.

What do others do in their measurement systems? If many others use a different method, please post and I will try to give my measurements in the consensus method.

It sure would be nice if most people used the same system. I am willing to change if I am doing it different than most.

Andy, Mark ?

marty,

my steps are different also, .068 .062 .060 .059 i use the 1/16 step for all my measurements becuase the chart is calculated for 1/16..

not sure if its the right way or not, but at least its consistent for me...hard to compare numbers though like you say..i know i have got props from others and i get different numbers when i measure them..

i guess all that really matters anyway is that you have your own consistent way of doing it..

Martin:

Have you compared your COB pitch vs Cup on your best props? As a percentage increase? If not, I think you would be interested in the ratio.

 

[shoboat]

Guys,

The Trailing Edge CUP is measured at .7 radi on the T.E. or 70% up from the hole.

The Center Of Blade Pitch is measured in a few spots and averaged together.

If you want to get close on C.O.B. go up from your cup measurement aprox. 1/4"

depending on the size of the propeller. This should be pretty close to the charts.

How did you measure your steps?

I have three of Steve's gauges and all three measure the same.

1st step is .192"

2nd step is .255"

subtract the difference = .063"

1/16 = .0625" pretty close for me!!!

Marty,

The pitch progression topic is a very interesting one.

I Will Check Back Later,

Mark Sholund

 

[mtruex]

Guys,

The Trailing Edge CUP is measured at .7 radi on the T.E. or 70% up from the hole.

The Center Of Blade Pitch is measured in a few spots and averaged together.

If you want to get close on C.O.B. go up from your cup measurement aprox. 1/4"

depending on the size of the propeller. This should be pretty close to the charts.

How did you measure your steps?

I have three of Steve's gauges and all three measure the same.

1st step is .192"

2nd step is .255"

subtract the difference = .063"

1/16 = .0625" pretty close for me!!!

Marty,

The pitch progression topic is a very interesting one.

I Will Check Back Later,

Mark Sholund

mark,

i also measure cup at 70% , i measured the height of each step on the guage, i only use the one that is .0625 or 1/16

 

[Marty Davis]

Guys,

The Trailing Edge CUP is measured at .7 radi on the T.E. or 70% up from the hole.

The Center Of Blade Pitch is measured in a few spots and averaged together. (Can't we arrive at something that is more fixed? OR, are you saying that the 1400 and 1600 series props are true pitch and it doesn't make any difference where you measure COB since it is all the same pitch?)

If you want to get close on C.O.B. go up from your cup measurement aprox. 1/4"

depending on the size of the propeller. This should be pretty close to the charts.

How did you measure your steps? Same as you did, subtract the first one from the second one and third one less the first one.I have three of Steve's gauges and all three measure the same.

1st step is .192"

2nd step is .255"

subtract the difference = .063" (Difference for me is .069" and it makes a lot of difference in the pitch.)

1/16 = .0625" pretty close for me!!!

(Difference on 2nd Step is .134")

Marty,

The pitch progression topic is a very interesting one.

I Will Check Back Later,

Mark Sholund

 

[Marty Davis]

Guys,

The Trailing Edge CUP is measured at .7 radi on the T.E. or 70% up from the hole.

The Center Of Blade Pitch is measured in a few spots and averaged together.

If you want to get close on C.O.B. go up from your cup measurement aprox. 1/4"

depending on the size of the propeller. This should be pretty close to the charts.

How did you measure your steps?

I have three of Steve's gauges and all three measure the same.

1st step is .192"

2nd step is .255"

subtract the difference = .063"

1/16 = .0625" pretty close for me!!!

Marty,

The pitch progression topic is a very interesting one.

I Will Check Back Later,

Mark Sholund

mark,

i also measure cup at 70% , i measured the height of each step on the guage, i only use the one that is .0625 or 1/16

OK, we can agree on the cup as being 70% and use the small first step (supposed to be 1/16"). That is what I do.

For the COB pitch, I have just been using the 2nd step which DOES include the cup since I set at the extreme bottom of the blade. (on upside down)

 

[Marty Davis]

For the pitch progression analysis I used the second step (cup) at 70% and then measure with the third (what I call COB) step at 70% and then calculate the progression in just that area. Might be even more revealing to use the fourth step and compare to 2nd and 3rd step pitch.

We KNOW that the smoothness of the change in pitch is SUPER IMPORTANT to cavitation so I bet that this progression analysis will show problems in the progression that could cause cavitation. It will also show some other important things like launchability and acceleration by having lower COB pitch and higher cup. IF YOU DON'T CREATE CAVITATION BY HAVING TOO MUCH PROGRESSION. That is really the reason that I want to do this analysis. I have found that my best props have lower COB and higher cup but not enough progression to cause cavitation.

Smoothness of the progression is critical too, but making the assumption that you have made the contour VERY smooth then we can analyze how much porgression you can use effectively.

 

[shoboat]

Marty,

Take .006" off the bottom of your disc and that should zero you in.

I am sure Steve will do it for you if needed.

I am not a big fan of T.E. cup as it does kill RPM and that does hurt

the ultimate speed of the boat and the acceleration rate.

I think you need to work more on the middle of the blade to increase

the C.O.B. and then I think you will have less progression and I think

that will work better on hydro set ups. The Monos I think like more

pitch progression in the blade than the hydros do. I can pass on some

results with the Mono pitch progression. As we increased the C.O.B. and

the T.E. cup together we started to go a whole lot faster with the 1614/3.

I can go back though my propeller boxes and measure the progressions on my

best hydro propellers and see what I find. I remember a few years back I had

a range that I liked to stay in with the progression rate on my hydros, I will

have to look back though some notes to find it all. I have been working on the

new propellers for the twin set ups and I have found the higher COB really helps

the big blocks with the acceleration and top end.

Thanks,

Mark Sholund

 

[shoboat]

Marty,

Maybe Andy will share his article that he wrote years ago on your forum?

It covered pitch progression quite well if I remember correctly?

Thanks,

Mark Sholund

 

[Marty Davis]

Marty,

Take .006" off the bottom of your disc and that should zero you in.

I am sure Steve will do it for you if needed.

I am not a big fan of T.E. cup as it does kill RPM and that does hurt

the ultimate speed of the boat and the acceleration rate.

I think you need to work more on the middle of the blade to increase

the C.O.B. and then I think you will have less progression and I think

that will work better on hydro set ups. The Monos I think like more

pitch progression in the blade than the hydros do. I can pass on some

results with the Mono pitch progression. As we increased the C.O.B. and

the T.E. cup together we started to go a whole lot faster with the 1614/3.

I can go back though my propeller boxes and measure the progressions on my

best hydro propellers and see what I find. I remember a few years back I had

a range that I liked to stay in with the progression rate on my hydros, I will

have to look back though some notes to find it all. I have been working on the

new propellers for the twin set ups and I have found the higher COB really helps

the big blocks with the acceleration and top end.

Thanks,

Mark Sholund

Interesting....

What got me started in this recent analysis was a prop that I bought that Andy did for his Borther-in-law. Probably a very special prop.

It ran 90 mph on my new 67 boat and launched well and milled well, etc.

Funny thing the COB pitch was fairly low and the pitch progression VERY high 10%+

Prop was amazing... I say was because it got trashed in Charleston. Good thing though, I had documented it thoroughly and can duplicate it fairly easily.

What I am thinking is that pitch progression is an area that can yield BIG dividends. The way that I have been pitching props for a long time is similar to this prop. I have always wanted a prop that would launch easily, mill well and run really fast. That is a tricky thing to accomplish.

I bent a couple props for a twin 91 (for Larry Beals) that were exceptional and had all these characteristics. The way that I did them was to use low COB pitch and high progression.

This is a neat area that deserves careful analysis and testing.

 

[Tom Foley]

QUOTE

I put this prop on my new Cougar 67 and I am convinced that it was running at or slightly over 90

It ran 90 mph on my new 67 boat and launched well and milled well, etc.

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Radar Gun or GPS ?

 

[Ian Inverarity]

OK, we can agree on the cup as being 70% and use the small first step (supposed to be 1/16"). That is what I do.

Why is 70% diameter used to measure cup? When cupping at points further out is the cup set to the same as set at 70%? Less? More? Has there been any testing to establish the diameter at which cupping is most effective?

Ian.

 

[Terry Keeley]

Interesting....

What got me started in this recent analysis was a prop that I bought that Andy did for his Borther-in-law. Probably a very special prop.

It ran 90 mph on my new 67 boat and launched well and milled well, etc.

Funny thing the COB pitch was fairly low and the pitch progression VERY high 10%+

Prop was amazing... I say was because it got trashed in Charleston. Good thing though, I had documented it thoroughly and can duplicate it fairly easily.

What I am thinking is that pitch progression is an area that can yield BIG dividends. The way that I have been pitching props for a long time is similar to this prop. I have always wanted a prop that would launch easily, mill well and run really fast. That is a tricky thing to accomplish.

I bent a couple props for a twin 91 (for Larry Beals) that were exceptional and had all these characteristics. The way that I did them was to use low COB pitch and high progression.

This is a neat area that deserves careful analysis and testing.

Just curious, what did that prop start life as?

1662? H-32? 1667?

 

[shoboat]

Ian,

Most propeller information available out there will tell

you that .7 radi is where most of the water comes off the blade.

You can cup anywhere you would like, but @ .7 is the most effective.

Ian,

Do you ever Google propellers? and read any technical articles?

HydroComp.com is a good one and there are all kinds of articles on

cupping.

Happy Reading,

Mark Sholund

 

[Chris Wood]

Marty,

Take .006" off the bottom of your disc and that should zero you in.

I am sure Steve will do it for you if needed.

I am not a big fan of T.E. cup as it does kill RPM and that does hurt

the ultimate speed of the boat and the acceleration rate.

I think you need to work more on the middle of the blade to increase

the C.O.B. and then I think you will have less progression and I think

that will work better on hydro set ups. The Monos I think like more

pitch progression in the blade than the hydros do. I can pass on some

results with the Mono pitch progression. As we increased the C.O.B. and

the T.E. cup together we started to go a whole lot faster with the 1614/3.

I can go back though my propeller boxes and measure the progressions on my

best hydro propellers and see what I find. I remember a few years back I had

a range that I liked to stay in with the progression rate on my hydros, I will

have to look back though some notes to find it all. I have been working on the

new propellers for the twin set ups and I have found the higher COB really helps

the big blocks with the acceleration and top end.

Thanks,

Mark Sholund

Interesting....

What got me started in this recent analysis was a prop that I bought that Andy did for his Borther-in-law. Probably a very special prop.

It ran 90 mph on my new 67 boat and launched well and milled well, etc.

Funny thing the COB pitch was fairly low and the pitch progression VERY high 10%+

Prop was amazing... I say was because it got trashed in Charleston. Good thing though, I had documented it thoroughly and can duplicate it fairly easily.

What I am thinking is that pitch progression is an area that can yield BIG dividends. The way that I have been pitching props for a long time is similar to this prop. I have always wanted a prop that would launch easily, mill well and run really fast. That is a tricky thing to accomplish.

I bent a couple props for a twin 91 (for Larry Beals) that were exceptional and had all these characteristics. The way that I did them was to use low COB pitch and high progression.

This is a neat area that deserves careful analysis and testing.

Marty,

when it had low CENTER OR BLADE pitch was the leading edge greater than the trailing edge?

chris

 

[Mike Larson]

Great Post!... Hit at exactly the right time..... 70% is just the unwritten "rule of thumb" we all, currently use, with that area of the blade in theory, doing the grunt work..... Mark has taken it down to 50-55 i'm sure in the past... results maybe?... and why?..

I had, a paper by possibly Brian Callahan, that had some serious water dynamics and formulas per prop testing on it given to me by K Bulifant years ago, maybe it's around in ether limbo..... I cant regain it, along with the other 10 years of literature I had compiled.. so... graciously, I appreciate the information here easily.

Mysteriously, I had completed rough in, and was starting to install cup in a few....

Apples to Apples: Marty, explain to figures: 3.1 2.8 2.4 2.1-(stock) with nominally a .3 jump,across the span... what %.... Formula for the lost?

Bad thing is, this is a tunnel hull prop, and with possible hull characteristics entering into the equation, it is almost guaranteed to cavitate and does, until that fateful moment the planet aligns and we're off...( tunnel gaining air, and balance, possibly) changing the percentage possibly over the span might be interesting....

Throw an orange in: best hydro propellor ( Mark did years ago) 3.4 3.1 2.8 2.4..... same nominal .3 progression?.... for the most part. Again on theory, maybe that allowing it to drop to stock easing the water off (back cut, aiding also?)....and yet easier reentry for another bite of water......

The current "ski style" hydros have amazed me, factly, as pulling previously thought off the chart cup and progression thought on other traditional style hull testing, it's fun to search out, and have a boat ask for more...( I didnt find it last year!)looking into percentage may allow me use of a few of the "duds" sitting around.....

Progression is just another deal, along with back, and barr cutting..... knowing the effects say of higher progression, possibly, would you see the need to in theory: back cut more with the higher leading edge progression?.. barr cut more, if you have serious boat pukin' cup on the trailing?..... ( hopefully the nomenclature is correct)..... where does overall diameter come into play?

I watch thrust cone,motor harmony, and overall speed gain.... searching for THE ONE, and then.... the machine will aid me to take it up from there... maybe.... 2 1/2 months to wait, and a beryllium pile. Only the water, the boat, and inherent variables, will tell.

Mentor and classic: Are you, testing to burn nitro, or are you making changes and learning?

Thanks for the winter stimulation... lets keep it going.... Mike

 

[Marty Davis]

Interesting....

What got me started in this recent analysis was a prop that I bought that Andy did for his Borther-in-law. Probably a very special prop.

It ran 90 mph on my new 67 boat and launched well and milled well, etc.

Funny thing the COB pitch was fairly low and the pitch progression VERY high 10%+

Prop was amazing... I say was because it got trashed in Charleston. Good thing though, I had documented it thoroughly and can duplicate it fairly easily.

What I am thinking is that pitch progression is an area that can yield BIG dividends. The way that I have been pitching props for a long time is similar to this prop. I have always wanted a prop that would launch easily, mill well and run really fast. That is a tricky thing to accomplish.

I bent a couple props for a twin 91 (for Larry Beals) that were exceptional and had all these characteristics. The way that I did them was to use low COB pitch and high progression.

This is a neat area that deserves careful analysis and testing.

Just curious, what did that prop start life as?

1662? H-32? 1667?

Terry:

I am not sure as all the markings were removed. It was a stainless prop that had a diameter of 2.425 and looks like an H32. Just a little smaller in diameter than an H32.