Speedmaster 20 mono, good day testing

[Luca Gray]

Mark

did you do the propeller for Phil,

to work this out,

cheers Luca

 

[Ian Inverarity]

Phil and Ian,

That is correct.

Simple math with the speed and pitch of the propeller.

Mark Sholund

Thanks Mark.

 

[Marty Davis]

Phil and Ian,

That is correct.

Simple math with the speed and pitch of the propeller.

Mark Sholund

Mark:

RPM sound resonable.

Please tell us how you arrived at the slip percentage and also what are you baseing the pitch on (root pitch, toungue pitch or tip pitch)?

We would be interested in the math for this conclusion. I have been working for years to define the perfect formula for speed/pitch/slip. Didn't think that it was possible. I thought that the slip variable was too hard to calculate since it is so dependnt on the boat/setup combination, etc.

 

[shoboat]

Marty,

On my web site under Prop Charts look at the propeller calculator.

I did the math and figured aprox. 15% slippage on an X-437/3 with 2.072" pitch

with a gear ratio of 1 and the speed of 58.6MPH radar from the testing session.

I think that is pretty close to what mine sounds like, and I have pipes that are very

close to an RPM spec.

Web site: http:www.props4u.com/prop_chart.htm

Thanks For Reading,

Mark Sholund

 

[Andy Brown]

My prop Math say's 37,000 rpm.

After working with the Eagle Tree system, I think Terry Keely would agree with me.

 

[El Zorro]

My audio tach says Andy is closer to the real number. I'm getting around 38,000 to 39,000. The tach I have is made from Radio Shack parts but was calibrated on equipment where I worked at. While it is almost 30 years old, I have checked it at the lake with John Finch's and Steve Speas' tachs on their gas boats and it is accurate. I have a drawing and a parts list for this in my files somewhere and it only cost $20.00 or so to build one. I'm sure the parts are a lot more now. I'll have to check on that. Great running boat, Phil! I didn't mind losing US-1 this year to a great running ( and well driven ) boat like this one is. Congratulations again!

Dick Tyndall

 

[Andy Brown]

Dick, Are you taking the on coming 58 mph doppler into account?

Even so, depending on how the X437/3 is worked/finished, 39K is very probable.

I've seen the MAC 21 buggy engine turn 45,000 many times and live.

On-road .21's turn 39,000 to 45,000 routinely.

 

[shoboat]

Fellas,

I doubt that pipe is capable of 37,332 RPM with 20% slippage at 58.6 MPH in a mono.

I think three blades have more efficency than you think. It really doesn't matter the boat

was going quite well.

I can tell you that a friend of mine has tested a 21 mono at over 70 MPH and he is turning

around 37,000 RPM with a three blade also.

Have Fun Testing,

Mark Sholund

 

[Andy Brown]

Mark, you say that as if 20% is not possible and that you have confirmed data about a 7.25" Copper pipe on an engine that you only know the Brand name and nothing of the internals. How do you know the prop slip is 15%? How do you know the X437/3 has 2.072" of pitch? Because the Octura prop chart says so? HA! Now that's something to laugh about!!!

Ever measure an Octura 2260? The Octura chart claims 5.192". However, the COB 6.2" and the trailing edge of that prop is 8.65".

Just a couple of weeks ago Terry Keely posted result of his STOCK CMB 67. 28,000 rpm on his Eagle Tree system! That's more than most would believe. Terry even mentioned about needing to rethink effective prop pitch.

 

[shoboat]

Andy,

I guess you just know it all.

I am entitled to my opinion here in America as are you.

We have tested quite extensively, and I know by our findings that the range of slip on a three blade can vary.

I would think the slippage is between 15% to 20%. And I never said that 20% was not possible, I just think

that set up is not making the RPM that you guys think it is. You thought about 37,000 RPM, and did you modify

the engine? We do not know the specs on the propeller, but I have measured plenty just like you, and I would

think the pitch is pretty close to what Octura says it is if it is a stock X-437/3. I measured five of them today and

they were all pretty close to that range.

We are talking about a 5% slippage difference get real.

You seem to know it all, so I guess we should just ask you all the questions.

Thanks For Reading,

Mark Sholund

 

[Ian Inverarity]

In this case the Doppler effect can be calculated with reasonable accuracy. At 75 degrees air temp the speed of sound will be about 743.4mph. With an approach speed of 58.6mph, an observed 38000rpm would work out to 35005 rpm at the engine. 39000rpm observed would be 35926rpm at the engine.

 

[Ian Inverarity]

Taking this one step further, with a radar speed of 58.6mph, observed RPM of 38000 to 39000 corrected for Doppler effect to 35005 to 35926rpm, the effective pitch or actual advance of the prop would be 1.77" to 1.72" respectively.

 

[Andy Brown]

Very good posts Ian. I based my 37K "guesstimate" on effective pitch of between 1.65" (36,435 rpm) and 1.7" (37,540 rpm). That's just from what I know about the X437/3 in general and of course the one on phil's boat is an unknown variable.

 

[Andy Brown]

Andy,

I guess you just know it all.

I am entitled to my opinion here in America as are you.

We have tested quite extensively, and I know by our findings that the range of slip on a three blade can vary.

I would think the slippage is between 15% to 20%. And I never said that 20% was not possible, I just think

that set up is not making the RPM that you guys think it is. You thought about 37,000 RPM, and did you modify

the engine? We do not know the specs on the propeller, but I have measured plenty just like you, and I would

think the pitch is pretty close to what Octura says it is if it is a stock X-437/3. I measured five of them today and

they were all pretty close to that range.

We are talking about a 5% slippage difference get real.

You seem to know it all, so I guess we should just ask you all the questions.

Thanks For Reading,

Mark Sholund

Mark,

You said 35,100 rpm. (your opinion)

I then said 37,000 rpm. (my opinion)

Then Mark you came back and said

Fellas,

 

I doubt that pipe is capable of 37,332 RPM with 20% slippage at 58.6 MPH in a mono.

 

I think three blades have more efficiency than you think.

So it seems you were opposing my opinion and promoting your superior knowledge of props and pipes.

Now you talk like 5% is not a big deal, but it puts the rpm at 27,300 as you mentioned. You said 37,000K is not possible. But at the same time you just said that 20% is possible. Are you confused?

Since you FIRST questioned my Opinion, I feel I am certainly entitled to question your opinion!

Mark, you are certainly entitled to your opinion as am I, and I will certainly be here to post my opinions. If you wish to counter my opinions I'm good with that. Just don't expect your counter to go unanswered.

 

[Ian Inverarity]

Very good posts Ian. I based my 37K "guesstimate" on effective pitch of between 1.65" (36,435 rpm) and 1.7" (37,540 rpm). That's just from what I know about the X437/3 in general and of course the one on phil's boat is an unknown variable.

Thanks Andy, the 38000 to 39000 observed rpm was from Dick Tyndall's calibrated audio tach reading, so your guesstimate was close! B)

 

[Ian Inverarity]

I can tell you that a friend of mine has tested a 21 mono at over 70 MPH and he is turning

around 37,000 RPM with a three blade also.

Have Fun Testing,

Mark Sholund

Mark,

70mph is impressive for a 21 mono! I presume that is a SAW boat? What pipe and engine?

Ian.

 

[Terry Keeley]

I think the differences of opinion here might be due to the many variables involved arriving at the numbers.

I've asked guys quoting pitch values what exactly they mean and everyone seems to have a different "standard". For the past few years I've been measuring at 75% at 3 different spots: the LE 1/3rd, TE 1/3rd (some call this cup) and an average over the whole blade. As Andy mentioned some props (like the Octura 22 series) have an incredible amount of progression while others have none (14 & 16 series). So depending on what "your" standard is "your" mileage may vary!

To me a 2170 has "moderate" progression. I measure the last 10* of pitch as just 1" greater than the first 10. A 2267 on the other hand measured 5.15" in the first 10* and a whopping 8.24" in the last! 1667's are "flat", measuring 4.32" anywhere on the blade.

I always thought you would go as fast as the LE pitch if you had a low drag, clean running hull and that progression only robs HP and doesn't make you go any faster. Now I'm not so sure.

Here's 3 passes with the same cut down 2170 that I measured 5.18" of LE pitch in the first 1/3rd of the blade:

Using the formula:

mph = pitch x rpm / 1057

I get slip values (using my measurements at my "standard") of 27.5%, 25.0% and 25.9% respectively, say around 26% average.

Looks like I'll need to up the efficiency if I want to catch Andy and these other fast guys!

 

[Ian Inverarity]

Terry,

How does it work out if you measure the LE pitch over 5 degrees from the LE? On a progressive pitch prop, the smaller angle you measure over at the LE will give lower pitch readings.

 

[Terry Keeley]

Terry,

How does it work out if you measure the LE pitch over 5 degrees from the LE? On a progressive pitch prop, the smaller angle you measure over at the TE will give lower pitch readings.

I measure the first 10* right around 5". With that "standard" the slip is around 22%.

See what I mean?

 

[Marty Davis]

Terry:

Nice post with a lot of "MEAT".

My point in my post initially was just to say that to make a blanket statement about what was going on with Phil's boat was impossible without some measurement device like the Eagle Tree System, etc. EACH BOAT will be different in it's slip percentage, depending on a host of variables.

Kind of like trying to define the pipe temp to design the perfect pipe. IMPOSSIBLE with so many variables to state that we run at a specific EGT. Loads, boat efficiency, etc, etc.

This is what makes this hobby so much fun. MANY things to think about and study. When you start to think that you know something, you find something else that leads you in a different direction.

Makes it humerous when someone says it is so, just because......

I tend to take note when AB says something. Look at the results, they speak for themselves. We have been getting a LOT of information lately from him - keep it coming, it is helping me, and others I am sure, understand some things that we have never researched. Gives me much more to look into....

When I finally graduated from the Hughey Pitch Gauge to the Woods model, it upped my game. I believe that the Eagle Tree stuff will do the same. I plan to start using it right away to answer some questions that I have had for years.