Open letter of apology to 45Auto and Everybody Else

[hwsiii]

I want to apologize to you specifically 45Auto for our discussion and some of my statements about maximum speeds attained using higher pitched props for attaining fuel economy while cruising. I am not positive that increasing pitch always results in better fuel economy while cruising with all props, as part of what is happening is that you are moving the RPM scale available from an engine from a higher RPM available to a lower RPM available from that same engine, so you will definitely see an increase in MPH available at any particular RPM setting and a commensurate amount of excess load applied to the engine the lower the maximum RPM falls. But your statement that any particular speed requires X amount of horsepower and that the more open the throttle is the more efficient the engine becomes DOES explain that, and I have to take that as the gospel, and I am sure that you are right. I do believe that it requires a search for the right prop using a GPS, tach and a fuel flow meter to ascertain which prop is better for fuel economy at cruising, and exactly what RPM the best fuel economy is attained with that prop.

What I was surprised by though, was that even though my numbers are right when using a 10% slip rate, they are NOT realistic in the real world, because of differences in prop slip and many other factors, and I have to thank you 45Auto for making me go back and run many new analysis of my numbers and the basis for why they do or don?t work. Since then I have spent a lot of time learning more about motors and fluid dynamics, and have learned more than I knew before, I hope in a year or more to better understand fluid flows, although at this time I am definitely a neophyte.

I also want to apologize to everyone else on here that has used my formula for increasing pitch size and the amount of expected changes in RPM. From doing an analysis of many different SS props that are the same make and model but different pitches on the same exact boat and motor I have found that my formulas do not consistently reflect the actual RPM change that I expected. I have found the problem to be that manufacturers do not always predict the PITCH and other changes that there props have correctly, even in the same manufacturer, make and series of prop. So I am at this time trying to find a better formula to represent these changes, although it will NEVER be EXACT, hopefully it will better represent the differences to be expected in general.

I am consistently trying to search for the truth about boats, motors and props, and to try and find ways to simplify our understanding and what an be expected when we change propellers. I have found that mathematics helps me have a better understanding and be able to replicate better what should be expected with certain changes made to a new prop. BUT it is NOT mathematically possible to find the EXACT best prop for any boat and motor, that requires knowledge and experience even to find a BETTER prop for any boat.

I hope everyone accepts my apology for giving them BAD information, I try the best I can to only give everyone good information here, and I also will try to do so in the future. If I find that I have given bad information, I will do the best I can to rectify that and let everyone know as soon as possible.


H

 

[QC]

Re: Open letter of apology to 45Auto and Everybody Else

All I have to say as I can't believe I missed a serious and well debated thread that included discussions of horsepower available vs. required and especially THROTTLING LOSSES. Holy flip Batman!! Good on ya mates

My favorite quote from that thread and of course comes from 45Auto:

This is an excellent example of how trying to force the non-linear real world into linear equations can cause errors.

LOL take it from a guy who spent a long time trying to force just that . . .

 

[smokeonthewater]

Re: Open letter of apology to 45Auto and Everybody Else

speaking of which I didn't mean to kill your debate..... I pretty much have my answer figured out.... feel free to resume on that thread to keep it all together.... I can even go in and edit out my whining

 

[hwsiii]

Re: Open letter of apology to 45Auto and Everybody Else

QC, the throttle part was my stupidity in not knowing enough about engines and flow theory to have an intelligent discussion with 45Auto. I have not studied flow theory at all, but that has changed recently and I am now reading all I can find on it, so I can at least have an intelligent discussion about the theory ,if not the reality, and at least I will get a chance to brush upon my higher math calculations.

Smoke, I am glad you figured out your answer and I didn't see anywhere you were whining, it was your thread.



H

 

[Texasmark]

Re: Open letter of apology to 45Auto and Everybody Else

Takes a big man to admit to error. You proved that sir.

Back when my brain was fully functional, I used mathematics to determine an outcome prior to the event in the cheapest form possible.....pencil (with an eraser which usually wore out prematurely) and paper. And as you are doing, if I knew not of a subject, I educated myself about it. That and a good deal of common sense secured a successful career beyond my wildest expectations......you had to have common sense to know where to put the decimal in your slide rule derived answers to your equations. (Bought the first scientific calculator TI produced (SR10) and the second one HP produced (HP 45 I think.)

Didn't take long to recognize the fact that I was filling in the blanks with assumptions and the outcome relied exclusively on the validity of these (and my arithmetic Ha.).

However, it gave me a place to start and reduce some waste in figuring out the answer.

The other thing it did was to give me time to think about what I was doing and to try other options (the worn out eraser) and observe the results.

I think props is an excellent place to get a jump on reality via mathematics, but as I have said many times, buy a prop from a dealer that will let you swap till you get it right for your application. I too have been surprised by what I have anticipated in selecting a new prop and what I got in the way of performance from it.

Mark

 

[QC]

Re: Open letter of apology to 45Auto and Everybody Else

QC, the throttle part was my stupidity in not knowing enough about engines

I have had a 30 year career in diesel engines. When I first learned that Otto cycle (throttle with spark plugs) engines were most efficient at WOT I had a scrunched up face for months . . . I have spent a good amount of time trying to explain that fact here, but it just messes people up. Fact is that almost all strategies for efficiency improvements for Otto engine applications revolve around reducing throttling losses. The one application with the least work done there is marine for the list of reasons that 45 does a good job of explaining. What you really need are 10 engines (or 100). Every 10% in additional power required just start up the next one and run it at WOT . . . Or another crappy way to do that is shut down cylinders i.e. Cylinder deactivation. Ring any bells?

 

[smokeonthewater]

Re: Open letter of apology to 45Auto and Everybody Else

QC if someone tries to sneak an 80's caddy 4,6,8, into my boat I'm gonna whip them.....lol.....
I thought very seriously about putting two merc 165's (250 gm I6) in the wellcraft for just that reason.... I would be running closer to full throttle at cruise speed. In the end I wanted more speed V.E. be damned lol

We are gonna put one in my old carver though...... It will be interesting to see how it performs and what mpg it can achieve compared to the v8 it has now

 

[wca_tim]

Re: Open letter of apology to 45Auto and Everybody Else

The bottom line is that even the very best efforts in engineering and mathematical modeling continue to fall far short of being able to reliably predict outcomes beyond narrow sets of circumstances. There are simply too many variables, too many degrees of freedom and not enough information to adequately address them all.

When it all comes down to it we try one thing, get closer, then another, etc... there is a substantial amount of "art" and intuition in even the most rigorous science. don't let anyone fool you into thinking otherwise.

the only way we can be able to truly learn and move forward is to be opn to reevaluate our own assumptions and ideas...

 

[MRS]

Re: Open letter of apology to 45Auto and Everybody Else

The bottom line is that even the very best efforts in engineering and mathematical modeling continue to fall far short of being able to reliably predict outcomes beyond narrow sets of circumstances. There are simply too many variables, too many degrees of freedom and not enough information to adequately address them all.

When it all comes down to it we try one thing, get closer, then another, etc... there is a substantial amount of "art" and intuition in even the most rigorous science. don't let anyone fool you into thinking otherwise.

the only way we can be able to truly learn and move forward is to be opn to reevaluate our own assumptions and ideas...

wca, and the rest of you that try to help the rest of us I for one am thankful for all the help. But I am not the sharpist nail in the bin I get real confused with all the numbers and formulas but you guys get me in the ballpark where I need to be. Then it is up to me to test and run different combs on my boat to see witch will work best for me,actually that is what I am doing now and it is looking real good Thanks again to all......

 

[hwsiii]

Re: Open letter of apology to 45Auto and Everybody Else

Mark, thank you very much, but I believe that most people admit when they make a major error as I did. And after I passed 60 it seems that I forget a LOT of things too. LOL

QC, Those North Star engines have been something else for Cadillac.

Tim, you are 100% right about being able to reassess the situation and recognize when I am wrong in my ideas. I guess that is why it is called research and theories.

And MRS I know you will be happy when you find the right one for your uses.



H

 

[QC]

Re: Open letter of apology to 45Auto and Everybody Else

I have a 5.3 V8 in my pickup that has 4 cyl deactivation. Barely noticeable. They're getting better at it for sure.

There is a much simpler technical solution to this throttle issue though . . . get rid of it, Rudy figured that out in 1893

 

[Texasmark]

Re: Open letter of apology to 45Auto and Everybody Else

I have a 5.3 V8 in my pickup that has 4 cyl deactivation. Barely noticeable. They're getting better at it for sure.

There is a much simpler technical solution to this throttle issue though . . . get rid of it, Rudy figured that out in 1893

I am running the Dodge HEMI with it and it changes over in 40 milliseconds. I've tried to detect it but can't. I certainly like the MPG it gives me. To keep the idle exhaust sound from sounding like a 4 banger, they just added another muffler which does a good job of "fooling your ears". But baby, when you put your spurs into her sides, you had better be hanging on cause she just gives you more and more and more.

Mark

 

[QC]

Re: Open letter of apology to 45Auto and Everybody Else

First time I drove the GM version it had as readout on the info screen and you could "see" when it changed from 8 to 4 cyl. The one I bought does not have the readout, I have finally developed an ear fro it though and I can tell. Nobody else in the truck knows. It took me a while, but I pretty much have it down now. There is absolutely no sensation when it transitions back to 8. Despite all of these comments, the point where it runs in 4 cyl mode is such a light load that a Marine equivalent would almost never run in the 4 cyl mode. Maybe at 1000 RPM in a large hull that would not be building a bow wave at all. Of course there could be a marine specific calibration that might change that.

 

[45Auto]

Re: Open letter of apology to 45Auto and Everybody Else

Hey Hwsii, no need to apologize to me! There's a lot of good data out there that I don't know how to use, I'm just glad that I can point someone in the right direction that can make some use out of it!

WCA_Tim said it very well:

The bottom line is that even the very best efforts in engineering and mathematical modeling continue to fall far short of being able to reliably predict outcomes beyond narrow sets of circumstances.

the only way we can be able to truly learn and move forward is to be open to reevaluate our own assumptions and ideas...

In my job, we use some of the most powerful computers in the world trying to predict fluids behavior. Still burn up and blow up lots of expensive stuff when the real world doesn't perform the way the numerical modeling predicts. So you incorporate that info into your next model and try again ....

Been off line for a couple of weeks, probably won't be back for a couple of more. Things are getting pretty wild down here in New Orleans with the Super Bowl coming up ......

 

[hwsiii]

Re: Open letter of apology to 45Auto and Everybody Else

Thank you very much for the kind words 45Auto, I am still on course for finding simpler ways to predict prop behavior on a particular boat and motor combination. That doesn't mean it will happen, but I am still trying.
Trial and error always goes hand in hand with research of any kind. But most of the time it requires discussions and debates between individuals to really find the errors in one persons theories and ideas, in order to move forward, like Tim says.
I do want to thank you again 45Auto for making me question my analysis, and made me go back and analyze my prior assumptions on pitch changes.

And I do know what you mean about things being hectic right now, as not only is the Superbowl with the Saints getting close, but also Mardis Gras is in full swing as well in New Orleans and over here in Pascagoula.



H