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  • Prop Talk

    I am new to boating. Had this or that for the last 20 years, but only last year got a real bost. Robalo R180. I started looking at props and got very frustrated. I hear 2 words, well 4, Hole Shot or Top End. No one wants to talk about where we spend 80% of our driving time. I call it crusing speed. Right away they all go back to WOT RPM. Yeam I get it. Or getting onto plane and holding. Again, yea, I get it. I want data on performance at 3700rpm to 4200rpm. Thats were most of us get the most mpg and cruse. Sure, sure, sure . Your the exception and run wot all day. I don't have money for fuel and engine replacement. I run around optimum engine performance speeds. Yet, no one wants to publish or really talk about what a prop is going to do there.

    In particular, i'm curious about a 4 blade vs 3 blade at crusing rpm, Will I go faster with a 4 blade or 3 blade at 4200 rpm. Really, your foing to start in with WOT talk. I get it. My Yamaha has to rev up to 5500 with what ever prop I get. Now, back to 4200 rpm. Whats the prop going to do there, No, I'm not asking about the hole shot, I'm not asking how long to get on plane. I'm saying i'm on plane on nice water any my motor is turning at 4200 rpm. What prop performs better. Wow, wait, why are you talking about WOT spec again. I will never drive at that speed. 4200 rpm info please. Owe, were vack to hole shot again. Sorry, I have to hang up now.

    Am I looking in the wrong place. How do I understand what prop performance is at 3700 rpm to 4200 rpm. What prop will give the best speed and mpg at 4200 rpm.

  • #2
    http://www.propellersafety.com/14913...view-boattest/

    This is what I believe is a good comparison. It pretty clearly shows how a prop performs at all the rpm ranges and has a decent enough comparison. Is it a perfect comparison. Well, it cant be. The props are different. But its good enough for me.

    FYI, I am on the list to get one if they ever come available.

    Comment


    • #3
      Originally posted by Kingrex View Post
      I am new to boating. Had this or that for the last 20 years, but only last year got a real bost. Robalo R180. I started looking at props and got very frustrated. I hear 2 words, well 4, Hole Shot or Top End. No one wants to talk about where we spend 80% of our driving time. I call it crusing speed. Right away they all go back to WOT RPM. Yeam I get it. Or getting onto plane and holding. Again, yea, I get it. I want data on performance at 3700rpm to 4200rpm. Thats were most of us get the most mpg and cruse. Sure, sure, sure . Your the exception and run wot all day. I don't have money for fuel and engine replacement. I run around optimum engine performance speeds. Yet, no one wants to publish or really talk about what a prop is going to do there.

      In particular, i'm curious about a 4 blade vs 3 blade at crusing rpm, Will I go faster with a 4 blade or 3 blade at 4200 rpm. Really, your foing to start in with WOT talk. I get it. My Yamaha has to rev up to 5500 with what ever prop I get. Now, back to 4200 rpm. Whats the prop going to do there, No, I'm not asking about the hole shot, I'm not asking how long to get on plane. I'm saying i'm on plane on nice water any my motor is turning at 4200 rpm. What prop performs better. Wow, wait, why are you talking about WOT spec again. I will never drive at that speed. 4200 rpm info please. Owe, were vack to hole shot again. Sorry, I have to hang up now.

      Am I looking in the wrong place. How do I understand what prop performance is at 3700 rpm to 4200 rpm. What prop will give the best speed and mpg at 4200 rpm.


      I have this conversation a few times every day
      Many people don't understand why we need to talk about anything other then cruise.
      This will be a long post, but hopefully it helps.

      To have any meaningful conversation about props you need to know what prop you have, and the RPM and GPS speed at both cruise AND wide open.
      more numbers you have the better.
      With that, we can figure out slip, and see how the prop is doing.
      "Slip" is just one thing to look at of many.
      but without any of this info, we are just wasting time.

      "I don't care about everything else, I want best CRUISE"
      Cruise can be harder to define then you think.
      Do you want the best economy....period, burn the least amount of fuel from point A to B ?
      Do you want the fastest speed at some arbitrary RPM you've chosen? in this case 4200 seems to be your favorite?
      Do you want the lowest fuel burn at that RPM?
      Do you want the best economy at a specific speed you have chosen?
      All of these are different statements. You actually used two different ones in your first post.
      1. i want to go the fastest speed at 4200.
      2. I want the best speed AND MPG at 4200 (This can't mathematically happen. You can always go up in pitch and go faster at the same RPM, but MPG will get worse eventually)

      Here is your Robalo R180 with an F115, First two reports I found, and this is a classic example.

      Yamaha got Best economy of 5.31 MPG at 4000 RPM and 23.5 MPH with a 17 pitch prop. https://yamahaoutboards.com/en-us/ho...2013-10-22_occ

      Boattest got Best economy of 5.28 MPG at 3500 RPM and 20 MPH with a 19 pitch prop
      for comparison at 4000, they got 5.19 MPG at 25.5 MPH with a 19 pitch prop.
      https://www.boattest.com/review/robalo/2673_r180

      ok, your looking at these reports....
      First thought, well the 19 goes faster at any given RPM winner right?
      Oh, but the 17 is actually getting slightly better economy, and doing so at a 17 % faster speed.
      Not to mention you get the added bonus of stronger acceleration and less sensitive to load.

      Most people can't wrap their head around the idea that you can turn more RPM at the same speed but burn less fuel... it just doesn't compute, and they go for the 19 every time.

      Now lets ask the question differently.
      your boat gets its best economy at 20-24 MPH, No matter what prop you put on there, the best economy will be in this same speed range.
      But lets say, you don't like puttin around at 20 MPH, you want to run 30 MPH.
      You have a 40 MPH boat, 30 is not a "crazy" speed to be cruising at, but its not the REAL optimum cruise speed for the BEST economy.
      Well the 19 pitch is better at 30 MPH.
      One guy wants the true "best economy of the boat" Winner, 17 pitch at 23.5 MPH (better economy at faster speed then the 19)
      Next guy wants the best economy at 30 MPH the speed HE likes to cruise, Winner 19 pitch
      Both guys initial request is (I want the best "cruise") but it takes a little while to figure out what they actually want.

      Then we have load.
      The prop that gets the best economy at "the chosen cruise speed" with a half tank of fuel in smooth conditions, may not get the best economy when your loaded with 4 people, full tank of fuel and a bunch of ice, in crappy conditions.
      So you have to make a choice, this will be based on the conditions and load you run most of the time, again, more questions I'll be asking you that you won't want to answer. (Why the hell does it matter who's on my boat, or what we are doing, I want the best cruise !!!)


      The reality.
      Most people believe there is a specific RPM that is "best" for your outboard efficiency.
      Contrary to this belief, the BOAT chooses the most economical speed.
      On your average hull its normally a 5 MPH range of speed where its going to get the best economy.
      Stepped hulls often have a 5-10 MPH range
      Doesn't matter how much HP you have, what brand of motor, how many motors, what RPM range/Gear ratio that particular motor. Or what RPM some mechanic told you would be the "best" RPM.
      That boat will get its best economy in that same speed range regardless. RPM is what it is, at that speed.

      Take the 2 reports we just looked at on your boat, same motor, same boat, one got best economy at 3500, one got it at 4000.
      If there is a "most economical RPM" they would have both got their best economy at the same RPM.
      But the reality is, the R180 runs most efficiently between 20-24 MPH, best economy will be in that speed range, RPM is what it is. in this case 3500 with the 19 pitch, and 4000 with the 17.

      Couple quick examples from yamaha's site. Same boats, with significantly different HP and motor options, magically the true BEST economy is always about the same speed every time.

      42 ft Scout
      triple 350 motors, at 32.7 MPH https://yamahaoutboards.com/en-us/ho...2015-06-08_occ
      Quad 300's, 31.9 MPH https://yamahaoutboards.com/en-us/ho...2015-04-21_occ

      39ST Contender
      Triple 350's best economy 36.5 MPH https://yamahaoutboards.com/en-us/ho...24_2-14-17_occ
      Triple 425's Best economy 36.6 MPH https://yamahaoutboards.com/en-us/ho...425_5-9-18_occ

      Here is a Robalo R200
      150 HP best economy, 22 MPH https://yamahaoutboards.com/en-us/ho...occ_17reliance
      115 HP best economy 21.7 MPH https://yamahaoutboards.com/en-us/ho...-13_occ_17alum

      3 or 4 blade?
      There is not a universal answer to that. If 4 blades always got better economy, you'd rarely ever see a 3 blade prop.
      This is where the conditions, load, speed all come in, as well as the handling characteristics of the boat.
      If I learn that your having to bury your trim tabs and keep the motor trimmed all the way down to make the boat ride like you want it to, I may suggest a 4 blade to help lift the stern, and keep you up on plane without you having to drag your tabs, less tab, less drag, better economy.
      and we may also start talking about engine height.

      often times 4 blades or a more aggressively cupped 3 blade might get better economy at slower speeds, but get worse economy at faster speeds.
      That is where I have to find out what speed you actually want to cruise.

      Why do I ask about wide open RPM and GPS speed?
      I know about what speed you "should" be getting, and if your significantly off on that, we will look for the reason why.
      You may not know how to properly trim the motor and tabs.
      You may have motor issues that you don't know about. Just cause the engine starts every time and runs smooth doesn't mean its all good.
      Prop may be worn or damaged and have no traction at all.
      Pitch could be too high or too low
      Engine height could be too high or too low
      Hull could have growth
      And countless other possibilities.

      If they give me numbers that are way Better then the expected performance I have to figure out if their gauges are off, are they running with a current, are they using numbers they have "heard" the boat "should" get, or are they telling me numbers that they are Actually getting ?


      When you call me, I'm trying to solve your problem.
      When people buy a prop from me, they can return it if they don't like it.
      Cost me money to take back props or swap them out, I make more money when I hit it right the first time.
      If you answer my questions on everything, I have a much better chance of doing that.

      EVERY question I ask you is for a reason. I'm not trying to dig into your private life, I'm ruling out potential problems and issues I've seen over the years. Way too many scenarios for me to explain why I'm asking each question.

      To answer your question.
      If you want the most MPH at 4200 RPM, put the biggest pitch prop on the motor that will still allow you to get on plane. You could probably get up on plane with a 21 pitch Yamaha.
      It will be a complete dog, and your economy will be bad, but it will have the fastest MPH at 4200
      If you want to get the best fuel economy for how you actually run your boat, Answer the questions, and I'll tell you the options and pros and cons of each.

      Ken Reeves
      [email protected]
      941-735-5808

      Comment


      • #4
        Just so you know, I know its annoying, like going to autozone and getting the same questions they have to put into the computer.

        But when I'm asking questions, there really is a reason.


        Ken Reeves
        [email protected]
        941-735-5808

        Comment


        • #5
          Originally posted by ken2 View Post
          Just so you know, I know its annoying, like going to autozone and getting the same questions they have to put into the computer.

          But when I'm asking questions, there really is a reason.

          Pretty sure its an automatic transmission as I don't have a clutch.

          Comment


          • #6
            Do you "true" props. Spin them to test balance and grind as necessary? Correct blade pitch as necessary?

            Comment


            • #7
              I don't, I just deal with new props. I have props that you can "test" for the weekend if there is something you want to try.
              If you buy a prop from me and decide you want a different style or pitch, you can swap out for $35 plus shipping.

              I mainly use Rich Junker at Leading Edge Propeller in Ellenton FL for any modifications or repairs. He does amazing work, but it takes a while for it to get done.
              But there are some other shops I like also, depending on your location.

              Ken Reeves
              [email protected]
              941-735-5808

              Comment


              • #8
                Originally posted by ken2 View Post



                I have this conversation a few times every day
                Many people don't understand why we need to talk about anything other then cruise.
                This will be a long post, but hopefully it helps.

                To have any meaningful conversation about props you need to know what prop you have, and the RPM and GPS speed at both cruise AND wide open.
                more numbers you have the better.
                With that, we can figure out slip, and see how the prop is doing.
                "Slip" is just one thing to look at of many.
                but without any of this info, we are just wasting time.

                "I don't care about everything else, I want best CRUISE"
                Cruise can be harder to define then you think.
                Do you want the best economy....period, burn the least amount of fuel from point A to B ?
                Do you want the fastest speed at some arbitrary RPM you've chosen? in this case 4200 seems to be your favorite?
                Do you want the lowest fuel burn at that RPM?
                Do you want the best economy at a specific speed you have chosen?
                All of these are different statements. You actually used two different ones in your first post.
                1. i want to go the fastest speed at 4200.
                2. I want the best speed AND MPG at 4200 (This can't mathematically happen. You can always go up in pitch and go faster at the same RPM, but MPG will get worse eventually)

                Here is your Robalo R180 with an F115, First two reports I found, and this is a classic example.

                Yamaha got Best economy of 5.31 MPG at 4000 RPM and 23.5 MPH with a 17 pitch prop. https://yamahaoutboards.com/en-us/ho...2013-10-22_occ

                Boattest got Best economy of 5.28 MPG at 3500 RPM and 20 MPH with a 19 pitch prop
                for comparison at 4000, they got 5.19 MPG at 25.5 MPH with a 19 pitch prop.
                https://www.boattest.com/review/robalo/2673_r180

                ok, your looking at these reports....
                First thought, well the 19 goes faster at any given RPM winner right?
                Oh, but the 17 is actually getting slightly better economy, and doing so at a 17 % faster speed.
                Not to mention you get the added bonus of stronger acceleration and less sensitive to load.

                Most people can't wrap their head around the idea that you can turn more RPM at the same speed but burn less fuel... it just doesn't compute, and they go for the 19 every time.

                Now lets ask the question differently.
                your boat gets its best economy at 20-24 MPH, No matter what prop you put on there, the best economy will be in this same speed range.
                But lets say, you don't like puttin around at 20 MPH, you want to run 30 MPH.
                You have a 40 MPH boat, 30 is not a "crazy" speed to be cruising at, but its not the REAL optimum cruise speed for the BEST economy.
                Well the 19 pitch is better at 30 MPH.
                One guy wants the true "best economy of the boat" Winner, 17 pitch at 23.5 MPH (better economy at faster speed then the 19)
                Next guy wants the best economy at 30 MPH the speed HE likes to cruise, Winner 19 pitch
                Both guys initial request is (I want the best "cruise") so I have to dig that info out of them to figure out what the hell they mean by that statement.

                Then we have load.
                The prop that gets the best economy at "the chosen cruise speed" with a half tank of fuel in smooth conditions, may not get the best economy when your loaded with 4 people, full tank of fuel and a bunch of ice, in crappy conditions.
                So you have to make a choice, this will be based on the conditions and load you run most of the time, again, more questions I'll be asking you that you won't want to answer. (Why the hell does it matter who's on my boat, or what we are doing, I want the best cruise !!!)


                The reality.
                Most people believe there is a specific RPM that is "best" for your outboard efficiency.
                Contrary to this belief, the BOAT chooses the most economical speed.
                On your average hull its normally a 5 MPH range of speed where its going to get the best economy.
                Stepped hulls often have a 5-10 MPH range
                Doesn't matter how much HP you have, what brand of motor, how many motors, what RPM range/Gear ratio that particular motor. Or what RPM some mechanic told you would be the "best" RPM.
                That boat will get its best economy in that same speed range regardless. RPM is what it is, at that speed.

                Take the 2 reports we just looked at on your boat, same motor, same boat, one got best economy at 3500, one got it at 4000.
                If there is a "most economical RPM" they would have both got their best economy at the same RPM.
                But the reality is, the R180 runs most efficiently between 20-24 MPH, best economy will be in that speed range, RPM is what it is. in this case 3500 with the 19 pitch, and 4000 with the 17.

                Couple quick examples from yamaha's site. Same boats, with significantly different HP and motor options, magically the true BEST economy is always about the same speed every time.

                42 ft Scout
                triple 350 motors, at 32.7 MPH https://yamahaoutboards.com/en-us/ho...2015-06-08_occ
                Quad 300's, 31.9 MPH https://yamahaoutboards.com/en-us/ho...2015-04-21_occ

                39ST Contender
                Triple 350's best economy 36.5 MPH https://yamahaoutboards.com/en-us/ho...24_2-14-17_occ
                Triple 425's Best economy 36.6 MPH https://yamahaoutboards.com/en-us/ho...425_5-9-18_occ

                Here is a Robalo R200
                150 HP best economy, 22 MPH https://yamahaoutboards.com/en-us/ho...occ_17reliance
                115 HP best economy 21.7 MPH https://yamahaoutboards.com/en-us/ho...-13_occ_17alum

                3 or 4 blade?
                There is not a universal answer to that. If 4 blades always got better economy, you'd rarely ever see a 3 blade prop.
                This is where the conditions, load, speed all come in, as well as the handling characteristics of the boat.
                If I learn that your having to bury your trim tabs and keep the motor trimmed all the way down to make the boat ride like you want it to, I may suggest a 4 blade to help lift the stern, and keep you up on plane without you having to drag your tabs, less tab, less drag, better economy.
                and we may also start talking about engine height.

                often times 4 blades or a more aggressively cupped 3 blade might get better economy at slower speeds, but get worse economy at faster speeds.
                That is where I have to find out what speed you actually want to cruise.

                Why do I ask about wide open RPM and GPS speed?
                I know about what speed you "should" be getting, and if your significantly off on that, we will look for the reason why.
                You may not know how to properly trim the motor and tabs.
                You may have motor issues that you don't know about. Just cause the engine starts every time and runs smooth doesn't mean its all good.
                Prop may be worn or damaged and have no traction at all.
                Pitch could be too high or too low
                Engine height could be too high or too low
                Hull could have growth
                And countless other possibilities.

                If they give me numbers that are way Better then the expected performance I have to figure out if their gauges are off, are they running with a current, are they using numbers they have "heard" the boat "should" get, or are they telling me numbers that they are Actually getting ?


                When you call me, I'm trying to solve your problem.
                When people buy a prop from me, they can return it if they don't like it.
                Cost me money to take back props or swap them out, I make more money when I hit it right the first time.
                If you answer my questions on everything, I have a much better chance of doing that.

                EVERY question I ask you is for a reason. I'm not trying to dig into your private life, I'm ruling out potential problems and issues I've seen over the years. Way too many scenarios for me to explain why I'm asking each question.

                To answer your question.
                If you want the most MPH at 4200 RPM, put the biggest pitch prop on the motor that will still allow you to get on plane. You could probably get up on plane with a 21 pitch Yamaha.
                It will be a complete dog, and your economy will be bad, but it will have the fastest MPH at 4200
                If you want to get the best fuel economy for how you actually run your boat, Answer the questions, and I'll tell you the options and pros and cons of each.
                Damn you are thorough!

                Comment


                • #9
                  "cruise fuel economy" is as much a function of the engine as it is of the prop. We play with props as that is the easiest to change parameters for each individual "engine". You can not necessarily assume what works on someone elses 225 Yamaha will work on your 225 Yamaha if the hull is different. And, NEVER assume lower cruise rpms equates to better economy!

                  Comment

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