Prop Recommendation

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  • Prop Recommendation

    Hey everyone, new to the forum, thanks for having me! I am about to splash a Mako 25 that is new to me and I have yet to run. Have been busy replacing almost everything on it. I have a yamaha 300 hpdi that I intend to hang on it. The motor was from a set of twins and has a 21 pitch prop on it which I am assuming is not ideal as a single. Would a 17 or 19 pitch be better? Is it worth running it with the 21 to see what the performance is? If the 21 is no good any recommendations for a prop that may be better suited? Thanks for any input given!

  • #2
    I'd go with a Quicksilver Thunderbolt 15 1/2 x 17 and expect mid to high 40's.
    they cost 539 new, plus 45 for a hub kit.

    Ken Reeves
    [email protected]


    • #3
      Hi Ken thanks for getting back to me. I have an old Yamaha 17m prop that is 15 1/4 diameter that I had on a '94 225 yamaha on a previous boat. It has some dings in the blades and one blade has a slight bend t the end from hitting a log. Could that be a decent fit if I get it repaired or would it be better kept as a spare if I get it fixed? I dont have an issue getting a new prop if that will give me better performance and efficiency.


      • #4
        Yes, I would absolutely throw that on there and see how it runs. very similar propeller.

        Ken Reeves
        [email protected]


        • #5
          So it's been a long road getting this boat ready for the water but I was finally able to splash it today. I put on the Yamaha 17M prop that I had repaired. I was getting about 6,100 RPM at WOT...which seemed high and was only there just briefly. I was getting 39 mph according to the gps. So the boat is a 1976 Mako 25, I had about 100 gallons of fuel, T-top, maybe 100 lbs of miscellaneous gear, and I didn't realize it until after I got back but about 15 gallons of water in the livewell. Does this sound about right? Other than the RPMs that is a little high. Is there something I should try that may get the WOT RPMs down closer to 5,500?


          • #6
            Well if your turning 6100 at 39 MPH that would be 30% slip which is pretty bad.
            You might be able to get that prop fixed, and make it run better.
            You could get a new 17 pitch Thunderbolt Like we mentioned.
            or you could go with a 4 blade Q4, that is a little more aggressive, it cost a little more, but would also run very well.

            Make sure that is 39 MPH and not KTS. if its KTS, your not as bad, but its still slipping quite a bit, even if it were KTS.

            Ken Reeves
            [email protected]


            • #7
              Thanks for the feedback Ken. I went out today and played around with some things. I wanted to make sure the hub was not slipping so I marked the backside with a punch on the hub and the prop, when I was done running around they still lined up, so I can take that off the list.

              The numbers were generally pretty dismal in terms of slip. The gps was set to mph, i confirmed that as well. I was getting

              4k rpm - 18mph
              4.5 - 26
              5 - 30
              5.5 - 35
              6.1 - 39

              Clearly I dont think this is the prop for me, it may be time to try the one you recommend. Do you have a trial program through the mail or anything like that for out of state people?


              • #8
                Yes, I do send out test props.
                In your situation, if you know your going to end up buying a prop, I'd say buy one, don't waste the time and shipping "testing" stuff.
                I'd go with a 17 Thunderbolt, or if you want the best traction, go 17 Q4.
                If you get one and decide you want a different pitch or style, you an swap out for $35 plus shipping, so your not stuck with anything if it does not perform as we expect.

                But if you like, you can pay $30 plus shipping to test one.
                run it for the weekend, figure out if you like it and then ship it back to me.
                the testing cost does not go toward the purchase price.

                Ken Reeves
                [email protected]


                • #9
                  Hey Ken,

                  I did run a Rev 4 19" that is close to the Q4 17 you recommend, so i wanted to get your take on it. Most I didn't like at all, I did run the repaired 17m 15.25 diameter that I had repaired that I mentioned earlier, and a 21m 14.875x21 that was on the motor when I bought it, motor was from a pair of twins. This is what I got for each, I was expecting a greater difference in RPM than I saw. Just wanted to run these by you to see if it influences your recommendation at all. I really liked how the Rev 4 ran so the Q4 17 definetly has my interest, if you still think its a good fit.

                  All of the numbers are the average of two runs, in opposite directions, just me, about 100gal of fuel, medium amount of gear.

                  RPM - MPH - slip
                  4 - 18 - 45
                  4.5 - 26 - 37
                  5 - 30 - 34
                  5.5 - 35 - 35
                  WOT 6.1 - 39 - 30

                  RPM - MPH - slip
                  2 - 9 - 60
                  3 - 14 - 59
                  3.5 - 19 - 52
                  4 - 25 - 45
                  4.5 - 28 - 44
                  5 - 34 - 40
                  5.5 - 38 - 38
                  WOT 5.8 - 40 - 42

                  Rev 4
                  RPM - MPH - slip
                  2 - 8 61
                  3 - 16 - 48
                  3.5 - 21 - 42
                  4 - 26 - 37
                  4.5 - 31 - 33
                  5 - 35 - 32
                  5.5 - 39- 31
                  WOT 5.9 - 41 - 31

                  I realize none of these are a great fit. I did really like how responsive the Rev 4 was and how it made the boat ride. Is the Q4 17 still a good fit or is there something that may be better? I was reading about the Powertech QFS4, would its larger diameter keep RPMs in check when dropping down to a 17"? Does its compare to the Rev 4 and Q4 as far as handling?

                  I really appreciate all the help.

                  Last edited by Fandarr; 01-19-2021, 07:04 PM.


                  • #10
                    Got a picture of the bottom of the boat near the transom?
                    Curious if you have anything mounted on the transom or bottom of the boat such as a transducer, or water pickup, or anything that is screwing up the water flow to the prop.
                    Might also want to double check the tachometer.
                    Very strange for everything you try to be so awful, I imagine something else is happening.

                    Ken Reeves
                    [email protected]


                    • #11
                      I dont have a picture of the bottom. There is an old airmar thru hull transducer that I dont use. It seems like its in an out of the way spot and its very low profile. Its about 4 feet forward of the transom and about 8 inches from the keel on the port side. The boat is in the water so I cant just snap a photo for you. I do have a transom mount transducer that I am currently using. It is probably 14 ish inches away from the keel on the starboard side. The tach has crossed my mind and I just picked up one of those RPM testers where you put a mark on the flywheel. The gauge is brand new and I have checked the dip switches multiple times. The sound of the motor passes the ear test for what its worth. I have had Yamahas in the past and had one on my last boat so I have a good idea of what the sound should be at certain ranges. And and WOT 5,800 to 6,000 with the props I have tested that thing is screaming. Regardless I will try and get out on it tonight and see if I can figure anything out with this tester.
                      Last edited by Fandarr; 10-08-2020, 03:41 PM.


                      • #12
                        let me know what you find.
                        Just a lot of slip with everything, and everything is running about the same speed.

                        Ken Reeves
                        [email protected]


                        • #13
                          I got out to the boat this evening with the rpm tester. Worked my way up to 2k rpm from idle while in neutral, was spot on each time. This weekend I can probably get some help to test it while underway and check it at some higher RPMs if necessary.

                          The mid range speeds had some variation, but i totally agree the WOT speeds were very similar, and the RPM didn't vary as much as I expected either.

                          I also ran a Turning Point Mach 3 Express 19, and an Enertia 21. Those were just for kicks since I had access to them. I really didn't like them, but can give you those numbers if it helps, though they are pretty ugly.

                          Does the diameter variation between the 17m, 21m and Rev 4 have much of an impact? I also have to take the 17m with a grain of salt since it was repaired, I think i mentioned that, one of the tips was reasonably bent. It looks good but perhaps they altered the blades and now it does not perform as well? Its pretty obvious they messed with all three blades to some degree because the leading edges were all cleaned up and the prop polished.


                          • #14
                            This is the 17m right after I got it back, maybe this will help?


                            • #15
                              Luckily I have gotten a lot of loaner props to mess around with.
                              Last edited by Fandarr; 01-19-2021, 07:06 PM.