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hitting revs with 21 prop

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    hitting revs with 21 prop

    I dont want to start another "prop thread" however Ive picked up an old 1998 1750 capri with 3.0l, runs great and in good condition.
    has a solas SS 14 3/4" x 20 prop.
    prop has a couple of small nicks in it however other than that its in great shape.

    2 people in boat, wot reaches 5K + easily and gets to around 40MPH on gauge.
    4 people with a 25KG cooler box again reached 5K+ RPM easy and circa 32MPH on gauge.

    Im thinking that the the boat is pretty heavily propped already yes? or should I go to up in pitch?
    I've spotted a well priced 14 1/4" x 21 Ali prop... should I give this a go or is something maybe wrong with my current SS prop.?

    I want a good all rounder however would like to tow tubes and wake board now n again...

    #2
    Sounds like the current prop is meeting your needs and other than having it reconditioned I would not do anything with it. You may want too use a phototach just to verify the boats tach.
    1997 Maxum 2400 SCR 5.7LX Bravo II

    Mike

    Comment


      #3
      5k is on the high side...perhaps add a blade and go down in pitch to a 19 should get you right in the WOT zone of 4200-4800.., would help with heavier loads as well to get up and on plane...wouldn’t lose much top end either...
      Hell, Michigan (yes we really live in a city named "Hell" in Michigan)
      2012 BR 185 - 3.0 TKS
      1999 Chaparral 233 Sunesta Ltd., 5.0 Volvo
      1985 Harris Flotebote Classic 240
      1993 Yamaha Waverunner III VXR
      1993 Yamaha Waverunner III
      1995 Yamaha Waverunner III GP
      1995 Yamaha Waverunner III VXR PRO

      Comment


        #4
        I have no idea what my WOT value was back in in 1998, but...…………….

        My 1998 3.0 came with a 21P 3 blade prop. I put on a 19P 3 blade prop for a better holeshot and better mid range control while pulling skiers and tubes. Both were aluminum.

        As a practical matter I never operated the boat at redline. I certainly went to WOT while pulling up a skier, but the throttle was then backed off as the boat and the skier came up on plane.

        We cruised for hours between 2500/3500 rpm while on the lake.

        A prop choice is a compromise...….what water speed/engine RPM numbers will the boat be operated at most of the time?

        How many people in the boat most of the time?
        Present Boat- 2018 VR5 4.5/200hp Mercruiser
        Last Boat- 1998 Capri 1950CL 3.0 Mercruiser

        Comment


          #5
          Thanks for the replies guys.

          ROB MICK - wouldn't going down in pitch from a 20P to 19P raise my WOT revs and not lower them?

          my concern is that even with the boat loaded up I can still EASILY reach 5K+ at WOT...? I haven't tried it but if I put the lever right forward to its "stop" WOT, then Im sure it would go to 5.5K.... certainly not a rev range i want to be in to go 33MPH...





          Comment


            #6
            Originally posted by gijoerambo View Post
            Thanks for the replies guys.

            ROB MICK - wouldn't going down in pitch from a 20P to 19P raise my WOT revs and not lower them?

            my concern is that even with the boat loaded up I can still EASILY reach 5K+ at WOT...? I haven't tried it but if I put the lever right forward to its "stop" WOT, then Im sure it would go to 5.5K.... certainly not a rev range i want to be in to go 33MPH...




            As I mentioned in post 2 you should verify the tach accuracy with a photo tach.

            What Rob Mick suggest was going to a 4 blade prop and decreasing one pitch size, however this should have little affect on the WOT rpm.
            1997 Maxum 2400 SCR 5.7LX Bravo II

            Mike

            Comment


              #7
              Agree, verify tach is reading accurately first
              Dave
              Edmonds, WA
              "THE FIX"
              '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
              (.030 over-Vortec top end-part closed cooled)
              The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
              Misc. projects thread
              https://www.baylinerownersclub.org/f...56-gctid789773

              Comment


                #8
                If you search for OEM data on your model if its posted....I would start with that prop. Believe it or not they deliver these units with the best ALL ROUND prop for the setup. IMO folks get all tangled up in the weeds trying to improve all round performance.

                in reality it's all a trade off from stock.....if you increase hole shot you lose top end and risk over rev. If you bump top end you will be climbing out of the hole. Only reason to swap pitch and blade count is if you favor hike over top speed or vice versa.

                This was explained to me simply by a prop shop tech 20 years ago when I went in wanting to solve everything with a pitch change.....he said pick what you wanna do most or stick with factory setup.......all I've done was switch aluminum for SS as I dont boat in shallows......alum is forgiving upon impact as far as damage but loses performance due to flex.

                In short....you cant make up HP with pitch
                2008 H210SS Four Winns
                Volvo Penta 5.7 GISX
                Prior: 1997 2050SS Bayliner
                Brad / Texas Gulf Coast

                Comment


                  #9
                  Originally posted by gijoerambo View Post
                  Thanks for the replies guys.

                  ROB MICK - wouldn't going down in pitch from a 20P to 19P raise my WOT revs and not lower them?

                  my concern is that even with the boat loaded up I can still EASILY reach 5K+ at WOT...? I haven't tried it but if I put the lever right forward to its "stop" WOT, then Im sure it would go to 5.5K.... certainly not a rev range i want to be in to go 33MPH...




                  You are correct. Going down in pitch would increase rpms. As others have said, verify the rm. For general use, you want to be able to hit the WOT rpm and not to exceed. If I remember correctly 1" in pitch will generally change rpm by 200 or so. Do you know what the WOT spec is?
                  Doug
                  Hanging Loose
                  98 Carver 350 Mariner
                  2013-
                  KRUSTY KRAB
                  2001 305
                  5.7 BII
                  2006-2013

                  Comment


                    #10
                    Originally posted by carguy View Post

                    You are correct. Going down in pitch would increase rpms. As others have said, verify the rm. For general use, you want to be able to hit the WOT rpm and not to exceed. If I remember correctly 1" in pitch will generally change rpm by 200 or so. Do you know what the WOT spec is?
                    I actually mentioned adding a blade which would slow the rpms down...and give better initial bite and holeshot...
                    Hell, Michigan (yes we really live in a city named "Hell" in Michigan)
                    2012 BR 185 - 3.0 TKS
                    1999 Chaparral 233 Sunesta Ltd., 5.0 Volvo
                    1985 Harris Flotebote Classic 240
                    1993 Yamaha Waverunner III VXR
                    1993 Yamaha Waverunner III
                    1995 Yamaha Waverunner III GP
                    1995 Yamaha Waverunner III VXR PRO

                    Comment


                      #11
                      Originally posted by RobMick View Post

                      I actually mentioned adding a blade which would slow the rpms down...and give better initial bite and holeshot...
                      Op only needs to reduce rpms by about 200 to get within acceptable WOT limits of 4400-4800 rpm
                      Hell, Michigan (yes we really live in a city named "Hell" in Michigan)
                      2012 BR 185 - 3.0 TKS
                      1999 Chaparral 233 Sunesta Ltd., 5.0 Volvo
                      1985 Harris Flotebote Classic 240
                      1993 Yamaha Waverunner III VXR
                      1993 Yamaha Waverunner III
                      1995 Yamaha Waverunner III GP
                      1995 Yamaha Waverunner III VXR PRO

                      Comment


                        #12
                        Hitting or exceeding WOT is a better scenario than not being able to get there. Sounds like op is fairly happy with the overall performance of his boat. Maybe he could just take it easy on the throttle lever.
                        Dave
                        Edmonds, WA
                        "THE FIX"
                        '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
                        (.030 over-Vortec top end-part closed cooled)
                        The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
                        Misc. projects thread
                        https://www.baylinerownersclub.org/f...56-gctid789773

                        Comment


                          #13
                          Originally posted by builderdude View Post
                          Hitting or exceeding WOT is a better scenario than not being able to get there. Sounds like op is fairly happy with the overall performance of his boat. Maybe he could just take it easy on the throttle lever.
                          Basically my point in post #2.
                          1997 Maxum 2400 SCR 5.7LX Bravo II

                          Mike

                          Comment


                          • builderdude
                            builderdude commented
                            Editing a comment
                            Yep👍🏼

                          #14
                          Make sure hubs not spinning in the prop or the cush drive maybe failing too if max revs reached when more load is put in theboat and it revs up but loses lots of speed.

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