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New 4 blade Turning Point Prop...meh

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  • New 4 blade Turning Point Prop...meh

    So after figuring out part of my previous issue was a bad tach (replaced), I was only hitting about 4600 at WOT for about 35 mph. 86 200 blackmax on a 21' Kevlar Hydrasport. Old prop was a stainless merc 23p 3 blade. Went to a 19p aluminum 4 blade. I only picked up about 200 rpm and lost 2-3 mph. I'm only getting about 32 mph out of a boat/motor combo that should do 50ish. Any ideas?
    DSiekman
    2000 Cobalt 293 Twin Volvo 5.0 Gi DP - Sold
    1978 (or 79?) Hydra-Sports 21' CC with 200 Black Max
    2001 F250 7.3 Powerstroke (With a few goodies)

  • #2
    Compression check, I'd think. Doesn't sound right at all. That boat and engine combo should fly and most likely require at least a 21"...23" more likely.

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    • #3
      Your not running on all cylinders. Not a prop issue check for spark on all cylinders and compression.
      2004 Caravelle 187

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      • #4
        Is your speed by GPS? With a 1.87:1 gear ratio. engine speed at 4800 rpm a 19 in prop, and 10% slip shows 42mph.

        I too think that your engine is not up to par. As mentioned, a compression test is order, also check the timing, also are the carbs opening fully, and does it have spark on all cylinders, the rpms you are getting are consistent to when one plug isn't firing

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        • #5
          By gps. Two adults, two kids under 5. .5-.75 tank of fuel.

          I agree something seems wrong with the engine. Carbs were rebuilt last fall and I'm pretty particular about stabilizing my fuel. I suppose it wouldn't hurt to swap the filter to be sure I'm not starving it of fuel.

          What I don't get is how engine issues have any bearing on speed at a given rpm. If the engine is turning 4800 I should be getting 42ish mph per the calculation. I could see that I would be limited in rpm but don't understand how that has any correlation to the math?
          DSiekman
          2000 Cobalt 293 Twin Volvo 5.0 Gi DP - Sold
          1978 (or 79?) Hydra-Sports 21' CC with 200 Black Max
          2001 F250 7.3 Powerstroke (With a few goodies)

          Comment


          • #6
            Originally posted by jimmbo View Post
            Is your speed by GPS? With a 1.87:1 gear ratio. engine speed at 4800 rpm a 19 in prop, and 10% slip shows 42mph.

            I too think that your engine is not up to par. As mentioned, a compression test is order, also check the timing, also are the carbs opening fully, and does it have spark on all cylinders, the rpms you are getting are consistent to when one plug isn't firing
            I should be able to visually inspect each plug and see a difference in one, correct? Like covered in fuel/oil vs clean.
            DSiekman
            2000 Cobalt 293 Twin Volvo 5.0 Gi DP - Sold
            1978 (or 79?) Hydra-Sports 21' CC with 200 Black Max
            2001 F250 7.3 Powerstroke (With a few goodies)

            Comment


            • #7
              I think if it was plugs...you would hear that it wasn't running on all 6. Good place to start, but Defo check compression and go from there.

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              • #8
                You can't always tell if a V6 is running on all cylinders by ear, or if one cylinder drops out at higher RPMs under a load, you need to actually check for spark.

                Have you confirmed the tach is reading correctly?

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                • #9
                  Originally posted by ondarvr View Post
                  You can't always tell if a V6 is running on all cylinders by ear, or if one cylinder drops out at higher RPMs under a load, you need to actually check for spark.

                  Have you confirmed the tach is reading correctly?
                  I just replaced the tach. The current readings seem believable.
                  DSiekman
                  2000 Cobalt 293 Twin Volvo 5.0 Gi DP - Sold
                  1978 (or 79?) Hydra-Sports 21' CC with 200 Black Max
                  2001 F250 7.3 Powerstroke (With a few goodies)

                  Comment


                  • #10
                    Originally posted by dsiekman View Post

                    I just replaced the tach. The current readings seem believable.
                    Is it on the correct setting?

                    Comment


                    • #11
                      Originally posted by dsiekman View Post

                      I only picked up about 200 rpm and lost 2-3 mph. I'm only getting about 32 mph out of a boat/motor combo that should do 50ish


                      What I don't get is how engine issues have any bearing on speed at a given rpm. If the engine is turning 4800 I should be getting 42ish mph per the calculation. I could see that I would be limited in rpm but don't understand how that has any correlation to the math?
                      The numbers aren't adding up.
                      You say you gained 200rpm so that should put you at 4800, then you say the speed dropped, and you are getting 32mph. Well as I said those rpms, gear ratio and some slip should yield approx 42mph.

                      Is the speed from a GPS or the water pressure speedo?
                      As asked before, is the tach set correctly? It reads alternator pulses, not ignition pulses.

                      BTW your engine is supposed to be running between 5000 - 5500 rpm, that would put it around 50mph, but...
                      Either your engine is not up to snuff, your boat has gained a lot of weight, the hull has issues(hook)
                      Are you trimming the engine up at higher speeds?

                      Comment


                      • #12
                        Did you use the thrust washer that came in the hub kit for the TP prop ? Those thrust washers are specific to the TP prop and must be used.
                        2004 Caravelle 187

                        Comment


                        • #13
                          Speed by gps. Tach set to 6p as I understand it is supposed to be.

                          I suppose hook is possible as is water logging. She sat for a long time.

                          One other thought. As old as the motor is and as many owners as it has had, it's possible someone put a lower hp powerhead on it. Is there any way to know for sure?
                          DSiekman
                          2000 Cobalt 293 Twin Volvo 5.0 Gi DP - Sold
                          1978 (or 79?) Hydra-Sports 21' CC with 200 Black Max
                          2001 F250 7.3 Powerstroke (With a few goodies)

                          Comment


                          • #14
                            Originally posted by 89retta View Post
                            Did you use the thrust washer that came in the hub kit for the TP prop ? Those thrust washers are specific to the TP prop and must be used.
                            Yep. Brand new hub, thrust washer, castle nut, etc.
                            DSiekman
                            2000 Cobalt 293 Twin Volvo 5.0 Gi DP - Sold
                            1978 (or 79?) Hydra-Sports 21' CC with 200 Black Max
                            2001 F250 7.3 Powerstroke (With a few goodies)

                            Comment


                            • #15
                              Sign up today
                              Originally posted by jimmbo View Post

                              The numbers aren't adding up

                              Are you trimming the engine up at higher speeds?
                              Correct, which is part of my frustration.

                              Yes, trimmed as high/out as she goes. I played with the trim quite a bit. I assumed I'd be able to essentially cause it to cavitate or blow out but it wouldn't raise that high under load. Not sure if that is part of the problem too. Weak trim system? I feel like I'm just grasping at straws at this point
                              DSiekman
                              2000 Cobalt 293 Twin Volvo 5.0 Gi DP - Sold
                              1978 (or 79?) Hydra-Sports 21' CC with 200 Black Max
                              2001 F250 7.3 Powerstroke (With a few goodies)

                              Comment

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