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Re: [J28Sailors]

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  • Jason Smith
    Also, if we use engine RPM max (continuous rating) = 3400, then HP should be 16 (not 18). If we use 18 HP, then max engine RPM should be 3600 (max output
    Message 1 of 18 , Sep 10, 2009
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      Also, if we use engine RPM max (continuous rating) = 3400, then HP should be 16 (not 18).
       
      If we use 18 HP, then max engine RPM should be 3600 (max output curve).  This may change some of the prop rec's.
       
      Jason

      On Thu, Sep 10, 2009 at 3:56 PM, Michael Puig <puig@...> wrote:
       

      Wow, based on what you gave me you are WAY OVER Prop't Look at the specs
      below for a 2 blade! You are really straining your engine -

      I dont know if you can really remove 4" of pitch on the prop without
      tearing the blade root (dont ask how I know) You might want to look into
      getting a used prop. Now would be a good excuse to get a martec or a kiwi...

      prop and power curve for engine should come together at 3200rpm - so you
      should spec hull speed for that. Above 3200 would be the extra punch you
      need for current and wind.

      http://www.marine-power.co.uk/2gm20f%20specs.htm

      Data Input
      Waterline length in feet: 24 feet
      Beam at the waterline in feet: 10 feet
      Hull draft in feet (excluding keel): 3 feet
      Vessel weight in pounds: 8000 lbs
      Engine Horsepower: 18 HP
      Number of engines: 1
      Total Engine Horsepower: 18 HP

      Engine R.P.M. (max): 3400 RPM
      Gear Ratio: 2.62:1
      Shaft R.P.M. (max): 1298 RPM

      Number of shaft bearings (per shaft): 1
      Desired speed in Knots: 7 knots
      Horsepower Calculations
      This will calculate the maximum horsepower and torque available at the
      prop(s).

      Total available horsepower at the engine(s): 18 HP
      Total available torque ft/lbs at the engine(s): 28 ft/lbs
      Horsepower loss of 3% per gearbox: - 0.5 HP
      Horsepower loss of 1.5% per shaft bearing: - 0.3 HP

      Total horsepower available at the propeller(s): 17.2 HP
      Total torque ft/lbs available at the propeller(s): 70 ft/lbs
      Speed & Power Calculations
      Basic displacement speed and horsepower required
      Displacement hull speed (1.34 X sqrt of waterline length): 6.56 Knots
      Minimum horsepower required at propeller(s) for Hull speed: 15.9 HP

      Calculations based on desired speed and available HP
      HP required at propeller(s) for desired 7 knots speed: 19 HP
      Estimated speed with existing 18 horsepower:
      This is the speed we will use for the propeller size. 6.71 Knots


      Recomended RPM for continuous operation
      Type of engine % of max RPM
      Light-duty gasoline and diesel automotive conversions 70 - 80%
      Light-duty or high output marine diesels 80 - 85%
      Intermittent-duty marine diesels 88 - 92%
      Continuous-duty heavy marine diesels 98 - 100%
      Propeller Size
      Number of blades Diameter (inches) Pitch (inches)
      2 Blade 15.9 X 10.1
      3 Blade 15.1 X 10.0
      4 Blade 14.2 X 9.8


    • Michael Puig
      http://www.vicprop.com/displacement_size.php
      Message 2 of 18 , Sep 10, 2009
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      • lenny_reich
        Jason: I agree that you may be over-propped. The Martec is notoriously inefficient, so it needs lots of pitch. When I sized a 15 VeriFold prop for my boat,
        Message 3 of 18 , Sep 10, 2009
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          Jason: I agree that you may be over-propped. The Martec is notoriously inefficient, so it needs lots of pitch. When I sized a 15" VeriFold prop for my boat, the company's strong recommendation was 15" x 12" and it seems just about right. One other point, the Yanmar tachs are not that accurate. An engine tech at the yard where I kept my boat over last winter told me that when they tried to assess a Yanmar problem somehow associated with RPM, they always used a strobe tach to get accurate readings.


          --- In J28Sailors@yahoogroups.com, Jason Smith <jason3317@...> wrote:
          >
          > I am looking for some subjective help from the group. Some of you may
          > know, I have been chasing a big vibration while under power.
          >
          > To date, we have eliminated or corrected all the driveline components,
          > including the prop, shaft, cutless bearing and associated couplings.
          > My yard just finished replacing the motor mounts, as we could see the
          > motor visibly rocking at certain RPM.
          >
          > After a 4 days cruise over Labor Day, I still think the problem
          > remains. There is vibration from 1400-1900 RPM, smoothing out around
          > 2400 RPM. Anything above 2600 RPM and the vibrations re-appear, and
          > the engine to my ear sounds "Harsh" and not very happy. I cannot
          > reach 3400 RPM (only 3100), but I don't feel like there is a loss of
          > power, the motor starts immediately even when cold and nor do I see
          > any obvious smoke, black or white. The hull and prop are clean. The
          > prop is a fixed 2 blade Michigan 16 x 14 (not very racy, yes I know,
          > but that's what I got). I realize these Yanmars will have an RPM
          > range that they don't like, but this is too broad.
          >
          > Now, the yard wants to pull the injectors and test/clean/replace as
          > necessary. They may also check the timing of the injector pump (not
          > sure I want to go there as it's really a delicate high-tolerance
          > piece).
          >
          > So, questions to the group: have you had these symptoms? Can you
          > reach full rated RPM (3400) in calm wind and water? Have you ever had
          > your injectors replaced or cleaned? If so, how many hours approx did
          > they have on them? Have you ever had a problem with the injector
          > pump? What RPM is your typical cruise RPM, and how does the boat
          > perform?
          >
          > Thanks in advance.
          >
          > Jason
          >
        • Jason Smith
          OK, supposing this is the case I am over-propped....would this cause the vibrations? Second, I have no noticed any classic symptoms of being
          Message 4 of 18 , Sep 10, 2009
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            OK, supposing this is the case I am over-propped....would this cause the vibrations?  Second, I have no noticed any classic symptoms of being over-pitched...black smoke, etc?  I'm looking for more corroborative evidence!
             
            Thanks guys.

            On Thu, Sep 10, 2009 at 9:36 PM, lenny_reich <lsreich@...> wrote:
             

            Jason: I agree that you may be over-propped. The Martec is notoriously inefficient, so it needs lots of pitch. When I sized a 15" VeriFold prop for my boat, the company's strong recommendation was 15" x 12" and it seems just about right. One other point, the Yanmar tachs are not that accurate. An engine tech at the yard where I kept my boat over last winter told me that when they tried to assess a Yanmar problem somehow associated with RPM, they always used a strobe tach to get accurate readings.

            --- In J28Sailors@yahoogroups.com, Jason Smith <jason3317@...> wrote:
            >
            > I am looking for some subjective help from the group. Some of you may
            > know, I have been chasing a big vibration while under power.
            >
            > To date, we have eliminated or corrected all the driveline components,
            > including the prop, shaft, cutless bearing and associated couplings.
            > My yard just finished replacing the motor mounts, as we could see the
            > motor visibly rocking at certain RPM.
            >
            > After a 4 days cruise over Labor Day, I still think the problem
            > remains. There is vibration from 1400-1900 RPM, smoothing out around
            > 2400 RPM. Anything above 2600 RPM and the vibrations re-appear, and
            > the engine to my ear sounds "Harsh" and not very happy. I cannot
            > reach 3400 RPM (only 3100), but I don't feel like there is a loss of
            > power, the motor starts immediately even when cold and nor do I see
            > any obvious smoke, black or white. The hull and prop are clean. The
            > prop is a fixed 2 blade Michigan 16 x 14 (not very racy, yes I know,
            > but that's what I got). I realize these Yanmars will have an RPM
            > range that they don't like, but this is too broad.
            >
            > Now, the yard wants to pull the injectors and test/clean/replace as
            > necessary. They may also check the timing of the injector pump (not
            > sure I want to go there as it's really a delicate high-tolerance
            > piece).
            >
            > So, questions to the group: have you had these symptoms? Can you
            > reach full rated RPM (3400) in calm wind and water? Have you ever had
            > your injectors replaced or cleaned? If so, how many hours approx did
            > they have on them? Have you ever had a problem with the injector
            > pump? What RPM is your typical cruise RPM, and how does the boat
            > perform?
            >
            > Thanks in advance.
            >
            > Jason
            >


          • Michael Puig
            IMHO, yes it could - what you would be hearing and feeling would be cavitation. The water flow is not attached to the prop. Remember, this is a displacement
            Message 5 of 18 , Sep 10, 2009
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              IMHO, yes it could - what you would be hearing and feeling would be
              cavitation. The water flow is not attached to the prop. Remember, this
              is a displacement boat - you want to shoot for hull speed. Some in an
              effort to have a more quiet cruise(read over prop) go to a higer pitch
              with the goal of hull at a lower rpm. That is fine if you live in Kansas
              or Nevada but you have current and wind and waves in the ocean. And
              doing so will strain your engine.

              Maybe you can find a used prop?

              Jason Smith wrote:
              >
              > OK, supposing this is the case I am over-propped....would this cause
              > the vibrations? Second, I have no noticed any classic symptoms of
              > being over-pitched...black smoke, etc? I'm looking for more
              > corroborative evidence!
              >
            • jfws88
              Jason, what is your hull speed at various RPM s, If your prop is cavitaing the boat should slow down when the vibration kicks. John
              Message 6 of 18 , Sep 11, 2009
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                Jason, what is your hull speed at various RPM's,

                If your prop is cavitaing the boat should slow down when the vibration kicks.

                John


                --- In J28Sailors@yahoogroups.com, Jason Smith <jason3317@...> wrote:
                >
                > OK, supposing this is the case I am over-propped....would this cause the
                > vibrations? Second, I have no noticed any classic symptoms of being
                > over-pitched...black smoke, etc? I'm looking for more corroborative
                > evidence!
                >
                > Thanks guys.
                >
                > On Thu, Sep 10, 2009 at 9:36 PM, lenny_reich <lsreich@...> wrote:
                >
                > >
                > >
                > > Jason: I agree that you may be over-propped. The Martec is notoriously
                > > inefficient, so it needs lots of pitch. When I sized a 15" VeriFold prop for
                > > my boat, the company's strong recommendation was 15" x 12" and it seems just
                > > about right. One other point, the Yanmar tachs are not that accurate. An
                > > engine tech at the yard where I kept my boat over last winter told me that
                > > when they tried to assess a Yanmar problem somehow associated with RPM, they
                > > always used a strobe tach to get accurate readings.
                > >
                > > --- In J28Sailors@yahoogroups.com <J28Sailors%40yahoogroups.com>, Jason
                > > Smith <jason3317@> wrote:
                > > >
                > > > I am looking for some subjective help from the group. Some of you may
                > > > know, I have been chasing a big vibration while under power.
                > > >
                > > > To date, we have eliminated or corrected all the driveline components,
                > > > including the prop, shaft, cutless bearing and associated couplings.
                > > > My yard just finished replacing the motor mounts, as we could see the
                > > > motor visibly rocking at certain RPM.
                > > >
                > > > After a 4 days cruise over Labor Day, I still think the problem
                > > > remains. There is vibration from 1400-1900 RPM, smoothing out around
                > > > 2400 RPM. Anything above 2600 RPM and the vibrations re-appear, and
                > > > the engine to my ear sounds "Harsh" and not very happy. I cannot
                > > > reach 3400 RPM (only 3100), but I don't feel like there is a loss of
                > > > power, the motor starts immediately even when cold and nor do I see
                > > > any obvious smoke, black or white. The hull and prop are clean. The
                > > > prop is a fixed 2 blade Michigan 16 x 14 (not very racy, yes I know,
                > > > but that's what I got). I realize these Yanmars will have an RPM
                > > > range that they don't like, but this is too broad.
                > > >
                > > > Now, the yard wants to pull the injectors and test/clean/replace as
                > > > necessary. They may also check the timing of the injector pump (not
                > > > sure I want to go there as it's really a delicate high-tolerance
                > > > piece).
                > > >
                > > > So, questions to the group: have you had these symptoms? Can you
                > > > reach full rated RPM (3400) in calm wind and water? Have you ever had
                > > > your injectors replaced or cleaned? If so, how many hours approx did
                > > > they have on them? Have you ever had a problem with the injector
                > > > pump? What RPM is your typical cruise RPM, and how does the boat
                > > > perform?
                > > >
                > > > Thanks in advance.
                > > >
                > > > Jason
                > > >
                > >
                > >
                > >
                >
              • jason3317@gmail.com
                John, Approximately: 1200 - 2-2.5 1500 - 3.0 2000 - 4-4.5 2400 - 5.5-6.0 2800 - 6.0-6.5 The boat does not seem to noticably slow down, just vibrates more and
                Message 7 of 18 , Sep 11, 2009
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                  John,
                  Approximately:

                  1200 - 2-2.5
                  1500 - 3.0
                  2000 - 4-4.5
                  2400 - 5.5-6.0
                  2800 - 6.0-6.5

                  The boat does not seem to noticably slow down, just vibrates more and sounds 'harsh'.

                  I am starting to agree that I am slightly over-pitched, but the vibration is also present with the prop off and running in the slings without load.

                  Jason

                  Sent from my Verizon Wireless BlackBerry


                  From: "jfws88"
                  Date: Fri, 11 Sep 2009 16:51:21 -0000
                  To: <J28Sailors@yahoogroups.com>
                  Subject: [J28Sailors] Re: Over-propped

                   



                  Jason, what is your hull speed at various RPM's,

                  If your prop is cavitaing the boat should slow down when the vibration kicks.

                  John

                  --- In J28Sailors@yahoogro ups.com, Jason Smith <jason3317@. ..> wrote:
                  >
                  > OK, supposing this is the case I am over-propped. ...would this cause the
                  > vibrations? Second, I have no noticed any classic symptoms of being
                  > over-pitched. ..black smoke, etc? I'm looking for more corroborative
                  > evidence!
                  >
                  > Thanks guys.
                  >
                  > On Thu, Sep 10, 2009 at 9:36 PM, lenny_reich <lsreich@... > wrote:
                  >
                  > >
                  > >
                  > > Jason: I agree that you may be over-propped. The Martec is notoriously
                  > > inefficient, so it needs lots of pitch. When I sized a 15" VeriFold prop for
                  > > my boat, the company's strong recommendation was 15" x 12" and it seems just
                  > > about right. One other point, the Yanmar tachs are not that accurate. An
                  > > engine tech at the yard where I kept my boat over last winter told me that
                  > > when they tried to assess a Yanmar problem somehow associated with RPM, they
                  > > always used a strobe tach to get accurate readings.
                  > >
                  > > --- In J28Sailors@yahoogro ups.com <J28Sailors% 40yahoogroups. com>, Jason
                  > > Smith <jason3317@> wrote:
                  > > >
                  > > > I am looking for some subjective help from the group. Some of you may
                  > > > know, I have been chasing a big vibration while under power.
                  > > >
                  > > > To date, we have eliminated or corrected all the driveline components,
                  > > > including the prop, shaft, cutless bearing and associated couplings.
                  > > > My yard just finished replacing the motor mounts, as we could see the
                  > > > motor visibly rocking at certain RPM.
                  > > >
                  > > > After a 4 days cruise over Labor Day, I still think the problem
                  > > > remains. There is vibration from 1400-1900 RPM, smoothing out around
                  > > > 2400 RPM. Anything above 2600 RPM and the vibrations re-appear, and
                  > > > the engine to my ear sounds "Harsh" and not very happy. I cannot
                  > > > reach 3400 RPM (only 3100), but I don't feel like there is a loss of
                  > > > power, the motor starts immediately even when cold and nor do I see
                  > > > any obvious smoke, black or white. The hull and prop are clean. The
                  > > > prop is a fixed 2 blade Michigan 16 x 14 (not very racy, yes I know,
                  > > > but that's what I got). I realize these Yanmars will have an RPM
                  > > > range that they don't like, but this is too broad.
                  > > >
                  > > > Now, the yard wants to pull the injectors and test/clean/replace as
                  > > > necessary. They may also check the timing of the injector pump (not
                  > > > sure I want to go there as it's really a delicate high-tolerance
                  > > > piece).
                  > > >
                  > > > So, questions to the group: have you had these symptoms? Can you
                  > > > reach full rated RPM (3400) in calm wind and water? Have you ever had
                  > > > your injectors replaced or cleaned? If so, how many hours approx did
                  > > > they have on them? Have you ever had a problem with the injector
                  > > > pump? What RPM is your typical cruise RPM, and how does the boat
                  > > > perform?
                  > > >
                  > > > Thanks in advance.
                  > > >
                  > > > Jason
                  > > >
                  > >
                  > >
                  > >
                  >

                • jfws88
                  Jason, With my folding martec I don t get 6 knots at all. Overpropped, maybe but if the vibration is present with the boat in a sling and the prop removed, or
                  Message 8 of 18 , Sep 11, 2009
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                    Jason,

                    With my folding martec I don't get 6 knots at all. Overpropped, maybe but if the vibration is present with the boat in a sling and the prop removed, or even if the prop is installed, the vibration isn't related to the prop over pitch. Period.

                    I have vibration issues also but mine aren't that bad. Right around 1800 RPM she shakes but at 2000 it's fine and again at around 2600 but again it's easy to get out of it by increaseing or decreaseing the motor speed.

                    Do you have the problem in forward and reverse?

                    The issue I'd have with the injectors and pump is those would also have syptoms of low power output but with your prop and the speed you get it seems your getting all the power the motor can put out.

                    Does the motor have that visible vibration at high idle speeds?

                    --- In J28Sailors@yahoogroups.com, jason3317@... wrote:
                    >
                    > John,
                    > Approximately:
                    >
                    > 1200 - 2-2.5
                    > 1500 - 3.0
                    > 2000 - 4-4.5
                    > 2400 - 5.5-6.0
                    > 2800 - 6.0-6.5
                    >
                    > The boat does not seem to noticably slow down, just vibrates more and sounds 'harsh'.
                    >
                    > I am starting to agree that I am slightly over-pitched, but the vibration is also present with the prop off and running in the slings without load.
                    >
                    > Jason
                    > Sent from my Verizon Wireless BlackBerry
                    >
                    > -----Original Message-----
                    > From: "jfws88" <jfws88@...>
                    >
                    > Date: Fri, 11 Sep 2009 16:51:21
                    > To: <J28Sailors@yahoogroups.com>
                    > Subject: [J28Sailors] Re: Over-propped
                    >
                    >
                    >
                    >
                    > Jason, what is your hull speed at various RPM's,
                    >
                    > If your prop is cavitaing the boat should slow down when the vibration kicks.
                    >
                    > John
                    >
                    >
                    > --- In J28Sailors@yahoogroups.com, Jason Smith <jason3317@> wrote:
                    > >
                    > > OK, supposing this is the case I am over-propped....would this cause the
                    > > vibrations? Second, I have no noticed any classic symptoms of being
                    > > over-pitched...black smoke, etc? I'm looking for more corroborative
                    > > evidence!
                    > >
                    > > Thanks guys.
                    > >
                    > > On Thu, Sep 10, 2009 at 9:36 PM, lenny_reich <lsreich@> wrote:
                    > >
                    > > >
                    > > >
                    > > > Jason: I agree that you may be over-propped. The Martec is notoriously
                    > > > inefficient, so it needs lots of pitch. When I sized a 15" VeriFold prop for
                    > > > my boat, the company's strong recommendation was 15" x 12" and it seems just
                    > > > about right. One other point, the Yanmar tachs are not that accurate. An
                    > > > engine tech at the yard where I kept my boat over last winter told me that
                    > > > when they tried to assess a Yanmar problem somehow associated with RPM, they
                    > > > always used a strobe tach to get accurate readings.
                    > > >
                    > > > --- In J28Sailors@yahoogroups.com <J28Sailors%40yahoogroups.com>, Jason
                    > > > Smith <jason3317@> wrote:
                    > > > >
                    > > > > I am looking for some subjective help from the group. Some of you may
                    > > > > know, I have been chasing a big vibration while under power.
                    > > > >
                    > > > > To date, we have eliminated or corrected all the driveline components,
                    > > > > including the prop, shaft, cutless bearing and associated couplings.
                    > > > > My yard just finished replacing the motor mounts, as we could see the
                    > > > > motor visibly rocking at certain RPM.
                    > > > >
                    > > > > After a 4 days cruise over Labor Day, I still think the problem
                    > > > > remains. There is vibration from 1400-1900 RPM, smoothing out around
                    > > > > 2400 RPM. Anything above 2600 RPM and the vibrations re-appear, and
                    > > > > the engine to my ear sounds "Harsh" and not very happy. I cannot
                    > > > > reach 3400 RPM (only 3100), but I don't feel like there is a loss of
                    > > > > power, the motor starts immediately even when cold and nor do I see
                    > > > > any obvious smoke, black or white. The hull and prop are clean. The
                    > > > > prop is a fixed 2 blade Michigan 16 x 14 (not very racy, yes I know,
                    > > > > but that's what I got). I realize these Yanmars will have an RPM
                    > > > > range that they don't like, but this is too broad.
                    > > > >
                    > > > > Now, the yard wants to pull the injectors and test/clean/replace as
                    > > > > necessary. They may also check the timing of the injector pump (not
                    > > > > sure I want to go there as it's really a delicate high-tolerance
                    > > > > piece).
                    > > > >
                    > > > > So, questions to the group: have you had these symptoms? Can you
                    > > > > reach full rated RPM (3400) in calm wind and water? Have you ever had
                    > > > > your injectors replaced or cleaned? If so, how many hours approx did
                    > > > > they have on them? Have you ever had a problem with the injector
                    > > > > pump? What RPM is your typical cruise RPM, and how does the boat
                    > > > > perform?
                    > > > >
                    > > > > Thanks in advance.
                    > > > >
                    > > > > Jason
                    > > > >
                    > > >
                    > > >
                    > > >
                    > >
                    >
                  • Michael Puig
                    J28 has a 24 waterline - max speed is 6.56 knts you are achieving hull speed at 2800 rpm. I believe the yanmar spins to 3500 rpm I would not pitch to 3500,
                    Message 9 of 18 , Sep 11, 2009
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                      J28 has a 24' waterline - max speed is 6.56 knts

                      you are achieving hull speed at 2800 rpm.

                      I believe the yanmar spins to 3500 rpm

                      I would not pitch to 3500, more like 3200 for 6.6 knts

                      This graph will explain it well.

                      http://www.artshot.net/prop_curve.gif

                      If you still have vibes with the prop of - check alignment and check
                      shaft to see if its straight.

                      Your cutlass bearing could be wallowed out.

                      You shaft strut could be loose

                      Mar-tecs are almost impossible to balance really well.

                      cheers

                      M




                      John,
                      >
                      > Approximately:
                      >
                      > 1200 - 2-2.5
                      > 1500 - 3.0
                      > 2000 - 4-4.5
                      > 2400 - 5.5-6.0
                      > 2800 - 6.0-6.5
                      >
                      > The boat does not seem to noticably slow down, just vibrates more and
                      > sounds 'harsh'.
                      >
                      > I am starting to agree that I am slightly over-pitched, but the
                      > vibration is also present with the prop off and running in the slings
                      > without load.
                      >
                      > Jason
                      >
                    • Jason Smith
                      Yes, the Martec is known to be inefficient. I agree that the boat is overpropped, but not sure this is the primary cause of the vibration. We can see the
                      Message 10 of 18 , Sep 11, 2009
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                        Yes, the Martec is known to be inefficient.  I agree that the boat is overpropped, but not sure this is the primary cause of the vibration.
                         
                        We can see the engine move around (rocking back and forth, port and starboard) around 1400-1900, and again over 2600.  At 2400, she firms up and purrs.  The vibration / rocking is present in gear and in neutral.  So, yes, it's been confusion 101...we definitely think it's something in the motor, but not entirely convinced.
                         
                        Will likely replace the injectors next week, relatively little $$.  Am also going to consider changing the prop, but that will probably have to wait a bit.

                        On Fri, Sep 11, 2009 at 2:59 PM, jfws88 <jfws88@...> wrote:
                         

                        Jason,

                        With my folding martec I don't get 6 knots at all. Overpropped, maybe but if the vibration is present with the boat in a sling and the prop removed, or even if the prop is installed, the vibration isn't related to the prop over pitch. Period.

                        I have vibration issues also but mine aren't that bad. Right around 1800 RPM she shakes but at 2000 it's fine and again at around 2600 but again it's easy to get out of it by increaseing or decreaseing the motor speed.

                        Do you have the problem in forward and reverse?

                        The issue I'd have with the injectors and pump is those would also have syptoms of low power output but with your prop and the speed you get it seems your getting all the power the motor can put out.

                        Does the motor have that visible vibration at high idle speeds?



                        --- In J28Sailors@yahoogroups.com, jason3317@... wrote:
                        >
                        > John,
                        > Approximately:
                        >
                        > 1200 - 2-2.5
                        > 1500 - 3.0
                        > 2000 - 4-4.5
                        > 2400 - 5.5-6.0
                        > 2800 - 6.0-6.5
                        >
                        > The boat does not seem to noticably slow down, just vibrates more and sounds 'harsh'.
                        >
                        > I am starting to agree that I am slightly over-pitched, but the vibration is also present with the prop off and running in the slings without load.
                        >
                        > Jason
                        > Sent from my Verizon Wireless BlackBerry
                        >
                        > -----Original Message-----
                        > From: "jfws88" <jfws88@...>
                        >
                        > Date: Fri, 11 Sep 2009 16:51:21
                        > To: <J28Sailors@yahoogroups.com>
                        > Subject: [J28Sailors] Re: Over-propped
                        >
                        >
                        >
                        >
                        > Jason, what is your hull speed at various RPM's,
                        >
                        > If your prop is cavitaing the boat should slow down when the vibration kicks.
                        >
                        > John
                        >
                        >
                        > --- In J28Sailors@yahoogroups.com, Jason Smith <jason3317@> wrote:
                        > >
                        > > OK, supposing this is the case I am over-propped....would this cause the
                        > > vibrations? Second, I have no noticed any classic symptoms of being
                        > > over-pitched...black smoke, etc? I'm looking for more corroborative
                        > > evidence!
                        > >
                        > > Thanks guys.
                        > >
                        > > On Thu, Sep 10, 2009 at 9:36 PM, lenny_reich <lsreich@> wrote:
                        > >
                        > > >
                        > > >
                        > > > Jason: I agree that you may be over-propped. The Martec is notoriously
                        > > > inefficient, so it needs lots of pitch. When I sized a 15" VeriFold prop for
                        > > > my boat, the company's strong recommendation was 15" x 12" and it seems just
                        > > > about right. One other point, the Yanmar tachs are not that accurate. An
                        > > > engine tech at the yard where I kept my boat over last winter told me that
                        > > > when they tried to assess a Yanmar problem somehow associated with RPM, they
                        > > > always used a strobe tach to get accurate readings.
                        > > >
                        > > > --- In J28Sailors@yahoogroups.com <J28Sailors%40yahoogroups.com>, Jason
                        > > > Smith <jason3317@> wrote:
                        > > > >
                        > > > > I am looking for some subjective help from the group. Some of you may
                        > > > > know, I have been chasing a big vibration while under power.
                        > > > >
                        > > > > To date, we have eliminated or corrected all the driveline components,
                        > > > > including the prop, shaft, cutless bearing and associated couplings.
                        > > > > My yard just finished replacing the motor mounts, as we could see the
                        > > > > motor visibly rocking at certain RPM.
                        > > > >
                        > > > > After a 4 days cruise over Labor Day, I still think the problem
                        > > > > remains. There is vibration from 1400-1900 RPM, smoothing out around
                        > > > > 2400 RPM. Anything above 2600 RPM and the vibrations re-appear, and
                        > > > > the engine to my ear sounds "Harsh" and not very happy. I cannot
                        > > > > reach 3400 RPM (only 3100), but I don't feel like there is a loss of
                        > > > > power, the motor starts immediately even when cold and nor do I see
                        > > > > any obvious smoke, black or white. The hull and prop are clean. The
                        > > > > prop is a fixed 2 blade Michigan 16 x 14 (not very racy, yes I know,
                        > > > > but that's what I got). I realize these Yanmars will have an RPM
                        > > > > range that they don't like, but this is too broad.
                        > > > >
                        > > > > Now, the yard wants to pull the injectors and test/clean/replace as
                        > > > > necessary. They may also check the timing of the injector pump (not
                        > > > > sure I want to go there as it's really a delicate high-tolerance
                        > > > > piece).
                        > > > >
                        > > > > So, questions to the group: have you had these symptoms? Can you
                        > > > > reach full rated RPM (3400) in calm wind and water? Have you ever had
                        > > > > your injectors replaced or cleaned? If so, how many hours approx did
                        > > > > they have on them? Have you ever had a problem with the injector
                        > > > > pump? What RPM is your typical cruise RPM, and how does the boat
                        > > > > perform?
                        > > > >
                        > > > > Thanks in advance.
                        > > > >
                        > > > > Jason
                        > > > >
                        > > >
                        > > >
                        > > >
                        > >
                        >


                      • Michael Puig
                        One more thing comes to mind. Motor Mounts. I can recall with the 3gm30 I had that it would shake like hell when I would decrease the throttle - it would go
                        Message 11 of 18 , Sep 11, 2009
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                          One more thing comes to mind. Motor Mounts. I can recall with the 3gm30
                          I had that it would shake like hell when I would decrease the throttle -
                          it would go through sort of a harmonic, sort of like when a helicopter
                          lands, there is a transition spot where all sorts of vibrations converge
                          the go away. In any case the mounts have been know to tear.


                          Jason Smith wrote:
                          >
                          > Yes, the Martec is known to be inefficient. I agree that the boat is
                          > overpropped, but not sure this is the primary cause of the vibration.
                          >
                          > We can see the engine move around (rocking back and forth, port and
                          > starboard) around 1400-1900, and again over 2600. At 2400, she firms
                          > up and purrs. The vibration / rocking is present in gear and in
                          > neutral. So, yes, it's been confusion 101...we definitely think it's
                          > something in the motor, but not entirely convinced.
                          >
                          > Will likely replace the injectors next week, relatively little $$. Am
                          > also going to consider changing the prop, but that will probably have
                          > to wait a bit.
                          >
                        • jason3317@gmail.com
                          Yep. Brand new motor mounts installed last month. Better, but still have the problem. Sent from my Verizon Wireless BlackBerry ... From: Michael Puig
                          Message 12 of 18 , Sep 11, 2009
                          • 0 Attachment
                            Yep. Brand new motor mounts installed last month. Better, but still have the problem.

                            Sent from my Verizon Wireless BlackBerry


                            From: Michael Puig
                            Date: Fri, 11 Sep 2009 15:18:56 -0500
                            To: <J28Sailors@yahoogroups.com>
                            Subject: Re: [J28Sailors] Re: Over-propped

                             

                            One more thing comes to mind. Motor Mounts. I can recall with the 3gm30
                            I had that it would shake like hell when I would decrease the throttle -
                            it would go through sort of a harmonic, sort of like when a helicopter
                            lands, there is a transition spot where all sorts of vibrations converge
                            the go away. In any case the mounts have been know to tear.

                            Jason Smith wrote:

                            >
                            > Yes, the Martec is known to be inefficient. I agree that the boat is
                            > overpropped, but not sure this is the primary cause of the vibration.
                            >
                            > We can see the engine move around (rocking back and forth, port and
                            > starboard) around 1400-1900, and again over 2600. At 2400, she firms
                            > up and purrs. The vibration / rocking is present in gear and in
                            > neutral. So, yes, it's been confusion 101...we definitely think it's
                            > something in the motor, but not entirely convinced.
                            >
                            > Will likely replace the injectors next week, relatively little $$. Am
                            > also going to consider changing the prop, but that will probably have
                            > to wait a bit.
                            >

                          • Marc
                            Sorry for the late response to this thread, but I have just joined the group. I was having a similar issue when I bought my J/28 a couple of years ago. I
                            Message 13 of 18 , Nov 15, 2009
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                              Sorry for the late response to this thread, but I have just joined the
                              group. I was having a similar issue when I bought my J/28 a couple of
                              years ago. I replaced my original Martec folding prop with a new one
                              last year. I was advised by Gary at Martec that the 14" pitch was too
                              much for my Yanmar and he recommended the 16 X 12 for a folding prop. I
                              can now run the Yanmar up to 3400 or 3600 rpm and my J/28 will go 7.25
                              knots. I don't cruise at this engine speed but it's good to have the
                              speed if I need to get out of the way of a ferry or tug boat. Maybe the
                              16 X 10 would match up better with the hull speed of the boat. The
                              Yanmar 2GM20 really likes to run at the higher RPM (3400 all day). I
                              experienced some vibration as well, but when I push throught the engine
                              speeds, 2500 to 3000, it goes away. I think there is some resonance in
                              the hull at these RPMs. There are certain RPMs that the boat and motor
                              like. I have found and set the throttle on them right away. For
                              example when I first start the motor I set the enging speed to 1250 or
                              1300 RPM. The motor smoothes right out.

                              Let me know how things work out.

                              Cheers, Marc


                              --- In J28Sailors@yahoogroups.com, Jason Smith <jason3317@...> wrote:
                              >
                              > I am looking for some subjective help from the group. Some of you may
                              > know, I have been chasing a big vibration while under power.
                              >
                              > To date, we have eliminated or corrected all the driveline components,
                              > including the prop, shaft, cutless bearing and associated couplings.
                              > My yard just finished replacing the motor mounts, as we could see the
                              > motor visibly rocking at certain RPM.
                              >
                              > After a 4 days cruise over Labor Day, I still think the problem
                              > remains. There is vibration from 1400-1900 RPM, smoothing out around
                              > 2400 RPM. Anything above 2600 RPM and the vibrations re-appear, and
                              > the engine to my ear sounds "Harsh" and not very happy. I
                              cannot
                              > reach 3400 RPM (only 3100), but I don't feel like there is a loss
                              of
                              > power, the motor starts immediately even when cold and nor do I see
                              > any obvious smoke, black or white. The hull and prop are clean. The
                              > prop is a fixed 2 blade Michigan 16 x 14 (not very racy, yes I know,
                              > but that's what I got). I realize these Yanmars will have an RPM
                              > range that they don't like, but this is too broad.
                              >
                              > Now, the yard wants to pull the injectors and test/clean/replace as
                              > necessary. They may also check the timing of the injector pump (not
                              > sure I want to go there as it's really a delicate high-tolerance
                              > piece).
                              >
                              > So, questions to the group: have you had these symptoms? Can you
                              > reach full rated RPM (3400) in calm wind and water? Have you ever had
                              > your injectors replaced or cleaned? If so, how many hours approx did
                              > they have on them? Have you ever had a problem with the injector
                              > pump? What RPM is your typical cruise RPM, and how does the boat
                              > perform?
                              >
                              > Thanks in advance.
                              >
                              > Jason
                              >
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