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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
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)

• http://www.vicprop.com/displacement_size.php
Message 1 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,
Message 1 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?
>
>
> Jason
>
• 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 1 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 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?
>
>
> Jason
>

• 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 1 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!
>
• 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 1 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
> > >
> >
> >
> >
>
• 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 1 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
> > >
> >
> >
> >
>

• 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 1 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
> > > >
> > >
> > >
> > >
> >
>
• 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 1 of 18 , Sep 11, 2009
View Source
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
>
> Jason
>
• 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 1 of 18 , Sep 11, 2009
View Source
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 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
> > > >
> > >
> > >
> > >
> >
>

• 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 1 of 18 , Sep 11, 2009
View Source
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.
>
• Yep. Brand new motor mounts installed last month. Better, but still have the problem. Sent from my Verizon Wireless BlackBerry ... From: Michael Puig
Message 1 of 18 , Sep 11, 2009
View Source
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.
>

• 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 1 of 18 , Nov 15, 2009
View Source
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?
>