[C320-list] Low speed under Load

[Marek Fluder]

Jeff,

Your input is always greatly appreciated.
I max out at 3600 rpm with 7.3 knots of speed (flat, no wind).
For longer runs my 3YM30 tends to run a bit hot - temp climbs to 180-190
with rpms closer to 3000.
I suspect I still have one of the original undersized heat exchanger cores
which were upgraded in later engines.

Kind regards,

Marek
#1028



On Tue, Jul 14, 2015 at 10:29 AM, Jeff Hare <Catalina at thehares.com> wrote:

> Marek,
> Interesting.  You also have the 3YM engine.  It has a bit more power than
> the 3GM.  In forward with normal to flat seas, if you can't get your engine
> up to at least ~3400 RPM *I think* it's most likely over pitched.  Yanmar
> would probably not approve the pitch if your engine cannot get up to RPM
> under load.
>
> If you get these speeds at those RPM and CAN rev the engine under load up
> to 3400 or so, then that's great and I think you're all set!
>
> Others who know the Yanmar diesels better could probably comment, but the
> engine doesn't have a throttle in the automotive sense, it has a speed
> governor.  So, you set the RPM lever for the engine speed you want, and the
> governor adjusts the fuel flow to try to hold the specific RPM the lever is
> set to.  That's why the engine speed stays constant and doesn't speed up
> when you surf down a wave and slow down when climbing up another one.  If
> you find that the engine won't reach the rated continuous RPM of around
> 3000+, it's over loaded and may not be burning quite all the fuel the
> governor is feeding it.
>
> The other aspect of reaching the proper RPM is that you need the engine to
> be reaching the proper exhaust and oil temps. The exhaust temp is important
> to control carbon buildup.  The oil temp is required to burn off the water
> that condenses in the oil which if isn't burned off becomes sulfuric acid
> because of the sulfur in the fuel.  We all know what sulfuric acid does to
> engine parts over the long haul.
>
> But, I'm no diesel mechanic.  This is just what I (think I) learned in my
> Mac Boering diesel engine class a few years back.
>
> Always interested in knowing what the "real" answer to this is!
>
> -Jeff
> #809
> -----Original Message-----
> From: C320-list [mailto:c320-list-bounces at lists.catalina320.com] On
> Behalf Of Marek Fluder
> Sent: Tuesday, July 14, 2015 9:25 AM
> To: C320-List at Catalina320.com
> Subject: Re: [C320-list] Low speed under Load
>
> Jeff,
>
> I have also Yanmar 3YM30 with fixed 3 blade 15R12 prop and found that my
> speeds are similar to Don's:
> 1500 - 4 knots
> 2000 - 5 knots
> 2500 - 6 knots
> Kanzaki transmission with 2.62 gear ratio.
> Am I over-pitched as well ?
>
> Marek
> #1028
>
>
>
> On Mon, Jul 13, 2015 at 3:26 PM, Jeff Hare <Catalina at thehares.com> wrote:
>
> > Well...
> >
> > First, to be getting 5kts at 2000 rpm means you're well over pitched
> > regardless of which prop you have.  So, you'll be building up carbon
> > in the elbow like crazy this way.  Even if it seems ok it isn't.  So
> > I'm guessing your exhaust elbow is probably clogged unless you can rev
> > to 3800 RPM easily in neutral.  Since your diver says your prop is
> > clean, there are really only a few things I can think of that can keep
> > you from getting over 2800 rpm under way.
> >
> > 1:  Over pitched prop
> > 2:  Clogged elbow
> > 3:  Dirty prop  (ruled this one out)
> > 4:  Dirty Primary or Secondary fuel filter
> >
> > I think #1 caused #2.
> >
> > -Jeff Hare
> > #809
> >
> > -----Original Message-----
> > From: C320-list [mailto:c320-list-bounces at lists.catalina320.com] On
> > Behalf Of Donald Lawson
> > Sent: Monday, July 13, 2015 2:33 PM
> > To: C320-List at Catalina320.com
> > Subject: [C320-list] Low speed under Load
> >
> > All
> > I have 2004 320 with a Yanmar 3YM30 fitted with a 15x9 MaxProp by PO.
> > Everything has worked well for 3 years. At last spring haulout I had
> > the prop serviced and bottom painted. Boat worked great. Recently I
> > get 5 knots at 2000 rpm, which is normal.  However there is no
> > increase in boat speed past 5 knots up to 2800rpm.  Cant' get above
> > 2800 rpm. Rpm to 3000+ easily in neutral.  No visible exhaust  at
> 2000rpm.
> > Skipper says some minor black smoke at 2800 rpm. Seemed like a mist to
> me.
> > Recently serviced.  Got fuel and air OK. Had diver check MaxProp.
> > Seems OK.
> > Diver cleans bottom and prop once a month.
> > Anyone had a transmission trouble with a Yanmar? Starting to grasp at
> > straws.
> >
> > Don Lawson
> > "Mandolin Wind"
> > Ventura, CA
> >
> >
>
>