[C320-list] Low speed under Load

[Rod Boer]

Marek and Jeff,
I had a similar exchange of emails with Chuck Hussick, who I work for in the
past, and who was one of the technical writers for Ocean Navigator as well
as other marine magazines.  It was in regard to a comment that was made by
another member of the C320 organization regarding the speed of his boat that
used an AutoProp.  The boat speed was high at a relatively low RPM and
maximum RPM could not be reached.  Chuck confirmed that the propeller was
over pitched and replied that it is important that the engine be able to
reach maximum horsepower.
Rod Boer   	

-----Original Message-----
From: C320-list [mailto:c320-list-bounces at lists.catalina320.com] On Behalf
Of Jeff Hare
Sent: Tuesday, July 14, 2015 10:30 AM
To: C320-List at Catalina320.com
Subject: Re: [C320-list] Low speed under Load

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
>
>