[C320-list] Low speed under Load

[Jeff Hare]

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
>
>