[C320-list] Engine noise

[Jeffrey Hare]

Hi Brian,

  As usual, I summarized in a way that isn't completely accurate.  There are
a lot more factors, and many of them I don't yet understand.  

Specifically, I should have said that motoring to a *specific destination*
at 1000RPM will typically take more fuel than motoring to that same
destination at 2900RPM.  The exception here might be if you have an autoprop
that self-pitches, or a Gori and can motor in overdrive, but the research I
was reading didn't address that.

I'm still studying this, but from what I understand so far, if you decouple
the engine from the prop and just look at fuel consumption over the RPM
range, lower RPM burn less fuel than higher RPM as you would expect.  But
that doesn't tell the story.

When looking at HP transmitted to the water, lower RPM burn more fuel per HP
transmitted to the water because (as I interpret it) the propeller curves
and engine curves  are only optimal around the engine's "sweet spot".  Which
is ~2900+ish for the Yanmar 3GM.  As you go outside that sweet spot with
lower RPM you're burning more fuel/HP transmitted to the water.

So... It seems that you do indeed burn less fuel at lower RPM, but getting
to a specific destination may require a little more fuel if you motor there
at low RPM.

This may account for why some people say the yanmar burns ~.5 gal/hr and
others say they use ~.7 gal/hr.  Different props, different RPM used on
average, etc...

If anyone out there has read the prevailing research and understands it
better, chime in.  :)  Typically you find this research when attempting to
compare the efficiency of diesel/electric vs. plain diesel drive systems.

-Jeff



-----Original Message-----
From: c320-list-bounces at catalina320.com
[mailto:c320-list-bounces at catalina320.com] On Behalf Of Amirault Family
Sent: Monday, July 16, 2007 5:51 PM
To: c320-list at catalina320.com
Subject: [C320-list] Engine noise

Jeff:

The diesel giving higher consumption at lower revs IS counter intuitive. 
Could you give a brief overview of the theory? It has me curious and an
understanding my lead me to begin using higher revs.

Brian Amirault
797 Waltzing Bear, too