On Sat, 24 Nov 2007 23:37:52 -0500, Wayne.B
wrote:

On Sun, 25 Nov 2007 10:23:55 +0700, Bruce in Bangkok
wrote:

Have there been any studies made of shutting down one engine? I know
that Beebe published some RPM/Miles/fuel consumption charts but those
were for a single screw drive.

I don't know if I'd call it a study, but based on my own statistics
there is a definite save, even with the drag of a freewheeling prop.
My situation may be different than some however since the engines are
oversized for 95% of my typical usage. As a result, running both
engines slowly is not only bad for them, but they would be operating
just above idle speed which is not an efficient operating point.

By running on a single engine, it is operating closer to it's design
point which is not only more efficient but minimizes potential
maintenance issues like carbonized valves, rings and exhaust manifold.

My statistics for RPM vs fuel burn vs horsepower vs speed agree fairly
closely with Beebe's numbers. Of course there is a fudge factor in
his equation which is different for every hull shape. It turns out
that the Grand Banks hull form is at the low end of the efficiency
scale.


I think that your case is where the "don't run the engines at low
load" came from. If you have a couple of them great big motors in case
you want to go fact and you end up running them at 1.000 RPM for days
at a time I suspect that they will carbon up pretty good as I'm not
sure how well the pumps are calibrated for speeds just above idle.

During the first oil crunch I was working at a power plant in N.
Thailand and the word came down from the Air Force to run the
generators at 90-95% of rated power as they said that was the most
efficient power setting.


Bruce-in-Bangkok
(Note:remove underscores
from address for reply)