On 2008-04-05 22:14:15 -0400, Bruce in Bangkok said:

On Sun, 06 Apr 2008 00:31:52 GMT, Jere Lull wrote:

On 2008-04-05 09:48:23 -0400, Bruce in Bangkok said:

I suspect, but can't prove that yacht engines are seldom run at maximum
continuous horsepower settings for any length of time while most
commercial engines are.

Talking around the docks, and here, I find that most 'yacht' engines
are also either at idle or 80+% of designed revs.

I'm a bit unusual that I normally power at less than 80% of the
engine's max revs to maximize fuel economy. At 70-75% of max revs, we
get 25-30 mpg. 80% has us pushing against hull speed. Full revs push us
over hull speed, and I've only done that twice in 15 seasons.

Most sailors run at high power when they motor. If they turn the motor
on, they're by definition in a hurry.

Your engine is too big, simple as that :-)

No disagreement, but it was an engine new to the market. Its
predecessor would have been just right, but I liked the idea of the
closed-loop fresh-water cooling.

I still prefer it, truth be told.

By the way, how do you calculate miles per gallon? No tides in the Chesapeake?

We have tides, more accurately we have currents that tend towards a
full knot southbound in our area, but I'm dividing average speed
through the water by average fuel burn. Speed over the ground will vary
with the current of course.

Over in the dry (N.E. monsoon) season you motor when there isn't any
wind, which is usually when the land breeze dies about 11:00 every
morning.

Exactly. You're in a hurry. Otherwise, you'd wait for the wind to come back.

;-)

Nothing wrong with that, since that's why we have auxiliaries, but few
sailors power much below hull speed. By dropping the speed a knot or
so, consumption drops dramatically.

If we have the auxiliary on and in gear, we pull nearly 3 knots at
idle. But our most economical speed is about 5 or 5.5 knots. Our
theoretical hull speed is 6.65 knots, though Xan is as comfortable at
7+ knots as 5 under sail.

Come to think about it, she's more comfortable above that speed than
below, but she is a known show-off that delights in breaking the rules.
She considers hull speed a suggestion, not a law.

--
Jere Lull
Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/