GL: Local cruising and fuel consumption

[Rich Gano]

I don't get too many opportunities to take off on really long trips; most of
the TIME I spend on the boat underway is in waters within 60 miles of home.
That means refueling once or twice a year, and I usually never go below a
half load.  Nonetheless, at today's diesel fuel prices, I am mindful of the
concept of conservation on a higher level of consciousness than I ever was
22 years ago when I filled this boat up at the Tuna Clipper piers in San
Diego for 68 cents a gallon.

For me to economize on fuel, getting over the mindset of an automobile
driver and into that of a trawler owner is important before casting off the
lines for a day on the local waters.  In the car, I tend to schedule myself
for X amount of time to make appointments, get to stores before they close,
get to restaurants at certain times, etc, etc.  That and the fact that there
are other drivers out there who don't want to dawdle along below the speed
limits tends to push me along at speeds I know will get me where I want to
be WHEN I want to be.  For the fifteen nautical mile one-way trip to our
favorite barrier island, I used to throttle up to 1750 RPM and cruise along
at hull speed of 8.6 knots.  Since there is never much more than a knot of
current either way over my course, I pretty much know when I have to be
underway if I want the anchor down at a certain time, say lunch-ish.  As to
nmpg, I guess I get 2.4 running 1400 and 1.8 going at 1750 RPM.

Nowadays, I tend to poke along at 7.2 knots at about 1400 RPM running
significantly less (about 40% less) fuel through the engines per hour and
taking 20 minutes longer to get there.  Since, for me, the journey is the
best part, it's win-win - I get to spend an extra forty minutes running my
boat for a day time to the island.  I am also getting 73 more hours of
boating time for a load of 660 gallons of diesel.

For an upcoming 216-nm round trip, I have been ruminating about how to go. I
could run at hull speed or nearly so (8.5 knots) over the length of the
voyage and get to the other end destination in 12.8 hours.  That uses about
58 gallons of fuel each way.  Running the whole one-direction distance at
1400 RPM takes 15 hours and requires 45 gallons of fuel each way - savings
of around $120 for the round trip at my last purchase price of $4.51/gal.

If we were to run two 2-part voyages spending a night on the hook in each
direction running the air conditioners (we don't normally run them
underway), we'd use an additional 14 gallons ($63) of fuel for the round
trip.

So going at 1400 RPM and spending a night each way requires 104 gallons
($469), while running at hull speed (1750 RPM) and also spending two nights
on the hook requires 130 gallons ($586), the slow speed savings remaining
about $120 as above.

Due to predicted thunderstorm activity during the daylight hours of our
trip, I am considering going at night (when slower is better anyway - COOLER
too), but anchoring out during the day to rest up for a second night's run
(especially on the second of July around here) would probably not be restful
at all.  Thus, a single 15-hour run each way may be the best option both
from a safety (I do NOT consider running at night a challenge as I do it
regularly professionally) as well as a fuel conservation point of view.
Running at the slower speed and NOT anchoring for a 10-hour rest each way
(as well as avoiding open water during T-strm activity) uses only 90 gallons
($406) saving another $63 over and above the $120 we'd save by avoiding a
two-part running at hull speed (30%).

Rich Gano
CALYPSO (GB-42 #295)
Southport, FL