Bowgus wrote:

And use that trim control for optimum speed/rpm combo.


Aha! I would have overlooked that, thanks.
Your point has been blatantly hijacked and included in my rough draft. :-)



Don't be so Fuelish!


Holy hydrocarbons! All the dead dinosaurs currently being pumped at the local
fuel docks must surely have been the thoroughbreds of their day. As the summer
cruise season gets underway, gas and diesel prices are high, yi, yi, yi, er
than we've ever seen, (if inflation isn't factored into the equation).

What's a boater to do? Fortunately, we have some realistic choices that go well
beyond staying ashore and moping. Without suffering major expense or
inconvenience, almost everyone can make some simple adjustments and systems
checks that will reduce fuel costs this summer. In some cases, the savings will
prove significant.

Boaters should always be careful to maintain a nice, clean bottom. Lack of
attention can result in an embarrassingly "hairy" surface, further plagued by
unsightly, crusty organisms clinging to formerly smooth, unblemished surfaces.
It it's been a while since the last careful examination, it may be time to take
your bottom (and the boat it's attached to, of course) to the nearest boatyard
for inspection, correction, and preventive maintenance. The "beard" of seaweed
and the hitch-hiking barnacles can retard a boat's progress through the water
and decrease fuel efficiency as a result.

The energy developed by burning fuel aboard a powerboat is ultimately
transmitted to the water by the prop. Boats fitted with a propeller pitched too
aggressively or too large in diameter will be "lugging", and the over-propped
condition will keep the boat from ever reaching the manufacturer's rpm rating.
If the engine is running at a wide open or well open throttle and not achieving
its potential speed, some fuel is being wasted. If a boat is equipped with an
undersized propeller, it will easily reach or exceed its full rpm rating but
will not convert the engine speed into boat speed with adequate efficiency.
Boaters who have been "putting up with" improperly sized propellers may find
this a compelling year to make the correction.

Engines that are running efficiently burn less fuel. Is it time for fresh
sparkplugs or other ignition components on a gas engine? Are the injectors
overdue for service on a diesel?
These and similar preventive maintenance chores can't be postponed forever, and
doing the work prior to setting off on an annual vacation cruise will allow the
immediate fuel savings to help defray a portion of the cost.

Prepare to lighten ship! The smaller the boat, the greater the difference an
extra thousand pounds of "stuff" will make when operating. Basic safety gear
and spares should remain aboard, of course, but a spike in the cost of fuel is
as good an excuse as any to go through lockers, lazarettes, etc, and review the
inventory. Most of us will be surprised at the amount of seldom or never used,
(sometimes even completely forgotten), stores, supplies, tools, and personal
belongings stowed aboard.

Don't boat "upstream" when avoidable. In most of our local tidal waters, there
are only the briefest periods when the current is truly slack. Prudent planning
and timing of a cruise can make a significant difference in net speed over
ground, (and therefore actual fuel efficiency). Displacement boats realize more
dramatic benefit from the advantageous use of currents than planing boats. An
eight-knot boat bucking a three-knot current will achieve a net five-knots,
while the same vessel running with a three-knot current will be logging
eleven-knots SOG, (more than twice the speed with the same fuel burn).

And last but far from least, slow down! (But perhaps not too much.) The two
most efficient speeds for typical planing hulls are pure idle, and the speed at
which the boat rises over the bow wave to assume a planing attitude. Backing
off the throttle to where a boat falls off plane will reduce the gph fuel
consumption, but can easily reduce the speed so disproportionately that the
nmpg is actually less at the lower speed. Once a vessel has achieved planing
status, additional throttle will often burn significantly more fuel to achieve
only relatively modest increases of speed.

Judicious use of trim tabs, when so equipped, can often help a boater achieve
or maintain plane at a slower engine rpm.

Even if it isn't practical to clean the bottom, tune or service the engine,
correct an improperly specified propeller, remove excess weight for the boat,
or plan cruises to take advantage of favorable currents, many of us can realize
significant savings merely by reviewing our customary cruising speeds.

Cruising a bit slower may sound almost heretical to many boaters, but let's
examine a real life example of the type of efficiencies that can be realized.
Douglas Silvestri, of Port Orchard, Washington, kept careful fuel consumption
records on his 36-foot Uniflite equipped with twin 460 gas engines and Flo-Scan
fuel meters. Silvestri recently traded for a different boat, but he kept his
old records.

"At 2700 rpm, I would make 14.1 kts in the Uniflite. My combined fuel burn at
that speed, for both engines, was 14.2 gallons per hour, or almost exactly
1nmpg."

"By slowing down to 2000 rpm, my speed dropped to 10 kts, but my fuel burn was
reduced to 8.2 gph, according to the Flo-Scans."

Doug's fuel efficiency, on a nmpg basis, was roughly 25% better at 2000 rpm and
10 kts than it was at 2700 rpm and 14. Doug actually got reasonably decent fuel
economy from the twin 460's in his Uniflite, many similar and larger boats use
significantly more fuel per hour and a decrease in speed could result in even
more dramatic savings.

Here in the Northwest, many boaters would hardly notice the difference in
Doug's two speeds, but most would appreciate the difference in fuel costs. A
250 nautical mile summer vacation cruise would require 25 cruising hours at
10-knots, or just under 18 cruising hours at 14.1. If the 250 nautical miles
were logged over ten days, the average running time per day would only be 42
minutes longer at the slower speed. Eighteen hours at 14 gph would burn 252
gallons at the higher speed, while 25 hours at 8.2 gph would burn only 205. By
spending an extra 42 minutes per day on the water, (and isn't that what boating
is supposed to be about?) Silvestri's old boat would use 47 fewer gallons on
that typical, but hypothetical, NW vacation cruise. At $2.80 a gallon, that
47-gallon savings would reduce the fuel costs by $131. One-hundred-thirty -one
dollars isn't a lot of money in the grand scheme of boating expenses, but its
an amount that almost anybody would stoop down to pick up if it were laying
unclaimed on the dock . For many of us, that much or considerably more almost
certainly is.