Every boat has a cruising "comfort zone" that yields an optimum mix of
speed and fuel efficiency. You could find that exact speed. All you'd
need do is borrow the radar gun, digital tachometer, transducers and
fuel-flow gauges used by our staff, then spend a morning on the lake
running at various throttle settings.


Or, you could get a 95-percent approximation of your boat's optimum
cruise speed by simply following a few simple rules our experts have
concocted after performing hundreds of detailed boat tests. These hints
apply primarily to gas-powered, planing-hull boats since this is the
type of boat most of our readership owns.
Somewhere between planning out and top speed, there is a combination of
speed and engine load that will yield the maximum number of miles per
gallon. To make a broad generalization, this "sweet spot" usually
occurs somewhere between half and three-quarter throttle.


If your boat is marginal on power, this generality may not apply, but
if you selected an engine that can hold your boat comfortably on plane
at half throttle or less, the formula works. For a large number of V-6-
and V-8-powered runabouts, optimum cruise speed falls somewhere between
3,000 and 3,500 rpm.
To further optimize fuel efficiency, make sure your boat is running
level and in trim. Weight distributed unevenly front to back or side to
side will cut into running efficiency, so you may want to move gear and
passengers to level the load.


If you have an outboard or I/O-powered boat, you can also adjust the
drive for optimum efficiency. Begin with the drive down, then gradually
raise it with your trim adjustment.
Notice how the speed and rpms increase as you raise the drive. Raising
the drive decreases the drag of the lower unit in the water, and it
also allows the bow to rise, which reduces the wetted surface of the
hull.


As you continue to raise the drive, you will eventually cause the
propeller to cavitate. Your optimum drive setting is a few degrees shy
of this mark.

Best regards
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