GEARHEAD
THE INFRARED PYROMETER
AND ITS MANY USES
Since infrared pyrometers became
readily available a few years ago,
they’ve had a tremendous impact
on the way boats are maintained
and troubleshot. Because of their
affordability, pyrometers are now
accessible to everyone, from the
skilled mechanic to the average
weekend boater.
An infrared (IR) pyrometer uses the
infrared radiation emitted by an object
to determine its temperature. The
variety of tasks an IR pyrometer can
perform is nearly limitless. When using
one, it’s important that you establish a
baseline on the equipment whose
temperature is being measured. For
instance, if you measure the oil filter
housing on your engine while under
way and it reads 180°F, you shouldn’t
be concerned, since that’s within the
normal range for most hardworking
diesel engines. If the temperature is
220°F—still within the normal range
for most engines—you’ll have no way
of knowing whether something is
wrong unless you’ve kept a record of
previous readings. Analyzing such
temperature trends is something that
can be done with the majority of gear
you might read with a pyrometer.
Stuffing boxes are especially worthy
of the pyrometer’s quick and easy
measurement abilities. Typically,
conventional stuffing boxes (the type
with waxed flax packing) operate
between 20° and 30°F above seawater
temperature, which can be measured
with your pyrometer at the raw-water
inlet seacock. Dripless boxes often run
somewhat cooler. Thus, if the water
temperature is 65°F, like it was during
a sea trial I conducted recently, the
stuffing box should be no hotter than
about 95°. After running at 80 percent
throttle for an hour, the stuffing
box on the boat I was sea-trialing
measured 135°. More troubling was
the shaft temperature: measured
Steve D’Antonio
Monitoring the temperature of a stuffing box will enable you to determine if it’s being
cooled and therefore working properly. Typically, stuffing boxes run about 30°F above
ambient water temperature; that number may be less for dripless models, like this one.
where it entered the stuffing box, it
was a sizzling 176°F.
Even before I had used my
pyrometer on this assembly, I could
see what appeared to be solidified
wax on the hull, slung perpendicular
to the shaft near the stuffing box. I
didn’t need trend analysis to know
that something was wrong. A stuffing
box’s flax packing wax should never
get hot enough to melt. If it does,
the stuffing box has been incorrectly
adjusted or is not getting enough
cooling water. The pyrometer reading
simply confirmed this concern.
In most other cases where an IR
pyrometer might be used, there are no
outwardly visible clues about what is
amiss. Take, for example, an alternator
installation I encountered once on
a small cruising boat. As I ran my
pyrometer over various parts of the
engine while the vessel was under
way, the temperature of the alternator
seemed unusually high: over 200°F
after just 15 minutes of run time. I
discovered that the alternator was
equipped with a unidirectional fan
designed to rotate in the opposite
direction from the way it was
turning. Instead of drawing cool air
through the alternator and expelling
it, the fan was attempting, and
failing, to draw air in and push it
through the alternator’s body. This
resulted in an overheated alternator.
