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What is the proper
technique for testing a battery with a hydrometer?
B. L., via e-mail
The
battery’s state of charge is determined by measuring its specific
gravity, which is a measure of its concentration of sulfuric acid. The
specific gravity of a battery ranges from 1.120 to 1.300, depending on
its state of charge.
Before testing, make
sure the battery is fully charged and the electrolyte is at the proper
level. If you must recharge, wait at least 30 minutes before taking the
first reading. A deeply discharged battery’s electrolyte is not
mixed well and will not be so until the battery begins to reach full charge
(which, because of the electrolyte condition, takes a long time) and starts
to gas. If you must add liquid before charging, make sure it is only distilled
water, as other water most likely contains minerals and impurities that
may prevent the electrochemical reaction from reaching its full potential.
Draw enough electrolyte
into the hydrometer barrel to allow the calibrated float to ride freely.
Then read the specific gravity where the surface of the liquid comes in
contact with the scale, allowing for the curvature of the liquid against
the glass parts. Note the value, and squeeze the electrolyte back into
the same cell from which it was drawn. Repeat this for each cell. The
readings among each cell should not have a difference of more than .050.
If they do, you will have to replace the battery.
When you’re finished
with the hydrometer, rinse it with fresh water to flush out any electrolyte
that may be left in the tube.
During a recent haul-out,
I noticed the trailing edge of my props seemed to be in the throes of
some sort of corrosion. All my zincs seem fine. What could be the problem?
T. R., via e-mail
It
sounds like erosion due to cavitation, the rapid formation and collapse
of bubbles just behind the prop blades. As the prop blades spin, air pockets
can form across the blades. When these bubbles collapse, water hits the
blades with such force, it’s as if thousands of tiny hammers were
at work. The result is erosion at the trailing edge of the blade that
you might mistake for galvanic corrosion.
Usually this is caused
by a blunt or squared front edge and is more often than not the result
of a nick or dent. Rounding that edge out can cure this. If there’s
not too much damage, your local prop shop can easily recondition your
wheels with a file or sander.
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